Optical, Thermal, and Mechanical Properties of Scheelite Molybdate and Tungstate Materials Using Atomistic Simulations

Solid-state Raman-active materials are instrumental in the development of advanced eye-safe lasers, laser guide stars, remote sensing, and medical diagnosis and treatment. Present work focuses on studying the properties of Scheelite crystal structures of BaWO4, CaWO4, BaMoO4, and CaMoO4 using atomistic simulations, to evaluate their suitability as Raman-active materials. Properties at zero external hydrostatic pressure such as band gap, dielectric function, refractive index, and thermal conductivity were studied using plane-wave density functional theory. Mechanical properties such as elastic constants, bulk modulus, shear modulus, young’s modulus, Debye temperature, average sound velocity, and anisotropy index were also calculated. The calculated properties were in close correspondence with the available experimental and theoretical literature values. A good Raman-active material should possess high thermal conductivity, good absorption in visible and near-infrared region, and low micro-hardness. Among the four crystals studied, CaWO4 showed higher thermal conductivity and lowest hardness (more flexible and therefore easy to process) and highest fracture toughness. Further, CaMoO4 showed highest refractive index indicating its suitability for optoelectronic applications to develop transparent/anti-reflective materials. Analysis of elastic constants and various mechanical properties infer that the barium based materials and specifically tungstate material is more ductile. Barium-based crystals showed superior anisotropy compared to calcium based crystals. Young’s modulus values infer that BaMoO4 is more ductile than BaWO4, CaMoO4, and CaWO4. Among the four crystals studied, CaWO4 showed highest thermal conductivity followed by CaMoO4. Overall comparison indicates the suitability of calcium-based molybdate and tungstate as Raman-active materials which offer more ease of processing.