<i>M</i> fergusonite DyTaO ₄ under compression: an insight from experiment and theory

Rare-earth orthotantalate, DyTaO₄is a technologically important material having unique combination of optical transparency, high dielectric constant and thermal robustness. In this study, we report the synthesis and ambient structural characterization of both<i>M</i>- and<i>M'</i>-type monoclinic phases of DyTaO₄. The high pressure (HP) behaviour of<i>M</i>-type (fergusonite) phase was investigated using synchrotron-based x-ray diffraction (XRD) and Raman spectroscopy up to ∼28 GPa and 38 GPa respectively. Signature of pressure-induced structural phase transition was observed near 24 GPa, marked by changes in both diffraction patterns and vibrational spectra. First-principles density functional theory calculations predict a transition to a tetragonal structure (space group (SG)<i>P</i>4/<i>nbm</i>) near 15 GPa from ambient pressure monoclinic structure (SG<i>I</i>2/<i>a</i>). The XRD data and theoretical simulations for low pressure (LP) phase shows anisotropic lattice compression being largest for<i>b</i>axis followed by<i>a</i>and<i>c</i>axis as has been reported for other isostructural compounds in the series. We also present the experimental and simulated values of bulk modulus for<i>M</i>phase. The positive pressure coefficient for all the Raman modes in LP phase indicates the dynamical stability of the compound up to 24 GPa. Additionally, Grüneisen parameters are reported for several Raman-active modes to understand the vibrational response of the material under pressure. These results provide new insights into the HP structural evolution of DyTaO₄and contribute to the broader understanding of pressure-induced phenomena in rare-earth orthotantalates.