Effects of the counter-cation nature and preparation method on the structure of La₂Zr₂O₇

Lanthanum zirconate with a pyrochlore structure exhibits interesting thermal and structural properties for thermal barrier coating applications operating at high temperature. This study focused on the synthesis of La₂Zr₂O₇ powders by soft chemistry (citrate, coprecipitation, and sol–gel methods), and the effects of the solvent and the nature of the precursors used on the powder properties were investigated. The nature of the counter-cation influenced the structural phase of the compound. A low polarizable counter-cation (chloride) permitted the elaboration of a pyrochlore structure within a larger range of parameters compared with highly polarizable counter-cations (nitrate and acetate). Moreover, the nature of the solvent, and specifically the strength of the interactions within it, had an impact on the particle size. Specifically, the use of water, which is a solvent with strong interactions, led to a smaller particle size than the use of ethanol, which has weaker interactions. Based on these results, the crystalline phase of the powders can be predicted as a function of the precursor and the solvent used for the different synthesis routes, and the particle size can be used to evaluate the reactivity of the powders.