Enhanced quality factor of MgTiO3 ceramics by isovalent Ti-site substitution

The micro we dielectric properties of MgTiO3 ceramics with isovalent substitutions of (((Li1/41+B3/45+))(4+), (Mg1/32+B2/35+))(4+), and ((Al1/23+B1/25+))(4+) (B =Nb5+ or Ta5+)) at the Ti-site were investigated. All isovalent-substituted MgTiO3 ceramics showed single phases of ilmenite structure with rhombohedral symmetry. Specimens with B=Ta5+ showed higher quality factors (Qf) and lower dielectric constants (K) than those with B=Nb5+, because of the high degree of average covalency in the ceramics. The Qf values of specimens substituted with (Mg1/3B2/3)(4+) at the Ti-site were higher than those of other isovalent-substituted MgTiO3 ceramics, because of the high Ti-site bond strength of (Mg1/3B2/3)(4+). Because (Li1/4B3/4)(4+) displayed the largest dielectric polarizability of the substituting species, MgTiO3 ceramics substituted (Li1/4B3/4)(4+) at the Ti-site showed the largest K value. The substituted specimens showed lower temperature coefficients of the resonant frequencies (TCF) than the pure MgTiO3 ceramics, because of the increased Ti-site octahedral distortion. The relationships between the microstructures and microwave dielectric properties of MgTiO3 ceramics were also discussed. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.