稀土RE-Bi-Te体系相图、相结构与化合物热电性能研究

The main obstacle to the large-scale application of bismuth telluride Bi2Te3 based thermoelectric materials lies in their low thermoelectric figure of merit (ZT). Recent studies have found that micro-alloying with rare-earth metals may be one of the important approaches to improve the thermoelectric figure of merit (ZT). The differences of the solid solubility as well as the substitution element of doped rare-earth elements may have significant influence on the resulting thermoelectric properties. The prediction of the thermoelectric figure of merit (ZT) of bismuth telluride Bi2Te3 based alloys in turn relies on the knowledge combining crystallization thermodynamics and kinetics, in which accurate thermodynamic database is the basis. In this project, the phase diagram of RE-Bi-Te(RE=La,Er,Dy,Yb)systems will be constructed with the equilibrium alloy and CALPHAD method; the thermodynamic database will be developed, based on which the heat capacities corresponding to a range of compositions and temperatures will be calculated and the heat conductivities will also be predicted. The effect of micro-alloying of rare earth metals on the thermoelectric figure of merit (ZT) of the Bi2Te3 based alloy systems will be investigated and the optimum micro-alloying composition range will be predicted. This study would provide fundamental knowledge and useful guidance for developing and designing Bi-Te alloys for thermoelectric applications.

Bi-Te系室温热电材料的低热电优值(ZT)已成为其广泛应用的主要障碍。近期研究发现稀土微合金化有可能成为提高其热电优值的重要途径。而稀土元素在Bi2Te3相中的固溶度大小与稀土元素取代基体中Bi或Te的不同将成为选择稀土元素种类和预测合金的热电优值(ZT)大小的重要依据。预测热电优值需结合晶体热力学与动力学知识, 准确的相图热力学数据库是这一预测方法的基础。本项目拟综合运用平衡合金法和相图热力学计算方法,系统研究 RE-Bi-Te(RE=La,Er,Dy,Yb)多元相图,建立相应的相图热力学数据库,计算该体系不同成分合金不同温度下的热容,预测其热导率,探讨稀土微合金化对Bi-Te系合金热电优值的影响, 预测微合金化最佳成分范围,为优化Bi-Te系室温热电材料提供关键基础数据。

Bi-Te系室温热电材料的低热电优值(ZT)已成为其广泛应用的主要障碍。近期研究发现稀土微合金化有可能成为提高其热电优值的重要途径。而稀土元素在Bi2Te3相中的固溶度大小与稀土元素取代基体中Bi或Te的不同将成为选择稀土元素种类和预测合金的热电优值(ZT)大小的重要依据。预测热电优值需结合晶体热力学与动力学知识, 准确的相图热力学数据库是这一预测方法的基础。本项目采用平衡合金法，结合电子探针显微分析技术（EPMA）、X射线衍射技术（XRD）及热分析（DSC）等检测分析手段，对Bi-Te二元相图以及Bi-Te-La、Bi-Te-Ce、Bi-Te-Yb、Bi-Te-Nd、Bi-Te-Sm、Bi-Te-Tb、Bi-Te-Er7个三元系相图进行了实验测定。依据新的实验相图结果，在已有热力学数据的基础上辅助以第一性原理计算，运用CALPHAD方法对二元系、三元系进行了热力学优化计算，得到了一组较为合理的热力学参数，并构建了Bi-Te-RE体系的多组元热力学数据库。综合分析7个体系，获得了稀土元素在Bi-Te基中的固溶度随稀土元素原子半径的减小而增大的关系。上述研究结果可以为设计新型BiTe基热电材料提供重要的基础。此外本项目所构建了Bi(铋）-Te（碲）-RE（稀土）体系多元相图热力学数据库，不仅可以用来研究在Bi-Te合金中掺杂稀土后对合金制备过程中组织与性能的影响，为新合金的开发中的组织演化模拟提供关键的热力学信息。