Microwave dielectric properties of Bi2(Zn1/3Ta2/3)2O7 polymorphs

Polymorphic phases of Bi-2(Zn1/3Ta2/3)(2)O-7 pyrochlore were studied. A metastable monoclinic structure was observed at temperatures below 950degreesC. This low-temperature phase possesses highly temperature-stable characteristics in the microwave frequency range (5-7 GHz) with a temperature coefficient of resonant frequency (tau(f)) = -8.8 ppm/degreesC. The addition of B2O3 to Bi-2(Zn1/3Ta2/3)(2)O-7 significantly lowered the sintering temperature, to 850degreesC, without an associated structural transition. Low-temperature sintering mechanisms have been investigated using dilatometry and transmission electron microscopy. Bi-2(Zn1/3Ta2/3)(2)O-7 with 0.5 wt% B2O3 can be suitable for application in low-temperature cofired ceramics (LTCC), due to its reduced sintering temperature and good microwave dielectric properties: quality factor (Q x f) = 3500 GHz at 6.7 GHz, dielectric constant (epsilon(r)) = 63.9 and tau(f) = -14.1 ppm/degreesC.