co nd - m at / 9 90 80 06 v 2 2 S ep 1 99 9 Characterisation , Raman , Magnetic and Resistivity measurements in polycrystalline samples of LaMnO 3 doped with Cd

We report a study of polycrystalline samples of the family La 1-x Cd x MnO 3+δ with different percentage of Mn 4+ ions. X-rays diffraction, Iodometric titration, Raman, Magnetic and Electrical Resistivity measurements provide a general characterisation of the physical properties. Results are qualitatively similar to the ones found in Ca doped manganese perovskites. The substitution of divalent ions of Ca, Sr, Ba, and Pb (position A') for the trivalent ions of La, Nd, Pr (position A) in compounds of the family A 1-x A' x MnO 3 has been studied intensively during the last years 1-3. An interesting feature of some of these materials is a paramagnetic insulator to ferromagnetic metal transition, accompanied by a high Magnetoresistance near the Curie temperature (Tc). Troyanchuk et al. 4,5 have reported structural, magnetic and resistivity measurements in La 1-x Cd x MnO 3 compounds. They found a paramagnetic to ferromagnetic transition, but not an insulator metal transition, in samples with x between 0.25 and 0.5, and interpreted their results in the framework of a superexchange interaction. On the other hand, M. Sahana et al. 6 studied polycrystalline and thin film samples of La 0.67 Cd 0.33 MnO 3 and found an insulator metal transition at the same temperature interval of the paramagnetic ferromagnetic transition. As far as we know, these are the only reports available in the literature about Cd substitutions in manganese perovskites. It would be interesting to investigate further whether the doublexchange or superexchange interaction is responsible for the physical properties in Cd doped manganese perovskites and make a comparison with closely related Ca doped compounds. Here, we report a study of four polycrystalline samples of the family La 1-x Cd x MnO 3+δ with different percentage of Mn 4+ ions. We used X-rays diffraction (XRD), Iodometric titration, Raman, Magnetic and Electrical Resistivity measurements to provide a general characterisation of the physical properties. 2-Experimental Polycrystalline samples with nominal composition La 0.8 Cd 0.2 MnO 3 and La 0.7 Cd 0.3 MnO 3 were prepared by solid-state reaction. Appropriate molar quantities of La 2 O 3 , CdO and MnO 2 were mixed, grounded and heat-treated at 800 0 C for 48 hours. After that, the samples were three times reground, pressed into pellets and sintered at 1000 0 C for 24 hours. We avoid using higher sintering temperatures to minimise the evaporation of Cd. Some samples from the same batch …