An insight into the effects of transition metals on the thermal expansion of complex perovskite compounds: an experimental and density functional theory investigation

Abstract

ABO₃ perovskite-type LaCoO₃, LaCo_0.5Fe_0.5O₃, LaCo_0.5Ni_0.5O₃, and LaCo_0.5Mn_0.5O₃ complex oxides were synthesized using the sol–gel method. The microstructure and the thermal expansion behavior of the oxides were investigated. Insights into phonon dispersion and the effects of doped transition metals on thermal expansion were obtained by first-principles calculations based on density functional theory. Thermal expansion coefficients (TECs) at finite temperatures were obtained by quasi harmonic approximation. B-site doping was found to reduce the size of the crystalline grains and the TECs of perovskite compounds. The average TECs of LaCoO₃, LaCo_0.5Fe_0.5O₃, LaCo_0.5Ni_0.5O₃, and LaCo_0.5Mn_0.5O₃ were 25 × 10⁻⁶ K⁻¹, 11 × 10⁻⁶ K⁻¹, 12.5 × 10⁻⁶ K⁻¹, and 5 × 10⁻⁶ K⁻¹, respectively, in the 0–1000 K temperature range. In addition, the TECs of LaCo_0.5Fe_0.5O₃ and LaCo_0.5Ni_0.5O₃ matched well with those of some common electrolytes.