Texture and high temperature transport properties of Ag xCa 3− xCo 4O 9 (0 ≤ x ≤ 0.6) compounds

Abstract

Polycrystalline Ag x Ca 3− x Co 4O 9 ( x = 0–0.6) compound samples were prepared by combining citrate acid sol–gel method with spark plasma sintering and the phase composition, orientation, texture and high temperature transport properties were investigated in detail. The results show that main phase Ag x Ca 3− x Co 4O 9 compounds are formed with a small quantity of silver phase which distributes unevenly in the Ag x Ca 3− x Co 4O 9 matrix and so greatly weakens the orientations of Ag x Ca 3− x Co 4O 9. All samples exhibit semiconductor transport properties except for the x = 0.6 sample which exhibits metallic transport characteristic. The electrical resistivity and the Seebeck coefficient are simultaneously decreased with increasing Ag substitution. The reasons are attributed to hole concentration adjustment and shortcut effect of distributed Ag in Ag x Ca 3− x Co 4O 9 matrix during conduction process. The power factor as a function of Seebeck coefficient and resistivity could be altered with x and it is enhanced at x = 0.3 with its value exceeding 6.8 μW/cm K 2 at 1033 K indicating that the electrical properties could be improved by optimizing the composition and texture in sol–gel process.