Superhigh thermoelectric figure of merit in silver halides AgCl and AgBr from first principles
Searching for the high-performance thermoelectric (TE) materials has always been a long-held dream in the thermoelectricity field. Recently, it is found in experiments that the largest figure of merit ZT of $2.6$ can be reached in SnSe crystals at 923 K and Cu2Se sample at 850 K, which arouses the enormous interest of seeking high-ZT materials. Based on first-principle calculations and Boltzman transport equation (BTE), we report in this letter that silver halides (AgCl and AgBr) in rocksalt structure have excellent TE performances. A superhigh ZT of about 7.0 at mid-temperature (~600K) is obtained in the p-type doped AgCl and AgBr crystals, which far exceeds the ZT values of all current bulk TE materials. This record-breaking ZT value is attributed to the ultralow intrinsic lattice thermal conductivity \kappa_L (e.g. \kappa_L ~0.10 and 0.09 Wm^{-1}K^{-1} for AgCl and AgBr at 600 K, respectively). Our results may be a feat that could revolutionize the field of the heat energy conversion.