Ultrahigh Thermal Conductivity in Boron Arsenide

The central scientific claim of the source archive boron arsenide dossier is that cubic boron arsenide (c-BAs) conducts heat at rates approaching or rivaling diamond, and that this behavior departs from the conventional theory of heat conduction in electrical insulators. The claim belongs to c-BAs specifically; the other forms of Boron Arsenide (BAs) treated in the dossier — B₁₂As₂ and hexagonal h-BAs — are not the subject of this thermal-conductivity record.

The mechanism

Unlike metals, where electrons carry heat, BAs is an electrical insulator. In such materials heat is carried by phonons — vibrational waves of the constituent atoms — and resistance to heat flow arises from phonon–phonon collisions.

Conventional criteria held that ultrahigh lattice thermal conductivity can occur only in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon processes. BAs combines a light element (boron) with a heavy one (arsenic), so it was expected to conduct heat poorly — estimated at about 10 times worse than diamond.

The 2013 first-principles prediction by Broido, Reinecke and Lindsay found instead a room-temperature thermal conductivity above 2000 W/(m·K), exceeding diamond at higher temperatures. The proposed explanation is phonon-band engineering: an unusual interplay of vibrational properties in which the expected phonon collisions are far less likely to occur in a certain frequency range, so large amounts of heat can be conducted there.

The measurement history

The dossier presents a progression of measured values, drawn from different samples, methods and groups. These are not a single reconciled figure:

The 2018 Science paper (Fei Tian et al.) reported a local room-temperature thermal conductivity exceeding 1000 W/(m·K) and an average bulk value reaching 900 W/(m·K). Its abstract states the result "departs from these long-held criteria" and "can only be explained by higher-order phonon processes." The accompanying summary notes that three research groups (Kang et al., Li et al. and Tian et al.) independently synthesized high-purity BAs with conductivities around 1000 W/(m·K) — roughly half that of diamond but more than double conventional metals.

The dossier's Wikipedia excerpt states that the 1300 W/(m·K) figure is "the highest among all metals and semiconductors."

A separate, secondary figure of >2100 W/(m·K) appears only in a ScienceHubNet video summary, attributed to Zhifeng Ren of the University of Houston and a collaboration between the Texas Center for Superconductivity, UC Santa Barbara and Boston College. It is not drawn from a primary paper in the retrieved passages and should be treated as a secondary claim.

Reconciling theory and measurement

Two corrections brought theory and measurement closer:

1. Four-phonon scattering reduces the predicted room-temperature conductivity from 2200 to 1400 W/(m·K). See Four-Phonon Scattering.
2. Antisite defects were identified as the primary suppressors of thermal conductivity in real crystals, explaining why early measurements fell far short of prediction. See Antisite Defects in Boron Arsenide.

Antisite defects

Antisite defects are extrinsic defect pairs in which boron and arsenic atoms occupy each other's lattice sites. In the dossier's narrative, they — rather than any intrinsic limit — account for the low early measurements (the 190 W/(m·K) figure) and for the gap between those measurements and the first-principles prediction. The ScienceHubNet summary attributes the same reasoning to Ren's team: "the key issue lay in the impurities within the material rather than its inherent ability," and refining the arsenide and improving manufacturing techniques produced crystals with significantly fewer defects. This is a claim about sample quality, and it is the dossier's explanation for the spread of measured values rather than a separately measured defect density.

Isotope enrichment

The 2025 Advanced Science paper on isotope-enriched c-BAs reports a room-temperature thermal conductivity of 1500 W/(m·K) for c-¹¹BAs — and notes that the measured values exceeded the ab initio calculations. The paper itself flags this discrepancy. The result is contested: prior isotope studies found "only minimal differences" between isotope-enriched and natural c-BAs, so the improvement attributed to isotope purity is not uniformly supported across the literature. See Isotope Enrichment and Thermal Conductivity.

Quantum phonon coherence

A 2026 Physical Review Letters paper (Tong Lin et al.) reports record-high, isotope-purity-limited phonon coherence in >98% enriched ¹¹BAs below 100 K, with a quality factor above 3.7×10³, attributed to near-elimination of three-phonon scattering for zone-center optical phonons over a wide temperature range. The Rice University summary describes optical phonons persisting nearly 10 times longer than in typical materials. This is a low-temperature coherence result and is distinct from the room-temperature thermal-conductivity measurements above.

Unresolved questions

• The measured values span 190 to ~1500 W/(m·K) across different samples and groups; they are not a single reconciled figure.
• The isotope-enriched result (1500 W/(m·K)) exceeds ab initio prediction, which the Advanced Science paper itself flags.
• Prior isotope studies found "only minimal differences" between isotope-enriched and natural c-BAs, so the isotope-enrichment improvement remains contested.
• A 2023 Nature study reported that under high pressure BAs decreases its thermal conductivity, contrary to the typical increase in most materials.
• The >2100 W/(m·K) figure rests on a secondary video summary rather than a primary paper in the retrieved passages.

Related pages

• Boron Arsenide (BAs)
• Four-Phonon Scattering
• Antisite Defects in Boron Arsenide
• Isotope Enrichment and Thermal Conductivity
• Boron Arsenide Claims vs. Evidence: Measured Values, Patent Claims and the Theory–Experiment Gap
• the source archive