## 1 Introduction  
Unlike traditional power generation systems, a thermoelectric power generator (TEG) produces electrical power based on the Seebeck effect, via the movement of charge carriers within thermoelectric materials under a temperature difference. Using the heat from radioisotopes, TEGs can supply electrical power for tens of years, and are now the only choice of power source for deep space explorers which fly far from the sun and therefore can no longer obtain sufficient sunlight energy [1; 2]. In the past decade, TEGs have been regarded as one of the most promising candidates to recover waste heat from industries or automobiles and turn them into electricity [3; 4], which can benefit from the remission of the fossil energy shortage and global warming. Recently, TEGs have become one of the research focuses, and are expected to act as power suppliers of wearable electronic equipment [5]. Intrinsically, the performance of a TEG depends on the property of the thermoelectric (TE) material, which is referred to as the dimensionless figure of merit of \(ZT\). Among the investigatedvarious systems of TE materials, silicides [6; 7; 8; 9], half-heuslers [10; 11], and tellurides (e.g., of Bi [12; 13; 14], Pb [15; 16; 17; 18] and Ge [19; 20]) have been widely studied and some have been practically applied in TEGs. Besides, a number of materials featuring excellent TE properties (high \(ZT\) value) and a relatively lower cost, low toxicity, and good mechanical properties, such as filled skutterudite (SKD), also attract extensive attention and have been actively pursued for being converted into TEGs [21; 22; 23; 24; 25; 26]. Thermoelectric joints, consisting of TE materials and electrodes, are the fundamental parts and also the key components of a TEG. In practical applications, the performance of a TEG not only depends on the property of TE materials, but also depends on the temperature difference between the hot- and cold-sides of the TE material bulks. Higher hot-side temperatures usually lead to a larger temperature difference, further enhancing the performance of the TEG. Meanwhile, a higher hot-side temperature also encourages interfacial diffusion and accelerates the degradation of the contact property, especially the contact (electrical) resistivity, which definitely deteriorates the performance and stability of the TEGs. Practically, the high temperature TEGs are expected to perform stably for a couple of years or even longer. For example, to make full use of the TE property, the hot side temperature of the CoSb\({}_{3}\)-based SKD joints should be 500 \({}^{\circ}\)C or higher. At such a high temperature, the major component in the SKD material, antimony, will react fiercely with most electrode materials (Cu, Ni, and Al, etc.) and then form single- or multi-layer interfacial intermetallics (IMC). The performance and stability of the TE joints are sensitively influenced by the microstructure and properties of the interface between the TE materials and electrode. To improve the interfacial stability of the SKD joints, a diffusion barrier layer is usually inserted between the electrode and the SKD material. [PERSON] et al. firstly reported using Ti as the barrier layer in the CoSb\({}_{3}\)[27]. [PERSON] et al. systematically studied the diffusion kinetics of the Ti/CoSb\({}_{3}\) interface at high temperatures and predicted a service life of over 20 years for Ti/CoSb\({}_{3}\) joints at 500 \({}^{\circ}\)C, using interfacial shearing strength as the criteria [28; 29]. In [PERSON]'s work, when the working temperature increased to 550 \({}^{\circ}\)C, the diffusion speed at the Ti/CoSb\({}_{3}\) interface increased by one order and the predicted service life dropped to within one year [28]. In 2014, similar interfacial evolution in Ti/Yb\({}_{0.6}\)Co\({}_{4}\)Sb\({}_{12}\) joints was found and the method was developed to improve the interfacial stability of CoSb\({}_{3}\)-based \(n\)-type SKD joints by introducing a Ti-Al barrier layer [30].