Experimental and theoretical equation of state of DyVO₄polymorphs

Abstract

DyVO 4 is known for its Jahn-Teller type transition [1] and interesting magnetic properties [2]. A promising application for DyVO 4 isthe catalysis in oxidative dehydrogenation of propane [3]. The DyVO 4 /V2O 5 mixture exhibits catalytic ability for decomposition of cyclohexanol [4] and strong photocatalytic activity in the decomposition of organics. A bismuth-containing solid solution, Bi 0.5 Dy 0.5 VO 4 , has been found to be useful in photoinduced water splitting [5]. DyVO 4 , like most of the RVO 4 family members, crystallizes in the zircon-type structure (I41/amd). At pressures in the range from 5 to 10 GPa, these compounds are known to undergo a phase transition into a scheelite-type polymorph (I41/a). The equation of state of a number of RVO 4 compounds has been already determined, but not for DyVO 4 . Regarding the phase transitions in DyVO 4 , in [6] the scheelite-type phase was observed at pressures above 6.5 GPa. In a recent Raman spectroscopy study [7], the zircon phase was observed up to 8 GPa, followed by a zircon-scheelite phase mixture at 8.8 and 9.2 GPa, and single-phase scheelite at 10.7 GPa and above. The aim of the present investigation is to determine the yet unknown complete set of equation-of-state parameters for both dysprosium orthovanadate polymorphs, to experimentally check, whether the transition from the zircon phase to the scheelite phase occurs in the available pressure range and to provide the theoretical coexistence pressure. To achieve this goal, X-ray diffraction experiments and density-functional-theory (DFT) calculations are applied for the first time to the study of this material at high pressures. Furthermore, the DFT calculations allowed for the determination of the variation with pressure of the internal structural parameters of the unit cells and interatomic distances. To our knowledge this information was not previously available for DyVO 4 polymorphs. The present work provides the first diffraction based experimental information on elastic properties of zircon-type and scheelite type dysprosium orthovanadates. The obtained experimental data compare well with the (first) theoretical DFT-based results. Namely, the bulk modulus equals 118 GPa (experimental) or 126 (theoretical) for the zircon phase, and equals 153 (experimental) and 142.9 (theoretical) for the scheelite phase. The good agreement supports the reliability of both, experimental and theoretical data obtained. Moreover, the quoted values are close to one of early evaluations for DyVO 4 , 126 GPa, and to those experimentally determined for some other RVO4 compounds.

Recent progress on the characterization of the high-pressure behaviour of AVO4 orthovanadates

“…This information supports the conclusions extracted from a transmissionelectron microscopy study of shock-deformed zircon (ZrSiO4) [138]. It also confirms the first-order character previously associated to the zircon-scheelite transition [24,25,28,29,33,58,59,97] and it is consistent with the non-reversibility of this transition.…”

“…In fact, C33/C11 is similar to the ratio of the axial compressibilities determined from XRD for the c-axis and a-axis in different zircon-type vanadates [24,25,28,29,33,58,59,97]. In case of CeVO4, calculations give C33/C11 = 1 [131], which is in contradiction with the known axial compressibilities of CeVO4, which in highly non isotropic [32,33].…”

“…After these reports, systematic HP investigations followed on RVO4 compounds by various researchers, including the authors of this review [25,26,28,29,33,36,59,96,97]. Measurements on these compounds now have established beyond doubt that the RVO4 compounds with smaller ionic radii (Sm-Lu) transform from the zircon to the scheelite phase below 10 GPa with nearly 10 % volume discontinuity.…”

“…As a result, significant efforts have been made to find low-compressibility materials with a bulk modulus comparable to that of diamond [236,237]. The compressibility of AVO4 orthovanadates has been extensively studied [5,20,24,25,27,28,29,30,32,33,36,37,38,40,41,44,50,58,59,63,81,82,95,96,97,102,123,238,239,240]. In particular, roomtemperature equations of state (EOS) have been determined for most of them.…”

Phase Stability of Lanthanum Orthovanadate at High Pressure

“…The thermodynamically stable phase at different pressures is obtained from the P-H curves of the analyzed candidate crystal structures. This methodology has been applied successfully to the study of several orthovanadates [8,12,14,15,18,22,27,51].…”