Densification, microstructure evolution, and microwave dielectric properties of Mg1-xCaxZrTa2O8 ceramics

Abstract In this study, the effects of the Mg 2+ ions replaced by Ca 2+ ions on the microwave dielectric properties of newly developed MgZrTa 2 O 8 were investigated. Mg 1-x Ca x ZrTa 2 O 8 (x = 0–1.0) ceramics were prepared via a solid-state reaction method. Calcination of the mixed powders was performed at 1200 °C and sintering of the powder compacts was accomplished at temperatures from 1200 to 1550 °C. The substitution of Ca 2+ significantly inhibited the densification of Mg 1-x Ca x ZrTa 2 O 8 , led to the expansion of the unit cells, and triggered the formation of a second phase, CaTa 2 O 6 . The porosity-corrected relative permittivity increased almost linearly with the x value because of the replacement of the less polarizable Mg 2+ ions by the more polarizable Ca 2+ ions. The variation in the Q × f values followed a similar trend as that of the sintered density, and the change trend in the τ f values was in accordance with that of relative permittivity. The best composition appeared to be Mg 0.9 Ca 0.1 ZrTa 2 O 8 , which showed excellent microwave dielectric properties of e r  = 22.5, Q × f = 231,951 GHz, and τ f  = −32.9 ppm/°C. The Q × f value obtained is the highest among the wolframite dielectric ceramics reported in literature.