Study On The Barrier Material Of Mg₂Ge_0.25Sn_0.73Bi_0.02 Thermoelectric Device

The thermoelectric material is a kind of new energy materials that can convert heat energy to and from electric energy.The thermoelectric generator device?TEG?prepared by the thermoelectric materials can be used in the thermoelectric power generation and thermoelectric cooling fields.The connection interface between the thermoelectric material and the electrode is an important part of the thermoelectric device,which directly affects the reliability and life of the device.In this paper,Mg₂Ge_0.25Sn_0.75-xBi_x alloys were prepared by high frequency melting and SPS sintering technique.The phase constituent and thermoelectric properties were tested.The alloy Mg₂Ge_0.25Sn_0.73Bi_0.02 with the best thermoelectric performance was selected as the base thermoelectric?TE?material,five metals Ni,Cu,Ti,Co and Al were used as barrier layers.The base TE and barrire layer was welded by two-step sintering method.The interface morphology and the diffusion reaction behavior after the aging treatment were investigated.The research results were showed in the following:?1?The metal Ni reacted quickly with the base TE material,forming a diffusion reaction layer of 60?m,which increased continuously after aging at 300°C.So metal Ni is not suitable for the barrier layer for the MgGeSn-based TEG.?2?The metal Cu also reacted with the base TE material,and the thickness increased with the agint time prolonging.The Kirkendal holes generated at the diffusion layer after aging at300°C damaged greatly the TEG interface.?3?When Ti was used as a barrier layer material,it did not react with the base TE material.But the interface layer cracked after aging treatment at 300°C,because the large thermal expansion coefficient difference lead to the weak bonding strength.In this way the metal Ti can not used as a barrier layer material for MgGeSn-based TEG.?4?The metal Co was bonded well with the substrate TE material,the thickness of the diffusion reaction layer growed slowly with the aging time increasing,showing well thermal stability.The contact resistivity between Co and the base TE material was 0.22??·cm²,which increased to 1.55??·cm² after the aging annealing at 300-400°C,.and the interface bonding strength decreased from 44.5 MPa to 33 MPa.Enen so,above properties can meet the practical application.Hence the metal Co can be used as a barrier layer material for MgGeSn-based TEG.?5?The thickness of the diffusion reaction layer was about 2?m in the case of metal Al was used as the barrier material.The growth rate of the diffusion layer was particularly slow after aging treatment and the thermal stability of the interface was good.The contact resistivity between Al and the thermoelectric substrate increased from 4.98??·cm² to4.92??·cm²after the aging annealing at 300-400°C for different time,and the interface bonding strength changed during 15.7 MPa and 21 MPa.Therefore,Al can also be used as a barrier material for MgGeSn-based TEG.Through the investigation of the interface structure,electrical properties and mechanical properties of each barrier layer material,the metal Co and Al can achieve a good connection with TE substrate without forming a serious diffusion reaction and destroying the thermoelectric material.Moreover the contact resistivity was considerable low comparing to that for MgGeSn-based TE material,which has little influence on the TEG efficiency in practical applications.Above all,the metals Co and Al were ideal candidates in barrier layer materials for MgGeSn-based TEG.