Thermoelectric properties and stability of Ba3Cu16-xSe11-yTey

Ba3Cu16-xSe11-yTey materials were synthesized with different compositions by a melting and slow cooling process. Measurement of the thermoelectric properties revealed changes during repeated measurements of the same samples. This scenario is different from the case of the isostructural sulfide variants, where the physical properties were consistently reproducible under the measurement conditions applied. Further investigations including single crystal studies after the measurements proved that this is a consequence of different Cu ion conductivity in selenides and sulfides. The reproducibility of the data was investigated by varying the maximum temperature as well as the current density. The stability of these selenides was highly dependent on the temperature; decreasing the highest measurement temperature led to full reproducibility. Finally, while the selenides exhibited larger electrical conductivity than the sulfides, their figure-of-merit zT only reached a maximum value of 0.49, compared to 0.88 of the sulfides, mostly caused by the smaller Seebeck values of the selenides.