Structural dependence of microwave dielectric properties of ixiolite structured ZnTiNb2O8 materials: crystal structure refinement and Raman spectra study

Abstract

Structural and property relationships of ixiolite structured ZnTiNb₂O₈ microwave dielectric materials were studied by structure refinement and Raman spectra analysis. The vibration modes which have Raman activities of the ixiolite structure were assigned for the first time. The bands with wavenumbers greater than 450 cm⁻¹ can be associated with several modes (A_g(2), B_3g(1), B_3g(2), A_g(1), B_1g(2), A_g(3), B_2g(2)) involving the stretching of the cation–O bonds. For wavenumbers between 250 and 450 cm⁻¹, the bands are due, principally, to the bending of O–cation–O (B_1g(1), B_2g(1), B_1g(3)). The origin of the bands with wavenumbers below 250 cm⁻¹ would be lattice vibrations (B_1g(4), A_g(4), B_3g(4), B_2g(4)), mainly associated with cation ions. The correlation between bond strength and packing fraction, Raman shift, full width at half maximum (FWHM) of Raman spectra were discussed. With increase of bond strength, the oxygen octahedron became rigid, the Raman shift increased, and the damping behavior became weaker. With increase of Raman shift, the dielectric constant decreased. With increase of packing fraction and decrease of FWHM, the Q_f (quality factor × resonance frequency) value increased. The τ_f (temperature coefficient of resonance frequency) decreased with increase of bond strength. And there was no direct relationship between oxygen octahedron distortion and τ_f. The excellent microwave dielectric properties of ZnTiNb₂O₈ in this work were: dielectric constant (ε) = 34.4, Q_f = 56 900 GHz, τ_f = −47.94 × 10⁻⁶/°C.