High-pressure transition to the post-barite phase in BaCrO 4 hashemite

Abstract

A recent high-pressure study on barium chromate BaCrO 4 reported a phase transition but the structure of the high-pressure phase structure could not be identified.This high-pressure phase was suggested to have a monoclinic structure different from other high-pressure forms of ABO 4 -type compounds. In this work, we have carried out x-ray diffraction measurements up to 46 GPa using He as quasi-hydrostatic pressure medium and Density-Functional Theory calculations. Our studies allow us identifying the high-pressure phase as the P2 1 2 1 2 1 post-barite-type phase, recently reported for

High-Pressure Single-Crystal X-ray Diffraction of Lead Chromate: Structural Determination and Reinterpretation of Electronic and Vibrational Properties

“…This formula gives an estimation of B 0 = 66 GPa (65 GPa) for monazite PbCrO 4 (SrCrO 4) , which confirms that the large compressibility of the monazite-type chromates is related to the presence of a large coordination polyhedron for Pb (Sr). This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å).…”

“…This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å). All these facts support the hypothesis that compressibility is mainly driven by the influence of pressure in PbO 8 or equivalent units (CrO 4 ) playing a negligible role.…”

“…In order to improve the knowledge of the HP behavior of PbCrO 4 , and ACrO 4 chromates in general, we have performed, for the first time, single-crystal XRD experiments in PbCrO 4 up to 6.28(4) GPa. In our experiments, we have found a direct first-order phase transition from monazite to scheelite at 4.40 (4) GPa. This conclusion is supported by ab initio calculations 22 and new Raman experiments that we have performed.…”

“…3−5 A phase transition has been reported near 27 GPa, and the crystal structure of the HP phase determined. 4 Interestingly, the existence of two soft-mode phonons has been found in the HP polymorph indicating that it is unstable at pressures higher than those achieved in the experiments. 4 In the case of YCrO 4 and lanthanide chromates, 6−11 a nonreversible phase transition from the ambient-pressure (AP) zircon-type structure to the HP scheelite-type structure occurs at pressures as low as 5 GPa.…”

High-Pressure Single-Crystal X-ray Diffraction of Lead Chromate: Structural Determination and Reinterpretation of Electronic and Vibrational Properties

“…This formula gives an estimation of B 0 = 66 GPa (65 GPa) for monazite PbCrO 4 (SrCrO 4) , which confirms that the large compressibility of the monazite-type chromates is related to the presence of a large coordination polyhedron for Pb (Sr). This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å).…”

“…This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å). All these facts support the hypothesis that compressibility is mainly driven by the influence of pressure in PbO 8 or equivalent units (CrO 4 ) playing a negligible role.…”

“…In order to improve the knowledge of the HP behavior of PbCrO 4 , and ACrO 4 chromates in general, we have performed, for the first time, single-crystal XRD experiments in PbCrO 4 up to 6.28(4) GPa. In our experiments, we have found a direct first-order phase transition from monazite to scheelite at 4.40 (4) GPa. This conclusion is supported by ab initio calculations 22 and new Raman experiments that we have performed.…”

“…3−5 A phase transition has been reported near 27 GPa, and the crystal structure of the HP phase determined. 4 Interestingly, the existence of two soft-mode phonons has been found in the HP polymorph indicating that it is unstable at pressures higher than those achieved in the experiments. 4 In the case of YCrO 4 and lanthanide chromates, 6−11 a nonreversible phase transition from the ambient-pressure (AP) zircon-type structure to the HP scheelite-type structure occurs at pressures as low as 5 GPa.…”

Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures

“…As the excitation power is decreased, the intensity of the lower energy band remarkably drops, broadens, and shifts to lower energy, whereas the higher energy band nearly vanishes (see Figure ). Because two coexisting crystallographic phases − in several inorganic perovskite materials of mixed − and pure − composition, including MAPbI 3 , have been already observed, we suggest that the measured emission in the low-temperature phase could be explained by supposing a very small relative volume fraction of low-energy sites attributable to small embodiments of individual tetragonal phase crystallites, where photoexcited carriers can be trapped . Therefore, the subgap sites in the tetragonal crystallites can only be partially filled under weak excitation by the few free carriers.…”

High-Pressure Single-Crystal X-ray Diffraction of Lead Chromate: Structural Determination and Reinterpretation of Electronic and Vibrational Properties

“…This formula gives an estimation of B 0 = 66 GPa (65 GPa) for monazite PbCrO 4 (SrCrO 4) , which confirms that the large compressibility of the monazite-type chromates is related to the presence of a large coordination polyhedron for Pb (Sr). This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å).…”

“…This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å). All these facts support the hypothesis that compressibility is mainly driven by the influence of pressure in PbO 8 or equivalent units (CrO 4 ) playing a negligible role.…”

“…In order to improve the knowledge of the HP behavior of PbCrO 4 , and ACrO 4 chromates in general, we have performed, for the first time, single-crystal XRD experiments in PbCrO 4 up to 6.28(4) GPa. In our experiments, we have found a direct first-order phase transition from monazite to scheelite at 4.40 (4) GPa. This conclusion is supported by ab initio calculations 22 and new Raman experiments that we have performed.…”

“…3−5 A phase transition has been reported near 27 GPa, and the crystal structure of the HP phase determined. 4 Interestingly, the existence of two soft-mode phonons has been found in the HP polymorph indicating that it is unstable at pressures higher than those achieved in the experiments. 4 In the case of YCrO 4 and lanthanide chromates, 6−11 a nonreversible phase transition from the ambient-pressure (AP) zircon-type structure to the HP scheelite-type structure occurs at pressures as low as 5 GPa.…”

Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures

“…As the excitation power is decreased, the intensity of the lower energy band remarkably drops, broadens, and shifts to lower energy, whereas the higher energy band nearly vanishes (see Figure ). Because two coexisting crystallographic phases − in several inorganic perovskite materials of mixed − and pure − composition, including MAPbI 3 , have been already observed, we suggest that the measured emission in the low-temperature phase could be explained by supposing a very small relative volume fraction of low-energy sites attributable to small embodiments of individual tetragonal phase crystallites, where photoexcited carriers can be trapped . Therefore, the subgap sites in the tetragonal crystallites can only be partially filled under weak excitation by the few free carriers.…”

High-Pressure Single-Crystal X-ray Diffraction of Lead Chromate: Structural Determination and Reinterpretation of Electronic and Vibrational Properties

“…This formula gives an estimation of B 0 = 66 GPa (65 GPa) for monazite PbCrO 4 (SrCrO 4) , which confirms that the large compressibility of the monazite-type chromates is related to the presence of a large coordination polyhedron for Pb (Sr). This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å).…”

“…This argument is also consistent with the fact that barite-type BaCrO 4 and its HP polymorphs, which are also formed by large BaO 8 dodecahedra (the polyhedral volume is 10% larger than in PbCrO 4 and SrCrO 4 ) and small CrO 4 tetrahedra, have a bulk modulus of 53 GPa . It is also consistent with the larger bulk modulus of zircon-type CaCrO 4 (104 GPa) and YCrO (136 GPa), in which the CaO 8 and YO 8 polyhedra have a volume that is more than 15% smaller than that of PbO 8 (for instance, the average Ca–O distance is 2.47 Å, where that of Pb–O is 2.64 Å). All these facts support the hypothesis that compressibility is mainly driven by the influence of pressure in PbO 8 or equivalent units (CrO 4 ) playing a negligible role.…”

“…In order to improve the knowledge of the HP behavior of PbCrO 4 , and ACrO 4 chromates in general, we have performed, for the first time, single-crystal XRD experiments in PbCrO 4 up to 6.28(4) GPa. In our experiments, we have found a direct first-order phase transition from monazite to scheelite at 4.40 (4) GPa. This conclusion is supported by ab initio calculations 22 and new Raman experiments that we have performed.…”

“…3−5 A phase transition has been reported near 27 GPa, and the crystal structure of the HP phase determined. 4 Interestingly, the existence of two soft-mode phonons has been found in the HP polymorph indicating that it is unstable at pressures higher than those achieved in the experiments. 4 In the case of YCrO 4 and lanthanide chromates, 6−11 a nonreversible phase transition from the ambient-pressure (AP) zircon-type structure to the HP scheelite-type structure occurs at pressures as low as 5 GPa.…”

Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures

“…As the excitation power is decreased, the intensity of the lower energy band remarkably drops, broadens, and shifts to lower energy, whereas the higher energy band nearly vanishes (see Figure ). Because two coexisting crystallographic phases − in several inorganic perovskite materials of mixed − and pure − composition, including MAPbI 3 , have been already observed, we suggest that the measured emission in the low-temperature phase could be explained by supposing a very small relative volume fraction of low-energy sites attributable to small embodiments of individual tetragonal phase crystallites, where photoexcited carriers can be trapped . Therefore, the subgap sites in the tetragonal crystallites can only be partially filled under weak excitation by the few free carriers.…”