Pressure-and temperature-dependent X-ray diffraction studies of NdCrO3 (original) (raw)
Related papers
Crystals
Gadolinium aluminate perovskite (GdAlO3) was studied at high pressures of up to 23 GPa in a diamond anvil cell (DAC) using monochromatic synchrotron X-ray powder diffraction. Evidence of a pressure-induced phase transformation from orthorhombic (Pbnm) to rhombohedral (R3¯c) structure was observed at 21 GPa and further proved by DFT calculations. Before phase transition, the volumetric ratio of polyhedron A and B (i.e., VA/VB for ABX3 general notation) in the Pbnm phase continuously increased towards the ideal value of five at the transition, indicating a pressure-induced decrease in the structural distortion as opposed to the trend in many other orthorhombic perovskites (e.g., CaSnO3, CaGeO3, MgSiO3 and NaMgF3). Pressure–volume data of the Pbnm phase were fitted to the third-order Birch–Murnaghan equation of state yielding a bulk modulus (Ko) of 216 ± 7 GPa with a pressure derivative of the bulk modulus (Ko′) of 5.8 GPa (fixed). This work confirms the pressure-induced phase transfor...
Physical review, 2018
SiO 3 perovskite is the most abundant mineral of the Earth's lower mantle, and compounds with the perovskite structure are perhaps the most widely employed ceramics. Hence, they attract both geophysicists and material scientists. Several investigations attempted to predict their structural evolution at high pressure, and recent advancements highlighted that perovskites having ions with the same formal valence at both polyhedral sites (i.e., 3+:3+) define different compressional patterns when transition metal ions (TMI) are involved. In this study, in situ high-pressure synchrotron XRD measurements coupled with ab initio simulations of the electronic population of NdCrO 3 perovskite are compared with the compressional feature of NdGaO 3. Almost identical from a steric point of view (Cr 3+ and Ga 3+ have almost the same ionic radius), the different electronic configuration of octahedrally coordinated ions-which leads to a redistribution of electrons at the 3d orbitals for Cr 3+-allows the crystal field stabilization energy (CFSE) to act as a vehicle of octahedral softening in NdCrO 3 or it turns octahedra into rigid units when CFSE is null as in NdGaO 3. Besides to highlight that different electronic configurations can act as a primary effect during compression of perovskite compounds, our findings have a deep repercussion on the way the compressibility of perovskites have to be modeled.
Effect of pressure on the global and local properties of cubic perovskite crystals
Physica Scripta, 2011
The influence of pressure on the structural, elastic, thermal and bonding properties of four perovskite-type oxides AMO 3 is studied from the point of view of the quantum theory of atoms in molecules. Ab initio investigations are performed by means of the full-potential linear augmented plane-wave method as implemented in the wien2k code. The integrated basin charges resulting from the topological analysis of electronic density provide a partition of the bulk modulus and compressibility into atomic contributions. Special attention is paid to the nonlinear behaviour of the local bonding properties. PACS numbers: 71.15.Mb, 71.15.−m, 62.20.de, 31.15.ae (Some figures in this article are in colour only in the electronic version.)
High-pressure structural evolution of a perovskite solid solution (La1−x,Ndx)GaO3
Journal of Solid State Chemistry, 2007
The structural evolution with pressure of six perovskites in the system La 1Àx Nd x GaO 3 with x ¼ 0.00, 0.06, 0.12, 0.20, 0.62 and 1.00 have been determined by single-crystal diffraction. At room pressure, all six samples have Pbnm symmetry. The room-pressure bulk moduli vary only slightly with composition, between K 0T ¼ 169(4) and 177(2) GPa, with K 0 0 ¼ ðdK=dPÞ P¼0 $6:5. As pressure is increased there is significant compression of the octahedral Ga-O bonds, the tilts of the GaO 6 octahedra decrease and the structures evolve towards higher symmetry. At room conditions the average Ga-O bond length increases with increasing compositional parameter x. However, the GaO 6 become stiffer with increasing x; the Ga-O bonds thus become stiffer as they become longer. Bond strengths in the octahedra in perovskites are therefore not a simple function of bond lengths but depend also upon the extra-framework cation.
Energy dispersive X-ray diffraction analysis of NdBr3 at pressures up to 52 GPa
Journal of Alloys and Compounds, 1993
Energy dispersive X-ray diffraction experiments on NdBr 3 have shown a possible distortion of the known PuBr3-type orthorhombic structure at high pressure but not the formation of a "new" crystal structure, as had been suggested from earlier work based on analysis of absorption and phonon Raman spectra. The bulk modulus B o and its pressure derivative B0' were calculated from the compression curve to 20 GPa to be about 17 _+ 1 GPa and 8.7 + 2 respectively.
High-pressure phase transformations and isothermal compression in CaTiO3 (perovskite)
Physics of the Earth and Planetary Interiors, 1986
A polycrystalline CaTiO3 (perovskite) was investigated under static pressures up to 38 GPa and temperatures up to 1000°Cby using a diamond anvil pressure cell, a YAG laser, and the ruby fluorescence pressure calibration system. In situ x-ray diffraction data reveal that at room temperature, the orthorhombic CaTiO3(I) transforms into a hexagonal CaTiO3(fl) at-10 GPa with a volume of change of 1.6%. At 1000°C,the orthorhombic CaTiO3(I) first transforms into a tetragonal CaTiO3(IH) at 8.5 GPa and then transforms further into a hexagonal CaTiO3(11') at-15 GPa with molar volume changes of 0% and 1.6%, respectively. All three high-pressure polymorphs found in this study are nonquenchable. Isothermal compressibility of the orthorhombic CaTiO3 was derived from measurements under truly hydrostatic environments (i.e., ç 10.4 OPa). By assuming K6 = 5.6 obtained ultrasonically on SrTiO3 perovskite, the value of the bulk modulus (K0) was calculated with the Birch-Murnaghan equation to be 210 ±7 GPa.
Solid State Communications, 2013
The effect of high-pressure on the electronic and magnetic properties in perovskite oxide NiCrO 3 is explored by using density-functional calculations. The results show that NiCrO 3 exhibits antiferromagnetic semiconductor when the external hydrostatic pressure is below $ 80 GPa, and then behaves as antiferromagnetic half-metal on increasing the pressure. The band gaps in the spin-up and spin-down channels decrease from 3.9 to 2.5 eV and 0.35 to 0 eV, respectively. The magnetic moments of Ni, Cr, and O ions are slightly changed in the whole range of the pressure, and the electronic configurations of both Ni and Cr ions are in the high-spin state. Based on the mean-field theory, the estimated Néel temperature of semiconducting NiCrO 3 increases from 270 K and reaches the maximum of 321 K around 60 GPa with increasing the pressure, and the Néel temperature of the half-metallic one is of about 309 K.
Phase stability and shear softening in CaSiO3 perovskite at high pressure
Physical Review B, 2007
We predict the phase diagram of CaSiO 3 perovskite, finding the tetragonal I4/mcm structure transforming to cubic Pm3m with increasing temperature. The transition temperature is 1150 K at 0 GPa, and 2450 K at 140 GPa. The c / a ratio of the tetragonal structure is 1.018 at 100 GPa and increases on compression, as does the static enthalpy difference between tetragonal and cubic structures. The elastic constants of the tetragonal phase at static conditions differ substantially from those of the cubic phase with the Voigt-Reuss-Hill shear modulus 29% less at 100 GPa. Computations are based on density functional theory in the local density and generalized gradient approximations. The phase diagram and high temperature elastic constants are computed using a mean field theory with parameters of the Landau potential determined via structurally constrained density functional theory calculations. We present a simple scheme for systematically searching for the ground state over all perovskite structures derivable from octahedral rotations within the context of symmetrypreserving relaxation, which confirms tetragonal I4/mcm as the ground state in density functional theory. We argue that the experimental x-ray diffraction pattern can be explained by the I4/mcm phase by considering the development of preferred orientation under uniaxial compression.
Journal of Applied Physics, 2016
The structure stability under high pressure and thermal expansion behavior of Na 3 OBr and Na 4 OI 2 , two prototypes of alkali-metal-rich antiperovskites, were investigated by in situ synchrotron X-ray diffraction techniques under high pressure and low temperature. Both are soft materials with bulk modulus of 58.6 GPa and 52.0 GPa for Na 3 OBr and Na 4 OI 2 , respectively. The cubic Na 3 OBr structure and tetragonal Na 4 OI 2 with intergrowth K 2 NiF 4 structure are stable under high pressure up to 23 GPa. Although being a characteristic layered structure, Na 4 OI 2 exhibits nearly isotropic compressibility. Negative thermal expansion was observed at low temperature range (20-80 K) in both transition-metal-free antiperovskites for the first time. The robust high pressure structure stability was examined and confirmed by first-principles calculations among various possible polymorphisms qualitatively. The results provide in-depth understanding of the negative thermal expansion and robust crystal structure stability of these antiperovskite systems and their potential applications.