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Ce-doped Pb 1Àx Ce x Te alloys with x = 0, 0.005, 0.01, 0.015, 0.03, and 0.05 were prepared by induction melting, ball milling, and spark plasma sintering techniques. The structure and thermoelectric properties of the samples were investigated. X-ray diffraction (XRD) analysis indicated that the samples were of single phase with NaCl-type structure for x less than 0.03. The lattice parameter a increases with increasing Ce content. The lower Ce-doped samples (x = 0.005 and 0.01) showed p-type conduction, whereas the pure PbTe and the higher doped samples (x = 0, 0.015, 0.03, and 0.05) showed n-type conduction. The lower Ce-doped samples exhibited a much higher absolute Seebeck coefficient, but the higher electrical resistivity and higher thermal conductivity compared with pure PbTe resulted in a lower figure of merit ZT. In contrast, the higher Ce-doped samples exhibited a lower electrical resistivity, together with a lower absolute Seebeck coefficient and comparable thermal conductivity, leading to ZT comparable to that of PbTe. The lowest thermal conductivity (range from 0.99 W m À1 K À1 at 300 K to 0.696 W m À1 K À1 at 473 K) was found in the alloy Pb 0.95 Ce 0.05 Te due to the presence of the secondary phases, leading to a ZT higher than that of pure PbTe above 500 K. The maximum figure of merit ZT, in the alloy Pb 0.95 Ce 0.05 Te, was 0.88 at 673 K.

The thermoelectric properties of Ag-doped and Ag/Sb codoped PbSe, prepared by furnace melting, quenching, ball milling and spark plasma sintering (SPS) techniques, were investigated. The X-ray diffraction (XRD) analysis indicated that all samples crystallize in the NaCl-type structure without noticeable secondary phase. The substitution of Ag1+ ion for Pb2+ ion in PbSe caused the compound changed from n-type semiconductor to p-type semiconductor. The lower Ag doped sample Pb1-xAgxSe with x = 0.002 remains n-type conduction of PbSe, shows high electrical resistivity and thus low figure of merit (ZT). However, the higher Ag doped samples Pb1-xAgxSe with x = 0.004, 0.006, 0.008 exhibit n-type conduction, low electrical resistivity and thus leads to the higher ZT. The maximum ZT of the alloy Pb0.996Ag0.004Se reaches 0.66 at 673K, much higher than 0.24 of PbSe at the same temperature. A proper Sb doping in the n-type semiconductor Pb0.998Ag0.002Se can remain its n-type semiconductor, modify the carrier concentration, decrease the electrical resistivity and thus enhance the thermoelectric property. The alloy Sb0.002Pb0.998Ag0.002Se shows a ZT value of 0.59 at 573K, much higher than 0.26 of the sample Pb0.998Ag0.002Se at the same temperature.

Martensitic transformation and magnetic entropy change in Co substituted Ni 50 Mn 35−x Co x Sn 15 (x = 0, 1.0, 1.5, 2.0, and 3.0) Heusler alloys have been investigated by X-ray powder diffraction analysis, differential scanning calorimetry, and magnetic measurements. X-ray diffraction analysis reveals that the Ni 50 Mn 35−x Co x Sn 15 alloys have L2 1 Heusler structure at room temperature. The phase decomposition of the sample with x = 3.0, after annealing 48 h at 1173 K, is confirmed by both Xray powder diffraction analysis and energy-dispersive x-ray spectroscopy in scanning electron microscopy. With the increase of the Co content from 0 to 2.0, the martensitic transformation temperature T M increases from 185 to 245 K, which is in good agreement with the rule of valence electron concentration e/a-dependence of T M . The magnetic entropy change ΔS M is investigated in the vicinity of the martensitic transformation.