Thermal conductivity measurements of a monocrystalline nonhomogeneous GaAs sample exhibit different conductivities with respect to the direction of heat flow across the sample. It is found that the same applied external temperature gradient causes two different distributions of the effective thermal conductivity coefficient, depending on the two opposite directions of heat flow.

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Investigations of the thermal conductivity of a non-homogeneous monocrystallineGaAs sample (1) revealed the presence of heat flux flow asymmetry with regard to the change of direction of the externally applied temperature difference. Experiments on four individual parts of the sample enabled to confirm that it wa8 really nonhomogeneous in the sense of thermal conductivity and manifested a dependence of the thermal conductivity coefficient (TCC) on temperature.Considering the above experimental facts, we write down the one-dimensional Fourier equation in the form dT q = -k(T, X)d x ' W e assume, in regard of the simplicity of the physical model, that the TCC, treated as a function of two variables, can be approximately presented in the form of two components: k f l , x) = klCT) + k2(X) .(2)The component k tivity on temperature. (In homogeneous samples the direction reversal of the externally applied temperature difference causes symmetry of the temperature distributions with regard to the geometrical midpoint. We call these distributions "conditionedtf by the pure relation of TCC to temperature. We a8sume that in our GaAs sample the experimentally obtained temperature distributions can be separated into those conditioned by material inhomogeneities and those conditioned by the temperature dependence of TCC only.) The component k preeents that part of material non-homogeneity which is not dependent on the direction of the externally applied temperature difference.presents the "pure" dependence of the sample thermal conduc-1 2 1) 95

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