Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25−xCo0.75−xCu2xO3−δ and LaMn0.75−xCo0.25−xCu2xO3−δ
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This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn0.25−xCo0.75−xCu2xO3−δ and LaMn0.75−xCo0.25−xCu2xO3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn0.25−xCo0.75−xCu2xO3−δ), the Mn-rich series (LaMn0.75−xCo0.25−xCu2xO3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (αmax = 19.6 × 10−6 K−1) and electrical conductivity (σmax = 730 S/cm at 800 °C) than the Mn-rich series (αmax = 10.6 × 10−6 K−1, σmax = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15.