New perspectives on the fluorite-pyrochlore phase transition in La2Zr2O7 and the importance of local oxygen-related disordered states

TL;DR

This study investigates the fluorite to pyrochlore phase transition in La2Zr2O7, revealing differences between surface and bulk regions and highlighting the role of local oxygen-related disordered states in the transition process.

Contribution

It provides new insights into the phase transition mechanism in La2Zr2O7, emphasizing the importance of local oxygen disorder and surface-bulk differences using combined diffraction and Raman techniques.

Findings

Phase transition occurs between 1000-1450°C.

Surface shows pure pyrochlore phase signatures.

Bulk contains oxygen-related disordered states.

Abstract

The fluorite to pyrochlore phase transition in La2Zr2O7 has been studied in the literature for decades in the context of thermal barrier coatings and reinforcement materials. However, the nature of the phase transition in this system is still not well understood. In this article we have investigated the phase transition in La2Zr2O7, calcined at different temperatures, using powder x-ray diffraction and Raman measurements. Rietveld analyses of the x-ray data suggest a fluorite to pyrochlore phase transition in the system occurring between 1000-1450oC. Nonetheless, Raman spectra, recorded with different excitation wavelengths (\lambda_ex) reveal that the dynamics of phase transition is different in the near-surface region and in the bulk inside. While the near-surface region carried the signatures of a pure pyrochlore phase, the temperature dependent Raman measurements with \lambda_ex=785 nm suggest that locally formed oxygen related disordered states are present in the bulk of the system.