Calculation: isotopically pure germanium carbide GeC reaches 1018 W m⁻¹ K⁻¹ at room temperature
Phonon calculations with three- and four-phonon scattering give cubic GeC a thermal conductivity above 1000 W m⁻¹ K⁻¹; molecular dynamics agrees. Theory only, no sample.
Authors of an arXiv · preprint, which has not yet been peer reviewed, report a calculated lattice thermal conductivity of 1018 W m⁻¹ K⁻¹ at room temperature for isotopically pure cubic germanium carbide (GeC). The value comes from solving the Boltzmann transport equation with both three- and four-phonon interactions included. The authors state that molecular dynamics simulations corroborate it arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
The result is theoretical: the work reports no measurement on a synthesized crystal.
Why high thermal conductivity matters
The authors note that heat fluxes in modern electronics are approaching 1000 W cm⁻², which calls for materials with thermal conductivity above 1000 W m⁻¹ K⁻¹. Only a few materials reach this range, among them diamond and isotopically enriched cubic boron nitride. Cubic boron arsenide (BAs) was predicted to be exceptional when only three-phonon scattering was considered. Four-phonon processes lowered that figure at room temperature, and measurements on BAs single crystals came out below the three-phonon prediction. An earlier study of GeC had also considered only three-phonon scattering.
Mechanisms and method
According to the authors, two effects produce the high value in GeC: a strong isotopic enhancement of 289% and a modest suppression of only 22% from four-phonon scattering. The latter holds even though GeC has a wide gap between acoustic and optical phonon branches, as BAs does. The authors attribute this to selection-rule-enhanced three-phonon scattering. The flat optical bands of GeC amplify acoustic-optical interactions, and the relatively weak bunching of acoustic branches sustains scattering among three acoustic phonons arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
Force constants at finite temperature were obtained with the sTDEP method on a 1024-atom supercell, using density functional theory forces from VASP with a 600 eV plane-wave cutoff. Scattering rates and conductivity were computed with the FourPhonon package. For independent verification the authors used molecular dynamics with the homogeneous non-equilibrium method.
The authors also examined hydrostatic pressure. At elevated temperatures, the thermal conductivity of isotopically enriched GeC varies non-monotonically with pressure, which does not follow the conventional Leibfried-Schlömann formula.
