title: Dynamic Stereochemical Activity of the Sn(2+) Lone Pair in Perovskite CsSnBr3.
abstract: Stable s(2) lone pair electrons on heavy main-group elements in their lower oxidation states drive a range of important phenomena, such as the emergence of polar ground states in some ferroic materials. Here we study the perovskite halide CsSnBr3 as an embodiment of the broader materials class. We show that lone pair stereochemical activity due to the Sn(2+) s(2) lone pair causes a crystallographically hidden, locally distorted state to appear upon warming, a phenomenon previously referred to as emphanisis. The synchrotron X-ray pair distribution function acquired between 300 and 420 K reveals emerging asymmetry in the nearest-neighbor Sn-Br correlations, consistent with dynamic Sn(2+) off-centering, despite there being no evidence of any deviation from the average cubic structure. Computation based on density functional theory supports the finding of a lattice instability associated with dynamic off-centering of Sn(2+) in its coordination environment. Photoluminescence measurements reveal an unusual blue-shift with increasing temperature, closely linked to the structural evolution. At low temperatures, the structures reflect the influence of octahedral rotation. A continuous transition from an orthorhombic structure (Pnma, no. 62) to a tetragonal structure (P4/mbm, no. 127) is found around 250 K, with a final, first-order transformation at 286 K to the cubic structure (Pm3̅m, no. 221).
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.
authors: Douglas H
authors: DH
authors: Fabini
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.
authors: Geneva
authors: G
authors: Laurita
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.
authors: Jonathon S
authors: JS
authors: Bechtel
authors: Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors: Constantinos C
authors: CC
authors: Stoumpos
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors: Hayden A
authors: HA
authors: Evans
authors: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , 15310 Athens, Greece.
authors: Athanassios G
authors: AG
authors: Kontos
authors: Physics Department, National Technical University of Athens , 15780 Zografou, Athens, Greece.
authors: Yannis S
authors: YS
authors: Raptis
authors: Institute of Nanoscience and Nanotechnology, NCSR Demokritos , 15310 Athens, Greece.
authors: Polycarpos
authors: P
authors: Falaras
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.
authors: Anton
authors: A
authors: Van der Ven
authors: Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , Evanston, Illinois 60208, United States.
authors: Mercouri G
authors: MG
authors: Kanatzidis
authors: Materials Research Laboratory, University of California , Santa Barbara, California 93106, United States.|Materials Department, University of California , Santa Barbara, California 93106, United States.|Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors: Ram
authors: R
authors: Seshadri