Magnetoresistance in La- and Ca-doped YBa2Cu3O7-δ.

We studied the microstructures, electronic, and magnetic properties on La-doped and La- and Ca-codoped YBa₂Cu₃O_7-δ (YBCO). The superconducting transition temperature remains unchanged up to 10% for La-doped YBCO. The competition between electrons and holons was assumed according to the variation of T_c0 in La and Ca codopings in YBCO. The magnetoresistance (MR) effect is about 8%, which is observed obviously near the critical temperature and is independent of the content of La in La-doped YBCO. MR increases up to about 40% with the incorporation of Ca in La-doped YBCO. We present here possible explanations for the magnetoresistance effect in polycrystalline samples based on the microstructure and the increase of oxygen vacancies at grain-boundary interface. [ABSTRACT FROM AUTHOR]