Mechanism of La ₂ CuO ₄ Solid‐State Powder Reaction by Quantitative XRD and Impedance Spectroscopy

Reaction kinetics for CuO + La 2 O 3 → La 2 CuO 4 were quantified by X‐ray diffraction on quenched samples reacted in air. The rate was successfully modeled by the Valensi‐Carter equation, taking into account the particle size distribution. Kinetics followed diffusion‐limited rather than reaction‐limited behavior; the activation energy was 265 kJ/mol. Conductivity‐time behavior from in situ impedance spectra confirmed the reaction model; CuO rapidly coats the La 2 O 3 particles and produces an La 2 CuO 4 diffusion barrier. This is consistent with the basic assumptions of the Valensi‐Carter equation. It is believed that copper diffusion controls the rate of reaction.