Anisotropic Thermal Conductivity in Single Crystal beta-Gallium Oxide
  The thermal conductivities of beta-Ga2O3 single crystals along four different crystal directions were measured in the temperature range of 80-495K using the time domain thermoreflectance (TDTR) method. A large anisotropy was found. At room temperature, the [010] direction has the highest thermal conductivity of 27.0+/-2.0 W/mK, while that along the [100] direction has the lowest value of 10.9+/-1.0 W/mK. At high temperatures, the thermal conductivity follows a ~1/T relationship characteristic of Umklapp phonon scattering, indicating phonon-dominated heat transport in the \b{eta}-Ga2O3 crystal. The measured experimental thermal conductivity is supported by first-principles calculations which suggest that the anisotropy in thermal conductivity is due to the differences of the speed of sound along different crystal directions. 
Zhi Guo, Amit Verma, Fangyuan Sun, Austin Hickman, Takekazu Masui,   Akito Kuramata, Masataka Higashiwaki, Debdeep Jena and ...
cond-mat.mtrl-sci