Equation of State and Amorphization of Ca9R(VO4)7 (R = La, Nd, Gd): A Combined High-Pressure X-ray Diffraction and Raman Spectroscopy Study
Autor: | Jaroslaw Z. Domagala, Roman Minikayev, François Fauth, Wojciech Paszkowicz, M. B. Kosmyna, Katarzyna M. Kosyl, Andrzej Suchocki, Olga Ermakova, Catalin Popescu, Alexei N. Shekhovtsov, Damian Włodarczyk |
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Rok vydání: | 2018 |
Předmět: |
010302 applied physics
Diffraction Phase transition Chemistry Analytical chemistry 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Isothermal process Synchrotron law.invention Inorganic Chemistry symbols.namesake law 0103 physical sciences X-ray crystallography symbols Vanadate Physical and Theoretical Chemistry 0210 nano-technology Raman spectroscopy Anisotropy |
Zdroj: | Inorganic Chemistry. 57:13115-13127 |
ISSN: | 1520-510X 0020-1669 |
Popis: | Ca9R(VO4)7 (R = rare earth) multicomponent oxides of a whitlockite-related structure are under consideration for applications in optoelectronics. In this work, the Czochralski-grown Ca9R(VO4)7 crystals were investigated as a function of pressure by powder X-ray diffraction and single-crystal Raman spectroscopy. The diffraction experiments were performed at the ALBA synchrotron under pressures ranging up to 9.22(5), 10.7(1), and 8.55(5) GPa for R = La, Nd, and Gd, respectively, to determine the third order equation of state (EOS) parameters. Fitting of the Birch-Murnaghan EOS provided the isothermal bulk moduli K0 = 63(4), 63(2), and 61(5) GPa for these three orthovanadates. These values are apparently lower than that reported for structurally related tricalcium vanadate Ca3(VO4)2. The compressibility anisotropy was observed; the lattice is markedly stiffer in [001] than in [100] direction. For Ca9Nd(VO4)7, the variation of the diffractograms just above 10 GPa provides an indication on the beginning of amorphization process; during pressure release the whitlockite-like structure is recovered. Raman spectroscopy measurements for single crystals of the above-mentioned rare-earth vanadates and Ca9Y(VO4)7 were performed (the maximum pressures achieved were 16.3(1), 21.2(1), 15.3(1), and 18.6(1) GPa for R = Y, La, Nd, and Gd, respectively). These measurements reveal a partially reversible phase transition interpreted as amorphization, with an onset at the pressure of ∼9-10 GPa, characterized by broadening of the peaks and their shift to lower energies. |
Databáze: | OpenAIRE |
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