高温度梯度定向凝固单相Mg2Sn合金的制备及其热电性能

Preparation and Thermoelectric Properties of Single-phase Mg2Sn Alloys by High Temperature-gradient Directional Solidification

摘要:

高温度梯度(180K/cm)定向凝固方法可制备单相Mg₂Sn晶体,通过凝固理论对平-胞转换临界速率进行了计算,并预测了单相Mg₂Sn晶体的生长距离,与试验结果相吻合。此方法获得的Mg₂Sn晶体由于去除了第二相Sn的影响,可以获得更好的热电性能,在测试温度区间(300-700K)内,未掺杂条件下最大Seebeck系数和电导率值分别可达-261μVK^_-1和525?^_-1m^_-1,通过Bi掺杂来对电导率进行优化后,功率因子最高可达2.29mWm^_-1K^_-2。单相Mg₂Sn晶体的热导率也得到大幅降低,500K时,最小值为4.3Wm^_-1K^_-1,Bi掺杂量为1.5at.%时,热电优值最高可达到0.21。这一方法可以为制备高性能的Mg₂B^_IV体系三元固溶体合金提供参考。

Abstract:

Single-phase Mg₂Sn crystal was successfully directionally solidified from the melt with a high temperature gradient of 180K/cm. The critical velocity of planar interface and solidified distance for the growth of single-phase Mg₂Sn crystal is predicted theoretically and agrees well with the experimental result. The grown Mg₂Sn crystals exhibit better thermoelectric performance without influence of the second phase Sn. At the temperature ranging from 300 to 700K, the maximum Seebeck coefficient S and electrical conductivity σ reached -261μVK^_-1 and 525?^_-1m^_-1, respectively. The top value of power factor is 2.29mWm^_-1K^_-2 after the doped Bi optimization. The minimum thermal conductivity κ was measured as 4.3Wm^_-1K^_-1 at T=500K. The maximum figure of merit is 0.21 at the doping concentration of 1.5at.%Bi. The method developed in this paper can provide a methodological reference for the preparation of ternary Mg₂B^_IV solid solution.