The influence of Ti deficiency on the sintering densification process and dielectric properties of 0.7CaTiO3-0.3NdAlO3 microwave ceramics

The dielectric properties of titanate-based microwave ceramics are usually degraded by oxygen vacancies induced by prolonged sintering at high temperature. In this study, the activation sintering and improvement of dielectric properties for 0.7CaTi 1-x O 3 -0.3NdAlO 3 ceramics could be achieved by slight adjusting the stoichiometric ratio of Ti 4+ ions at B-site (CTNA, x = 0.0000, 0.0025, 0.0050, 0.0075). As x increasing from 0.0000 to 0.0050, the relative densities, maximum densification rate, and maximum densification rate temperature all increase. This is attributed to the generation of oxygen vacancy defects that can facilitate atomic diffusion. When x further increase to 0.0075, even though the number of oxygen vacancies continues to increase, the substitution of Nd 3+ with larger ionic radius (1.27 Å) at B-site, compared to Ti 4+ (0.605 Å), induce significant lattice distortion. Consequently, the relative densities of CTNA ceramics (x = 0.0075) remains comparable to that of CTNA ceramics (x = 0.0050). The substitution of Ti 4+ by smaller Al 3+ (0.535 Å) at B-site in CTNA ceramics (x = 0.0050) result in a reduced lattice constant and unti cell volume, which is conducive to the reduction of intrinsic loss and the improvement of dielectric properties: ε r  = 45.92; Q × f  = 43,900 GHz, and τ f  = 2.88 ppm/°C.