Tuning the transport and thermoelectric properties of In2O3 bulk ceramics through doping at In-site

Abstract

Bulk ceramics In2−xMxO3, with a metal-like behavior, have been synthesized in air for M=Ti4+, Zr4+, Sn4+, Ta5+, and Nb5+, with rather low solubility limits xℓ, ranging from 0.01 to 0.1. An abrupt increase in the electrical conductivity and of the carrier concentration with x is observed in the monophasic region (x<xℓ), whereas in the biphasic region (x>xℓ) these values do not vary significantly. These results show that the valence of the doping element plays a crucial role in such properties, similar to degenerated semiconductors. Similarly, the thermopower |S| value is correlated with this evolution decreasing as x increases for x<xℓ. For the Sn doped samples, the maximum carrier concentration n=10.8×1020 cm−3 and electrical conductivity σ=5×103 S cm−1 are both achieved at x=0.06–0.1 (∼3–5 at. %) for a thermopower S of −20 μV/K at room temperature. In comparison, the minimum |S| and maxima σ and n of In2O3 compounds doped with the other cations occur at lower doping levels, e.g., xℓ∼0.02 and xℓ∼0.015 for Ti and Zr/Nb/Ta doped In2O3, respectively. The relationship between the values of room temperature Hall mobility and carrier concentration shows that numbers and/or effects of multicharged scattering centers of electrons are different depending on the doping element. In2O3 doped with M(IV) elements shows maximum values of mobility close to x=0.006, whereas the doping with M(V) cations induces a decrease in the Hall mobility even for small doping levels. The thermoelectric performances are significantly improved at these low doping levels, with ZT values close to 0.3 at 1000 K in the doped materials against 0.1 mW/mK2 for the undoped phase.

In2O3-Based Thermoelectric Materials: The State of the Art and the Role of Surface State in the Improvement of the Efficiency of Thermoelectric Conversion

“…It can be seen that as a result of these studies, that it was possible to substantially increase the ZT of n-type oxides. However, devices based on n-type conductive metal oxides have until now had a low efficiency of thermoelectric conversion [28,31,[38][39][40]42,70,71], which made their utilization in thermoelectric generators economically unprofitable. The demand for a good n-type thermoelectric oxide proceeds from the fact that it usually is being utilized as a partner for a p-type material in thermoelectric modules.…”

“…The experiment showed that various doping additives such as Sn [143][144][145], Ti [71], Zr [146,147], Mo [148], W [149] and Ge [70] can be used for these purposes. It is important to note here that with such doping it is possible to reach an exceptionally high carrier mobility in In 2 O 3 -based oxides even with a carrier concentration higher than 10 20 cm −3 (see Table 1).…”

“…In the case of In 2 O 3 :Sn (ITO), the maximum conductivity is observed at the Sn/In composition ratio of 5-10% [144]. It should be noted that the most noticeable changes in the thermoelectric characteristics of doped In 2 O 3 are also observed near the dopant concentrations corresponding to the limiting solubility in In 2 O 3 [71,132,136,137]. Source: Data extracted from [150][151][152].…”

The thermoelectric properties of In2O3 thin films deposited by direct current magnetron sputtering

“…There is some theoretical [13] and experimental work about the thermoelectric properties of In 2 O 3 and its dopants [2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18] . There is work [5][6][7][8][9][10] about In 2 O 3 bulk and its dopant. For example, J. Lan et al studied the thermoelectric properties of In 2 O 3 codoped with Zn and Ge [5].…”

Phase segregation in Mn-doped In2O3: in situ high-pressure high-temperature synchrotron studies in multi-anvil assemblies

“…A typical approach to achieve certain functional properties is to stabilize a preferred polymorph and/or control its defect chemistry. [1][2][3] Research Centre were employed (Fig. 2).…”