Synthesis and properties of disubstituted derivatives of layered calcium cobaltite

摘要

Disubstituted solid solutions Ca(2.8)Ln(0.1)Bi(0.1)Co(4)O(9 + delta), Ca3Co3.85Fe0.075Bi0.075O9 + delta, and Ca(2.8)Ln(0.2)Co(3.85)M(0.15)O(9 + delta) (Ln = Tb, Er; M = Fe, Bi) are synthesized based on layered calcium cobaltite by the citrate method; the parameters of their crystalline structures are defined, and their thermal, electrophysical, and thermoelectric properties are studied. It is shown that the resulting oxides are p-type semiconductors whose thermal conductivity and linear thermal expansion coefficient decline and the apparent electroconductivity activation energy increases upon substitution of the calcium and cobalt ions for the heavier metal ions. It is established that the highest power factor is demonstrated by the Ca2.8Tb0.2Co3.85Bi0.15O9 + delta solid solution (P (1100) = (0.1)40 mW/(m K-2)), and the highest thermoelectric merit index is manifested by Ca2.8Er0.2Co3.85Bi0.15O9 + delta (ZT (423) = 0.009), which are higher than the corresponding values of the basic phase Ca3Co4O9 + delta at the same temperatures by 40 and 50%, respectively.