Synthesis and properties of Na0.55Co0.9M0.1O2 (M = Sc, Ti, Cr–Zn, Mo, W, Pb, Bi) solid solutions

Abstract

Ceramic samples of Na_0.55Co_0.9M_0.1O₂ (M = Sc, Ti, Cr–Zn, Mo, W, Pb, Bi) solid solutions are synthesized using the solid-phase method; their crystal structure parameters are determined; their microstructure, thermal expansion, thermal and electrical conductivity, and thermal e.m.f. are studied; and the values of their power factor and thermoelectric figure of merit are calculated. It is revealed that Na_0.55Co_0.9M_0.1O₂ cobaltites are p type conductors with the linear thermal expansion coefficient (LTEC) changed within limits of (12.2–16.2) × 10^–6 K^–1. The effect of the substitution of other metal cations for cobalt cations in Na_0.55CoO₂ on the parameters of the crystal structure, as well as the physicochemical and functional properties of Na_0.55Co_0.9M_0.1O₂ solid solutions, which are formed, is analyzed. It is shown that ceramic samples of the Na_0.55Co_0.9Cr_0.1O₂ and Na_0.55Co_0.9Bi_0.1O₂ compositions have the maximal power factor values among those studied at 0.917 and 1.018 mW/(m K²), respectively, at a temperature of 1100 K.