Synthesis, characterization, and phase stability of high temperature thermoelectric metal borides and silicides

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Thermoelectric (TE) materials are used for converting waste heat into electricity. The TE technology is attractive because it uses solid-state devices that are immovable, highly reliable, and eco-friendly. Currently, the TE materials have low conversion efficiencies at higher temperatures and uses expensive elements (Te, Ge, etc.) for TE power generation. Investigation was made on selected alkaline earth metal borides (CaB6, and SrB6,) and silicides (Mg2Si and CaSi) and transition metal borides and silicides of ABX-type (A = Ti/ Nb/ Mn; B = Co; X = B/Si). Screening of the alloys were done based on the available literature/calculations of energy band gaps, crystal structure, transport, and thermodynamic properties. Experiments were conducted on alkaline earth metal silicides (Mg2Si and metal-doped Mg2Si), transition metal boride (TiB2), and transition metal silicide (Mn4Si7). The selected alloys were synthesized and analyzed. Thermodynamic properties (specific heat, change in enthalpy, entropy, Gibbs energy, and activities) of the alloys were determined at higher temperatures using differential scanning calorimetry (DSC), differential thermal analyzer (DTA), and solid-state galvanic or EMF cell methods. Reaction kinetic studies on Mg2Si and metal-doped Mg2Si (Mg2Si: mX; X = Ti, Nb, Mn, Co; m = 0 - 0.08 mol) were conducted. Thermodynamic modelling tools were used to calculate the thermodynamic properties and phase equilibria of alloys. This research work provide the fundamental knowledge on thermodynamic and thermoelectric properties of metal borides and silicides.

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Materials science, Engineering, Energy