Sin-Wook You

Solid-state synthesis and thermoelectric properties of Mg 2+x Si 0.7 Sn 0.3 Sb m

Mg2+xSi0.7Sn0.3Sbm (0 ≤ x ≤ 0.2, m = 0 or 0.01) solid solutions have been successfully prepared by mechanical alloying and hot pressing as a solid-state synthesis route. All specimens were identified as phases with antifluorite structure and showed ntype conduction. The electrical conductivity of Mg-excess solid solutions was enhanced due to increased electron concentrations. The absolute values of the Seebeck coefficient varied substantially with Sb doping and excess Mg, which was attributed to the change in carrier concentration. The onset temperature of bipolar conduction was shifted higher with Sb doping and excess Mg. The lowest thermal conductivity of 1.3W/mK was obtained for Mg2Si0.7Sn0.3Sb0.01. A maximum ZT of 0.64 was achieved at 723K for Mg2.2Si0.7Sn0.3Sb0.01.

Solid-State Synthesis and Thermoelectric Properties of Mg2+xSi0.7Sn0.3Sbm

Mg2+xSi0.7Sn0.3Sbm (0 ≤ x ≤ 0.2, m = 0 or 0.01) solid solutions have been successfully prepared by mechanical alloying and hot pressing as a solid-state synthesis route. All specimens were identified as phases with antifluorite structure and showed ntype conduction. The electrical conductivity of Mg-excess solid solutions was enhanced due to increased electron concentrations. The absolute values of the Seebeck coefficient varied substantially with Sb doping and excess Mg, which was attributed to the change in carrier concentration. The onset temperature of bipolar conduction was shifted higher with Sb doping and excess Mg. The lowest thermal conductivity of 1.3W/mK was obtained for Mg2Si0.7Sn0.3Sb0.01. A maximum ZT of 0.64 was achieved at 723K for Mg2.2Si0.7Sn0.3Sb0.01.

Solid-State Synthesis and Thermoelectric Properties of Mg2Si0.5Ge0.5Sbm

Mg2Si0.5Ge0.5Sbm (m = 0, 0.005, 0.01, 0.02, and 0.03) solid solutions were synthesized by a solid-state reaction and consolidated by hot pressing. All specimens showed n-type conduction, and carrier concentrations were increased from 4.0 × 1017 cm−3 to 3.2 × 1021 cm−3 by Sb doping. The electrical conductivity remarkably increased with increasing Sb doping content, but the absolute value of the Seebeck coefficient was reduced as the Sb doping content increased, which was attributed to the increased carrier concentration. The lowest thermal conductivity was 2.3 W/mK for Mg2Si0.5Ge0.5Sb0.02 at 723 K, and the maximum ZT value of 0.56 was obtained for Mg2Si0.5Ge0.5Sb0.02 at 823 K.

Solid-state synthesis and thermoelectric properties of N-type Mg2Si

Group BIII (Al, In)-, BV(Bi, Sb) and BVI(Te, Se)-doped Mg2Si compounds were synthesized by solid-state reaction and mechanical alloying. Electronic transport properties (Hall coefficient, carrier concentration and mobility) and thermoelectric properties (Seebeck coefficient, electrical conductivity, thermal conductivity and figure-of-merit) were examined. Mg2Si powder was synthesized successfully by solid-state reaction at 773 K for 6 h and doped by mechanical alloying for 24 h. It was fully consolidated by hot pressing at 1073 K for 1 h. All doped Mg2Si compounds showed n-type conduction, indicating that the electrical conduction is due mainly to electrons. The electrical conductivity increased greatly by doping due to an increase in the carrier concentration. However, the thermal conductivity did not changed significantly by doping, which was due to much larger contribution of the lattice thermal conductivity over the electronic thermal conductivity. Group BV(Bi, Sb) elements were much more effective to...

Solid-State Synthesis and Thermoelectric Properties of Al-Doped MnSi1.75-δ

Al-doped higher manganese silicides (HMS), MnSi1.75-δ:Alx were synthesized by solid state reaction and hot pressing. Through X-ray diffraction analysis of the synthesized HMS, the optimum conditions for solid state reaction were determined to be 1273 K for 6 h. Phase fractions of HMS with compositional variation (δ) had no significant difference, but the MnSi1.75:Al0.005 specimen had the highest fraction of HMS at approximately 98.36%. All specimens showed p-type conduction at all temperatures examined, and exhibited degenerate semiconductor characteristics, in that the electrical conductivity decreased and the Seebeck coefficient increased with increasing temperature. Al doping shifted the onset temperature of intrinsic conduction to higher temperature. Thermoelectric figure of merit (ZT) of HMS increased with increasing temperature, and further improvement was achieved by Al doping. The maximum ZT was obtained as 0.41 at 823 K for MnSi1.73:Al0.005.

Thermoelectric properties of In z Co 4 Sb 12-y Te y skutterudites

In-filled and Te-doped CoSb3 skutterudites were prepared by encapsulated induction melting, and their thermoelectric properties were investigated from 300 K to 700 K. Single delta-phase was successfully obtained by the subsequent heat treatment at 823 K for 5 days. In-filled and Te-doped InzCo4Sb12-yTey showed the n-type conduction at all temperatures examined, indicating that Te atoms successfully acted as electron donors by substituting Sb atoms. Electrical resistivity was reduced by In filling and Te doping, and the Te doping effect on the resistivity decrease was predominant. Thermal conductivity was considerably reduced by In filling as well as Te doping due to the increase in phonon scattering, which shows that the lattice thermal conductivity is much larger than the electronic thermal conductivity in the InzCo4Sb12-yTey systems.

Solid-State Synthesis and Thermoelectric Properties of Mg2

Mg2+xSi0.7Sn0.3Sbm (0 ≤ x ≤ 0.2, m = 0 or 0.01) solid solutions have been successfully prepared by mechanical alloying and hot pressing as a solid-state synthesis route. All specimens were identified as phases with antifluorite structure and showed ntype conduction. The electrical conductivity of Mg-excess solid solutions was enhanced due to increased electron concentrations. The absolute values of the Seebeck coefficient varied substantially with Sb doping and excess Mg, which was attributed to the change in carrier concentration. The onset temperature of bipolar conduction was shifted higher with Sb doping and excess Mg. The lowest thermal conductivity of 1.3W/mK was obtained for Mg2Si0.7Sn0.3Sb0.01. A maximum ZT of 0.64 was achieved at 723K for Mg2.2Si0.7Sn0.3Sb0.01.

Thermoelectric Properties of Co1-xNbxSb3 Prepared by Induction Melting

Induction melting was attempted to prepare the undoped and Nb-doped CoSb3 compounds, and their thermoelectric properties were investigated. Single phase d-CoSb3 was successfully obtained by induction melting and subsequent annealing at 400°C for 2 hours in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased with increasing temperature, indicating mixed behaviors of metallic and semiconducting conductions. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with the increasing amount of Nb doping, mainly originated from the Seebeck coefficient variation.