Correlation between vibrational modes and dielectric properties in (Ca_1-3xBi_2xΦ_x)MoO₄ ceramics

The Raman, infrared reflectivity and terahertz spectra of A-site deficient scheelite materials (Ca_1-3xBi_2xΦ_x)MoO₄ (Φ: A-site vacancy) were studied to evaluate the correlation between the vibrational modes and the dielectric properties. The Raman spectra were fitted with the Lorentzian model and the changes of resonance frequencies and full width at half maximum of the resonance were discussed. With the substitution of Bi into the A site of CaMoO₄, the associated ionic compensation produces an increase in disorder which can contribute to an increase in dielectric losses. The harmonic oscillator model was used to fit infrared reflectivity spectra and the obtained complex dielectric response was extrapolated down into the terahertz and microwave region. The contributions of each mode to the microwave dielectric properties were investigated. It was found that the modes at low frequencies which are related to AO₈ polyhedra play the most important role in the microwave dielectric properties of (Ca_1-3xBi_2xΦ_x)MoO₄.