Abstract A systematic investigation was carried out to evaluate the effect of Ni electrodeposit on the microstructure evolution and electrical resistance of the P-type Bi2Te3-based thermoelectric (TE) joint. In this study, two systems (SAC305/(Bi,Sb)2Te3 and SAC305/Ni/(Bi,Sb)2Te3) were set up. The intermetallic compounds (IMCs) were mainly detected by using scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). A model of overlapping joint was set up for electrical resistance testing. Results indicated that the SnTe phase was the major and thermodynamically stable product in the SAC305/(Bi,Sb)2Te3 system, and its porous structure determined the presence of micro-tunnels, which facilitated the diffusion process of Sn and Te atoms, therefore the SnTe layer continuously grew in the whole reflowing duration. In this system, the time exponent was analyzed to be 1.2741, indicating that the growth of the IMC layer followed the linear law, and was reaction-controlled. In the SAC305/Ni/(Bi,Sb)2Te3 system, it was remarkable that the Ni barrier inhibited the rapid growth of the IMC layer, and the dominated product was detected to be (Ni,Cu)3Sn4 whose dense distribution could effectively suppress the diffusion of Sn atoms. The time exponent in this system was 0.5010, indicating that the growth of the Ni–Cu–Sn ternary IMC followed the parabolic laws and was mainly volume diffusion-controlled. After reflowing treatment, the electrical resistance remained at 2.203 mΩ for NiTL (the TE leg with the Ni electrodeposit) system while that of TL (the TE leg without the Ni electrodeposit) system rapidly increased to a higher value about 4.879 mΩ. Owing to the lower growth rate of the IMC layer in NiTL system, it could reasonably conclude that the Ni electrodeposit was of great importance in depressing the electrical resistance.

中文翻译：

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Ni电沉积对P型Bi2Te3焊点微观结构演变和电阻的影响

摘要 为了评估Ni电沉积对P型Bi2Te3基热电（TE）接头的微观结构演变和电阻的影响，进行了系统研究。在这项研究中，建立了两个系统（SAC305/(Bi,Sb)2Te3 和 SAC305/Ni/(Bi,Sb)2Te3）。金属间化合物（IMCs）的检测主要采用扫描电子显微镜（SEM）、X射线衍射仪（XRD）和透射电子显微镜（TEM）。建立了重叠接头模型用于电阻测试。结果表明，SnTe 相是 SAC305/(Bi,Sb)2Te3 体系中主要的热力学稳定产物，其多孔结构决定了微隧道的存在，促进了 Sn 和 Te 原子的扩散过程，因此，SnTe 层在整个回流过程中不断生长。在该系统中，时间指数分析为 1.2741，表明 IMC 层的生长遵循线性规律，并且是反应控制的。在SAC305/Ni/(Bi,Sb)2Te3体系中，Ni势垒明显抑制了IMC层的快速生长，检测到主导产物为(Ni,Cu)3Sn4，其密集分布可以有效抑制Sn原子的扩散。该系统中的时间指数为 0.5010，表明 Ni-Cu-Sn 三元 IMC 的生长遵循抛物线规律，主要受体积扩散控制。回流处理后，电阻保持在2。NiTL（带镍电沉积的 TE 支路）系统的电阻为 203 mΩ，而 TL（不带 Ni 电沉积的 TE 支路）系统的电阻值迅速增加到更高的值，约为 4.879 mΩ。由于 NiTL 系统中 IMC 层的生长速率较低，可以合理地得出结论，Ni 电沉积对于降低电阻非常重要。