MECHANISM OF LA2CUO4 SOLID-STATE POWDER REACTION BY QUANTITATIVE XRD AND IMPEDANCE SPECTROSCOPY

Reaction kinetics for CuO + La2O3 --> La2CuO4 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 La2O3 particles and produces an La2CuO4 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.