First-principles study of octahedral tilting and ferroelectric-like transition in metallicLiOsO3

Abstract

The octahedral tilting and ferroelectric-like structural transition of LiOsO 3 metallic perovskite [Y. Shi et al., Nat. Mater. 12, 1024(2013] is studied using first-principles density-functional theory. In LiOsO 3 , the a − a − a − octahedral tilting mode is responsible for cubic (F m3m) to rhombohedral structure (R3c), which is stable phase at room temperature, and at low temperature, noncentrosymmetric transition to R3c rhombohedral transition is realized as a result of zone center phonon softening. By using density-functional calculation and phonon calculation, the phase transition behavior of LiOsO 3 can be fully understood. We also present electronic structure change and Fermi surface change due to electron lattice coupling effect. The change of carrier density of state across phase transition is associated with experimental temperature dependence of resistivity, heat capacity, and susceptibility.Recently, there has been considerable interest in octahedral tilting transition and noncentrosymmetric transition in perovskite oxides not only for their technological importance as new ferroelectric materials and multistage memory devices but also from a fundamental point of view [1][2][3][4]. In this pursuit, first-principles density-functional theory has played a key role in explaining new physical states as well as predicting new realizations of physical states of materials [5][6][7]. LiOsO 3 is one of the important and unique additions to a new oxide material with pervoskite structure. According to a recent report from Shi et al. [8], LiOsO 3 is a perovskite oxide material with metallic properties. Interestingly, around 140 K, a centrosymmetric (R3c) phase to noncentrosymmetric (R3c) phase transition is reported. They also reported an anomaly in temperature dependence of heat capacity, susceptibility, and resistivity and indicate that such a structural phase transition is equivalent to the ferroelectric transition of LiNbO 3 materials.In both centrosymmetric (R3c) and non-centrosymmetric (R3c) phases, the octahedral tilting is one of the important ingredients [9][10][11][12]. The three-dimensional network of OsO 6 octaheral tilting in LiOsO 3 can be easily characterized by Glazer notation [9]. Glazer notation describes the octahedral tilting using the symbol a # b # c # , in which the literals refer to tilt around the [100], [010], and [001] directions of the cubic perovskite, and the superscript # takes the value 0, +, or − to indicate no tilt or tilts of successive octahedra in the same or opposite sense. The rhombohedral (R3c and R3c) structure of LiOsO 3 can be classified by a − a − a − tilting [8,9]. This tilting of LiOsO 3 is basically the same as LiNbO 3 [13-20] and originates from the rigidity of the OsO 6 octahedron and the large ionic size difference of the Li and Os ions.In addition to octahedral tilting, the zone center soft mode is the main source of the centrosymmetric (R3c) and noncentrosymmetric (R3c) phases. In LiNbO 3 , the phase transition from a centrosymmetric (R3c) to a noncentrosymmetric...

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