Structural stability of the robust GdYTi2O7 pyrochlore under high pressure

Abstract

Complex ceramics with pyrochlore (A₂B₂O₇) and defect-fluorite ((A, B)₄O₇) type structures experience structural modifications under high pressure. Here, we used mechanical milling and sintering followed by compression in diamond anvil cell to determine the high-pressure behavior using in-situ synchrotron diffraction. Raman spectroscopy and X-ray diffraction at ambient pressure confirm the pyrochlore phase of as-prepared GdYTi₂O₇ ceramic. In-situ high-pressure experiments reveal no structural phase transition in GdYTi₂O₇ pyrochlore up to approximately 50 GPa. The variation in the x positional coordinate of O_48f oxygen and cation–anion bond lengths shows that disordering occurs at high pressure above ∼43 GPa. The Rietveld refinement results indicate the pyrochlore phase of GdYTi₂O₇ ceramic at the highest pressure of ∼50 GPa. Compared to Y₂Ti₂O₇, the equal substitution of Y³⁺ and Gd³⁺ at the A-site increases phase stability at high pressures. The experimental results indicate that mainly cation disordering occurs with increasing pressure, and lower compressibility of < Ti–O_48f > bonds should play a significant role in the robustness of GdYTi₂O₇ pyrochlore to sustain pyrochlore structure up to very high pressures. DFT-derived cation–anion bond lengths and bulk modulus value agree with the experimental results in supporting the robustness of the GdYTi₂O₇ pyrochlore.