Effects of Zr-Substitution on Microwave Dielectric Properties 
of Na0.5Nd0.2Sm0.3Ti1−xZrxO3 Ceramics (x = 0.00 ∼ 0.30)
In this paper, the compound Na0.5Nd0.2Sm0.3Ti1−xZrxO3 (NNSTZx, x = 0.00, 0.01, 0.02, 0.05, 0.09, 0.14, 0.20, 0.30) ceramics were prepared by the conventional solid-state route. The main phase of all NNSTZx samples were indexed as an orthorhombic perovskite structure. The permittivity (εr) and quality factor (Q × f) were improved because of improvement of relative density and homogeneous microstructure with minor Zr substitution (x ≤ 0.02). When x ≤ 0.14, the temperature coefficient of the resonant frequency (τf) could be effectively tuned to a relatively low value of 110.3 ppm/°C due to a continuous decrease of tolerance factors. A remarkable decrease of τf from 110.3 ppm/°C to −2.38 ppm/°C was obtained since a certain amount of Nd2Ti2O7 phase was observed with x ≥ 0.20. Typically, the NNSTZx (x = 0.20) ceramic sintered in air at 1450°C for 2 h exhibited good microwave dielectric properties of εr = 75.4, Q × f=6813 GHz, and τf = 67.8 ppm/°C.