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Materials Chemistry C
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Cite this: J. Mater. Chem. C, 2016,
4, 4889
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Multiple phase and dielectric transitions
on a novel multi-sensitive [TPrA][M(dca)3]
(M: Fe2+, Co2+ and Ni2+) hybrid inorganic–organic
perovskite family†
J. M. Bermúdez-Garcı́a,*a M. Sánchez-Andújar,a S. Yáñez-Vilar,ab S. Castro-Garcı́a,a
R. Artiaga,c J. López-Beceiro,c L. Botana,d A. Alegrı́ade and M. A. Señarı́s-Rodrı́guez*a
The hybrid inorganic–organic [TPrA][M(dca)3] (M: Fe2+, Co2+ and Ni2+) compounds, where TPrA is the
tetrapropylammonium cation and dca is the dicyanamide anion, are unique multi-sensitive compounds
that display multiple phases and dielectric transitions. These materials exhibit up to three first-order
structural transitions (between the polymorphs I, Ia, Ib and II) associated with the same number of
dielectric transitions in the temperature range of 210–360 K. The mechanisms responsible for these
dielectric responses are found to be novel within the hybrid perovskites, involving ionic displacements of
the A-site cations (TPrA) and order/disorder processes of the X anions (dca). In addition, the phase
Received 19th February 2016,
Accepted 14th April 2016
transitions and dielectric transition temperatures can be tuned by applying external hydrostatic pressure
DOI: 10.1039/c6tc00723f
This multi-sensitive response towards temperature, external and internal pressure opens up promising
or by inducing internal pressure by modifying the tolerance factor through ionic substitution in the B-sites.
technological applications for this family of materials, such as dielectric transductors or multistimuli-
www.rsc.org/MaterialsC
sensors, whose response can be modulated in a wide range of temperatures and pressures.
1. Introduction
Perovskites, and the phase transitions they can experience as a
function of temperature, pressure, etc., have been at the center
of a vast amount of research in solid state and material science
over the last decades1 in view of their huge scientific and
technological interest. In that context, early studies on conventional
inorganic perovskites, ABX3 (A: lanthanides, alkaline-earth
metals or similar cations, B: transition metal cations and X:
oxide, sulphide or halide anions, etc.), specially mixed oxides,
a
QuiMolMat Group, Department of Fundamental Chemistry, Faculty of Science and
CICA, University of A Coruña, Campus A Coruña, 15071 A Coruña, Spain.
E-mail: j.bermudez@udc.es, m.senaris.rodriguez@udc.es
b
Department of Applied Physics, University of Santiago de Compostela,
15782 Santiago de Compostela, Spain
c
Department of Industrial Engineering II, University of A Coruña, Campus Ferrol,
15403 Ferrol, Spain
d
Material Physical Center, CSIC-UPV/EHU, P. Manuel de Lardizabal 5,
20018 Donostia-San Sebastian, Spain
e
Material Physical Department, University of the Basque Country, PO Box 1072,
20008 Donostia-San Sebastian, Spain
† Electronic supplementary information (ESI) available: Powder XRD patterns,
details of the crystal structure, graphics of the variation of the phase transition
temperatures with the tolerance factor and external pressure, table of enthalpy
and entropy values obtained by DSC, summary of crystallographic data and CIF
(CSD number: 431135–431145). See DOI: 10.1039/c6tc00723f
This journal is © The Royal Society of Chemistry 2016
highlighted the exceptional functional and even multi-functional
properties. This is the case, among others, of the very wellknown and widely used ferroelectric BaTiO3, the piezoelectric
Pb(Zr1xTix)O3 (PZTs),2 the high temperature superconductor
YBa2Cu3O7d,3 the colossal magnetoresistive La1xCaxMnO3,4
the mixed ionic–electronic conductors La1xSrxCoO3d,1a or more
recently, the multiferroic BiFeO3.5
Interestingly, in the last few years, significant efforts have
been devoted to the development of new members of the
versatile family of the so-called perovskite-like hybrid inorganic–
organic materials,6 where the A- and/or X-site inorganic moieties
of the conventional perovskites have been replaced by organic
building blocks. Some of these materials, despite their recentness,
have already revealed very remarkable functional properties. This
is the case of the (MA)PbI3 (MA = methylammonium cation),7
which has revealed unprecedented photoconductivity; or the noteworthy [AmineH][M(X)3] families (AmineH = midsized protonated
amines in the A-site position of the perovskite, M = different
divalent transition metal cations in the B-site, X = different
bidentate-bridge ligands in the X-site position, such as N3, CN
or HCOO), which exhibit cooperative magnetic, electric or elastic
order, even multiferroicity, associated in many cases to very
interesting thermally-induced phase transitions.8–17 Very remarkably, magnetoelectric coupling has been recently reported experimentally in the paramagnetic state of [(CH3)2NH2][Fe(HCOO)3],16
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and ferroelectricity induced by magnetic order has been demonstrated in [CH3NH3][Co(HCOO)3],17 opening the large, flexible,
multifunctional and designable family of hybrid perovskites to
magnetically induced multiferroic behaviour.
Another related, but so far much less explored, family of
potentially interesting compounds is that of metal-dicyanamides
with the formula [AmineH][M(dca)3] and has perovskite-like
structure. In these compounds, the dicyanamide anions,
[N(CN)2] (dca), bridge the transition metal cations (up to now,
M: Mn2+ ref. 18 and 19 and Ni2+ ref. 18) in a m1,5-dca end-to-end
mode, forming a 3D framework. Meanwhile, the protonated
amines (so far tetrapropylammonium, [(CH3CH2CH2)4N]+ or
TPrA) are located in the resulting pseudo-cubooctahedral cavities.18
In our previous work,19 we have revisited the Mn compound
[TPrA][M(dca)3], finding a structural transition at 330 K, and
studied the influence of external pressure on the structural and
dielectric properties of this compound. Interestingly enough,
we found that this material had a new type-I multiferroicity that
was very sensitive to temperature and external pressure.
In the present work, we enlarge the family of [TPrA][M(dca)3]
perovskites with two new members (M: Fe2+ and Co2+) that we
describe for the first time; and we shed light on the unexplored
structural features of the Ni compound, for which two structural
transitions had been previously reported at 160 K and 210 K,18
and we present two new additional polymorphs.
We also explore the dielectric properties of these materials
and present a systematic and careful study of the effect of
external and internal pressure on the structural transitions and
dielectric responses of these three [TPrA][M(dca)3] (M: Fe2+,
Co2+ and Ni2+) compounds.
Very interestingly, and as we will show below, we have found
that these Fe, Co, and Ni compounds display multiple phase
transitions responsible for multiple dielectric transitions that
are both very sensitive to temperature as well as to external and
internal pressure.
2. Experimental
2.1
Synthesis
[TPrA][M(dca)3] (M: Fe2+, Co2+ and Ni2+) materials were prepared
from commercially available FeCl24H2O (98%, Sigma-Aldrich),
Co(NO3)26H2O (98%, Sigma-Aldrich), Ni(NO3)26H2O (Z98.5%,
Sigma-Aldrich), (TPrA)Br (98%, Aldrich), Na(dca) (96%, Aldrich)
and absolute ethanol (Panreac), which were used as purchased
without further purification. A reagent amount of deionised
water was also used in the synthesis.
The synthetic route used here is an adaptation of the previously
reported method for the preparation of the [TPrA][M(dca)3]
compounds (M: Mn2+ and Ni2+),18 where synthesis of the metal
dicyanamide frameworks were templated by alkylammonium
cations and accomplished through a mild solution chemistry
method at room temperature.
In a typical experiment, 10 ml of an aqueous solution
containing 2 mmol of FeCl24H2O or M(NO3)26H2O (M: Co2+
and Ni2+), was placed at the bottom of a glass tube. This solution
4890 | J. Mater. Chem. C, 2016, 4, 4889--4898
Journal of Materials Chemistry C
was layered by a mixture of a solution of (TPrA)Br (2 mmol) in
10 ml of ethanol and a solution of Na(dca) (6 mmol) in 10 ml
of water.
Single crystals of the three compounds (cubic colourless for
M: Fe2+, cubic pink for M: Co2+, and cubic green for M: Ni2+)
were obtained after one week and they were collected by
filtration and washed several times with ethanol.
The compounds were obtained as single phase materials
and their purity was confirmed by comparison of their experimental
powder X-ray diffraction (PXRD) patterns at room temperature
with those simulated from the single-crystal X-ray diffraction
(SCXRD) data, see Fig. S1 of ESI.†
2.2
Single-crystal X-ray diffraction
Single-crystal data sets were collected in a Bruker-Nonius x8
ApexII X-ray diffractometer equipped with a CCD detector and
using monochromatic MoKa1 radiation (l = 0.71073 Å) at
different temperatures: 368 K, 323 K, 300 K (293 K in the case
of the Fe compound), 200 K (180 K for the Ni compound) and
100 K. Suitable crystals of each sample were chosen and
mounted on a glass fiber using instant glue. For the 100 K and
200 K (or 180 K) sets, the crystal temperature was maintained
using a cold stream of nitrogen from a Kyroflex cryostream
cooler. Data integration and reduction was performed using the
Apex2 V.1.0 27 (Bruker-Nonius, 2005) suite software. The intensity
collected was corrected for Lorentz and polarization effects, and
for absorption by semi-empirical methods on the basis of
symmetry-equivalent data using SADABS (2004) from the suite
software. The structures were solved by the direct method using
the SHELXS-97 program20 and were refined by the full-matrix
least-squares method on the SHELXL-97 program,20 both programs
are available within the WinGX package.21 To solve the structures,
anisotropic thermal factors were employed for the non-H atoms and
non-disordered atoms. In the case of ordered TPrA cations, the
hydrogen atoms of the propyl groups were added to the ideal
positions and isotropic thermal factors were refined.
2.3
Powder X-ray diffraction
A Siemens D-5000 diffractometer using CuKa radiation (l =
1.5418 Å) was used to study these compounds by X-ray powder
diffraction (XRPD) at room temperature. The XRPD pattern was
compared with the profile obtained from the single crystal
structure that was generated using Mercury 3.5.1 software.22
2.4
Differential scanning calorimetry
Differential scanning calorimetry (DSC) studies were carried
out in a TA Instruments MDSC Q2000 equipped with a liquid
nitrogen cooling system. The samples (each with a mass
around 5 mg) were heated and cooled with a rate of 20 K min1
(2 K min1 in the case of the Ni compound) from 135 to 375 K
under a nitrogen atmosphere.
Additionally, pressure differential scanning calorimetry (PDSC)
tests were performed in a TA Instruments pressure cell
mounted on a Q2000 modulated DSC. The cell was calibrated
for temperature and heat with indium at each of the pressures
to be used in the measuring tests. The effect of pressure on the
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melting temperature and enthalpy of indium was taken into
account.23 In a typical experiment, about 5 mg of each sample
was confined inside a pinhole aluminum capsule. The experiments
were performed in N2 atmosphere at a constant pressure (from 1 to
69 bar) while keeping a constant flow of 50 ml min1 of N2. The
samples under a constant external pressure were heated and
cooled at a rate of 2 K min1 from room temperature to 343 K.
2.5
Pressure–volume–temperature (PVT) analysis
To study the dilatometry of the materials at different pressures,
PVT 100 SWO/ThermoHaake equipment was used. In a typical
experiment, about 440 mg of powder material was loaded
inside a cylinder between two pistons that transmit an axial
compressive force from 200 to 1600 bar to the samples. After
applying the external pressure, the samples were heated at a
rate of 5 K min1 from 183 K to 373 K and the axial thermal
expansion of the samples was registered.
2.6
Dielectric measurements
The complex dielectric permittivity (er = er 0 ier00 ) of the coldpress pelletized samples were measured as a function of
frequency and temperature with a parallel-plate capacitor
coupled to a Solartron 1260A Impedance/Gain-Phase Analyzer,
capable of measuring in the frequency range from 10 mHz to
32 MHz using an amplitude of 2 V. The capacitor was mounted
in a Janis SVT200T cryostat refrigerated with liquid nitrogen,
and with a Lakeshore 332 incorporated to control the temperature
from 78 to 400 K. Data were collected upon heating.
Pelletized samples, made from cold-press non-oriented single
crystals with an area of approximately 133 mm2 and a thickness of
approximately 1.3 mm, were prepared to fit into the capacitor, and
gold was sputtered on their surfaces to ensure a good electrical
contact with the electrodes.
All the dielectric measurements were carried out in a nitrogen
atmosphere where several cycles of vacuum and nitrogen gas
were performed to ensure that the sample environment was free
of water.
Additionally, dielectric measurements were carried out in a
pressure cell supplied by Novocontrol GmbH. The cell, basically
a stainless steel cylinder with a hermetic seal, was filled with a
silicone fluid that transmits an isostatic pressure from the
piston to the sample. The dielectric response was measured
for 103–106 Hz frequencies. The measurements were performed
as a function of temperature (310–380 K) for constant pressures
up to 2000 bar.
3. Results and discussion
3.1
Fig. 1 DSC results as a function of temperature obtained by heating and
cooling the samples (TPrA)[M(dca)3] (M: Fe2+, Co2+ and Ni2+) at a rate
of 20 K min1. Inset: Detail of the DSC curve for the Ni compound around
T1 (a) on heating at a rate of 20 K min1, and (b) on cooling at a rate of
2 K min1.
Studies at ambient pressure
3.1.1 DSC results. As shown in Fig. 1, the DSC curves of the
three compounds show three pairs of endothermic/exothermic
peaks in the heating/cooling runs, revealing that each of them
undergoes three reversible phase transitions in the temperature
interval 135–375 K. The temperatures for such transitions are
summarized in Table 1.
This journal is © The Royal Society of Chemistry 2016
Table 1 Summary of structural transition temperatures for Fe, Co and Ni
compounds obtained from DSC analysis on heating and cooling
Heating
Fe
Co
Ni
Cooling
T1 (K)
T2 (K)
T3 (K)
T1 (K)
T2 (K)
T3 (K)
286
246
216
300
301
302
331
341
356
279
230
175
292
292
291
330
339
355
The observed thermal hysteresis indicates the first order
character of such transitions, whose associated enthalpy and
entropy changes are indicated in Table S1 of the ESI.†
Taking into account that for an order–disorder transition
DS = R ln(N), where R is the gas constant and N is the ratio of
the number of configurations in the disordered and ordered
system, a value of N B 1.2–2.6 is calculated for each transition,
depending also on the given compound (see Table S1 of ESI†).
Such values are much lower than in the case of the analogue
Mn compound, [TPrA][Mn(dca)3], that exhibits a single phase
transition with N B 8.19
In the case of the Ni compound, we have to note that we
identified, by DSC, the previously reported high temperature
structural transition at B210 K.18 Nevertheless, we were not
able to also find the reported lower temperature structural
transition (B160 K), not even when measuring at the slow
temperature rate of 2 K min1. As we will show below,18 this
result is in agreement with our single-crystal X-ray diffraction
analysis, which also does not show the previously reported
re-entrant structural transition at 160 K for this compound. We
attribute this lack of transition to kinetic factors.
3.1.2 Crystal structures and structural transitions as a
function of temperature. In order to understand the origin of
these phase transitions, the crystal structures of the Fe, Co and
Ni compounds were investigated at different temperatures.
According to SCXRD, these compounds display four polymorphs
(hereafter named as I, Ia, Ib and II) from 100 K to 368 K, all
based on perovskite-like structures.
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In the following paragraphs, we will comparatively describe
the obtained structures, paying special attention to the novel
polymorphs (four, in the case of the Fe and Co compounds, two
in the case of the Ni compound), and focussing on details that
are relevant to understand the properties.
The crystallographic data for the four polymorphs of each of
the three compounds are compiled in Tables S2–S4 of the ESI,†
and a summary of selected bond lengths and angles is provided
in the Tables S5–S8 of the ESI.†
Polymorph I. Below 286 K (M: Fe2+), 246 K (M: Co2+) and
216 K (M: Ni2+) the structure of these compounds is tetragonal,
space group P4% 21c (non-centrosymmetric), and it can be described
as a 2a 2a 2a perovskite super-structure.
The asymmetric unit is defined by one independent metal
cation, three dca anions and three TPrA cations. The metal
cations are in a distorted [MN6] octahedral environment with
six different M–N distances, see Table S5 of the ESI.† The
resulting [MN6] octahedra are rotated cooperatively along
the main crystallographic axes (tilt systems ab+c at Glazer
notation).24 The TPrA cations are located inside the cavities of
the resulting framework.
As it also occurs in the other polymorphs, and as it could be
expected, as the size of the M (perovskite B-site cation) decreases
from Fe2+ to Ni2+, the unit cell volume and the M–N bond
lengths were observed to decrease. In addition, the octahedra
tilting in the ab plane decreases.
As seen in Fig. 2, the structures exhibit a certain disorder in
the dca anions (in the N-amide atoms along the c-axis) and in
the C atoms of the TPrA cations, as it was previously described
for the Ni and Mn compounds.18,19 In addition, we remark a
most interesting new feature: half of the TPrA cations inside
the pseudo-cubooctahedral cavities (those located on a 2-fold
axis) show a cooperatively off-center shift along the c-axis,
Fig. 2 Conventional perovskite structure view and unit cell of polymorph
I. The dca ligands act as m1–5 bridges between the M cations. The N-amide
atom of the dca ligands along the c-axis are modeled in two crystallographic
positions. The TPrA cations are located inside the pseudo-cubooctahedral
cavities, and two of the three present in the asymmetric unit display
crystallographic disorder in the C atom positions. The H-atoms of the
TPrA cations have been omitted to facilitate visualization of the structure.
4892 | J. Mater. Chem. C, 2016, 4, 4889--4898
Journal of Materials Chemistry C
following an antiferrodistortive up-down/up-down pattern, see
Fig. S2 of the ESI.†
Such displacement, that increases as the size of the M (B-site
cation) decreases, is 0.095(9) Å (M: Fe2+), 0.069(0) Å (M: Co2+)
and 0.038(2) Å (M: Ni2+).
The characteristics of this low temperature polymorph are
similar to those recently reported for polymorph I of the Mn
analogue19 where the TPrA shift along the c-axis is even larger
(0.105(3) Å).
In the case of the Ni compound, for which this polymorph I
has already been described before,18 a re-entrant phase transition
from polymorph I to polymorph Ia (described below) at 160 K
is also reported.18 Nevertheless, our SCXRD data (supported by
our DSC analysis) do not reveal this structural transition.
The polymorph I is maintained down-to 100 K. Therefore, we
rationalize that the previously reported re-entrant structural
transition could be related to kinetic factors that depend on
the cooling rate and stabilization time.
Polymorph Ia. At T1 (see Table 1), the structure of polymorph I
transforms into that of polymorph Ia of orthorhombic symmetry,
space group Pnna (centrosymmetric) and a different 2a
E2O2a E2O2a perovskite super-lattice, where apol.Ia E cpol.I,
and bpol.Ia, cpol.Ia E O2apol.I, see Tables S2–S4 of the ESI.†
The asymmetric unit contains two independent metal cations,
eight dca anions and four TPrA cations. As in polymorph I, each
metal cation is in a distorted octahedral environment with six
different M–N distances (see Table S6 of the ESI†) and the [MN6]
octahedra are cooperatively rotated following an ab+c tilt system.
On the other hand, and as could be expected, this polymorph
Ia shows a slightly larger disorder than polymorph I (Fig. 3). The
positions of the N-amide of the dca ligands along the a-axis had
to be modeled occupying two (or three positions depending on
the dca ligand) with equal occupancies; also, three of the four
TPrA cations in the asymmetric unit present disorder in the C
atom positions of their propyl groups.
Fig. 3 Perovskite structure view and unit cell of polymorph Ia. The
N-amide atom of the dca ligands along the c-axis show more thermal
disorder than in polymorph I and they are modeled in either two or three
crystallographic positions. In addition, three of the four TPrA cations in the
asymmetric unit show disorder in the C atoms. The H atoms of the TPrA
cations have been omitted to facilitate visualization of the structure.
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And most remarkably, all the TPrA cations are in off-center
positions following a cooperative pattern different from that
shown by polymorph I, see Fig. S3 of the ESI:† (a) half of them
(those located on a 2-fold axis along the a-axis) show a cooperative
off-center shift (about 0.23 Å, B15% larger than in polymorph I
along such a direction) along the a-axis towards one side
of these cavities. These displaced TPrA cations are antiferrodistortively arranged along the b-axis, displaying an up-downup-down pattern. (b) The other half of the TPrA cations
(those located on a 2-fold axis along the c-axis) show an
even larger cooperative off-center shift (up to 0.62 Å) along the
c-axis towards one edge of these cavities, following an antiferrodistortive pattern.
Polymorph Ib. At T2, the structure of these [TPrA][M(dca)3],
(M: Fe2+, Co2+ and Ni2+) compounds changes again: even if its
symmetry remains orthorhombic, its space group changes to
Ibam (centrosymmetric), and it has to be described on the basis
of a different EO2a EO2a 2a super-lattice, see Tables S2–S4
of the ESI.†
In this case, the asymmetric unit contains one independent
metal cation, two dca anions and one TPrA cation. The transition metal cations are in a slightly distorted octahedral environment with three different M–N bond lengths, see Table S7 of
the ESI.† And differently from polymorph I and polymorph Ia,
here the [MN6] octahedra are cooperatively rotated within the
ab plane and display an anticlockwise arrangement along the
c-axis (tilt systems a0a0c at Glazer notation).
Also, in this polymorph, the dca ligands show a much larger
disorder than in the case of polymorph Ia, especially along the
c-axis, so that the N-amide atom and the C atom had to be
modeled occupying the 8 and 4 positions, respectively. This
increase suggests a dynamic disorder along such a direction
that would imply the rotation of the dca ligands around the
c-axis axis, see Fig. 4.
As for the TPrA cations, which are also more disordered than
in polymorph Ia, the most important remark is that they are
located at the center of the cavities (Fig. 4). This is in contrast to
the previous polymorphs. As indicated above, half (polymorph I)
or all of them (polymorph Ia) are off-shifted.
Polymorph II. At T3 (see Table 1) the structure of these compounds
changes again and transforms into that of polymorph II with
tetragonal symmetry and space group I4/mcm (centrosymmetric),
even if the same perovskite super-lattice as polymorph Ib,
EO2a EO2a 2a. In fact, the space group of that lower
temperature polymorph is a subgroup of polymorph II.
In that context, both polymorphs Ib and II are quite similar
and their main differences rely on their symmetry and the even
larger disorder of the dca ligands and TPrA cations in this
higher temperature polymorph, see Fig. 5. On the other hand,
and as in polymorph Ib, the TPrA cations remain centered in
the cavities.
Therefore, different from the previous transitions, this
occurs only at T3 and involves order/disorder phenomena with
no ionic displacements.
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Fig. 4 Crystal structure view and unit cell of polymorph Ib. The N-amide
and C atoms of the dca ligands along the c-axis are modeled in the 8 and 4
crystallographic positions, respectively. Moreover, the N-amide atom of
the dca ligands in the ab plane is modeled in two crystallographic
positions. As for the TPrA cations, all of them display thermal disorder in
the C atoms.
Fig. 5 Conventional perovskite structure view and unit cell of polymorph
II. Similar to polymorph Ib, the N-amide and C atoms of the dca ligands
along the c-axis are modeled in the 8 and 4 crystallographic positions,
respectively. Meanwhile, the N-amide and C atoms of the dca ligands
in the ab plane are modeled in 5 and 3 crystallographic positions,
respectively. In addition, all the TPrA cations display and even higher
disorder in the C atoms.
This polymorph II of the Fe, Co and Ni compounds is similar
to that recently reported for the Mn compound above 330 K.19
3.1.3 Dielectric properties. The temperature dependence of
the real part of the complex dielectric permittivity, er 0 , (also
known as the dielectric constant) of (TPrA)[M(dca)3] (M: Fe2+,
Co2+ and Ni2+) is shown in Fig. 6. Very interestingly, as can be
seen in Fig. 6, in the three compounds, three anomalies are
detected in the vicinity of the structural phase transition, those
occurring at T1 and T2 being sharper than that taking place at
T3, specially the first one.
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This situation is reminiscent of that recently described for
the Mn analogue, where a dielectric anomaly is observed above
room temperature, Tt B 330 K, associated to the change from a
cooperative to a non-cooperative electric behaviour (antiferroelectric (AFE) to paraelectric (PE) transition). The former
implies an AFE distribution of electric dipoles in polymorph
I, related to an off-shift of the apolar TPrA cations and the
order–disorder of the polar dca ligands mechanisms.
Nevertheless, in the case of here studied, (TPrA)[M(dca)3]
(M: Fe2+, Co2+ and Ni2+), they not only show one but multiple
dielectric anomalies that are related to the richer assortment of
crystal structures displayed by these compounds.
Another aspect that should be emphasized is the significant
difference in the origin of the dielectric transitions displayed by
these (TPrA)[M(dca)3] (M: Mn2+, Fe2+, Co2+ and Ni2+) compounds,
and those previously reported for nother hybrid perovskites such
as [AmineH][M(X)3], (AmineH: midsized alkylammonium cations,
X: N3, CN or HCOO ligands).8–17 These latter contain polar
cations inside the cubooctahedral cavities and/or H-bonds
between the cations and the framework, and their dielectric
transitions arise from order–disorder processes of the guest
polar molecules.
Nevertheless, in the case of this novel dicyanamide family of
[TPrA][M(dca)3] (M: Mn2+, Fe2+, Co2+ and Ni2+), the guest TPrA
cations are non-polar and cannot form H-bonds, so that the
mechanisms associated with the dielectric response are completely
different, namely: (a) this response is related to a contribution of a
cooperative off-shift of the guest TPrA cations inside the cavities
that is reminiscent of the behaviour shown by ceramic ferroelectrics with perovskite structure, such as BaTiO3 (where the
B-site cation is the one experiencing the temperature dependent
reversible displacement, giving rise to the electric order). (b) It is
also related to order–disorder processes driven by the polar dca
ligands. This interesting feature can provide a novel mechanism
to couple the magnetic and dielectric response of these compounds
since the dca bridges are also involved in the magnetic interaction
between the metal cations.
Fig. 6 Temperature dependence of the dielectric constant (er 0 ) of
the Fe, Co and Ni compounds measured at different frequencies
(105–106 Hz).
Taking into account the previous structural information, we
ascribe such anomalies to the following processes:
(a) At T1, the dca ligands remain disordered in both polymorphs
mainly due to the cooperative displacement of the TPrA cations
between two different antiferrodistortive arrangements that
involve off-centered positions. (b) At T2, we relate it to the
displacement of the TPrA cations (which are off-center shifted
in polymorph Ia) to center positions in polymorph Ib. In
addition, the increase disorder experienced by the polar dca
ligands could also be contributing to the observed dielectric
anomaly. (c) Finally, at T3, we relate it to the additional order/
disorder transition experienced by both the dca ligands and
TPrA cations on passing from polymorph Ib to polymorph II.
4894 | J. Mater. Chem. C, 2016, 4, 4889--4898
3.2 Influence of external and internal pressure on the
structural and dielectric transition
In what follows, we will show that these compounds are very
sensitive to both applied external pressures, even small ones
(P o 2 kbar), as well as to internal chemical pressure induced
by modifying the size of the B-site cations.
3.2.1 Influence of external pressure. We have studied the
behaviour of the axial dilatometry of these samples under
applied external pressures in the range 200 r P(bar) r 1600.
As it can be seen in Fig. 7, the PVT analysis allows an easy
monitoring of the transition temperatures as a function of
pressure, as a kink-shaped anomaly is observed in the curves
at T1, T2 and T3.
Interestingly, the kinks at T1 and T3 are highly pressure
dependent, while no significant pressure dependence is observed
for that appearing at T2.
As for the kink observed at T1, that implies an increase in
the axial length. It gets progressively displaced towards higher
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Fig. 7 PVT graphic showing the length variation of the Co sample as a
function of temperature measured at different axial pressures (from 200 to
1600 bar). Dash lines signal the temperature shift of T1, T2 and T3 as a function
of pressure. Similar results are obtained for the other Fe and Ni compounds.
temperatures as pressure increases, that is, it exhibits positive
pressure dependence, dTt/dP E +23 K kbar1. This value is of
the same order for the Mn compound previously reported,
dTt/dP = +24.2 K kbar1.19 Meanwhile, the anomaly observed
at T3, which implies a sharp decrease in the axial length,
gets progressively displaced towards lower temperatures upon
application of increasing pressures. This means that this
transition displays a negative pressure dependence, dTt/dP o 0,
whose absolute value is similar to that of the previous case, even
if negative, dTt/dP E 23 K kbar1.
To further deepen the peculiar pressure dependence of
the transition occurring at T3, we have performed additional
pressure differential scanning calorimetry (PDSC) studies applying
smaller pressures (up to 69 bar).
As can be seen in Fig. 8, both the endothermic and exothermic
peaks associated with this transition experience a progressive
displacement towards lower temperatures as pressure is increased,
with a value of dTt3/dP = 18.4 K kbar1, of the same order
to that found in the PVT experiments. Meanwhile, we observed
that the enthalpy (DH) and entropy (DS) changes involved
in such a transition remained constant under the applied
external pressure.
Fig. 8 Pressure differential scanning calorimetry (PDSC) curves for the T3
transition of the Co compound. Similar behaviour is found in the Fe and Ni
compounds.
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Paper
Fig. 9 Temperature dependence of the dielectric constant (er 0 ) of the Co
compound, measured at 105 Hz under hydrostatic pressure conditions,
from 1 to 2000 bar. The curves have been normalized and displaced for a
better view. The Fe and Ni compounds exhibit a similar behaviour.
We have also studied the effect of external pressures (up to
P r 2000 bar) in the temperature dependence of the dielectric
permittivity of these compounds. As an example of such
behaviour, we show in Fig. 9 the effect of external pressure on
the dielectric response of the Co-compound in the temperature
range where the anomaly at T3 is detected.
As can be seen, for P o 1500 bar, the kink observed at T3 in
the er 0 vs. T curve experiences a progressive displacement
towards lower temperatures as pressure increases, in agreement
with previous experiments.
Meanwhile, and very interestingly, when pressures that are
higher than those previously used are applied, P Z 1500 bar,
the shape of the kink changes and a new transition (TN) is
found, which gets shifted to higher temperatures as pressure is
further increased.
Taking into account that the shape and pressure dependence
of such a peak is similar to that experienced by the Mn
compound,19 we ascribe it to a new pressure-induced structural
transition transforming directly polymorph I to polymorph II in
these Fe, Co and Ni compounds.
This in turn means that polymorphs Ia and Ib become
thermodynamically unstable under applied pressure, and that
both will disappear for P 4 1600 bar. In fact, for higher
pressures, a single structural transition between polymorph I
and II is expected, similar to the case of the Mn analogue.19
3.2.2 Influence of internal chemical pressure. Chemical
pressure is a well-established physical variable that can greatly
affect the properties of perovskites, as widely recognized in the
field of perovskite oxides ABO3.3,4,25–27
As it is well-known in those compounds, the origin of the
internal chemical pressure is in the size mismatch that occurs
when the A-site ions are too small to fill the space in the threedimensional network of the [MO6] octahedral. This mismatch
can be estimated as Z = 1 a, which is the deviation of the
tolerance factor (a) of the structure from the ideal value.25–27
Extending this idea to the here studied [TPrA][M(dca)3]
(M = Mn2+, Fe2+, Co2+ and Ni2+) perovskite compounds, where
the ionic radius of the B-site cations follows the sequence
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rB: Mn2+ 4 Fe2+ 4 Co2+ 4 Ni2+, it can be expected that the
tolerance factor will increase along the series while the internal
pressure will decrease.
Moreover, we have calculated the value of such tolerance
factors (a) following the approach recently introduced by
Kieslich et al.28 to extend the concept of Goldschmidt’s tolerance
factor to hybrid inorganic–organic perovskites.
For that purpose, and using the modified Goldschmidt’s
equation, a = (rA(eff) + rX(eff))/O2(rB + 0.5hX(eff)),28 we have
calculated the value of a from experimental room temperature
crystallographic data of A-site (TPrA) and X-site (dca) ions and
using the Shannon ionic radii tables29 for the B-site (transition
metal) cations.
From the obtained values, which are summarized in Table
S6 of the ESI† and range between 1.02(6) (M: Mn2+) and 1.05(9)
(M: Ni2+), it is worth highlighting two aspects: (a) they reflect
the expected increase in the tolerance factor as the size of B
decreases, even if the large values of X (and A) prevent them
from a larger variation. (b) Taking into account the large and
complex A and X ions involved, and the simplicity of the model
assumed to calculate their effective ionic sizes, the values
obtained for the tolerance factor are extremely good. They fit
very nicely within the TF region for which perovskite structures
are expected to form (between 0.8–1.0 6%)28 even if in this
particular [TPrA][M(dca)3] system the upper limit is going to
be slightly larger. These results also indicate that, in this
dicyanamide series, the formation of hexagonal polytypes will
require at least a 4 1.05(9).
Another very interesting point that comes out from these
results is the parallelism between the effect on internal pressure
and external pressure on the structure of these dicyanamide
compounds: both increasing external pressure or increasing the
size of B reduces the temperature range in which the intermediate polymorphs Ia and Ib exist, until they finally disappear,
as observed for the case of the Mn compound and for external
pressures above 1500 bar, see Fig. S4 of the ESI.†
A final aspect that is worth referring to is the origin of the
different pressure dependences displayed by the three consecutive
temperature-induced phase transitions, and whose trend is
again similar in the case of external and internal pressure. In
that context, and as mentioned before, while the transition
occurring at T1 shows the more commonly observed dTt/dP 4 0,
that at T3 shows a more scarcely seen pressure dependence of
the negative sign dTt/dP o 0, and that at T2 is almost pressure
independent.
To understand this behaviour, it is interesting to revisit
previous studies carried out on oxidic and halidic perovskites,
which have established that the sign of dTt/dP can depend on
two factors: (a) the mechanism of the phase transition, whether
it is displacive or an order–disorder type, and (b) the value of
the tolerance factor that determines the change of stability of
its cubic phase under P.30
As for (a), order–disorder transitions can be responsible for
dTt/dP o 0, while displacive transitions give dTt/dP 4 0.30 In the
case of (b), when a is below the ideal value 1, the pressure
reduces the stability of the cubic phase and favours those of
4896 | J. Mater. Chem. C, 2016, 4, 4889--4898
Journal of Materials Chemistry C
lower symmetry, resulting in dTt/dP 4 0. Meanwhile in systems
with a 4 1 and hexagonal stacking, pressure stabilizes the cubic
stacking at the expense of the former, resulting in dTt/dP o 0.25
In the case of the here studied [TPrA][M(dca)3] series, where
the four compounds exhibit perovskite-like distorted structures
and none of them the hexagonal stacking expected for a 4 1,
we relate the different pressure dependences displayed by
the three consecutive temperature-induced phase transitions
to the prevailing mechanism of each of them: this would be
the displacive one in the transition occurring at T1 and the
order–disorder one in the case of T3. Meanwhile, the close
competition between these two mechanisms in the case of T2
will result in almost no pressure dependence.
These external/internal pressure-responses reveal an easy
tuning of the structural transition temperature for these hybrid
perovskites. Since these structural transitions are in turn related
to the dielectric properties, they can be used to modulate
different dielectric responses in a wide range of temperatures
near room temperature (from 210 to 360 K) either by applying
small external pressures (P o 2 kbar) or simply by making
appropriate ionic substitutions.
Therefore, this family of [TPrA][M(dca)3] dicyanamides provides
promising technological applications as dielectric transductors,
sensitive towards small changes of temperature and pressure
values, that can even be easily modulated by appropriate ionic
substitutions.
4. Conclusions
The hybrid inorganic–organic [TPrA][M(dca)3] (M: Fe2+, Co2+
and Ni2+) compounds are singular materials with perovskitetype structure. In these materials, [MN6] octahedral are linked
by m1,5-dca bridges forming pseudo cubooctahedral cavities,
that hold TPrA cations inside. Remarkably, they exhibit multiple
phase transitions, that display up to three first-order structural
transition between four different polymorphs (I, Ia, Ib and II) in
a range of temperatures near room temperature (210–360 K).
This finding is in contrast with the analogous Mn compound
that only displays one first-order transition at Tt B 330 K.
Interestingly, these compounds also show multiple dielectric
anomalies that are related to their richer assortment of crystal
structures. Another aspect that should be emphasized is the
significant difference in the origin of the dielectric transitions
displayed by these (TPrA)[M(dca)3] (M: Fe2+, Co2+ and Ni2+)
compounds, and those previously reported for other hybrid
perovskites. In the case of these novel dicyanamide perovskitelike compounds, the guest TPrA cations are non-polar and
cannot form H-bonds, so that the mechanisms associated with
the dielectric response are related to: (a) the contribution of a
cooperative off-shift of the guest TPrA cations inside the cavities;
and (b) order–disorder processes driven by the polar dca ligands.
In addition, we have studied the parallelism between the
effect of the external hydrostatic pressure (P o 2 kbar) and the
internal chemical pressure (by modifying the ionic radii and thereby
the tolerance factor) on the phase and dielectric transitions.
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It is important to highlight that we can modulate the structural
and dielectric transition temperature as a function of external/
internal pressure: by increasing the external pressure or increasing
the M (perovskite B-site cations) ionic radii (decreasing the
tolerance factor), we can reduce the thermal stability of the
intermediate polymorphs Ia and Ib, and even suppress them.
Therefore, the hybrid perovskites [TPrA][M(dca)3] (M: Fe2+,
2+
Co and Ni2+) are unique multi-sensitive materials where their
multiple phase and dielectric transitions can be easily tuned as
a function of external pressures as well as by internal chemical
pressure. To our knowledge, these are the first examples of
hybrid inorganic–organic perovskite-like materials with multiple
dielectric transitions that offer easy temperature, pressure and
chemical modulation. In that event, these singular materials offer
potential interest for future technological applications such as
temperature and pressure sensing.
Acknowledgements
The authors are grateful for the financial support from Ministerio
de Economı́a y Competitividad MINECO (MINECO) ENE201456237-C4-4-R and Xunta de Galicia under the project GRC2014/
042. J. M. B.-G. also wants to thank Barrié Foundation for a
predoctoral fellowship and S. Y.-V. to the Xunta de Galicia for a
postdoctoral grant (Plan I2C).
Notes and references
1 (a) P. Granger, V. I. Parvulescu, S. Kaliaguine and W. Prellier,
Perovskites and Related Mixed Oxides: Concepts and Applications,
Wiley-VCH, Weinheim, Germany, 2015; (b) F. S. Galasso,
Structure, properties, and preparation of perovskite-type compounds,
Pergamon Press, New York, 1969; (c) M. A. Peña and
J. L. G. Fierro, Chem. Rev., 2001, 101, 1981–2018.
2 (a) M. E. Lines and A. M. Glass, Principles applications of
ferroelectric and related materials, Oxford Unviersity Press,
New York, 2001; (b) F. Jona and G. Shirane, Ferroelectric
Crystals, Pergamon Press, Oxford, 1962.
3 J. M. Tarascon and B. G. Bagley, in Chemistry of superconducting materials, ed. T. A. Vanderah, Noyes Publications,
1992.
4 C. N. R. Rao and B. Raveau, Colossal magnetoresistance,
charge ordering and related properties of Manganese oxides,
World Scientific Publications, Hackensack, NJ, USA, 2004.
5 N. A. Spaldin and M. Fiebig, Science, 2005, 309, 391–392.
6 D. Mitzi, in Prog. Inorg. Chem., ed. K. D. Karlin, John Wiley &
Sons, New York, USA, 1999, ch. 1, vol. 48.
7 (a) M. M. Lee, J. Teuscher, T. Miyasaka, T. N. Murakami and
H. J. Snaith, Science, 2012, 338, 643–647; (b) J. Burschka,
N. Pellet, S. J. Moon, R. Humphry-Baker, P. Gao, M. K.
Nazeeruddin and M. Grätzel, Nature, 2013, 499, 316–319;
(c) N. J. Jeon, J. H. Noh, W. S. Yang, Y. C. Kim, S. Ryu, J. Seo
and S. I. Seok, Nature, 2015, 517, 476–480; (d) M. Sessolo
and H. J. Bolink, Science, 2016, 350, 917.
This journal is © The Royal Society of Chemistry 2016
Paper
8 (a) X.-H. Zhao, X.-C. Huang, S.-L. Zhang, D. Shao, H.-Y. Wei
and X.-Y. Wang, J. Am. Chem. Soc., 2013, 135, 16006–16009;
(b) Z.-Y. Du, Y.-P. Zhao, W.-X. Zhang, H.-L. Zhou, C.-T. He,
W. Xue, B.-Y. Wang and X.-M. Chen, Chem. Commun., 2014,
50, 1989–1991; (c) Z.-Y. Du, Y.-P. Zhao, C.-T. He, B.-Y. Wang,
W. Xue, H.-L. Zhou, J. Bai, B. Huang, W.-X. Zhang and
X.-M. Chen, Cryst. Growth Des., 2014, 14, 3903–3909;
(d) Z.-Y. Du, Y.-Z. Sun, S.-L. Chen, B. Huang, Y.-J. Su,
T.-T. Xu, W.-X. Zhang and X.-M. Chen, Chem. Commun.,
2015, 51, 15641–15644; (e) Z.-Y. Du, T.-T. Xu, B. Huang,
Y.-J. Su, W. Xue, C.-T. He, W.-X. Zhang and X.-M. Chen,
Angew. Chem., 2015, 127, 928–932; ( f ) L. C. Gómez-Aguirre,
B. Pato-Doldán, A. Stroppa, L.-M. Yang, T. Frauenheim,
J. Mira, S. Yáñez-Vilar, R. Artiaga, S. Castro-Garcı́a,
M. Sánchez-Andújar and M. A. Señarı́s-Rodrı́guez, Chem. –
Eur. J., 2016, DOI: 10.1002/chem.201503445.
9 (a) W. Zhang, Y. Cai, R.-G. Xiong, H. Yoshikawa and
K. Awaga, Angew. Chem., Int. Ed., 2010, 122, 6758–6760;
(b) W. Zhang, H.-Y. Ye, R. Graf, H. W. Spiess, Y.-F. Yao,
R.-Q. Zhu and R.-G. Xiong, J. Am. Chem. Soc., 2013, 135,
5230–5233; (c) X. Zhang, X.-D. Shao, S.-C. Li, Y. Cai,
Y.-F. Yao, R.-G. Xiong and W. Zhang, Chem. Commun.,
2015, 51, 4568–4571; (d) W.-J. Xu, S.-L. Chen, Z.-T. Hu,
R.-B. Lin, Y.-J. Su, W.-X. Zhang and X.-M. Chen, Dalton
Trans., 2016, 45, 4224–4229.
10 (a) P. Jain, N. S. Dalal, B. H. Toby, H. W. Kroto and A. K.
Cheetham, J. Am. Chem. Soc., 2008, 130, 10450–10451; (b) P. Jain,
V. Ramachandran, R. J. Clark, H. D. Zhou, B. H. Toby, N. S.
Dalal, H. W. Kroto and A. K. Cheetham, J. Am. Chem. Soc., 2009,
131, 13625–13627; (c) Z. Zhang, W. Li, M. A. Carpenter,
C. J. Howard and A. K. Cheetham, CrystEngComm, 2015, 17,
370–374; (d) G. Kieslich, A. C. Forse, S. Sun, K. T. Butler,
S. Kumagai, Y. Wu, M. R. Warren, A. Walsh, C. P. Grey and
A. K. Cheetham, Chem. Mater., 2016, 28, 312–317; (e) G. Kieslich,
S. Kumagai, K. T. Butler, T. Okamura, C. H. Hendon, S. Sun,
M. Yamashita, A. Walsh and A. K. Cheetham, Chem. Commun.,
2015, 51, 15538–15541.
11 (a) R. Shang, G.-C. Xu, Z.-M. Wang and S. Gao, Chem. – Eur. J.,
2014, 20, 1146–1158; (b) S. Chen, R. Shang, K.-L. Hu, Z.-M. Wang
and S. Gao, Inorg. Chem. Front., 2014, 1, 83–98; (c) S. Chen,
R. Shang, B.-W. Wang, Z.-M. Wang and S. Gao, Angew. Chem.,
2015, 127, 11245–11248; (d) R. Shang, S. Chen, B.-W. Wang,
Z.-M. Wang and S. Gao, Angew. Chem., 2016, 128, 2137–2140.
12 (a) M. Sánchez-Andújar, S. Presedo, S. Yáñez-Vilar, S. CastroGarcı́a, J. Shamir and M. A. Señarı́s-Rodrı́guez, Inorg. Chem.,
2010, 49, 1510–1516; (b) B. Pato-Doldán, M. SánchezAndújar, L. C. Gómez-Aguirre, S. Yáñez-Vilar, J. LópezBeceiro, C. Gracia-Fernández, A. A. Haghighirad, F. Ritter,
S. Castro-Garcı́a and M. A. Señarı́s-Rodrı́guez, Phys. Chem.
Chem. Phys., 2012, 14, 8498–8501; (c) J. López-Beceiro,
C. Gracia-Fernández, S. Gómez-Barreiro, S. Castro-Garcı́a,
M. Sánchez-Andújar and R. Artiaga, J. Phys. Chem. C, 2012,
116, 1219–1224; (d) B. Pato-Doldán, L. C. Gómez-Aguirre,
J. M. Bermúdez-Garcı́a, M. Sánchez-Andújar, A. Fondado,
J. Mira, S. Castro-Garcı́a and M. A. Señarı́s-Rodrı́guez,
RSC Adv., 2013, 3, 22404–22411; (e) M. Sánchez-Andújar,
J. Mater. Chem. C, 2016, 4, 4889--4898 | 4897
View Article Online
Open Access Article. Published on 14 April 2016. Downloaded on 1/26/2021 1:47:38 PM.
This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.
Paper
L. C. Gómez-Aguirre, B. Pato-Doldán, S. Yáñez-Vilar, R. Artiaga,
A. L. Llamas-Saiz, R. S. Manna, F. Schnelle, M. Lang, F. Ritter,
A. A. Haghighirad and M. A. Señarı́s-Rodrı́guez, CrystEngComm,
2014, 16, 3558–3566; ( f ) L. C. Gómez-Aguirre, B. Pato-Doldán,
A. Stroppa, S. Yáñez-Vilar, L. Bayarjargal, B. Winkler, S. CastroGarcı́a, J. Mira, M. Sánchez-Andújar and M. A. Señarı́sRodrı́guez, Inorg. Chem., 2015, 54, 2109–2116.
13 (a) B. Zhou, Y. Imai, A. Kobayashi, Z.-M. Wang and H. Kobayashi,
Angew. Chem., Int. Ed. Engl., 2011, 50, 11441–11445; (b) Y. Imai,
B. Zhou, Y. Ito, H. Fijimori, A. Kobayashi, Z. M. Wang and
H. Kobayashi, Chem. – Asian J., 2012, 7, 2786–2790.
14 (a) A. Stroppa, P. Barone, P. Jain, J. M. Perez-Mato and S. Picozzi,
Adv. Mater., 2013, 25, 2284–2290; (b) Y. Tian, A. Stroppa, Y.-S.
Chai, P. Barone, M. Perez-Mato, S. Picozzi and Y. Sun, Phys.
Status Solidi RRL, 2015, 9, 62–67; (c) M. Ptak, M. Mczka, A. Ggor,
A. Sieradzki, A. Stroppa, D. Di Sante, J. M. Perez-Mato and
L. Macalik, Dalton Trans., 2016, 45, 2574–2583.
15 (a) M. Mczka, A. Ciupa, A. Ggor, A. Sieradzki, A. Pikul, B. Macalik
and M. Drozd, Inorg. Chem., 2014, 53, 5260–5268; (b) M. Mczka,
A. Pietraszko, B. Macalik and K. Hermanowicz, Inorg. Chem.,
2014, 53, 787–794; (c) M. Mczka, A. Ggor, B. Macalik, A. Pikul,
M. Ptak and J. Hanuza, Inorg. Chem., 2014, 53, 457–467; (d) M.
Mczka, A. Ggor, K. Hermanowicz, A. Sieradzki, L. Macalik and
A. Pikul, J. Solid State Chem., 2016, 237, 150–158.
16 (a) Y. Tian, A. Stroppa, Y. Chai, L. Yan, S. Wang, P. Barone,
S. Picozzi and Y. Sun, Sci. Rep., 2014, 4, 6062; (b) Y. Tian,
S. Shen, J. Cong, L. Yan, S. Wang and Y. Sun, J. Am. Chem.
Soc., 2016, 138, 782–785.
17 L. C. Gómez-Aguirre, B. Pato-Doldán, J. Mira, S. Castro-Garcı́a,
M. A. Señarı́s-Rodrı́guez, M. Sánchez-Andújar, J. Singleton and
V. S. Zapf, J. Am. Chem. Soc., 2016, 138, 1122–1125.
4898 | J. Mater. Chem. C, 2016, 4, 4889--4898
Journal of Materials Chemistry C
18 J. A. Schlueter, J. L. Manson and U. Geiser, Inorg. Chem.,
2005, 44, 3194–3202.
19 J. M. Bermúdez-Garcı́a, M. Sánchez-Andújar, S. Yáñez-Vilar,
S. Castro-Garcı́a, R. Artiaga, J. López-Beceiro, L. Botana,
A. Alegrı́a and M. A. Señarı́s-Rodrı́guez, Inorg. Chem., 2015,
54, 11680–11687.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr.,
Theor. Gen. Crystallogr., 2008, 64, 112–122.
21 L. J. Farrugia, Appl. Crystallogr., 2012, 45, 849–854.
22 Mercury 3.5.1 (Build RC5) – Crystal Structure Visualisation
(CCDC) http://www.ccdc.cam.ac.uk/mercury.
23 (a) J. D. Dudley and H. T. Hall, Phys. Rev., 1960, 118, 1211–1216;
(b) G. W. H. Höhne, W. Dollhopf, K. Blankenhorn and
P. U. Mayr, Thermochim. Acta, 1996, 273, 17–24.
24 A. M. Glazer, Acta Crystallogr., Sect. B: Struct. Sci., 1972, 28,
3384–3392.
25 J. B. Goodenough, J. A. Kafalas and J. M. Longo, in Preparative
methods in Solid State Chemistry, ed. P. Hagenmüller, Academic
press, New York, USA, 1972, ch. 1.
26 K. I. Kugel, A. L. Rakhmanov, A. O. Sboychakov, N. Poccia
and A. Bianconi, Phys. Rev. B: Condens. Matter Mater. Phys.,
2008, 78, 165124.
27 H. Y. Hwang, T. T. Palstra, S.-W. Cheong and B. Batlogg, Phys.
Rev. B: Condens. Matter Mater. Phys., 1995, 52, 15046–15049.
28 (a) G. Kieslich, S. Suna and A. K. Cheetham, Chem. Sci., 2014,
5, 4712–4715; (b) G. Kieslich, S. Suna and A. K. Cheetham,
Chem. Sci., 2015, 6, 3430–3433.
29 R. D. Shannon, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1976, 32, 751.
30 K. S. Aleksandrov, J. Bartolome, M. V. Gorev and I. N. Flerov,
Phys. Status Solidi B, 2000, 217, 785–791.
This journal is © The Royal Society of Chemistry 2016