The effect of the B-site size on the structural, magnetic and electrical properties of La0.7Ca0.3MnO3−δ compounds

The perovskite-type ceramic La0.7Ca0.3MnO3−δ was prepared by the solid-state reaction with 0.00⩽δ⩽0.15. X-ray diffraction, electrical and magnetic measurements were performed to examine the effect of the B-site size on the properties of these materials. We have found that the structure is orthorhombic for 0.00⩽δ⩽0.075 and becomes rhombohedral for 0.10⩽δ⩽0.15. The measurements of the magnetization as a function of the temperature, M(T), shows a ferromagnetic-paramagnetic transition at the Curie temperature TC for δ=0.00. When increasing δ, these curves report the presence of two types of transitions. The first one is from the ferromagnetic to the antiferromagnetic state, indicating the existence of a charge-ordering state (TCO). The second antiferromagnetic-paramagnetic transition occurs at the Neel temperature TN. The temperature dependence of the resistivity ρ(T), indicates a metallic behaviour at low temperature (TTp) for δ=0.00. For 0.05⩽δ⩽0.10, the ρ(T) curves shows a semiconductor behaviour revealing the disappearance of the metallic state which reappear at low temperature for δ=0.125 and 0.150.