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Structural Polymorphism in MnGa 2 Se 4
Author(s) -
Cannas M.,
Garbato L.,
Geddo Lehmann A.,
Lampis N.,
Ledda F.
Publication year - 1998
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/(sici)1521-4079(1998)33:3<417::aid-crat417>3.0.co;2-2
Subject(s) - tetragonal crystal system , orthorhombic crystal system , crystallography , polymorphism (computer science) , crystal structure , powder diffraction , ternary operation , space group , diffraction , materials science , electron diffraction , lattice (music) , phase (matter) , chemistry , x ray crystallography , physics , optics , biochemistry , organic chemistry , computer science , genotype , programming language , acoustics , gene
The polymorphic behaviour of the adamantane‐type compound MnGa 2 Se 4 is reinvestigated by X‐ray powder diffraction and electron microscopy techniques carried out on annealed and quenched samples. The low‐temperature modification (γ‐phase) is confirmed to crystallize in the defect tetragonal thiogallate structure (space group I4‐) with lattice parameters a = 5.677(1) Å and c = 10.761(2) Å. Samples quenched from high temperature (750 °C) show the coexistence of two ternary phases both having the MnGa 2 Se 4 composition but different crystal structures: the main phase is still tetragonal with slightly different lattice parameters (γ′‐phase); the secondary phase exhibits an orthorhombic cell with approximate dimensions a = 13.5 Å, b = 8.0 Å, c = 6.5 Å and possible space group Pna2 1 (ε‐phase). This latter polymorph is identified as the β‐ZnAl 2 S 4 ‐type form of MnGa 2 Se 4 . TEM analyses performed on the ε‐phase show the presence of ferroelastic twins, confirmed by electron diffraction. The connections among the three structures are shortly discussed.