Thermoelectric performance of Li doped, p-type Mg2(Ge,Sn) and comparison with Mg2(Si,Sn)

Abstract

Solid solutions with chemical formulaMg 2 (Si,Ge,Sn) are promising thermoelectric materials with very good properties for the n-type material but significantly worse for the p-type. For power generation applications good n-and p-type materials are required and it has been shown recently that Li doping can enhance the carrier concentration and improve the thermoelectric properties for p-type Mg 2 Si 1x Sn x .We have investigated the potential of p-type Mg 2 (Ge,Sn) by optimizing Mg 2 Ge 0.4 Sn 0.6 using Li as dopant. We were able to achieve high carrier concentrations (1.4 × 10 20 cm −3) and relatively high hole mobilities resulting in high power factors of 1.7 × 10 −3 W m −1 K −2 at 700 K, the highest value reported so far for this class of material. Exchanging Ge by Si allows for a systematic comparison of Mg 2 (Ge,Sn) with Mg 2 (Si,Sn) and shows that Si containing samples exhibit a lower power factor but also a lower thermal conductivity resulting in comparable thermoelectric figure-of-merit. The data is furthermore analyzed in the framework of a single parabolic band model to gain insight on the effect of composition on band structure. 2 , here is the electrical conductivity, the thermal conductivity, the Seebeck coefficient, and the absolute temperature. A large fraction of the potentially available waste heat can be found in the mid-temperature region

Synthesis of p-type Mg2Si1-xSnx with x = 0-1 and optimization of the synthesis parameters

“…were weighed according to nominal composition. No excess Mg was added as excess Mg can occupy the interstitial position and serve as an n-type donor [11,16]. The desired elements were transferred into a stainless steel jar with a ball to powder ratio 1 Ultra 55.…”

“…On the other hand, for binary Mg 2 Si, a milling duration of 6 h was found to be sufficient as also reported previously [28,29], presumably because only one phase could be formed. We study the effects of sintering temperature and holding time especially in Mg 1.98 Li 0.02 Si 0.4 Sn 0.6 because this composition has so far the best properties with the > 0.5 [10,11]. Fig.…”

“…However, p-type Mg 2 (Si,Sn) has inferior properties in comparison to n-type, partially due to a less favourable band structure, lower dominant carrier type mobility and insufficient dopant activation [10]. Recently, there has been progress on fabricating complementary p-type materials and improved zT > 0.5 has been observed [9,[11][12][13]. Zhang encapsulation with zT ~ 0.7.…”

“…However, the formation of MgO seems to be the cause of increasing thermal conductivity [12]. High energy ball milling has been employed to synthesize p-type Mg 2 (Si,Sn) reaching zT > 0.5 [11,13]. This synthesis method is promising due to little or no oxidation or impurities, reduced Mg loss, and good dopant incorporation [15].…”

From sol–gel prepared porous silica to monolithic porous Mg2Si/MgO composite materials

“…1) [1]. In recent years, it has attracted an increasing amount of interest for a wide range of applications in various fields, such as thermoelectrics and optics and in lithium-ion batteries, largely due to its low toxicity, unique optical and electrical properties, low costs of production, and environmental compatibility [2][3][4][5][6][7][8].…”