Pressure induced structural phase transition in rare earth sesquioxide Tm2O3: Experiment and ab initio calculations

Abstract

Among the small cation sized rare earth sesquioxides, the reported transition pressure of cubic Tm2O3 is ambiguous. Pressure induced structural phase transition in cubic Tm2O3 has been reinvestigated using the synchrotron X-ray diffraction, Raman spectroscopy, and ab initio density functional theory (DFT) calculations up to a pressure of 25 GPa. Both the X-ray diffraction and Raman spectroscopic measurements revealed an irreversible polymorphic structural phase transition from type-C cubic to type-B monoclinic at around 12 GPa, whereas the same is predicted to be 8 GPa from the density functional theory. The phase transition observed at 12 GPa is in contrast to the literature and the reasoning has been established by other studies, viz., Raman spectroscopy and DFT. A third order Birch-Murnaghan equation of state fit to the experimental compressibility curve yielded a zero pressure bulk modulus of 149(2) GPa with the pressure derivatives 4.8(5) for the parent cubic phase and 169(2) GPa with the pressure derivative 4 for the high pressure monoclinic phase, respectively. These values are in good agreement with the calculated bulk modulus of 146 and 151 GPa for the cubic and monoclinic phases, respectively. Raman modes for the monoclinic phase of Tm2O3 are measured and reported for the first time. The mode Grüneisen parameter of different Raman modes for both cubic and monoclinic phases of Tm2O3 has also been determined. The experimental results are correlated with changes in the density of states near the Fermi level, which are indicative of structural instabilities in the parent cubic structure.

Microstrain-assisted polymorphic phase transitions in (Eu1−x La x )2O3

“…B and B ! A transitions are 6.5-10% and 1-2%, respectively Zhang et al, 2008;Irshad et al, 2018;Sahu et al, 2012;Guo et al, 2007;Jiang et al, 2010).…”

“…x x(O) y(O) z(O) U iso  10 2 (Å 2 ) 0 0.96939 (4) 0.3901 (4) 0.1507 (4) 0.3804 (5) 0.406 (8) 0.1 0.96981 (3) 0.3898 (4) 0.1511 (4) 0.3812 (4) 0.482 (7) 0.2 0.97022 (4) 0.3911 (5) 0.1508 (5) 0.3824 (6) 0.641 (8) 0.3 0.97054 (5) 0.3914 (6) 0.1503 5 Chandra Jiang et al, 2013;Wu et al, 2007;Sahu et al, 2012;Zinkevich, 2007;Irshad et al, 2018).…”

Thermal Analysis of High Entropy Rare Earth Oxides

“…All rare earth sesquioxides can be obtained in their ground-state C-type structure at room temperature. The B-type structure is both a high pressure and a high temperature phase for sesquioxides from Sm to Ho, and high pressure phase for sesquioxides from Er to Lu, Y and Sc [ 85 , 86 , 87 , 88 ]. In Figure 5 , volumes of C and B phases for samples studied in this work are plotted vs. average ionic radius together with volumes of pure sesquioxides.…”

Structural and Lattice-Dynamical Properties of Tb2O3 under Compression: A Comparative Study with Rare Earth and Related Sesquioxides

“… 13 , 14 The effect of HP on RE SOs has been extensively studied by several research groups, and their pressure-induced PTs have been recently reviewed. 15 In fact, since the cubic phase can be synthesized in a number of them, from Lu to Sm as well as in Mn 2 O 3 , In 2 O 3 , and Tl 2 O 3 , its behavior under compression has been widely studied, as for instance in Lu 2 O 3 , 16 , 17 Yb 2 O 3 , 18 , 19 Tm 2 O 3 , 20 , 21 Er 2 O 3 , 22 − 24 Ho 2 O 3 , 25 − 28 Dy 2 O 3 , 29 , 30 Gd 2 O 3 , 31 − 38 Eu 2 O 3 39 − 45 Sm 2 O 3 , 34 , 46 , 47 Sc 2 O 3 , 48 − 50 Y 2 O 3 , 34 , 51 − 61 Mn 2 O 3 , 62 − 65 In 2 O 3 , 66 − 70 and Tl 2 O 3 . 71 Moreover, the equation of state of several RE SOs of C-, B-, and A-type has been studied comparatively.…”