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Quaternary Chalcogenides La 3 Sn 0.5 InS 7 and La 3 Sn 0.5 InSe 7
Author(s) -
Iyer Abishek K.,
Yin Wenlong,
Lee Emma J.,
Bernard Guy M.,
Michaelis Vladimir K.,
Mar Arthur
Publication year - 2017
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201700200
Subject(s) - octahedron , crystallography , antibonding molecular orbital , valence (chemistry) , chemistry , tetrahedron , band gap , crystal structure , materials science , physics , condensed matter physics , atomic orbital , organic chemistry , quantum mechanics , electron
The quaternary chalcogenides La 3 Sn 0.5 InS 7 and La 3 Sn 0.5 InSe 7 were prepared by reactions of the elements at 1050 °C and 950 °C, respectively. They adopt noncentrosymmetric structures [hexagonal, space group P 6 3 , Z = 2; a = 10.2993(11) Å, c = 6.0921(6) Å for La 3 Sn 0.5 InS 7 ; a = 10.6533(7) Å, c = 6.4245(4) Å for La 3 Sn 0.5 InSe 7 ] in which the half‐occupancy of Sn atoms within octahedral sites classifies them as belonging to the La 3 Mn 0.5 SiS 7 ‐type branch of the large family of quaternary rare‐earth chalcogenides RE 3 M 1– x M ′ Ch 7 . The site distribution in La 3 Sn 0.5 In Ch 7 , with higher‐valent Sn atoms occupying octahedral instead of tetrahedral sites, is reversed from the typical situation observed in other RE 3 M 1– x M ′ Ch 7 compounds. The ordered distribution of Sn atoms in octahedral sites and In atoms in tetrahedral sites was evaluated by bond valence sum analyses. Moreover, 119 Sn solid‐state nuclear magnetic resonance (NMR) spectroscopy confirms the occupation of Sn 4+ species exclusively within octahedral sites. An optical bandgap of 1.45 eV was found for La 3 Sn 0.5 InS 7 . Band structure calculations on an ordered superstructure model of La 3 Sn 0.5 InS 7 reveal that avoidance of strongly Sn–S antibonding levels is an important driving force for the Sn deficiency.