First-principles study on the lattice thermal conductivities of NbBO4 and TaBO4

Oxide materials, particularly ternary oxides, generally exhibit low lattice thermal conductivity due to their complex crystal structures. Here, using first-principles calculations, we demonstrate that the zircon-type borates NbBO4 and TaBO4 exhibit even higher lattice thermal conductivities, reaching κxx = κyy = 40.1 W m−1 K−1, κzz = 45.4 W m−1 K−1 for NbBO4 and κxx = κyy = 46.3 Wm−1K−1, κzz = 47.2 W m−1 K−1 for TaBO4 at room temperatures. Despite their structural complexity and high average atomic mass, the thermal conductivities of both materials surpass those of most binary and ternary oxides. We attribute their exceptionally high thermal conductivities primarily to the large bulk moduli of 273 GPa for NbBO4 and 293 GPa for TaBO4. These findings not only elucidate the thermal transport mechanism in zircon-type borates but also suggest a potential strategy for designing complex oxides with high thermal conductivity for thermal management applications.