High-temperature thermoelectric performance of spinel MgGa2O4 through a first-principles and Boltzmann transport study

The structural, electronic, and thermoelectric properties of spinel MgGa₂O₄, a wide-bandgap material crystallizing in the Fd-3 m (No.227) cubic structure, are investigated in this work. In the WIEN2k framework with the GGA + mBJ potential, first-principles calculations employing the FP-LAPW approach show a direct band gap of 4.9 eV at the Γ-point. Significant impacts of temperature and chemical potential (μ) on the Seebeck coefficient (S) result in a thorough analysis of the transport properties using BoltzTraP. Near μ = ±0.05 eV, S had exceptional thermoelectric activity at 600 K, surpassing ± 20,000 μV/K. However, bipolar conduction forms as the temperature rises, which drastically lowers the Seebeck coefficient. A consistent asymmetry in the doping response remains throughout the temperature range, and trends in thermal conductivity (κ/τ) and electrical conductivity (σ/τ) favor S. P-type transport. Through enhanced carrier excitation, decreased lattice thermal conductivity, and optimal entropy filtering, the calculated ZT values surpass 1.2 at 1200 K. The balanced n-type and p-type performance of the material is highlighted by broad, symmetric ZT peaks around μ = 0. These results highlight the potential of MgGa₂O₄ as a high-temperature thermoelectric material that can be utilized for energy conversion and waste heat recovery in extreme environments. It further demonstrates the importance of doping and temperature optimization in maximizing thermoelectric efficiency in wide-bandgap oxides. The material is suitable for energy storage at temperatures below 600 K.