Influence of Thermal Aging Phenomena on Thermoelectric Properties of Al-Substituted ZnO

Abstract

The thermoelectric properties and stability of Al-substituted ZnO as a potential high-temperature n-type material were studied in heating-cooling cycles. Zn 1Àx Al x O(x = 0.02, 0.06) was prepared by soft chemistry and solidstate reaction synthesis methods. Cycling during the thermoelectric measurement leads to an increase of the electrical resistivity and Seebeck coefficient values. The reason for this aging phenomenon can be assigned to a change in composition due to oxygen uptake along with modification in the defect concentrations. The aging is enhanced if the cycling is performed in oxygen. ZT value of 0.21 is reached at 1275 K for samples with 2% Al substitution made by soft chemistry synthesis.

Thermal conductivity of thermoelectric Al‐substituted ZnO thin films

“…Above 1000 K, both the resistivity and the absolute value of the Seebeck coefficient for the films on sapphire decrease again to values of 0.09 Ω cm and –420 μV/K at 1260 K, respectively. This can be explained by the release of oxygen from ZnO at elevated temperatures which results in a higher carrier concentration as it was already observed for bulk ZnO:Al samples described by the authors elsewhere 21.…”

“…The main part of the thermal energy is conducted by the phonons. Figure 2a illustrates a comparison of the thin film to bulk values of samples synthesized by soft chemistry (synthesis described elsewhere 21). Bulk thermal conductivities at RT are almost one order of magnitude higher than for thin films.…”

Thermoelectric properties of pulsed current sintered nanocrystalline Al-doped ZnO by chemical vapour synthesis

“…Undoped ZnO sintered at 900°C exhibits a room temperature thermal conductivity of about 40 W/mK similar to the bulk value 3,27,28. This is expected as the specimen contains grains in the micrometer range (seeFig.…”

A High-Temperature Thermoelectric Generator Based on Oxides

“…If stability at high temperature comes into account, oxide ceramics are the materials of choice and quite some stoichiometries and crystal structures have been investigated so far; see Koumoto et al (2013), Ohtaki (2011), Wunderlich (2013. Among the oxides, n-type Zn 0:98 Al 0:02 O and p-type Ca 3 Co 4 O 9 constitute the most promising compositions, and they were used in our study to construct a thermoelectric harvester for the high-temperature range; see Vogel-Schäuble et al (2011).…”