Flux-assisted polytypism in the [Na2Cl]GaQ2 heterolayered salt-inclusion chalcogenide family

Abstract

Two polytypic heterolayered salt-inclusion chalcogenides, o-[Na₂Cl]GaQ₂ and t-[Na₂Cl]GaQ₂, were obtained via a NaCl/NaI flux-assisted synthesis, as part of an investigation of the Na–Ga–Q (Q = S and Se) system. The use of a different flux, NaBr/NaI, in the Na–Ga–Se system did not lead to the formation of salt-inclusion phases, but instead the novel Na₂GaSe₃ and Na₄Ga₂Se₅ phases were obtained. Thermal and electronic properties of [Na₂Cl]GaS₂ materials were investigated with differential scanning calorimetry, post-quenching ex situ powder X-ray diffraction (PXRD), high-temperature PXRD, and enthalpy and electronic structure calculations via density functional theory. Those studies determined the absence of any temperature-induced phase transition between the o-[Na₂Cl]GaS₂ and t-[Na₂Cl]GaS₂ polytypic compounds. Moreover, we probed the suitability of the heterolayered [Na₂Cl]GaS₂ single crystals as a sorbent for UO₂²⁺ uptake and monitored this process by energy-dispersive and infrared spectroscopies and PXRD, which revealed that the [Na₂Cl]⁺ insert could be exchanged with UO₂²⁺ on the surface while the UO₂²⁺ intercalation decomposes the [Na₂Cl]GaS₂ structure.