Giant Reduction in the Thermal Conductivity of Porous β-Ga2O3 with Multiple Heat-Blocking Mechanisms

In this work, multiple strategies have been adopted to suppress the lattice thermal conductivity in β-Ga2O3 by point defects, grain boundaries, secondary phases, and pores. Porous β-Ga2O3 was prepared by a convenient calcination method together with spark plasma sintering technology. Positron annihilation lifetime and cathodoluminescence measurements reveal the existence of small micropores and various vacancies in the as-sintered β-Ga2O3. Macropores with sizes on the order of hundreds of nanometers are also observed by scanning electron microscopy. Due to these pores, the as-sintered β-Ga2O3 shows a high porosity of 63.4% and possesses abundant boundaries between the solid matrix and the air. In addition, the secondary phase of ε-Ga2O3 is also revealed by X-ray diffraction. The above microstructures cause strong enhancement in phonon scattering. As a result, an extremely low thermal conductivity of 0.30 W m–1 K–1 is obtained at room temperature in the as-sintered β-Ga2O3, which is far below the amorphous limit (1.15 W m–1 K–1) and is the lowest value reported so far for β-Ga2O3. Our work provides an avenue to reduce the thermal conductivity for the β-Ga2O3 materials and is believed to be more widely applicable for many other materials.