title: Reversible reconstructive phase transition of Ba2SnSe5: a new high temperature modification with completely different structural motifs.
abstract: A new modification of Ba(2)SnSe(5) was prepared by high temperature synthesis. In contrast to its low temperature modification that adopts the orthorhombic space group P2(1)2(1)2(1), the new beta-Ba(2)SnSe(5) crystallizes in the monoclinic system, space group P2(1)/c, with the lattice parameters a = 9.3949(6) A, b = 8.8656(6) A, c = 12.5745(7) A, beta = 113.299(4) degrees, V = 961.9(1) A(3), Z = 4. alpha-Ba(2)SnSe(5) is comprised of Sn(3)Se(10)(8-) units, SnSe(4)(4-) tetrahedra, and isolated Se(3)(2-) units, while beta-Ba(2)SnSe(5) contains only SnSe(5)(4-) units, wherein Sn is tetrahedrally coordinated by four Se atoms. The fifth Se atom is connected to one Se atom of the SnSe(4)(4-) tetrahedron, thereby forming a Se(2)(2-) dumbbell. Different band gaps are a result of the different structure motifs, which are reflected in different colors of the two Ba(2)SnSe(5) modifications, the alpha-form being dark brown and the beta-form being red.
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
authors.forename: Mariya
authors.initials: M
authors.lastname: Zelinska
authors.forename: Abdeljalil
authors.initials: A
authors.lastname: Assoud
authors.forename: Christian
authors.initials: C
authors.lastname: Graf
authors.forename: Holger
authors.initials: H
authors.lastname: Kleinke