Synthesis and thermophysical properties of AMoO₄ (A = Ca, Sr, Ba)

The alkaline earth molybdates AMoO₄ (A=Ca, Sr, Ba) belong to Scheelite type crystal structure with space group 14₁/a, and are naturally occurring minerals. They are often found as secondary phases in irradiated oxide nuclear fuels as a product of fission product interaction. These compounds can also form as microcrystallites when the high-level nuclear waste is vitrified. As high temperature ceramics, they find applications as sensor materials, oxide ion conductors, etc. The thermophysical properties of these molybdates are essential for understanding their impact on the high temperature properties of the systems and devices containing them. In the present study, these compounds were synthesized by solid state reaction route in air at 823 K, and characterized by powder XRD and TG/DTA. The thermal expansion behavior was investigated by dilatometry in the temperature range of 300-800 K in air. The % thermal expansion of BaMoO₄ was found to be the lowest among the three compounds. The electrical conductivity of the compounds was measured by AC-impedance spectroscopy, and the conductivity was found to be in the range of 10^-4 S.cm^-1 at 1073 K in air. The activation energy of electrical conduction was measured to be about 1.3 eV. (author)