Five-Fold Ordering in High-Pressure Perovskites RMn₃O₆ (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) RMn₃O₆ perovskites with R = Gd–Tm and Y. R³⁺, Mn²⁺, and Mn³⁺ cations are ordered at the A site in two separate chains consisting of R³⁺ and alternating Mn²⁺ (in tetrahedral coordination) and Mn³⁺ (in square-planar coordination), while Mn³⁺ and mixed-valent Mn³⁺/Mn⁴⁺ are ordered at the B site in layers. The ordering can be represented as [R³⁺Mn²⁺_0.5Mn³⁺_0.5]_A[Mn³⁺Mn^3.5+]_BO₆. The triple cation ordering observed at the A site is very rare, and the layered double-B-site ordering is also scarce. RMn₃O₆ 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 DyMn₃O₆ at 213 K, and they are structurally related to CaFeTi₂O₆. They are prone to nonstoichiometry, R_1−δMn₃O_6–1.5δ, 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 BiPd₂O₄ with Pd²⁺ and Pd⁴⁺ Ordering and PbPd₂O₄

BiPd₂O₄ and PbPd₂O₄ were synthesized at high pressure of 6 GPa and 1500 K. Crystal structures of BiPd₂O₄ and PbPd₂O₄ were studied with synchrotron X-ray powder diffraction. BiPd₂O₄ is isostructural with PbPt₂O₄ 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). PbPd₂O₄ is isostructural with LaPd₂O₄ and BaAu₂O₄ and crystallizes in a tetragonal system (space group <i>I</i>4₁/<i>a</i>, <i>a</i> = 5.76232(1) Å, and <i>c</i> = 9.98347(2) Å at 293 K). BiPd₂O₄ shows ordering of Pd²⁺ and Pd⁴⁺ ions, and it is the third example of compounds with ordered arrangements of Pd²⁺ and Pd⁴⁺ in addition to Ba₂Hg₃Pd₇O₁₄ and KPd₂O₃. In PbPd₂O₄, the following charge distribution is realized Pb⁴⁺Pd²⁺₂O₄. PbPd₂O₄ shows a structural phase transition from <i>I</i>4₁/<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). BiPd₂O₄ is nonmagnetic while PbPd₂O₄ exhibits a significant temperature-dependent paramagnetic moment of 0.46μ_B/f.u. between 2 and 350 K. PbPd₂O₄ shows metallic conductivity, and BiPd₂O₄ is a semiconductor between 2 and 400 K

Crystal Structures and Properties of Perovskites ScCrO₃ and InCrO₃ with Small Ions at the A Site

ScCrO₃ and InCrO₃ were synthesized at high pressure of 6 GPa and 1500 K. Crystal structures of ScCrO₃ and InCrO₃ were studied with synchrotron X-ray powder diffraction. They crystallize in the GdFeO₃-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 ScCrO₃ and <i>a</i> = 5.35536(1) Å, <i>b</i> = 7.54439(1) Å, <i>c</i> = 5.16951(1) Å for InCrO₃). The physical properties of ScCrO₃ and InCrO₃ were investigated with specific heat, ac/dc magnetization, and dielectric measurements and compared with those of YCrO₃ with nonmagnetic Y³⁺ ions at the A site. Antiferromagnetic transitions occur at <i>T</i>_N = 73 K in ScCrO₃ and 93 K in InCrO₃ in agreement with the general trend of ACrO₃ (A = Y and rare earths) where <i>T</i>_N decreases with decreasing the radius of the A ions. Extremely weak ferromagnetism was found in ScCrO₃ and InCrO₃ in contrast to YCrO₃. Ac magnetization measurements revealed some peculiarities in behavior of ScCrO₃ and InCrO₃, namely, double-peak anomalies just below <i>T</i>_N. Dielectric anomalies were observed in both compounds at <i>T</i>_N indicating magnetoelectric coupling in contact with YCrO₃ where no dielectric anomalies were found. ScCrO₃ and InCrO₃ are very stable for high-pressure phases: no decomposition of ScCrO₃ was observed after heating up to 1340 K in air, and InCrO₃ only partially decomposed at 1340 K to give Cr₂O₃ and ambient- and high-pressure modifications of In₂O₃ 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 cm² V^–1s^–1. 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 cm² V^–1s^–1. 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 cm² V^–1s^–1. 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 S₃ in a Porous Coordination Network and the Direct X‑ray Observation

S₃ is one of the basic allotropes of sulfur but is still a mysterious labile species. We selectively trapped S₃ in a pore of a thermally stable coordination network and determined S₃ structure by <i>ab initio</i> X-ray powder diffraction analysis. S₃ in a pore has a <i>C</i>_2<i>v</i> bent structure. The network containing trapped S₃ is remarkably stable under ambient conditions and is inert to photoirradiation. S₃ in the network could be transformed to S₆ by mechanical grinding or heating in the presence of NH₄X (X = Cl or Br). S₆ could be reverse-transformed to S₃ by photoirradiation. We also determined the structure of the network containing S₆ by <i>ab initio</i> X-ray powder diffraction analysis

Anion Order-to-Disorder Transition in Layered Iron Oxyfluoride Sr₂FeO₃F 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, Sr₂FeO₃F, 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 Sr₂BO₃F (B = Co or Ni) with the fully disordered state. ⁵⁷Fe 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 S₃ in a Porous Coordination Network and the Direct X‑ray Observation

S₃ is one of the basic allotropes of sulfur but is still a mysterious labile species. We selectively trapped S₃ in a pore of a thermally stable coordination network and determined S₃ structure by <i>ab initio</i> X-ray powder diffraction analysis. S₃ in a pore has a <i>C</i>_2<i>v</i> bent structure. The network containing trapped S₃ is remarkably stable under ambient conditions and is inert to photoirradiation. S₃ in the network could be transformed to S₆ by mechanical grinding or heating in the presence of NH₄X (X = Cl or Br). S₆ could be reverse-transformed to S₃ by photoirradiation. We also determined the structure of the network containing S₆ by <i>ab initio</i> X-ray powder diffraction analysis

High-Pressure Synthesis, Crystal Structure, and Properties of In₂NiMnO₆ with Antiferromagnetic Order and Field-Induced Phase Transition

In₂NiMnO₆, a new compound extending the family of double rare-earth perovskites <i>R</i>₂NiMnO₆ (<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>2₁/<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 Mn⁴⁺ and Ni²⁺ ions was observed. The dc and ac magnetization and specific heat measurements showed that In₂NiMnO₆ is an antiferromagnet with a Néel temperature <i>T</i>_N of 26 K. Its antiferromagnetism puts it apart from other members of the <i>R</i>₂NiMnO₆ family where a ferromagnetic ground state was observed, which is attributed to the superexchange interaction between Mn⁴⁺ and Ni²⁺ 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 In₂NiMnO₆ 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