High-Pressure High-Temperature Stability and Thermal Equation of State of Zircon-Type Erbium Vanadate

The zircon to scheelite phase boundary of ErVO4 has been studied by high-pressure and high-temperature powder and single-crystal X-ray diffraction. This study has allowed us to delimit the best synthesis conditions of its scheelite-type phase, determine the ambient-temperature equation of state of the zircon and scheelite-type structures, and obtain the thermal equation of state of the zircon-type polymorph. The results obtained with powder samples indicate that zircon-type ErVO4 transforms to scheelite at 8.2 GPa and 293 K and at 7.5 GPa and 693 K. The analyses yield bulk moduli K0 of 158(13) GPa for the zircon phase and 158(17) GPa for the scheelite phase, with a temperature derivative of dK0/dT = -[3.8(2)] × 10-3 GPa K-1 and a volumetric thermal expansion of α0 = [0.9(2)] × 10-5 K-1 for the zircon phase according to the Berman model. The results are compared with those of other zircon-type vanadates, raising the need for careful experiments with highly crystalline scheelite to obtain reliable bulk moduli of this phase. Finally, we have performed single-crystal diffraction experiments from 110 to 395 K, and the obtained volumetric thermal expansion (α0) for zircon-type ErVO4 in the 300-395 K range is [1.4(2)] × 10-5 K-1, in good agreement with previous data and with our experimental value given from the thermal equation of state fit within the limits of uncertainty. Copyright © 2018 American Chemical Society.J.R.-F. and D.S.-P. thank the Spanish Ministry of Economy and Competitiveness (MINECO) for support from the the Juan de la Cierva (IJCI-2014-20513) and Ramoń y Cajal (RyC-2014-15643) Programs. This work was supported by the MINECO with the project MAT2016-75586-C4-1-P/2-P. The ALBA-CELLS synchrotron is acknowledged for granting beamtime at the MSPD beamline under projects 2016081784 and 2017022036. Parts of this research were carried out at the light source PETRA III at DESY (Project No. I-20160082 EC), a member of the Helmholtz Association (HGF). British Crown Owned Copyright 2018/AWE. Published with permission of the Controller of Her Britannic Majesty’s Stationery Office. The authors thank the financial support of Generalitat Valenciana through the Project Prometeo/2018/123EFIMA.Peer reviewe