Ba8Zr2Se11(Se2): The first polychalcogenide of the ternary Ba-Zr-Q (Q = S/ Se/Te) system

We report the synthesis of crystals of a new ternary polyselenide Ba8Zr2Se11(Se2). The title compound has a pseudo-zero-dimensional crystal structure (space group: C2/c) with a unique structure type as determined by a single-crystal X-ray diffraction study. Each Zr atom of the structure is connected to six Se atoms, forming a distorted octahedral coordination geometry. The ZrSe6 octahedron is fused with the one neighboring octahedral unit via the sharing of one corner to form isolated dimeric [Zr2Se11]14-units. Some of the Se atoms of the structure form Se22-dimers and are only coordinated to the Ba atoms. A polycrystalline Ba8Zr2Se11(Se2) sample is found to be a semiconductor (Eg = 1.9(2) eV). A small total thermal conductivity of 0.59 Wm- 1K-1 (at 773 K) was observed for the sample. The solar cell study on the Ba8Zr2Se11(Se2) powder showed an efficiency enhancement of 9.8% with its inclusion in the cell based on TiO2/CdS as the photoanode, due to a suppressed electron-hole recombination rate. DFT calculations are also carried out to study the electronic structure of the compound.