title: Octahedral Rotation Preferences in Perovskite Iodides and Bromides.
abstract: Phase transitions in ABX3 perovskites are often accompanied by rigid rotations of the corner-connected BX6 octahedral network. Although the mechanisms for the preferred rotation patterns of perovskite oxides are fairly well recognized, the same cannot be said of halide variants (i.e., X = Cl, Br, or I), several of which undergo an unusual displacive transition to a tetragonal phase exhibiting in-phase rotations about one axis (a(0)a(0)c(+) in Glazer notation). To discern the chemical factors stabilizing this unique phase, we investigated a series of 12 perovskite bromides and iodides using density functional theory calculations and compared them with similar oxides. We find that in-phase tilting provides a better arrangement of the larger bromide and iodide anions, which minimizes the electrostatic interactions, improves the bond valence of the A-site cations, and enhances the covalency between the A-site metal and Br(-) or I(-) ions. The opposite effect is present in the oxides, with out-of-phase tilting maximizing these factors.
authors.affiliation: Department of Materials Science and Engineering, Drexel University , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Joshua
authors.initials: J
authors.lastname: Young
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: James M
authors.initials: JM
authors.lastname: Rondinelli
mesh_terms: D001965:Bromides / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: D001965:Bromides; D017610:Calcium Compounds; D007454:Iodides; D010087:Oxides; C059910:perovskite; D014025:Titanium