New Cu₃TeO₆ ceramics: phase formation and dielectric properties.

Targeting low temperature cofired ceramics (LTCC) applications and base-metal electrode multilayer ceramic capacitors (BME-MLCCs), ceramics of a new composition, tricopper tellurate (Cu3TeO6), are reported here. The crystal structure of Cu3TeO6 was determined to be cubic, Ia3, with the unit cell parameter a = 9.538 Å. The sequence of phase formation is proposed with the oxidation of tetravalent tellurium (Te(4+)) into hexavalent tellurium (Te(6+)) as a key step for the formation of Cu3TeO6. Ceramics sintered at 865 °C with densities of 94% exhibit two dielectric anomalies in the temperature dependence of the dielectric response, around -150 °C and +50 °C, respectively, accompanied by obvious frequency dispersion of the relative permittivity (ε(r)) and dielectric losses (tan δ), with an Arrhenius like behavior. A temperature stable dielectric region (near room temperature) formed between the two anomalies with ε(r) ∼ 12 and tan δ ∼ 0.01, and a very low positive temperature coefficient of the relative permittivity (TCε(r)), 2.07 × 10(-4) °C(-1), was obtained in the same region. The low temperature dielectric anomaly is associated with the possible mixed Cu(+)/Cu(2+) valence in Cu3TeO6 ceramics, while the high temperature anomaly is attributed to point defect ordering, including VO, CuCu2+(+)', which might be formed during sintering. Therefore, Cu3TeO6 ceramics are of interest in view of not only the possible applications in BME-MLCCs, LTCC, and related technologies, but also for their possible compatibility with low cost abundant Cu electrodes.