Effect of static local distortions vs. dynamic motions on the stability and band gaps of cubic oxide and halide perovskites

Journal Article · Fri Aug 20 00:00:00 EDT 2021 · Materials Today

DOI:https://doi.org/10.1016/j.mattod.2021.05.021· OSTI ID:1977425

Zhao, Xin-Gang ^[1]; Wang, Zhi ^[2]; Malyi, Oleksandr I. ^[1]; Zunger, Alex ^[1]

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1. Univ. of Colorado, Boulder, CO (United States)
2. Univ. of Colorado, Boulder, CO (United States); Chinese Academy of Sciences (CAS), Beijing (China)

Ternary ABX₃ perovskites made of corner-sharing BX₆ octahedra have long featured prominently in solid-state chemistry and condensed matter physics. Still, the joint understanding of their two main subgroups—halides and oxides—has not been fully developed. Indeed, unlike the case in simpler compounds having a single, robust repeated motif (“monomorphous”), certain cubic perovskites can manifest a non-thermal (= intrinsic) distribution of local motifs (“polymorphous networks”). Such static deformations can include positional degrees of freedom (e.g., atomic displacements and octahedral tilting) or magnetic moment degrees of freedom in paramagnets. Unlike thermal motion, such static distortions do not time-average to zero, being an expression of the intrinsic symmetry breaking preference of the chemical bonding. Here, the present study compares electronic structure features of oxide and halide perovskites starting from the static polymorphous distribution of motifs described by Density Functional Theory (DFT) minimization of the internal energy, continuing to finite temperature thermal disorder modeled via finite temperature DFT molecular dynamics. We find that (i) different oxide vs. halide ABX₃ compounds adopt different energy-lowering symmetry-breaking modes. The calculated pair distribution function (PDF) of SrTiO₃ from the first-principles agrees with recently measured PDF. (ii) In both oxides and halides, such static distortions lead to band gap blueshifts with respect to undistorted cubic Pm-3m structure. (iii) For oxide perovskites, high-temperature molecular dynamics simulations initiated from the statically distorted polymorphous structures reveal that the thermally-induced distortions can lead to a band gap redshift. (iv) In contrast, for cubic halide perovskite CsPbI₃, both the intrinsic distortions and the thermal distortions contribute in tandem to band gap blueshift, the former, intrinsic effect being dominant. (v) In the oxide SrTiO₃ and CaTiO₃ (but not in halide) perovskites, octahedral tilting leads to the emergence of a distinct Γ–Γ direct band gap component as a secondary valley minimum to the well-known indirect R–Γ gap. Understanding such intrinsic vs. thermal effects on oxide vs. halide perovskites holds the potential for designing target electronic properties.

• Research Organization: Univ. of Colorado, Boulder, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0010467
• OSTI ID: 1977425
• Alternate ID(s): OSTI ID: 1868701
• Journal Information: Materials Today, Vol. 49, Issue C; ISSN 1369-7021
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Perovskites
Symmetry breaking
Band gap renormalization
Pair distribution function
Polymorphous networks
SrTiO3
CaTiO3
CsPbI3