Phase stability, mechanical and electronic properties of Hf-Te alloys from first-principles calculations

Because of their wide applications, Hf-Te compounds have been attracting more attention. Although they have been investigated, the unsystematic and uncomparable nature of the investigations have limited our understanding. Hence, first-principles calculations based on density functional theory are used here to obtain the phase stability, mechanical and electronic properties of Hf-Te alloys. The calculated formation enthalpies indicate that all the Hf-Te alloys are thermodynamically stable. The calculated elastic constants with the mechanical stability criteria reveal that all the Hf-Te alloys are mechanical stable. The bulk modulus B, shear modulus G, Young's modulus E, Debye temperature Θ_D and sound velocity v_m have positive correlations with an increasing atomic fraction Hf. The non-zero electronic bandgaps show that all the alloys are conductors. Furthermore, the electronic properties are also described by analyzing the bond population and charge distribution, which are needed to successfully estimate the phase stability. The bond and charge characteristics demonstrate that the stable phases for HfTe₂ and HfTe₅ have a more covalent character, in contast, Hf₃Te₂, Hf₂Te and Hf₅Te₄ are more metallic. The moduli and populations show that the Hf₃Te₂, Hf₂Te and Hf₅Te₄ alloys have higher moduli due to their metallic bonds. In addition, Hf-Te alloys have a low thermal conductance with a high electronic conductivity, from this one can predict them to be widely used as thermoelectric material.