Improvement in Dielectric Properties of Low Temperature Sintered Alumina Containing a Small Quantity of a CuO–Nb₂O₅ Additive by Substitution of Titanium Dioxide

Abstract

The substitution of TiO₂ to alumina was examined in low temperature sintered alumina containing a small quantity of a CuO–Nb₂O₅-type additive. The purpose of this research was to both maintain sinterability at a temperature lower than the melting point of Cu, 1357 K, and to improve the dielectric properties, especially the temperature coefficient of resonant frequency (TCF). As a result, we found that both low temperature sinterability at 1308 K and TCF zeroing were achieved simultaneously. Analyses by XRD and TEM–EDS revealed that substituted TiO₂ does not react with Al₂O₃ and does not produce Al₂TiO₅ which inhibits TCF zeroing at the firing temperature of this study; hence, this is the cause of achieving TCF zeroing. The developed material fired at 1308 K in an air atmosphere with the composition of TiO₂ substitution amount of 12 mol% showed great properties: a relative density of approximately 98%, a relative permittivity (ε_r) of 13.6, a product of quality factor and resonant frequency (Q·f) of 28000 GHz, a TCF of ±0 ppm/K, and a high thermal conductivity of 20 W/mK. Further, similar properties were obtained for samples fired at 1323 K in a nitrogen atmosphere.