Ca(Zn_1/3Nb_2/3)O₃-based Microwave Dielectric Ceramics With Complex Perovskite Structure

The rapid development of microwave communication systems require the dielectric materials with high dielectric constant, high quality factor and near-zero temperature coefficient of resonant frequency. In the present work, Ca(Zn₁/3Nb₂/3)O₃ ceramics were investigated with respect to the relationship of microwave dielectric properties and microstructures. The modification was performed by A- and B- site substitution in Ca(Zn₁/3Nb₂/3)O₃ ceramic to obtain near-zero temperature coefficient of resonant frequency combined with the intermediate dielectric constant and high quality factor.Structure of Ca(Zn₁/3Nb₂/3)O₃ ceramics was refined in the monoclinic space group P2j/c (14) with 1:2 long-rang ordering in B-site, resulting from b"b"c+ titling system. The dielectric constant of Ca(Zn₁/3Nb₂/3)O₃ ceramics showed slight variation with sintering condition and annealing, but the Qf value was significantly affected by the sintering temperature and post densification annealing. Qf value increased at first and then tended to decrease with increasing sintering temperature, and the annealing in oxygen indicated significant improvement in Qf, especially for the samples sintered at higher temperature. These phenomena reflected the combined effects of grain boundary and oxygen vacancy on the dielectric loss.XRD spectra showed that Ca[(Ti_x(Zn₁/3Nb₂/3)₁-x]O₃ ceramics formed solid solutions with complex perovskite structure in the full range of x. The 1:2 long range ordering reflections did not exist when Ti4+ was added. But the A1g modes near 807cm"1 band on Raman spectra suggested there were still 1:2 short-range ordering in the ceramics. The dielectric constant and temperature coefficient of resonant frequency showed a nonlinear increase with increasing x. The ordering domain size and oxygen vacancies were considered to be the reason of variation of Qf values The best combination of microwave dielectric properties was obtained in the present ceramics with x=0.4 annealed in oxygen: εr=52, Qf=13,091GHz and =0ppmModification of .Ca(Zn₁/3Nb₂/3)O₃ microwave dielectric ceramics was performed by Ba substitution for Ca on the A-site of perovskite structure. XRD spectra showedthat two phases existed at most range of compositions. Solid solution indicated by hexagonal structure and space group of P 3 ml was obtained only for the phase of Ba2+ content greater than 90mol%. 1:2 long-range ordering reflections were existed in full range of substitution. The dielectric constants and temperature coefficients varied abnormally because of the "rattling" of Ca2+ in A-site. The maximum value of Qf was obtained when Ba2+ content is 10mol %.