CdO-CuO-TiO2 ternary dielectric systems: Subsolidus phase diagram and the effects of Cu segregation

Valence of Cu cations and Cu segregation of CdCu3Ti4O12 ceramics are initially examined by establishing the subsolidus phase diagram of Cd1-xCu3+x+2yTi4-yO12 (−7 ≤ x ≤ 0.07, −1.333 ≤ y ≤ 2.91) systematically. Different from CaO-CuO-TiO2 system, the co-existence of hexagonal and orthorhombic CdTiO3 phases is observed in the line between CdTiO3 and CuO. Basing on the obtained phase diagram, three typical ceramics with Cu-equal (CdCu3Ti4O12), Cu-rich (Cd0.930Cu3.070Ti4O12), and Cu-poor (Cd1.137Cu2.863Ti4O12), showing high dielectric constant, are chosen as target samples to investigate the role of Cu valence and segregation in dielectric behaviors. Cu3+ ions, rather than Cu+ ones as reported previously, forms in the grain to act as the hopping charge carriers as demonstrated by X-ray photoelectron spectroscopy and High-energy X-ray absorption Near Edge Structure. This work would give a hint in tuning the stoichiometry for achieving more fascinating structures and properties in new ceramic material design.