Structural, elastic, electronic and vibrational properties of a series of sulfates from first principles calculations

The structural, elastic, electronic and vibrational properties of crystalline sulfates MSO4 (M = Mg, Ca, Zn, Sr, Ba, Pb) were investigated within the framework of density functional theory using CRYSTAL program. The geometrical parameters, elastic constants and moduli, hardness, sound velocities, thermal conductivity, band gaps, densities of states, atomic charges and vibrational frequencies were computed. The computed structures are in good agreement with experimental ones if dispersion correction is taken into account. The unit cell volume and metal-oxygen distance almost linearly increase as the cationic radius increases. Compression anisotropy is shown to be more significant for magnesium sulfate and zinc sulfate; for them linear modulus is maximal along the shortest axis and along S-O bond, respectively. As the cationic radius increases, elastic moduli, hardness, sound velocities and thermal conductivity have a tendency to decrease. Low thermal conductivities reveal that sulfates can be used as thermal barrier coatings. It has been established that cationic charges and band gaps almost linearly decrease with increase of cationic electronegativity. Infra-anionic vibrational frequencies have a tendency to increase as electrostatic forces between cations and oxygens become stronger.