High-pressure behavior ofCaMoO4

Abstract

We report a high-pressure study of tetragonal scheelite-type CaMoO4 up to 29 GPa. In order to characterize its high-pressure behavior, we have combined Raman and optical-absorption measurements with density-functional theory calculations. We have found evidence of a pressure-induced phase transition near 15GPa. Experiments and calculations agree in assigning the high-pressure phase to a monoclinic fergusonitetype structure. The reported results are consistent with previous powder x-ray-diffraction experiments, but are in contradiction with the conclusions obtained from earlier Raman measurements, which support the existence of more than one phase transition in the pressure range covered by our studies. The observed scheelitefergusonite transition induces significant changes in the electronic band gap and phonon spectrum of CaMoO4.We have determined the pressure evolution of the band gap for the low-and high-pressure phases as well as the frequencies and pressure dependences of the Raman-active and infrared-active modes. In addition, based upon calculations of the phonon dispersion of the scheelite phase, carried out at a pressure higher than the transition pressure, we propose a possible mechanism for the reported phase transition. Furthermore, from the calculations we determined the pressure dependence of the unit-cell parameters and atomic positions of the different phases and their room-temperature equations of state. These results are compared with previous experiments showing a very good agreement. Finally, information on bond compressibility is reported and correlated with the macroscopic compressibility of CaMoO4. The reported results are of interest for the many technological applications of this oxide.

Understanding the White-Emitting CaMoO4 Co-Doped Eu3+, Tb3+, and Tm3+ Phosphor through Experiment and Computation

“…The projected DOS for RE 3+ = Eu 3+ , Tb 3+ , and Tm 3+ , (Figure 6(a-c) right panel) reveal that the upper levels of the VB mainly consist of O 2p orbitals; whereas the conduction band (CB) is predominantly formed by Mo 6+ 4d and RE 3+ 4f orbitals, with a small amount of Ca 2+ orbitals. In addition, the doping was found to cause a decrease in the energy levels of the CB with respect to the fundamental band gap of pure CaMoO4 (~4.9 eV) 10 ; the calculated value is similar to that obtained by V. Panchal et al 107 and Ryu et al 108 .…”

Exploring the nature of the fergusonite–scheelite phase transition and ionic conductivity enhancement by Mo6+doping in LaNbO4

“…13) and CaMoO 4 (ref. 14), also support this view. However, a few authors have argued that the transition is in fact rst-order with "quasicontinuous" character, 15,16 citing eeting phase coexistence observed near the phase transition in several studies of undoped and Ca-doped LaNbO 4 .…”

High-pressure characterization of the optical and electronic properties of InVO4, InNbO4, and InTaO4

“…Many ternary metal oxide compounds of the form AMO 4 have been extensively studied during the last decade due to their physical properties and technological applications including their low cost and environment friendliness [1][2][3][4][5][6]. Among this family of oxides, InMO 4 compounds (M = V 5+ , Nb 5+ , or Ta 5+ ) are of particular interest due to their excellent photocatalytic activity for water splitting under visible-light irradiation [7,8].…”