High temperature crystal chemistry and thermal expansion of synthetic powellite (CaMoO4): A high temperature X-ray diffraction (HT-XRD) study

Abstract

In this communication, the high temperature crystal chemistry of scheelite type (space group: I41/a) CaMoO4 (powellite) is reported. The details of the high temperature crystal structures were obtained by high temperature X-ray diffractometer (HT-XRD) data in the temperature range of 25–1000 °C. The lattice thermal expansions of this compound show the an-isotropic behavior, with the coefficient of thermal expansion along c-axis (αc) is almost double of that along the a-axis (αa). The average values of thermal expansion coefficient for CaMoO4 are: αa=13.5×10−6 and αc=22.8×10−6 °C. The typical thermal expansion behavior is basically controlled by the temperature-induced expansion of the Ca–O bonds, i.e. by the thermal expansion of the CaO8 polyhedra. The MoO4 polyhedra acts as typical rigid unit, with virtually no expansion. The preliminary data analysis for CaWO4 indicates almost similar values of thermal expansion coefficients, viz. αa=12.7×10−6 and αc=21.4×10−6/°C (for CaWO4) in the same temperature range. The further details are explained in this manuscript.