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

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.