Thermoelectric properties of Al–Pd–Re quasicrystal sintered by Spark Plasma Sintering (SPS): effect of improvement of microstructure

Abstract

Quasicrystals / Thermoelectric properties / Microstructure / Spark Plasma Sintering (SPS) / Al--Pd--Re Abstract. We report the thermoelectric properties of poly-grain Al--Pd--Re icosahedral quasicrystals and discuss an effect of improvement of their microstructure. The improvement of microstructure by using Spark Plasma Sintering (SPS) method resulted into a large increase of the electrical conductivity but less increase of the thermal conductivity. The relative density dramatically increased up to more than 90% by SPS. On the other hand, the microstructure itself does not have critical influence on the Seebeck coefficient, which is found to be strongly correlated with e=a (sample's compositions). Consequently, the dimensionless figure of merit (ZT) increased three times from 0.05 to 0.15.

Thermoelectric Properties of Al–Ga–Pd–Re Icosahedral Quasicrystals

“…7), there was no significant difference in S for Al 66 Ga 4 Pd 21 Re 9 QCs before and after SPS, confirming that the sample's microstructure has no influence on S. 20) the power factor, S 2 ·, was dramatically enhanced by Ga substitution owing to the increase in · and S, as seen in Fig. 8.…”

“…After SPS, · improved by about six fold without changing the temperature dependence. Compared with Al 71 Pd 20 Re 9 QC, 20) · increased about 1.4 times in the measured temperature range. This increase can again be attributed to the precipitation of metallic secondary phases.…”

“…Although the local compositions were examined by SEM-EDX, the observed sample compositions deviated from nominal ones due to the weight loss during arc-melting and widely scattered depending on the probe position. When discussing the composition dependence of Seebeck coefficient, we adopted the nominal composition instead of the SEM-EDX analyzed one to compare with other quasicrystals, 20) because there were no systematic composition dependence in the latter case.…”

“…The negative e/a values of transition metals reflect these mentioned effects, though the reason for the absolute value is not clear. Figure 4 shows the e/a dependence of S at 523 K for various compositions of the AlGaPdRe QCs, together with those for AlPdRe 12,20) and AlPdMn 20) QCs. Both AlPdRe and AlPdMn QCs give a similar trend with the maximum S 523K near e/a = 1.80 and minimum S 523K above e/a = 1.86.…”

“…Peak broadening after SPS was also observed in Al 71 Pd 20 Re 9 QC. 20) The electrical conductivities, ·, of (a) the arc-melted and annealed, and (b) the sintered Al 66 Ga 4 Pd 21 Re 9 QCs, together with the sintered Al 71 Pd 20 Re 9 QC, 20) are plotted in Fig. 6.…”