ICT2014 Abstracts

 Thermoelectric (TE) power generation is attracted as a new energy source using waste heat. Various types of materials have been proposed for it, for example, alloys, oxides, and so on. Among them, we focused on the oxide, silver antimonite (AgSbO₃ (ASO)), as the n-type material. ASO is expected to show high conversion efficiency because ASO has high electrical conductivity and low thermal conductivity. It is suggested that high electrical conductivity is promoted by metallic Ag islands aggregated at grain boundary of sintered ASO. To investigate in details the effects of metallic Ag islands, we tried to remove such metallic Ag from ASO by HNO₃ treatment. In addition, ASO is rather difficult to be highly sintered into a dense pellet because of high vapor pressure of Sb, and then we introduced spark plasma sintering (SPS) process.

 After the HNO₃ treatment, excess Ag particles were removed and, simultaneously the lattice constant of ASO was decreased. HNO₃ treatment caused elimination of Ag from the ASO lattice, as well as metallic Ag at grain boundary. HNO₃ treated ASO has lower electrical conductivity and higher Seebeck coefficient than non-treatment ASO. The SPS prepared ASO had higher relative density (85%) than normal sintering (60%). However, the SPS caused the segregation of metallic Ag and reduction of ASO, causing higher electrical conductivity with a metallic behavior and lower Seebeck coefficient, compared to the ASO obtained by normal sintering.

 Then, we combined the HNO₃ treatment and SPS process. That is, HNO₃ treated ASO was underwent by the SPS. Then, we succeeded in the improvement of relative density and electrical conductivity with a metallic behavior, and restraint of decrease of Seebeck coefficient.