Antisite defects are point defects in which an atom occupies the "wrong" lattice site in a compound crystal. In boron arsenide, the source dossier reports that As_B–B_As antisite pairs — an arsenic atom on a boron site next to a boron atom on an arsenic site — are the primary lattice defects suppressing thermal conductivity.
The finding
The Physical Review Letters paper "Antisite Pairs Suppress the Thermal Conductivity of BAs" (Qiang Zheng et al.) investigated why measured BAs thermal conductivity fell short of the ~2000 W/(m·K) prediction. Using aberration-corrected scanning transmission electron microscopy (STEM), the authors looked for the As vacancies widely thought to dominate thermal resistance — and did not find a large concentration of them.
Instead, the STEM results showed an enhanced intensity of some B columns and a reduced intensity of some As columns, indicating antisite defects with As_B and B_As. Additional calculations showed that the antisite pair with As_B next to B_As is energetically preferred among the point defects investigated, and confirmed that such defects lower the thermal conductivity.
Quantitative estimate
From a concentration of 1.8(8)% (6.6±3.0×10²⁰ cm⁻³ in density) for the antisite pairs estimated from STEM images, the thermal conductivity was estimated at 65–100 W/(m·K) — in reasonable agreement with the measured value. The paper concludes that As_B–B_As antisite pairs are the primary lattice defects suppressing thermal conductivity of BAs, and proposes approaches for growing high-quality crystals or films with high thermal conductivity.
Significance
This finding is one of the two corrections (alongside four-phonon scattering) that reconciled BAs theory with measurement, and it reframed the problem as defect-limited rather than intrinsic. It supports the broader narrative in the dossier that material purity, not inherent ability, was the limiting factor in early BAs samples. See Ultrahigh Thermal Conductivity in Boron Arsenide and Four-Phonon Scattering.
Related pages
Source notes & attribution
- https://rexresearch.com/BoronArsenide/BoronArsenide.html