The Thermal Conductivities of Mg[sub 2]Si and Mg[sub 2]Ge

The temperature dependence of the thermal conductivity j(T), electrical resistivity q(T), and Seebeck coefficient S(T) of Mg 2 Sn:Ag crystals with 0 at.% to 1 at.% Ag content were measured at T = 2 K to 400 K. The crystals were cut from ingots that were prepared by the vertical Bridgman method. Undoped samples show a dramatic j µ T 3 rise at low temperatures to a peak value j 15K = 477 W m À1 K À1 . This leads to exceptionally large phonon drag effects causing giant thermopower with S rising sharply to a peak value S 20K = 3000 lV K À1 . At higher temperatures S decreases and changes sign to intrinsic values S % À60 lV K À1 . The addition of Ag changes the transport properties as follows: (a) j decreases systematically, the peak shifts to 30 K and falls to 7 W m À1 K À1 ; (b) q changes from high to low values; (c) S(T) changes to a linear dependence with S 300K % 150 lV K À1 to 200 lV K À1 .

Section: Resultsmentioning

confidence: 70%

Thermal Conductivity and Other Transport Properties of Mg2Sn:Ag Crystals

Savvides

Chen

2009

“…Environmentally benign Mg 2 Si has been identified as a thermoelectric (TE) material with relevant performance in the temperature range from 500 K to 900 K, [1][2][3][4] and one that fits well with the operating temperatures of industrial furnaces, automobile exhausts, and incinerators. The important features of Mg 2 Si include the fact that it has been identified as an environmentally benign material, that its constituent elements are abundant in the Earth's crust, and that it is nontoxic.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric Behavior of Sb- and Al-Doped n-Type Mg2Si Device Under Large Temperature Differences

Sakamoto

Iida

Kurosaki

et al. 2011

The thermoelectric (TE) characteristics of Sb-and Al-doped n-type Mg 2 Si elemental devices fabricated using material produced from molten commercial doped polycrystalline Mg 2 Si were examined. The TE devices were prepared using a plasma-activated sintering (PAS) technique. To complete the devices, Ni electrodes were fabricated on each end of them during the sintering process. To realize durable devices for large temperature differences, thermodynamically stable Sb-doped Mg 2 Si (Sb-Mg 2 Si) was exposed to the higher temperature and Al-doped Mg 2 Si (Al-Mg 2 Si) was exposed to the cooler temperature. The devices consisted of segments of Sb-Mg 2 Si and Al-Mg 2 Si with sizes in the following ratios: Sb-Mg 2 Si:Al-Mg 2 Si = 4:1, 1:1, and 1:4. A device specimen composed solely of Sb-Mg 2 Si showed no notable deterioration even after aging for 1000 h, while some segmented specimens, such as those with Sb-Mg 2 Si:Al-Mg 2 Si = 1:1 and 1:4, suffered from a considerable drop in output current over the large DT range. The observed power generated by specimens with Sb-Mg 2 Si:Al-Mg 2 Si = 1:1 and 1:4 and sizes of 2 mm 9 2 mm 9 10 mm were 50.7 mW and 49.5 mW, respectively, with higher and lower temperatures of 873 K and 373 K, respectively. For the sample composed solely of Sb-Mg 2 Si, a power of 55 mW was demonstrated. An aging test for up to 1000 h for the same DT range indicated drops in output power of between $3% and 20%.

“…[1][2][3][4][5][6] Recent work 7 has shown that ZT % 1.1 can be achieved in Mg 2 Si 1Àx Sn x solid solutions prepared by direct co-melting. Other preparation methods such as mechanical alloying, 8 solid-state reaction, 9 spark plasma sintering, 10 and hot pressing 11,12 have also been used.…”

Section: Introductionmentioning

confidence: 99%

Eutectic Microstructure and Thermoelectric Properties of Mg2Sn

Chen

Savvides

2010

Ingots of undoped and Ag-doped Mg 2 Sn were prepared from the melt using a rocking Bridgman furnace at different cooling rates: slow cooling (0.1 K/min), moderate cooling (1 K/min), and rapid quenching. The ingots show very different microstructure and thermoelectric properties. Slow-cooled ingots consist of large Mg 2 Sn crystals with minor inclusions. Moderate-cooled ingots show significant variation in composition and microstructure, with Mg-rich material at the topmost section of the ingot and Sn-rich material at the bottom surface of the ingot. Rapid quenching results in ingots with finely dispersed Mg + Mg 2 Sn eutectic microstructure in the form of lamellae 200 nm to 500 nm in thickness. Measurements of the Seebeck coefficient and electrical conductivity in the temperature range of T = 80 K to 700 K were carried out to establish correlations between the microstructure and the thermoelectric properties.