θ-TaN: Redefining the Thermal Conductivity Limit of Metallic Materials

Abstract

Thermal management has become a critical bottleneck for the performance and reliability of modern electronics. For over a century, the thermal conductivity (κ) of metallic materials was believed to have an inherent upper limit of approximately 400 W·m⁻¹·K⁻¹, constrained by strong electron-phonon coupling and lattice anharmonicity. However, a groundbreaking study by Li et al. (Science, 2026) experimentally realized single-crystalline θ-phase tantalum nitride (θ-TaN), a metastable transition metal nitride with a room-temperature thermal conductivity of ~1100 W·m⁻¹·K⁻¹ along the a-axis and ~928 W·m⁻¹·K⁻¹ along the c-axis, nearly three times that of copper. This work shatters the long-standing thermal conductivity limit for metals and validates theoretical predictions. The exceptional performance of θ-TaN arises from its unique hexagonal crystal structure (space group P6m2), featuring a large acoustic-optical phonon gap (~8 THz) and acoustic phonon bunching, which suppress phonon-phonon scattering. Additionally, weak electron-phonon coupling and minimal isotope scattering contribute to phonon-dominated heat transport. The authors synthesized high-quality single crystals via a flux-assisted metathesis reaction, overcoming challenges of conventional high-pressure routes. Using time-domain thermoreflectance and inelastic X-ray scattering, they confirmed the intrinsic ultrahigh thermal conductivity and mapped the phonon band structure. This discovery introduces a new class of high-thermal-conductivity metals, opening transformative opportunities for thermal management in electronics, aerospace, and energy systems.

1. Introduction

The relentless drive towards smaller, faster, and more powerful electronics has made thermal management a critical bottleneck for performance and reliability. For over a century, the thermal conductivity (κ) of metallic materials has long been considered to have an inherent upper limit for thermal conductivity, plateauing ~400 W·m⁻¹·K⁻¹. This ceiling is rooted in fundamental physics: in typical metals, heat is primarily carried by electrons, and their transport is severely hampered by strong electron-phonon coupling and inherent lattice anharmonicity. These intrinsic scattering mechanisms have historically confined the thermal performance of metals. This limit has posed a critical bottleneck for advanced electronics, where escalating power densities (projected to reach 1 MW/cm² by 2030) demand more efficient heat dissipation.

However, a groundbreaking study published in Science (Science (2026), doi:10.1126/science.aeb1142) by Li et al. shatters this barrier through the experimental realization of single-crystalline θ-phase tantalum nitride (θ-TaN), a metastable transition metal nitride with a room-temperature thermal conductivity of ~1100 W·m⁻¹·K⁻¹, nearly three times that of copper. This work not only validates decades of theoretical predictions but also introduces a new class of high-thermal-conductivity metals, opening transformative opportunities for thermal management in electronics, aerospace, and energy systems.