Jaiswal, A.; Sakharov, K.A.; Lekina, Y.; Kamonsuangkasem, K.; Tomm, Y.; Wei, F.; White, T.J.: High-Temperature Polymorphism and Band-Gap Evolution in BaZrS3. Inorganic Chemistry 63 (2024), p. 24157-24166
10.1021/acs.inorgchem.4c03895
Abstract:
Barium zirconium trisulfide (BZS) is a three-dimensional (3D) perovskite with optoelectronic properties suitable for photovoltaic (PV) and light-emitting diode (LED) applications that is conventionally reported in the orthorhombic Pnma (62) symmetry. Synchrotron X-ray diffraction, thermal analysis, and Raman and absorption spectroscopy revealed three high-temperature polymorphs that appear when BZS is heated in air prior to complete oxidation (BaZrS3 + 5O(2) -> BaSO4 + ZrO2 + 2SO(2)up arrow) at 700 degrees C with the approximate stability ranges: BaZrS3 IV Pnma (62) T < 400 degrees C BaZrS3 III Cmcm (63) 400 degrees C <= T <= 500 degrees C BaZrS3 II 14/mcm (140) 500 degrees C <= T <= 700 degrees C Differential scanning calorimetry (DSC) revealed exothermic features accompanying the IV -> III and III -> II phase changes. Furthermore, the direct band gap varied inversely with temperature with distinct energies for each polymorph (1.84 eV <= IV <= 1.65 eV; 1.65 eV <= III <= 1.54 eV; 1.54 eV <= II <= 1.52 eV). Raman spectroscopy found that polymorphic changes up to 600 degrees C were reversible with bands characteristic of BaZrS3 IV entirely restored upon cooling to room temperature (RT). This more complete understanding of BSZ polymorphism provides a basis for producing crystallochemical variants with enhanced optoelectronic properties under ambient conditions.