Thermoelectric and structural characterization of Ba₂Ho (Cu _3-xCox) O_6+y

The search for thermoelectric materials for power generation and for solid-state cooling has led to increased interest of layered cobalt-containing oxides because of their thermal stability at high temperature and their desirable thermoelectric properties. This paper examines the effect of substitution of Co in the layered pervoskite Ba2 Ho (Cu3-x Cox) O6+y (x=0.3, 0.4, 0.5, 0.6, and 1.0). Structural analysis using the neutron Rietveld refinement technique reveals that when x0.4, Co substitutes mainly for Cu in the "chain sites" of the Ba2 Ho (Cu3-x Cox) O6+y structure. As x0.4, Co also enters in the Cu-O "plane sites" as well. The thermoelectric properties of polycrystalline Ba2 Ho (Cu3-x Cox) O6+y samples were studied in the temperature range of 10-390 K. In general, as the cobalt content x increases, the resistivity and Seebeck coefficient of these samples increase while the thermal conductivity decreases. Among the five Ba2 Ho (Cu3-x Cox) O6+y compositions, the x=0.4 member gives the highest figure of merit ZT of ≈0.02 at approximately 270 K.