Metal-chalcogenide compounds with perovskite-type compositions have drawn increasing attention for their optical properties for solar energy conversion. Herein, a new α-type polymorph of the ternary sulfide SrHfS3 is described, crystallizing in the NH4CdCl3 structure type. The yellow-colored plate-shaped crystals were synthesized at 1173 K using an elemental tin flux in an evacuated sealed tube. Its crystal structure was characterized at room temperature using single crystal X-ray diffraction to form in the orthorhombic Pnma space group, with the refined cell parameters of a = 8.5041(4) Å, b = 3.8004(2) Å, c = 13.8935(6) Å, and V = 449.02(4) Å3. The structure comprises five independent crystallographic sites, having one Sr, one Hf, and three S sites. The structure can be described as containing one-dimensional chains of distorted HfS6 octahedra extending down the b-axis to form 1∞HfS32− strips of edge-sharing octahedra. The Sr atoms act as charge-balancing space fillers in the structure. High-purity bulk samples of α-SrHfS3 could be prepared for measurement of its bandgap by optical diffuse-reflectance spectroscopy, showing a direct bandgap of 2.1(1) eV. Results of electronic structure calculations are consistent with this bandgap and type. The conduction and valence band edges stem from the respective empty Hf d-orbitals and the filled S p-orbital states. In summary, crystal growth of the α-type polymorph of SrHfS3 has been demonstrated using a Sn flux approach, which can facilitate future broader synthetic explorations at lower temperatures.
Reddy et al. (Thu,) studied this question.