For bulk ceramic materials, small substitutions ofAl2O3inTa2O5are shown to cause a moderate enhancement of the dielectric constant. For compositions near 0.95Ta2O5–0.05Al2O3,the temperature coefficient of the dielectric constant at 20 °C dramatically decreases, from more than 200 ppm/°C for pureTa2O5to less than 20 ppm/°C. The quality factors(Q)at 1 MHz, are 2000–5000. Measurements to 14 GHz at 20 °C show that the dielectric constant is maintained to microwave frequencies, with aQof ∼600 at 5 GHz. ©1997 American Institute of Physics.