35 research outputs found
Five-Fold Ordering in High-Pressure Perovskites RMn<sub>3</sub>O<sub>6</sub> (R = Gd–Tm and Y)
Cation and anion
ordering plays an important role in the properties of materials, in
particular, in the properties of perovskite materials. Here we report
on unusual 5-fold cation/charge ordering in high-pressure-synthesized
(at 6 GPa and ∼1670 K) RMn<sub>3</sub>O<sub>6</sub> perovskites
with R = Gd–Tm and Y. R<sup>3+</sup>, Mn<sup>2+</sup>, and
Mn<sup>3+</sup> cations are ordered at the A site in two separate
chains consisting of R<sup>3+</sup> and alternating Mn<sup>2+</sup> (in tetrahedral coordination) and Mn<sup>3+</sup> (in square-planar
coordination), while Mn<sup>3+</sup> and mixed-valent Mn<sup>3+</sup>/Mn<sup>4+</sup> are ordered at the B site in layers. The ordering
can be represented as [R<sup>3+</sup>Mn<sup>2+</sup><sub>0.5</sub>Mn<sup>3+</sup><sub>0.5</sub>]<sub>A</sub>[Mn<sup>3+</sup>Mn<sup>3.5+</sup>]<sub>B</sub>O<sub>6</sub>. The triple cation ordering
observed at the A site is very rare, and the layered double-B-site
ordering is also scarce. RMn<sub>3</sub>O<sub>6</sub> compounds crystallize
in space group <i>Pmmn</i> with <i>a</i> = 7.2479(2)
Å, <i>b</i> = 7.4525(3) Å, and <i>c</i> = 7.8022(2) Å for DyMn<sub>3</sub>O<sub>6</sub> at 213 K, and
they are structurally related to CaFeTi<sub>2</sub>O<sub>6</sub>.
They are prone to nonstoichiometry, R<sub>1−δ</sub>Mn<sub>3</sub>O<sub>6–1.5δ</sub>, where δ = −0.071
to −0.059 for R = Gd, δ = 0 for R = Dy, δ = 0.05–0.1
for R = Ho and Y, and δ = 0.12 for R = Er and Tm. They show
complex magnetic behaviors with several transition temperatures, and
their magnetic properties are highly sensitive to the δ values
High-Pressure Synthesis, Crystal Structure, and Properties of BiPd<sub>2</sub>O<sub>4</sub> with Pd<sup>2+</sup> and Pd<sup>4+</sup> Ordering and PbPd<sub>2</sub>O<sub>4</sub>
BiPd<sub>2</sub>O<sub>4</sub> and PbPd<sub>2</sub>O<sub>4</sub> were synthesized at high pressure of 6 GPa and 1500 K. Crystal
structures of BiPd<sub>2</sub>O<sub>4</sub> and PbPd<sub>2</sub>O<sub>4</sub> were studied with synchrotron X-ray powder diffraction. BiPd<sub>2</sub>O<sub>4</sub> is isostructural with PbPt<sub>2</sub>O<sub>4</sub> and crystallizes in a triclinic system (space group <i>P</i>1̅, <i>a</i> = 5.73632(4) Å, <i>b</i> = 6.02532(5) Å, <i>c</i> = 6.41100(5) Å,
α = 114.371(1)°, β = 95.910(1)°, and γ
= 111.540(1)° at 293 K). PbPd<sub>2</sub>O<sub>4</sub> is isostructural
with LaPd<sub>2</sub>O<sub>4</sub> and BaAu<sub>2</sub>O<sub>4</sub> and crystallizes in a tetragonal system (space group <i>I</i>4<sub>1</sub>/<i>a</i>, <i>a</i> = 5.76232(1)
Å, and <i>c</i> = 9.98347(2) Å at 293 K). BiPd<sub>2</sub>O<sub>4</sub> shows ordering of Pd<sup>2+</sup> and Pd<sup>4+</sup> ions, and it is the third example of compounds with ordered
arrangements of Pd<sup>2+</sup> and Pd<sup>4+</sup> in addition to
Ba<sub>2</sub>Hg<sub>3</sub>Pd<sub>7</sub>O<sub>14</sub> and KPd<sub>2</sub>O<sub>3</sub>. In PbPd<sub>2</sub>O<sub>4</sub>, the following
charge distribution is realized Pb<sup>4+</sup>Pd<sup>2+</sup><sub>2</sub>O<sub>4</sub>. PbPd<sub>2</sub>O<sub>4</sub> shows a structural
phase transition from <i>I</i>4<sub>1</sub>/<i>a</i> to <i>I</i>2/<i>a</i> at about 240 K keeping
basically the same structural arrangements (space group <i>I</i>2/<i>a</i>, <i>a</i> = 5.77326(1) Å, <i>b</i> = 9.95633(2) Å, <i>c</i> = 5.73264(1) Å,
β = 90.2185(2)° at 112 K). BiPd<sub>2</sub>O<sub>4</sub> is nonmagnetic while PbPd<sub>2</sub>O<sub>4</sub> exhibits a significant
temperature-dependent paramagnetic moment of 0.46μ<sub>B</sub>/f.u. between 2 and 350 K. PbPd<sub>2</sub>O<sub>4</sub> shows metallic
conductivity, and BiPd<sub>2</sub>O<sub>4</sub> is a semiconductor
between 2 and 400 K
Crystal Structures and Properties of Perovskites ScCrO<sub>3</sub> and InCrO<sub>3</sub> with Small Ions at the A Site
ScCrO<sub>3</sub> and InCrO<sub>3</sub> were synthesized
at high
pressure of 6 GPa and 1500 K. Crystal structures of ScCrO<sub>3</sub> and InCrO<sub>3</sub> were studied with synchrotron X-ray powder
diffraction. They crystallize in the GdFeO<sub>3</sub>-type perovskite
structure (space group <i>Pnma</i>, <i>a</i> =
5.35845(1) Å, <i>b</i> = 7.37523(1) Å, <i>c</i> = 5.03139(1) Å for ScCrO<sub>3</sub> and <i>a</i> = 5.35536(1) Å, <i>b</i> = 7.54439(1) Å, <i>c</i> = 5.16951(1) Å for InCrO<sub>3</sub>). The physical
properties of ScCrO<sub>3</sub> and InCrO<sub>3</sub> were investigated
with specific heat, ac/dc magnetization, and dielectric measurements
and compared with those of YCrO<sub>3</sub> with nonmagnetic Y<sup>3+</sup> ions at the A site. Antiferromagnetic transitions occur
at <i>T</i><sub>N</sub> = 73 K in ScCrO<sub>3</sub> and
93 K in InCrO<sub>3</sub> in agreement with the general trend of ACrO<sub>3</sub> (A = Y and rare earths) where <i>T</i><sub>N</sub> decreases with decreasing the radius of the A ions. Extremely weak
ferromagnetism was found in ScCrO<sub>3</sub> and InCrO<sub>3</sub> in contrast to YCrO<sub>3</sub>. Ac magnetization measurements revealed
some peculiarities in behavior of ScCrO<sub>3</sub> and InCrO<sub>3</sub>, namely, double-peak anomalies just below <i>T</i><sub>N</sub>. Dielectric anomalies were observed in both compounds
at <i>T</i><sub>N</sub> indicating magnetoelectric coupling
in contact with YCrO<sub>3</sub> where no dielectric anomalies were
found. ScCrO<sub>3</sub> and InCrO<sub>3</sub> are very stable for
high-pressure phases: no decomposition of ScCrO<sub>3</sub> was observed
after heating up to 1340 K in air, and InCrO<sub>3</sub> only partially
decomposed at 1340 K to give Cr<sub>2</sub>O<sub>3</sub> and ambient-
and high-pressure modifications of In<sub>2</sub>O<sub>3</sub> as
impurities. No anomalies were also found with differential scanning
calorimetry up to 870 K and differential thermal analysis up to 1340
K, indicating the absence of high-temperature phase transitions
Two-Dimensional Brickblock Arrangement in Bis-Fused Tetrathiafulvalene Semiconductors
Molecular packing arrangement is
a very important factor in the
charge carrier mobility of organic semiconductors, but its rational
design has not been established as yet. Two-dimensional (2D) lamellar
packing is an advantageous arrangement for high charge mobility, but
few examples have been reported thus far. Herein we show crystal structures
and the electronic properties of newly designed bis-fused tetrathiafulvalene
(TTF) semiconductors with hetero substituent groups with distinct
electronic effects. Unprecedented 2D lamellar alignment is achieved
in a single crystal, where the bis-fused TTF rings interact three
dimensionally with face-to-face and side-by-side intermolecular S···S
contacts up to a total of 20 sites per π molecule and form graphitelike
“brickblock” structure. The charge mobility of a single
crystal is as high as 0.78 cm<sup>2</sup> V<sup>–1 </sup>s<sup>–1</sup>. Systematic investigations of the semiconductors
reveal a key role of intramolecular S···O interaction
between a bis-fused TTF ring and a methoxycarbonyl group in controlling
efficient arrangement, leading to high mobility
Two-Dimensional Brickblock Arrangement in Bis-Fused Tetrathiafulvalene Semiconductors
Molecular packing arrangement is
a very important factor in the
charge carrier mobility of organic semiconductors, but its rational
design has not been established as yet. Two-dimensional (2D) lamellar
packing is an advantageous arrangement for high charge mobility, but
few examples have been reported thus far. Herein we show crystal structures
and the electronic properties of newly designed bis-fused tetrathiafulvalene
(TTF) semiconductors with hetero substituent groups with distinct
electronic effects. Unprecedented 2D lamellar alignment is achieved
in a single crystal, where the bis-fused TTF rings interact three
dimensionally with face-to-face and side-by-side intermolecular S···S
contacts up to a total of 20 sites per π molecule and form graphitelike
“brickblock” structure. The charge mobility of a single
crystal is as high as 0.78 cm<sup>2</sup> V<sup>–1 </sup>s<sup>–1</sup>. Systematic investigations of the semiconductors
reveal a key role of intramolecular S···O interaction
between a bis-fused TTF ring and a methoxycarbonyl group in controlling
efficient arrangement, leading to high mobility
Two-Dimensional Brickblock Arrangement in Bis-Fused Tetrathiafulvalene Semiconductors
Molecular packing arrangement is
a very important factor in the
charge carrier mobility of organic semiconductors, but its rational
design has not been established as yet. Two-dimensional (2D) lamellar
packing is an advantageous arrangement for high charge mobility, but
few examples have been reported thus far. Herein we show crystal structures
and the electronic properties of newly designed bis-fused tetrathiafulvalene
(TTF) semiconductors with hetero substituent groups with distinct
electronic effects. Unprecedented 2D lamellar alignment is achieved
in a single crystal, where the bis-fused TTF rings interact three
dimensionally with face-to-face and side-by-side intermolecular S···S
contacts up to a total of 20 sites per π molecule and form graphitelike
“brickblock” structure. The charge mobility of a single
crystal is as high as 0.78 cm<sup>2</sup> V<sup>–1 </sup>s<sup>–1</sup>. Systematic investigations of the semiconductors
reveal a key role of intramolecular S···O interaction
between a bis-fused TTF ring and a methoxycarbonyl group in controlling
efficient arrangement, leading to high mobility
Selective Trapping of Labile S<sub>3</sub> in a Porous Coordination Network and the Direct X‑ray Observation
S<sub>3</sub> is one of the basic
allotropes of sulfur but is still
a mysterious labile species. We selectively trapped S<sub>3</sub> in
a pore of a thermally stable coordination network and determined S<sub>3</sub> structure by <i>ab initio</i> X-ray powder diffraction
analysis. S<sub>3</sub> in a pore has a <i>C</i><sub>2<i>v</i></sub> bent structure. The network containing trapped S<sub>3</sub> is remarkably stable under ambient conditions and is inert
to photoirradiation. S<sub>3</sub> in the network could be transformed
to S<sub>6</sub> by mechanical grinding or heating in the presence
of NH<sub>4</sub>X (X = Cl or Br). S<sub>6</sub> could be reverse-transformed
to S<sub>3</sub> by photoirradiation. We also determined the structure
of the network containing S<sub>6</sub> by <i>ab initio</i> X-ray powder diffraction analysis
Anion Order-to-Disorder Transition in Layered Iron Oxyfluoride Sr<sub>2</sub>FeO<sub>3</sub>F Single Crystals
Controlling the distribution of mixed
anions around a metal center
is a long-standing subject in solid state chemistry. We successfully
obtained single crystals of an iron-based layered perovskite compound,
Sr<sub>2</sub>FeO<sub>3</sub>F, by utilizing a high-pressure and high-temperature
technique. The phase prepared at 1300 °C and 3 GPa crystallized
in tetragonal space group <i>P</i>4/<i>nmm</i> with O/F atoms at the apical sites being ordered. However, a temperature
of 1800 °C and a pressure of 6 GPa resulted in partial O/F site
disordering. The degree of anion disordering, which was 5%, showed
that the anion-ordered arrangement was quite robust, in sharp contrast
to that of Sr<sub>2</sub>BO<sub>3</sub>F (B = Co or Ni) with the fully
disordered state. <sup>57</sup>Fe Mössbauer spectroscopy measurements
revealed no large difference in Néel temperatures between the
two phases, but the phase prepared under the latter condition exhibited
a quasi-continuous distribution of hyperfine fields caused by O/F
site disordering. We discuss the mechanism of the anion order-to-disorder
transition observed in related oxyfluoride perovskites
Selective Trapping of Labile S<sub>3</sub> in a Porous Coordination Network and the Direct X‑ray Observation
S<sub>3</sub> is one of the basic
allotropes of sulfur but is still
a mysterious labile species. We selectively trapped S<sub>3</sub> in
a pore of a thermally stable coordination network and determined S<sub>3</sub> structure by <i>ab initio</i> X-ray powder diffraction
analysis. S<sub>3</sub> in a pore has a <i>C</i><sub>2<i>v</i></sub> bent structure. The network containing trapped S<sub>3</sub> is remarkably stable under ambient conditions and is inert
to photoirradiation. S<sub>3</sub> in the network could be transformed
to S<sub>6</sub> by mechanical grinding or heating in the presence
of NH<sub>4</sub>X (X = Cl or Br). S<sub>6</sub> could be reverse-transformed
to S<sub>3</sub> by photoirradiation. We also determined the structure
of the network containing S<sub>6</sub> by <i>ab initio</i> X-ray powder diffraction analysis
High-Pressure Synthesis, Crystal Structure, and Properties of In<sub>2</sub>NiMnO<sub>6</sub> with Antiferromagnetic Order and Field-Induced Phase Transition
In<sub>2</sub>NiMnO<sub>6</sub>, a new compound extending the family
of double rare-earth perovskites <i>R</i><sub>2</sub>NiMnO<sub>6</sub> (<i>R</i> = rare earth, Y) to smaller <i>R</i> ions, was prepared using a high-pressure and high-temperature technique
(6 GPa and 1600 K). Its crystal structure was investigated by synchrotron
X-ray powder diffraction at room temperature: space group <i>P</i>2<sub>1</sub>/<i>n</i> (No. 14, cell choice 2), <i>Z</i> = 2, <i>a</i> = 5.13520(1) Å, <i>b</i> = 5.33728(1) Å, <i>c</i> = 7.54559(4) Å, and
β = 90.1343(1)°. A significant degree of ordering of Mn<sup>4+</sup> and Ni<sup>2+</sup> ions was observed. The dc and ac magnetization
and specific heat measurements showed that In<sub>2</sub>NiMnO<sub>6</sub> is an antiferromagnet with a Néel temperature <i>T</i><sub>N</sub> of 26 K. Its antiferromagnetism puts it apart
from other members of the <i>R</i><sub>2</sub>NiMnO<sub>6</sub> family where a ferromagnetic ground state was observed, which
is attributed to the superexchange interaction between Mn<sup>4+</sup> and Ni<sup>2+</sup> ions according to the Kanamori–Goodenough
rules. A field-induced phase transition to a ferromagnetic state was
observed from 18 kOe at 5 K, indicating that In<sub>2</sub>NiMnO<sub>6</sub> is close to the antiferromagnetic–ferromagnetic transition
boundary. First-principles calculations allowed us to explain its
antiferromagnetism and the field-induced phase transition and predict
the E* type antiferromagnetic ground state