Structural phases arising from reconstructive and isostructural transitions in high-melting-point oxides under hydrostatic pressure: A first-principles study

Abstract

High-melting-point oxides of chemical formula ABO3, with A = Ca, Sr, Ba and B = Zr, Hf, are investigated as a function of hydrostatic pressure up to 200 GPa, by combining first-principles calculations with a particle swarm optimization method. Ca-and Sr-based systems (1) first undergo a reconstructive phase transition from a perovskite state to a novel structure that belongs to the post-post-perovskite family; and (2) then experience an isostructural transition to a second, also new post-post-perovskite state at higher pressure, via the sudden formation of a specific out-of-plane B-O bond. In contrast, the studied Ba-compounds evolve from a perovskite phase to a third novel post-post-perovskite structure, via another reconstructive phase transition. Original characteristics of these three different post-post-perovskite states are emphasized. Unusual electronic properties, including significant piezochromic effects and an insulator-metal transition, are also reported and explained.

Stability of the tetragonal phase of BaZrO3 under high pressure

“…We also considered the possibility for a transition to the (a − b + a − ) tilt system, corresponding to the very common and stable orthorhombic P nma structure. For this case, the system relaxes back to the orthorhombic Imma (a − b 0 a − ) phase suppressing the b + rotation, also in line with past studies [27,57]. Therefore, this highlights that, in BaZrO 3 , the condensation of one rotational mode suppresses the partner one.…”

“…Instead, predictions have been made for the appearance of ferroelectricity in combination with tilts in BaZrO 3 at high enough pressures [23][24][25]. Also, the possibility for transitions to completely different polymorphs has been considered [26,27]. A transition to a post-perovskite phase in particular was predicted to occur at pressures as low as 70 GPa and cause a first-order transition into a semiconducting orthorhombic phase with a 7.9% volume collapse.…”

Strain-induced structural phase transition, electric polarization and unusual electric properties in photovoltaic materials CsMI3 (M = Pb, Sn)

“…Such striking electronic properties hint towards unusual optical properties-such as electric dipole transition and piezochromic effects. [64][65][66] In fact, we numerically found (see Fig. 4(b)) that such feature also exists in CsSnI 3 lm but the band gap changes from 0.42 eV to 0 eV with strain-induced insulator-to-metal transitions under À3.8% compressive strain, which further emphasizes the signicance.…”

Pressure-Induced High-κ Dielectric Properties and Multiple Phase Transitions between Novel Nonperovskite and Perovskite Phases in LiSbO3: A First-Principles Study

“…Information about all structures can also be obtained from Tables S1 and S2 in the Supporting Information. Figure d shows that the Pnma structure consists of tilted LiO 6 octahedra along three different directions and an oxygen coordination polyhedron of Sb cations (a – a – c + tilting pattern, indicated by Glazer’s notations), which is similar to the GdFeO 3 -type structure, such as the ground state of NaZnF 3 and CaZrO 3 materials. , However, there is an obvious interchange of A and B sites, as shown in Figure d,e. Therefore, we define such a Pnma phase as Sb:A Pnma , different from the GdFeO 3 -type phase (denoted as Sb:B Pnma in this study).…”