Abstract: Thermal transport properties of two antiperovskite compounds Sr₃XO （X=Sb， Bi） were systematically investigated using semiclassical Boltzmann transport theory combined with first-principles calculations. The elastic constants and phonon spectra indicate that both Sr₃XO （X=Sb， Bi） compounds exhibit mechanical and dynamical stability， with melting temperatures of 1 062.4 K and 1 030.5 K， respectively， broadening their potential applications under extreme conditions. Sr₃SbO and Sr₃BiO maintain low lattice thermal conductivity （κ_L） at both room and elevated temperatures. At 300 K， the κ_L values of Sr₃SbO and Sr₃BiO are 1.472 and 3.122 W·m^-1·K^-1， respectively， with Sr₃SbO exhibiting a lower κ_L than the classic thermoelectric material PbTe （2.3 W·m^-1·K^-1）. At 700 K， the κ_L values decrease to 0.671 and 1.343 W·m^-1·K^-1 for Sr₃SbO and Sr₃BiO， respectively. Compared with Sr₃BiO， Sr₃SbO exhibits stronger anharmonicity. Additionally， a comparative analysis of heat capacity， phonon group velocity， and phonon lifetime was conducted for both compounds. This study elucidates the microscopic mechanisms underlying the low lattice thermal conductivity in these compounds and provides theoretical insights for the future design of novel functional materials with low thermal conductivity.

Key words: anti-perovskite compound; Sr₃XO（X=Sb， Bi）; mechanical property; lattice thermal conductivity; phonon thermal transport; first-principle