Crystal Structures and Properties of Perovskites ScCrO3 and InCrO3 with Small Ions at the A Site (original) (raw)
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High-pressure synthesis, crystal structure and magnetic properties of TlCrO3 perovskite
Dalton transactions (Cambridge, England : 2003), 2015
TlMO3 perovskites (M(3+) = transition metals) are exceptional members of trivalent perovskite families because of the strong covalency of Tl(3+)-O bonds. Here we report on the synthesis, crystal structure and properties of TlCrO3 investigated by Mössbauer spectroscopy, specific heat, dc/ac magnetization and dielectric measurements. TlCrO3 perovskite is prepared under high pressure (6 GPa) and high temperature (1500 K) conditions. The crystal structure of TlCrO3 is refined using synchrotron X-ray powder diffraction data: space group Pnma (no. 62), Z = 4 and lattice parameters a = 5.40318(1) Å, b = 7.64699(1) Å and c = 5.30196(1) Å at 293 K. No structural phase transitions are found between 5 and 300 K. TlCrO3 crystallizes in the GdFeO3-type structure similar to other members of the perovskite chromite family, ACrO3 (A(3+) = Sc, In, Y and La-Lu). The unit cell volume and Cr-O-Cr bond angles of TlCrO3 are close to those of DyCrO3; however, the Néel temperature of TlCrO3 (TN ≈ 89 K) is ...
Chemistry of Materials, 1999
Strongly distorted RNiO 3 (R) Gd, Dy) perovskites, containing Ni 3+ , have been prepared under high-pressure conditions: 90 MPa of O 2 pressure (R) Gd) or 2 GPa of hydrostatic pressure in the presence of KClO 4 (R) Dy). These materials have been characterized by X-ray diffraction, neutron powder diffraction (NPD) (for DyNiO 3), DSC, magnetic measurements, and specific heat measurements. In contrast with the next member of the series, HoNiO 3 , which shows a subtle monoclinic distortion at room temperature, DyNiO 3 exhibits orthorhombic symmetry, as shown by NPD data. A noticeable distortion is observed in NiO 6 octahedra, at variance with the almost regular octahedra exhibited by the first members (R) La, Pr, Nd) of the series: it is interpreted as a manifestation of the Jahn-Teller character of the Ni 3+ cation, enhanced in the RNiO 3 perovskites with heavier rare earths, showing weaker, less covalent Ni-O bonds. DSC measurements show sharp endothermic peaks at 510.9 K (Gd) and 564.1 K (Dy) in the heating run, which have been assigned to the corresponding metal-insulator transitions of both charge-transfer perovskites, based on the analogous behavior observed for the precedent members of the RNiO 3 series. Subtle slope variations in the susceptibility vs T curves, highly dominated by the strong paramagnetic signal of Gd 3+ and Dy 3+ , indicate the onset of antiferromagnetic ordering of the Ni 3+ sublattice, confirmed by specific heat measurements, below T N values of 185 and 154 K, respectively. Additionally, the Dy 3+ sublattice becomes ordered below 8 K.
Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution LaxSm1–xCrO3
Inorganic Chemistry, 2013
A new mixed rare-earth orthochromite series, La x Sm 1−x CrO 3 , prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370°C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group Pnma over the full composition range. Unit cell volumes and Cr−O−Cr bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm −1 is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr 3+ spins with weak ferromagnetic component at Neél temperatures (T N) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr 3+ and Sm 3+ ions are examined with enhanced susceptibilities below T N due to polarization of Sm 3+ moments. At low temperatures the Cr 3+ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility.
Science and Technology of Advanced Materials, 2015
We synthesize ScCoO 3 perovskite and its solid solutions, ScCo 1−x Fe x O 3 and ScCo 1−x Cr x O 3 , under high pressure (6 GPa) and high temperature (1570 K) conditions. We find noticeable shifts from the stoichiometric compositions, expressed as (Sc 1−x M x)MO 3 with x = 0.05-0.11 and M = Co, (Co, Fe) and (Co, Cr). The crystal structure of (Sc 0.95 Co 0.05)CoO 3 is refined using synchrotron x-ray powder diffraction data: space group Pnma (No. 62), Z = 4 and lattice parameters a = 5.26766(1) Å, b = 7.14027(2) Å and c = 4.92231(1) Å. (Sc 0.95 Co 0.05)CoO 3 crystallizes in the GdFeO 3-type structure similar to other members of the perovskite cobaltite family, ACoO 3 (A 3+ = Y and Pr-Lu). There is evidence that (Sc 0.95 Co 0.05)CoO 3 has non-magnetic low-spin Co 3+ ions at the B site and paramagnetic high-spin Co 3+ ions at the A site. In the irondoped samples (Sc 1−x M x)MO 3 with M = (Co, Fe), Fe 3+ ions have a strong preference to occupy the A site of such perovskites at small doping levels.
Inorganic Chemistry, 2013
A new mixed rare-earth orthochromite series, La x Sm 1−x CrO 3 , prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370°C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group Pnma over the full composition range. Unit cell volumes and Cr−O−Cr bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm −1 is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr 3+ spins with weak ferromagnetic component at Neél temperatures (T N) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr 3+ and Sm 3+ ions are examined with enhanced susceptibilities below T N due to polarization of Sm 3+ moments. At low temperatures the Cr 3+ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility.
Structure, microstructure and magnetic properties of Sr1−xCaxCrO3 (0⩽x⩽1)
Journal of Solid State Chemistry, 2008
The effect of the calcium concentration on the structural, microstructural and magnetic properties of Sr (1Àx) Ca x CrO 3 with 0pxp1 has been studied. The compounds were prepared using high pressure and high temperature synthesis. X-ray diffraction shows that the samples evolve from the cubic Pm-3m space group for x ¼ 0-0.2 to tetragonal I4/mcm for x ¼ 0.4-0.5, then to the orthorhombic Pbnm space group for x ¼ 0.6, 0.8 and 1.0. Electron diffraction and high-resolution transmission electron microscopy confirmed the respective cells for the end compositions: a p  a p  a p (Pm-3m) for SrCrO 3 ; and the ffiffi ffi 2 p a p  ffiffi ffi 2 p a p  2a p (Pbnm) for CaCrO 3 . For intermediate compositions some extra spots appear in the electron diffraction patterns while the electron micrographs indicate the presence of microdomains. Magnetic measurements show Curie-Weiss behaviour at high temperature for all the samples. A sharp antiferromagnetic (AFM) transition at about 91.5 K appears for x ¼ 0.8-1 together with a weak ferromagnetic ordering below T N .
Pressure effects on crystal structures and magnetic properties of RCo5 (R = Y or Gd) compounds
2013
The pressure dependences of crystal structures and magnetic properties of YCo5 and GdCo5 compounds are analysed based on band structure calculations. Isomorphic transitions were evidenced for relative volumes v/v0 = 0.91 and 0.86, for YCo5 and GdCo5, respectively. At the transition, there is a higher decrease of cobalt moments at 3g sites as compared to those located in 2c ones. The induced polarizations on Y4d and Gd5d bands, by short range interactions, are linearly dependent on the magnetizations of cobalt atoms situated in their neighborhood. The isomorphic transitions are analysed in correlations with band structures.
Inorganic Chemistry, 2013
A new perovskite, CaCo 2+ 3 V 4+ 4 O 12 , has been synthesized at high-pressure and high-temperature (HP-HT) conditions. The properties of this perovskite were examined by a range of techniques. CaCo 3 V 4 O 12 was found to adopt a double-perovskite cubic lattice [a = 7.3428(6) Å] with Im3̅ symmetry. We have established that this new perovskite is stable at ambient conditions, and its oxidation and/or decomposition at ambient pressure begins above 500°C. It undergoes an abrupt antiferromagnetic transition around 98 K. Electrical resistivity data suggest semimetallic conductivity in the temperature range of 1.6−370 K. We have established that the Co 2+ ions in CaCo 3 V 4 O 12 are in the high-spin state with a sizable orbital moment, even though their square-planar oxygen coordination could be more suitable for the low-spin state, which is prone to Jahn−Teller distortion. Electrical resistivity curves also exhibit a distinct steplike feature around 100 K. CaCo 3 V 4 O 12 is a first example of perovskite in which the sites A′ are fully occupied by Co 2+ ions, and hence its synthesis opens the door to a new class of double perovskites, ACo 3 B 4 O 12 , that may be derived by chemical substitution of the A sublattice by lanthanides, sodium, strontium, and bismuth and by other elements and/or of the B sublattice by some other transition metals.