The synthesis and structure–property relation analysis of metal chalcohalide crystals Cs2InPS4X2 (X = Cl, Br) with mixed anions

Abstract

Inorganic metal chalcohalides are significant semiconductive materials for photovoltaics, photodetetion and infrared optics. Thus it is considerably rewarding to develop a new synthetic strategy to provide more degrees of freedom for atomic coordination to tune the optical and electronic properties of metal chalcohalides. In this work, the mixed-anion strategy is performed to synthesize two new metal chalcohalides Cs₂InPS₄X₂ (X = Cl, Br) with mixed-anion structure by the reaction of InPS₄ and CsX. Single-crystal X-ray diffraction analysis shows that they are isostructural and crystallize in the centrosymmetric space group P2₁/n, consisting of zero-dimensional structure [In₂P₂S₈X₄]⁴⁻ (X = Cl, Br) built from tetrahedral [PS₄]³⁻ and octahedral [InS₄X₂]⁷⁻ (X = Cl, Br) through edge-sharing, with Cs cations filling in intervening voids. The UV-vis-NIR diffuse reflectance spectroscopy measurement reveals that Cs₂InPS₄Cl₂ and Cs₂InPS₄Br₂ exhibit large optical bandgaps of 3.21 eV and 3.12 eV, respectively. The electronic structure calculations show that the bandgap mainly originates from the [InS₄X₂]⁷⁻ (X = Cl, Br) mixed-anion groups. First-principles calculations indicate that the birefringence of Cs₂InPS₄Cl₂ and Cs₂InPS₄Br₂ is ∼0.08 and ∼0.05 at 2090 nm, respectively. Furthermore, thermal analysis reveals that the Cs₂InPS₄X₂ (X = Cl, Br) are thermostable up to 400 °C. This discovery enriches the structural diversity of inorganic chalcohalides and provides an insight for the exploration of new semiconductive materials.