Pressure-induced bandgap engineering of lead-free halide double perovskite (NH4)2SnBr6

Structural, electronic, optical, elastic, thermodynamic and thermal transport properties of Cs2AgInCl6 and Cs2AgSbCl6 double perovskite semiconductors using a first-principles study

In this study, we employ the framework of first-principles density functional theory (DFT) computations to investigate the physical, electrical, bandgap and thermal conductivity of Cs2AgInCl6-CAIC (type I) and Cs2AgSbCl6-CASC (type II) using the GGA-PBE method. CAIC possesses a direct band gap energy of 1.812 eV, while CASC demonstrates an indirect band gap energy of 0.926 eV. The CAIC and CASC exhibit intriguingly reduced thermal conductivity, which can be attributed to the notable reduction in their respective Debye temperatures, measuring 182 K and 135 K, respectively. The Raman active modes computed under ambient conditions have been compared with real-world data, showing excellent agreement. The thermal conductivity values of CAIC and CASC compounds exhibit quantum mechanical characteristics, with values of 0.075 and 0.25 W m-1 K-1, respectively, at 300 K. It is foreseen that these outcomes will generate investigations concerning phosphors and diodes that rely on single emitters, with the aim of advancing lighting and display technologies in the forthcoming generations.

Pressure-Induced Metallization of Lead-Free Halide Double Perovskite (NH4 )2 PtI6

Metallization has recently garnered significant interest due to its ability to greatly facilitate chemical reactions and dramatically change the properties of materials. Materials displaying metallization under low pressure are highly desired for understanding their potential properties. In this work, the effects of the pressure on the structural and electronic properties of lead-free halide double perovskite (NH₄ )₂ PtI₆ are investigated systematically. Remarkably, an unprecedented bandgap narrowing down to the Shockley-Queisser limit is observed at a very low pressure of 0.12 GPa, showing great promise in optoelectronic applications. More interestingly, the metallization of (NH₄ )₂ PtI₆ is initiated at 14.2 GPa, the lowest metallization pressure ever reported in halide perovskites, which is related to the continuous increase in the overlap between the valence and conduction band of I 5p orbital. Its structural evolution upon compression before the metallic transition is also tracked, from cubic Fm-3m to tetragonal P4/mnc and then to monoclinic C2/c phase, which is mainly associated with the rotation and distortions within the [PtI₆ ]^2- octahedra. These findings represent a significant step toward revealing the structure-property relationships of (NH₄ )₂ PtI₆ , and also prove that high-pressure technique is an efficient tool to design and realize superior optoelectronic materials.