R&D: Thermal Transport of Amorphous PCM Materials Using Population-Coherence Theory, First-Principles Study

Journal of Physics D: Applied Physics has published an article written by Lei Yang^, and Bing-Yang Cao,Key Laboratory of Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, People’s Republic of China.

Abstract: “Thermal conduction plays a vital role in applications of phase change memory (PCM) materials. Phonon-based theory and Wiedemann-Franz-Lorenz rule have been widely utilized to describe the thermal transport in crystalline PCM materials, while the understanding of heat conduction in the amorphous phase remains insufficient. Here, we quantify the coherences’ (coupling of vibrational modes) and populations’ (phonon-like) contribution to the thermal conduction of amorphous Ge2Sb2Te5 (GST) and GeTe4, two kinds of typical PCM materials. The coherences’ and populations’ contributions are calculated by using the theory proposed by Allen and Feldman (AF theory) and single-mode relaxation time approximation of Boltzmann transport equation based on first-principles calculation. Our results demonstrate that coherences contribute more than 97% of the total thermal conductivities for both amorphous GST and GeTe4 above Debye temperature, while populations’ contribution is negligible. Besides, the temperature dependence of the thermal conductivities is predicted and analyzed, allowed by the AF theory with the mode linewidths dependent broadening method introduced in this paper. The predicted positive temperature dependence of amorphous GeTe4 above Debye temperature, in good agreement with the experimental results, is due to the unique nature of coherences, i.e., larger contribution to heat conduction from stronger couplings between different normal modes at a higher temperature. Our calculation provides new insight into thermal transport in amorphous PCM materials and reveals the physical mechanisms of temperature-dependent thermal conductivities above Debye temperature, and the calculation framework can also be extended to other disordered systems.“