Enhanced quality factor ( 336,800 GHz) of MgTiO₃ ceramic by Hf substitution for Ti-site

Mg(Ti1-xHfx)O-3 (0 <= x <= 0.1) microwave dielectric ceramics were synthesized by solid-state reaction method. The effects of Hf substitution for the Ti-site on the phase composition, structure, and microwave dielectric properties of MgTiO3 ceramic were systematically investigated. The study demonstrated that Hf substitution significantly improved the quality factor of MgTiO3 ceramic. A single phase was confirmed at x = 0.002 and 0.005 by XRD and SEM, while secondary phases were observed at x >= 0.02. The Rietveld refinement of XRD data implied that the distortion of [Ti(Hf)O-6] octahedron started with alleviation and then gradually deteriorated with an increase in Hf content. Raman spectra displayed that the frequencies of the vibrational modes were high when there was low distortion in [Ti(Hf)O-6] octahedron, manifesting that the low distortion weakened the effect of non-harmonic vibration. The quality factor of the samples with x <= 0.05 was far higher than that of undoped MgTiO3, which may be related to low distortion in [Ti(Hf)O-6] octahedron and high relative density. Notably, the excellent microwave dielectric properties of Q x f similar to 336,829 GHz, epsilon(r) similar to 17.2 and tau(f) similar to -49.7 ppm/degrees C were achieved for the Mg(Ti0.995Hf0.005)O-3 ceramic. The greatly improved quality factor of MgTiO3-based microwave ceramics through Hf substitution makes it a suitable candidate material for ceramic filters.