The normal state transport properties of NdBa2−xLaxCu3O7−δ: Evidence of localization hole by La

The transport properties of sintered samples NdBa2−xLaxCu3O7−δ with 0 ⩽ x ⩽ 0.30 have been studied in the normal state by X-ray diffraction, the resistivity, and the thermoelectric power measurements. La doping results in a larger normal state resistivity, the thermoelectric power, a lower critical temperature Tc, a larger pseoudogap temperature Tg, and a change from a metal-like to a semiconductor-like behavior at low temperature and high doping concentration. The strong increase in the room temperature resistivity for x ⩾ 0.05 suggested that hole filling picture is not only mechanism to decrease hole concentration but there is also another mechanism such as mobile hole localization. The results of the resistivity as a function of temperature and doping concentration was analyzed within bipolaron model while the thermoelectric power was analyzed within a phenomenological narrow band model. A good agreement between models and data were obtained. An increased tendency for localization is found within both models. Therefore, the results of both models suggested that both hole localization and hole filling mechanisms decrease the hole concentration.