Ab initio lattice thermal conductivity of bulk and thin-film $\alpha$-Al$\mathrm{_2}$O$\mathrm{_3}$

TL;DR

This study uses first-principles calculations to determine the thermal conductivity of bulk and thin-film alpha-Al2O3, comparing LDA and GGA methods, and finds significant reductions in thin films.

Contribution

It provides the first-principles calculation of thermal conductivity for both bulk and thin-film alpha-Al2O3, highlighting the effects of film thickness and exchange-correlation approximations.

Findings

LDA agrees well with experimental data at room temperature.

GGA significantly underestimates thermal conductivity.

Thin films show up to 79% reduction in thermal conductivity at 10 nm thickness.

Abstract

The thermal conductivities ($\kappa$) of bulk and thin-film $\alpha$-Al$_2$O$_3$ are calculated from first principles using both the local density approximation (LDA), and the generalized gradient approximation (GGA) to exchange and correlation. The room temperature single crystal LDA value $\sim39~$W/m$~$K agrees well with the experimental values $\sim35-39~$W/m$~$K, whereas the GGA values are much smaller $\sim$26$~$W/m$~$K. Throughout the temperature range, LDA is found to slightly overestimate $\kappa$ whereas GGA strongly underestimates it. We calculate the $\kappa$ of crystalline $\alpha$-Al$\mathrm{_2}$O$\mathrm{_3}$ thin films and observe a maximum of 79$\%$ reduction for $10~$nm thickness.