Effect of Zr4+substitution on the phase evolution and microwave dielectric properties of (Cu1/3Nb2/3)0.25Ti0.75-xZrxO2 ceramics

The effect of Zr4+ substitution for Ti4+ on the phase evolution and microwave dielectric properties of (Cu1/3Nb2/ 3)0.25Ti0.75-xZrxO2 (0 = x <= 0.35) ceramics prepared via conventional solid-state method has been investigated. With the increase of Zr substitution, the ceramics exhibit a gradual phase transition from a tetragonal rutile phase to an orthorhombic srilankite phase, where the synthesis of the srilankite phase at atmospheric pressure and temperature below 1200 degrees C in this study is reported for the first time. The crystal structure is tetragonal rutile type for the unsubstituted composition, orthorhombic srilankite type for the compositions with x > 0.30, and the compositions in between is a two-phase region with a mixture of rutile and srilankite. The Zr substitution has a great influence on the microstructure of the ceramics. In particular, for compositions where x > 0.1, the grain boundaries are surrounded by elongated powdery particles. The microwave dielectric properties of the ceramics are closely related to the phase transition process, in which Q x f is significantly improved and tau f decreases almost linearly with the increase of the content of srilankite phase. Optimum microwave dielectric properties with a permittivity of 35.1, a Q x f value of 7270 GHz, and a near-zero tau f of 9.0 ppm/degrees C are obtained in the ceramics with x = 0.3 sintered at 1150 degrees C for 4 h, which provides a new option for microwave devices requiring medium-permittivity dielectric ceramics.