Effect of Zn substitution for Co on the transport properties of YBaCo4O7

Electrical resistivity and Seebeck coefficients of YBaCo4-xZnxO7 (x = 0.0, 0.5, 1.0, 2.0) were investigated in the temperature range 350-1000 K. It was found that the electrical resistivity and activation energy increase with increasing Zn concentration, while Seebeck coefficients do not increase but decrease when electrical resistivity increases. We explained the increase of electrical resistivity and the drop of Seebeck coefficients for Zn-substituted samples by the decrease of carrier mobility, rather than of carrier concentration. The effect of oxygen absorption and desorption on the electrical resistivity and Seebeck coefficients was also investigated. An abrupt change of transport properties happens at about 650 K for x = 0.0 and 0.5 samples measured in oxygen. For x = 1.0 and 2.0 samples, however, such change disappears and the transport behavior in oxygen is almost same as that in nitrogen due to the significant suppression of oxygen diffusion caused by the higher Zn concentration in these samples. (C) 2007 Elsevier Ltd. All rights reserved.