Thermal Conductivity and Other Transport Properties of Mg2Sn:Ag Crystals

Abstract

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 .

High quality Mg2Sn crystals prepared by RF induction melting

“…It should be noted, however, that the PPMS apparatus tends to overestimate the thermal conductivity at temperatures above about 250 K [21]. As discussed previously [17,18] and observed here, the decrease in thermal conductivity with increasing addition of silver results from phonon scattering at point defects due to the substitutional silver atoms (i.e., at dopant sites) and by boundary scattering of phonons at the finely dispersed eutectic clusters and submicronsize Sn precipitates. It is noticeable, however, that the overlap of k data are very poor at higher silver contents ( Z0.3 at%).…”

“…The carrier concentration was determined from Hall resistivity measurements using a PPMS apparatus (Physical Properties Measurement System, Quantum Design Inc.) on samples 1 Â 3 Â (8À 10) mm 3 cut adjacent to the samples used for the transport measurements. The thermal conductivity of RF samples was measured in the range 300-700 K using a laser flash apparatus (Netzsch LFA-427) [18], and is compared to that of the Bridgman samples using previously published data [17] in the range 2-400 K obtained using the PPMS.…”

“…Fig. 9 presents thermal conductivity k data of selected samples, albeit of different temperature regimes, to allow comparison of the RF samples to the corresponding BR samples whose k data were reported in our earlier papers [17,18]. Also included are data for an undoped sample from Zaitsev et al [20].…”

“…Recently we reported on the preparation and properties of single and large-grain polycrystalline Mg 2 Sn thermoelectric materials prepared by the Bridgman method [8,9,16,17]. Here, we report on the preparation of Mg 2 Sn ingots doped with Ag (0-1 at%) prepared by the RF induction melting.…”

Eutectic Microstructure and Thermoelectric Properties of Mg2Sn

“…3b) and thus causes the observed enhancement of the power factor. Based on the thermal conductivity values presented in our companion paper 22 and the values measured above 300 K, 23 j = 4.5 W/m/K to 5 W/m/K at 400 K to 600 K for Mg 2 Sn samples doped with 1 at.% Ag, we estimate ZT max = 0.45 for sample 4B.…”