First-Principles Study of Cr-Doped Diamond: Thermal Conductivity, Electronic Transport and Magnetism

Diamond has the highest thermal conductivity and an ultra-wide band gap, and Cr doping can introduce magnetism. However, the effect of Cr doping on the physical properties of diamond lacks systematic research. For the first time, we combine density functional theory (DFT) with the phonon Boltzmann transport equation to systematically investigate the structure, electronic and magnetic properties, phonon spectrum, lattice thermal conductivity, electronic transport, and thermodynamics of Cr-doped diamond (12.5 at%). The mode-resolved Klemens model is used to extrapolate lattice thermal conductivity to low-doping regions. Results show that Cr doping expands the lattice constant by 7.7% and induces a magnetic moment of 2.00 μB. At 300 K, the lattice thermal conductivity drops sharply from 2085 to 49.4 W·m−1·K−1, mainly due to lattice softening, impurity modes, and enhanced anharmonicity. Electronic transport calculations reveal that Cr-doped diamond is a magnetic semiconductor with thermally activated doping-tunable conductivity. At 300 K, conductivity rises from 4.10 × 10−2 to 646 S·m−1 (n-type) and from 0.367 to 3.87 × 103 S·m−1 (p-type) between 1.99 × 1014 and 4.39 × 1018 cm−3. Concentration extrapolation indicates that merely 1 at% Cr reduces thermal conductivity to 100–250 W·m−1·K−1. This work provides a theoretical basis for synergistically tuning the thermal conductivity and magnetism of Cr doped diamond.