Electronic structure and carrier effective masses in scheelite-type ABO4 compounds (A = Ca, Sr, and Ba; B = Mo and W): Insights into carrier transport

Scheelite-type molybdates and tungstates have attracted considerable interest in condensed-matter physics because of their versatile electronic and optical properties. In this work, the electronic structure, chemical bonding, and carrier effective masses of scheelite-type ABO 4 compounds (A = Ca, Sr, Ba; B = Mo, W) were systematically investigated using density functional theory calculations. Crystal structures were optimized using the GGA-PBEsol functional, while the modified Becke–Johnson (mBJ) exchange potential was employed for the electronic-structure calculations. All investigated AMoO 4 compounds, as well as SrWO 4 and CaWO 4 , exhibit direct band gaps at Γ, whereas BaWO 4 has an indirect gap, with the valence-band maximum at Γ and the conduction-band minimum at Z. The mBJ band gaps range from 4.0–4.6 eV for the molybdates and 5.1–5.7 eV for the tungstates, increasing systematically from Ca to Sr to Ba. Bonding analysis reveals predominantly ionic A–O interactions and stronger covalent B–O bonding. The effective-mass tensors reveal pronounced transport anisotropy, particularly for holes, with conductivity effective masses below 3m 0 for electrons and 6m 0 for holes for both tungstates and molybdates. Moreover, the density-of-states effective mass is systematically larger for holes than for electrons. The hole-to-electron effective-mass ratio further quantifies the asymmetry between electron and hole transport characteristics.