Pressure-Dependent Mechanical and Thermal Properties of Lead-Free Halide Double Perovskite Cs2AgBX6 (BIn, Bi; XCl, Br, I)

Lead-free halide double perovskites Cs2AgB '' X-6 (B '' In, Bi; XCl, Br, I) are emerging as excellent photoelectric materials. Investigating their mechanical and thermodynamic properties under hydrostatic pressure is vital for designing high-performance photoelectric devices. Although Cs2AgB '' X-6 exhibits similar cubic structures, the bond length and strength characteristics of Cs2AgInX6 are different to those of Cs2AgBiX6, and Cs2AgB '' X-6 exhibits obvious mechanical anisotropic. Upon experiencing pressure, the stablility of Cs2AgB '' X-6 is improved and without phase transition, and its bond characteristics are unified, which is different to lead halide perovskites. Compared to Cs2AgBiX6, Cs2AgInX6 may be more suitable to flexible devices due to its higher shear and bulk modulus. In addition, the thermal conductivities of Cs2AgBiX6 (XCl, Br) and Cs2AgBiX6 (XCl, Br, I) are 0.41, 0.32, 0.37, 0.29, 0.23 W m(-1) K-1, and can be enlarged by pressure and surpass that of lead halide perovskite. Moreover, all the Cs2AgB '' X-6 (B '' In, Bi; XCl, Br, I) possess the same saturated heat capacity of about 249.3 J mol(-1) K-1. These variations of mechanical and thermal properties are elucidated by the bonds. These results maybe also applicable to other double perovskites, and beneficial for designing devices with better optoelectronic performance.