Thermal Conductivity of Isotopically Enriched 28Si Revisited

TL;DR

This study precisely measured the thermal conductivity of highly enriched 28Si across various temperatures, revealing it exceeds natural silicon's conductivity by about 10% at room temperature and up to 8 times at low temperatures, challenging previous reports.

Contribution

It provides new high-precision measurements of 28Si thermal conductivity, clarifying discrepancies with earlier studies and emphasizing the effects of isotope enrichment and sample shape.

Findings

28Si's thermal conductivity exceeds natural Si by 10% at room temperature.

Maximum thermal conductivity occurs near 26 K, exceeding natural Si by a factor of 8.

Natural Si's thermal conductivity is about 3% lower than literature values.

Abstract

The thermal conductivity of isotopically enriched 28Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of 4 samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched 28Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 102 %. This finding is in disagreement with an earlier report by Ruf et al. At 26 K the thermal conductivity of 28Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of 8 for a 99.982% 28Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be 3% lower than the values recommended in the literature.