Effects of divalent cation substitution on sinterability and electrical properties of lacro₃ ceramics

A series of LaCr_1-xM_xO₃ (M = Mg, Cu, Zn, Ni) ceramics was fabricated by a conventional sintering process in air and Ar gas. Relative density, electrical conductivity, and magnetic susceptibility were measured to investigate the electrical conduction mechanism of the doped LaCrO₃ ceramic. The apparent density was improved up to 95% of theoretical density, especially in the cases of M = Cu²⁺ and Zn²⁺. The electrical conductivity (σ) increased with increasing quantities of doped divalent cation (x), and log(σT) showed a linear relationship to (1/T). Magnetic data and chemical analysis indicated that the presence of Cr⁴⁺, rather than oxygen deficiencies, is preferential for the charge compensation. As a result, the electrical conduction was substantially governed by the hopping of small polarons between Cr³⁺ and Cr⁴⁺ ions. The substitution of Ni ions resulted in lower than expected unit cell volumes, somewhat different conductivities, and a different antiferromagnetic response, all of which pointed to the role of Ni³⁺ as of the source of an additional band conduction mechanism.