The principle of improving material performances of thermoelectric cooler （II）

In the ion conduction type conductor, the carrier may be positive ion or negative ion. In the electronic conduction type conductor, carrier is electron and current can be formed by electron movement. With the increasing of carrier concentration, thermoelectric coefficient α will reduce and thermal conductivity σ will increase. In the thermal coefficientλ, the lattice thermal conductivity λP (about 90%) is irrelevant to the carrier concentration, while the electron thermal conductivity λe is proportional to the carrier concentration. So the appropriate carrier concentration n is selected to make  get the maximum difference. Figure of merit z and other three parameters α, ρ, λ have a certain relationship with carrier concentration n. When n is close to 1019cm-3, the value of Z can be the maximum.

Though controlling the carrier concentration n, thermal conductivity σ and thermoelectric coefficient α can be improved and thermal conductivity λe can be reduced. So the current investigators of TEC materials should try to reduce thermal conductivity λp. One of the effective ways to reduce the lattice thermal conductivity is to increase phonon scattering factors, but grain boundary structure, grain boundary content and the interaction of the grain boundary and the phonon need to be further studied.

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