Low-temperature Sintering Mechanism, Dielectric, and Thermal Properties of CuO-TiO₂-Nb₂O₅-containing Al₂O₃ Ceramics Featuring Superior Thermal Conductivity

Abstract

CuO-TiO₂-Nb₂O₅ was utilized as additive (5 wt%) to obtain densified alumina using the firing temperature of 885 °C for 96 h. Densification started at ~835 °C, which was lower than the melting point of the additive (~967 °C). The melting temperature of the powder mixture consisting of the additive and alumina was measured, but no significant changes were observed compared with the melting temperature of the additive. Furthermore, the lattice constants measurements of the alumina sample obtained after heat treatment at 885 °C revealed an increase in unit cell volume, which suggested the incorporation of Cu and Ti components into alumina according to the TEM-EDS analysis. In addition, the timing of the increase in alumina lattice constant and that of the rapid increase in the sintered density of the additive-containing alumina coincided. These results indicated that the densification of the sample occurred in solid state (solid-state-activated sintering). The sample fired at 935 °C for 6 h exhibited the thermal conductivity of 22 W/mK, which was higher than that of conventional low-temperature co-fired ceramic materials (~2–7 W/mK), the relative dielectric constant (ε_r) of 10.2, the quality factor multiplied by the resonant frequency (Q × f) value of 47000 GHz, and the temperature coefficient of resonant frequency (τ_f) of –50 ppm/K.