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Time : 2015-05-06 16:06Source :analogtechnologies Author : Analog Click :

The material figure of merit Z is an important parameter to measure the cooling capacity of TEC and its expression is. In order to improve Z value, conductivity σ and Seebeck coefficient α should be improved and thermal conductivity λ should be reduced. λ consists of phonon thermal conductivity λp (about 90%) and electronic conductivity λe. These three parameters are not independent of each other, which all are the function of carrier concentration n and temperature T. In the condition of different environment temperature, the value of Z is different. In general, the dimensionless factor ZT is used to describe material’s performance. Bi₂Te₃ is the most widely used thermoelectric material and the value of ZT can be up to 0.9. However, the cooling efficiency of TEC made by Bi₂Te₃is only 30% of compression refrigeration.

In recent fifty years, the performance of thermoelectric materials has been increased by roughly 20%. At present, there are many kinds of developing thermoelectric materials, such as non-oxide semiconductor thermoelectric materials, oxide thermoelectric materials, low dimensional thermoelectric materials, super lattice thermoelectric materials and so on. 

Semiconductor thermoelectric materials of the earliest and most mature is (Bi,Sb) ₂(Te, Se) ₃, which is a solid solution material. Most of the current TEC are using this material, which can increase α and reduce λ. 

Currently, the semiconductor oxide material is one of oxide thermoelectric materials, which has many advantages of no pollution, stable performance and can work for a long time at high temperature. This material mainly includes Na-Co-O and Ca-Co-O.

The left research progress of thermoelectric refrigeration technology will be introduced in the next article.

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