Kosyl, Katarzyna M. Paszkowicz, Wojciech Ermakova, Olga Wlodarczyk, Damian Suchocki, Andrzej Minikayev, Roman Domagala, Jaroslaw Z. Shekhovtsov, Alexei N. Kosmyna, Miron Popescu, Catalin Fauth, François Equation of State and Amorphization of Ca<sub>9</sub>R(VO<sub>4</sub>)<sub>7</sub> (R = La, Nd, Gd): A Combined High-Pressure X‑ray Diffraction and Raman Spectroscopy Study Ca<sub>9</sub>R­(VO<sub>4</sub>)<sub>7</sub> (R = rare earth) multicomponent oxides of a whitlockite-related structure are under consideration for applications in optoelectronics. In this work, the Czochralski-grown Ca<sub>9</sub>R­(VO<sub>4</sub>)<sub>7</sub> 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 <i>K</i><sub>0</sub> = 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 Ca<sub>3</sub>(VO<sub>4</sub>)<sub>2</sub>. The compressibility anisotropy was observed; the lattice is markedly stiffer in [001] than in [100] direction. For Ca<sub>9</sub>Nd­(VO<sub>4</sub>)<sub>7</sub>, 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 Ca<sub>9</sub>Y­(VO<sub>4</sub>)<sub>7</sub> 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. Raman spectroscopy measurements;powder X-ray diffraction;EOS;whitlockite-like structure;bulk moduli K 0;amorphization process;10 GPa;whitlockite-related structure;Raman Spectroscopy Study;pressure release;order equation;ALBA synchrotron;Gd;multicomponent oxides;single-crystal Raman spectroscopy;Nd;phase transition;rare-earth vanadates;7 crystals;VO 4;compressibility anisotropy;tricalcium vanadate;La;diffraction experiments 2018-10-11
    https://acs.figshare.com/articles/journal_contribution/Equation_of_State_and_Amorphization_of_Ca_sub_9_sub_R_VO_sub_4_sub_sub_7_sub_R_La_Nd_Gd_A_Combined_High-Pressure_X_ray_Diffraction_and_Raman_Spectroscopy_Study/7195577
10.1021/acs.inorgchem.8b01182.s001