Structural modulation induced by MIIIA metals in Ba3MQ4X (M = Al, Ga, In; Q = S, Se; X = Cl, Br): an experimental and computational analysis

Abstract

Four new chalcohalides Ba₃AlQ₄X (Q = S, Se; X = Cl, Br) have been discovered by a conventional high-temperature method. All of them crystallize in the Pnma space group. The structure is composed of zigzag XBa layers and isolated AlQ₄ tetrahedra. Detailed structural comparisons show that the cation size of the M^IIIA metals and variable coordination modes of the Ba²⁺ cations cooperatively influence the framework geometries of the title compounds. The first principles method was also used to investigate the electronic structures and optical properties. Their calculated birefringences range from 0.044 to 0.050 @1064 nm. Real space atom cutting analysis shows that the AlS₄, GaS₄, and InS₄ tetrahedra make the main contribution to the birefringence.