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We report a joint experimental and theoretical investigation of thehigh-pressure structural and vibrational properties of terbium sesquioxide(Tb2O3). Powder x-ray diffraction and Raman scattering measurements show thatcubic (C-type) Tb2O3 undergoes two phase transitions up to 25 GPa. We observe afirst irreversible reconstructive transition to the monoclinic (B-type) phaseat ~7 GPa and a subsequent reversible displacive transition from the monoclinicto the trigonal (A-type) phase at ~12 GPa. Thus, Tb2O3 is found to follow thewell-known C-B-A phase transition found in other cubic rare-earth sesquioxideswith cations of larger atomic mass than Tb. Our ab initio theoreticalcalculations predict phase transition pressures and bulk moduli for the threephases in rather good agreement with experimental results. Moreover,Raman-active modes of the three phases have been monitored as a function ofpressure and lattice-dynamics calculations have allowed us to confirm theassignment of the experimental phonon modes in the C-type phase as well as tomake a tentative assignment of the symmetry of most vibrational modes in the B-and A-type phases. Finally, we extract the bulk moduli and the Raman-activemodes frequencies together with their pressure coefficients for the threephases of Tb2O3. These results are thoroughly compared and discussed inrelation to those reported for rare-earth and other related sesquioxides. It isconcluded that the evolution of the volume and bulk modulus of all the threephases of these technologically relevant compounds exhibit a nearly lineartrend with respect to the third power of the ionic radii of the cations.

Structural and lattice-dynamical properties of Tb2O3 under compression: a comparative study with rare-earth and related sesquioxides