Deficiency effects on the physical properties of the lacunar La0.5Ca0.5-xMnO3 manganese oxides

We investigate the effects of calcium deficient on the structural and magnetotransport properties of non-stoichiometric La0.5Ca0.5-x and square;xMnO3 manganese oxides. Powder samples have been elaborated using the solid-state reaction technique. Our synthesized samples crystallize in the orthorhombic perovskite structure with Pnma space group. Electrical measurements versus temperature in magnetic applied field up to 8 T on La0.5Ca0.5-x and square;xMnO3 compounds have been performed. Resistivity measurements of the stoichio-metric sample La0.5Ca0.5MnO3 show a semiconducting behaviour in the whole temperature range of 20-300 K. An increase of the resistivity at very low temperature can be attributed to the charge ordering (CO) effect. Calcium defect leads to an important decrease of the resistivity at low temperature and consequently a destruction of the CO effect observed at very low temperature in the parent compound. Electrical measurements show that 5% of calcium deficiency induces a semiconducting-metallic transition with decreasing temperature. The electrical transition temperature increases with increasing deficient content. 5% of calcium deficient induces the same effect produced by an applied magnetic field of 8 T on the parent compound. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)