Design and Optimization of Gradient Interface of Ba0.4In0.4Co4Sb12/Bi2Te2.7Se0.3 Thermoelectric Materials

Abstract

A series of Ba0.4In0.4Co4Sb12/Bi2Te2.7Se0.3 (FS/BT) thermoelectric (TE) materials were fabricated by a two-step spark plasma sintering method. The samples contained various numbers of gradient layers between FS and BT as follows: one gradient layer (1GL) with FS/BT volume ratio of 5:5, three GLs with ratios of 3:7, 5:5, and 7:3 (denoted as 3GLs-I with 3:7–5:5–7:3), 3GLs-II with 7:3–5:5–3:7, 5GLs-I with 3:7–4:6–5:5–6:4–7:3, and 5GLs-II with 2:8–3:7–5:5–7:3–8:2. The interfacial structure and mechanical properties of the FS/BT TE materials were investigated in this work. In FS/BT TE materials with no GLs, a large number of macroscopic cracks occurred on the FS bulk material side. It was discovered that designing and optimizing GLs between the FS and BT bulk materials could effectively relax the thermal stress induced by the large difference in coefficient of thermal expansion, eliminating the macroscopic cracks and resulting in a remarkable enhancement of the interfacial mechanical properties of the FS/BT TE materials. The flexural strength of the FS/BT TE material with 1GL reached 9.67 MPa, increased by 85% compared with that of the FS/BT TE material with no GLs. The present work indicates that increasing the BT content in the GL near to the FS bulk material side is an effective method to completely eliminate macroscopic cracking. The optimized gradient interface of the FS/BT TE material was 3GLs-II with FS/BT volume ratios of 3:7–5:5–7:3. The highest flexural strength reached 12.76 MPa, representing a 144% increase.