Thermoelectric properties of pseudobrookite-based ceramics prepared from natural Fe-Ti-rich heavy mineral sand concentrate

Pseudobrookites (Fe2TiO5-FeTi2O5) are promising candidates for high-temperature oxide thermoelectrics. In this work, we used natural Fe-Ti-rich heavy mineral sand (HMS) as an abundant and environmentally friendly raw material for the preparation of pseudobrookite-based ceramics. The main components of the initial powder were ilmenite (FeTiO3) and pseudorutile (Fe2Ti3O9) with various degrees of alteration. Pre-oxidation of the as-received powder was used for modification of the Fe2+:Fe3+ ratio and exsolution of rutile. The starting powders were densified by conventional sintering (CS; 1200 C, 5 h, pressureless) and spark plasma sintering (SPS; 1100 C, 5 min, 150 MPs) in argon. The thermoelectric properties of the sintered compacts depend mainly on the Fe:Ti ratio, the Fe2+:Fe3+ ratio, and the fraction and distribution of rutile in the microstructures. The samples exhibit comparable properties as the pseudobrookite-based ceramics prepared from high-purity chemicals indicating that, with some further optimization, natural Fe-Ti-rich HMS are an interesting alternative for the preparation of pseudobrookite-based ceramics for thermoelectric applications.