The influence of ZnNb 2O 6 on the microwave dielectric properties of ZrTi 2O 6 ceramics

Ceramics in the system (1-x)ZrTi 2O 6-xZnNb 2O 6 (for 0.1≤x≤0.85) have been prepared by the mixed oxide route; specimens fired in oxygen at 1260°-1300°C achieved 97% theoretical density for most compositions. X-ray diffraction analysis confirmed the co-existence of a disordered α-PbO 2-type structured phase and a rutile-structured second phase for 0.1≤x≤0.25, a single phase having a disordered α-PbO 2-type structure for 0.3≤x≤0.7, and a columbite-type structured phase for x≥0.85. Wavelength dispersive spectroscopy (WDS) revealed that the TiO 2-rich second phase contained significant amounts of ZrO 2, Nb 2O 5, and ZnO. In the two-phase region relative permittivities (ε r) are predominantly in the range 39-47 (with a peak at x=0.24), quality factor (Q×f) values peak at 34 000 GHz, and temperature coefficient of resonant frequency (τ f) decreases with increase in ZnNb 2O 6 content and tune through zero at x=0.24. In the single-phase α-PbO 2 region ε r decreases, Q×f increases to 49 000 GHz and τ f decreases to -58 ppm/°C with increasing ZnNb 2O 6. In the ordered columbite structure region (x≥0.85) the ε r falls to 28, Q×f increases to 59 000 GHz and τ f is more positive (-20 ppm/°C). Ceramics with x=0.24 exhibited an excellent combination of properties: ε r=47, Q×f=34 000 GHz, and τ f∼0 ppm/°C. © 2005 The American Ceramic Society.