Optimizing Thermoelectric Efficiency of La 3-x Te 4 with Calcium Metal Substitution

La 3-x Te 4 is a state-of-the-art high temperature n-type thermoelectric material with a previously reported maximum zT~1.1 at 1273 K. Computational modeling suggests the La atoms play a crucial role in defining the density of states for La 3-x Te 4 in the conduction band. In addition to controlling charge carrier concentration, substitution with Ca 2+ atoms on the La 3+ site is explored as a potential means to tune the density of states and result in larger Seebeck coefficients. High purity, oxide-free samples are produced by ball milling of the elements and consolidated by spark plasma sintering. Powder XRD and electron microprobe analysis are used to characterize the material. High temperature thermoelectric properties are reported and compared with La 3-x Te 4 compositions. A maximum zT of 1.3 is reached at 1273 K for the composition La 2.22 Ca 0.775 Te 4 .