Heat Treatment System For Non-chemical Ratio Of La <sub> 0.67 </ Sub> Of Sr <sub> 0.18 </ Sub> The ¡õ <sub> 0.15 </ Sub> Of Mno <sub> 3-¦Ä </ Sub> Structure And Transport The Nature Of The Impact

Rare-earth manganites have been receiving special attentions in the community of condensed matter physics owing to colossal magnetoresistance. The carrier has high polarization and they have giant magnetoresistance around T_C. In other hand, manganites are prototypical of strongly-correlated electron systems in which spin, charge, and orbital degrees of freedom are coupled. We are convinced that the comprehension of complex problems posed by the manganites has the potential to produce a substantial advance in the theory of condensed matter physics, and will eventually shed light into other unsolved problems, for example, high-Tc superconductivity.In this article, we studied the influence of thermal treatment on structure and transport properties in the nonstoichiometric perovskite-type oxides La_0.67Sr_0.18â–¡_0.15MnO_3-δ. The precursors of hole-doped bulk manganese oxides La_0.67Sr_0.18â–¡_0.15MnO_3-δwere synthesized using the sol-gel reaction technique. We got the final samples after the precursors were treated with different thermal treatment. The Rietveld refinements of powder X-ray diffraction patterns showed that all the samples were single phase, with rhombohedral symmetry and space group R3c. There is no change in structural symmetry through different thermal treatment. The lattice parameters and volume of unit cell vary distinctly because of the different sintering temperature, sintering time, sintering atmosphere and annealing environment. This phenomenon probably reflected that different preparation process will influence the degree of lattice distortion. The bond angle of Mn-O-Mn and O-Mn-0 deviates from 180°and 90°, indicative of the presence of Jahn-Teller effect in MnO₆ octahedron. This is due to the mismatch of molar ratio among A-site atom, Mn atom and O atom. These mismatch will introduce lattice vacancy(including cation vacancy and anion vacancy) and interstitial atom which will induce local lattice distortion.The features of the hole-doped manganese oxides indicate that the lattice deformation directly influences the Mn-O bond length and Mn-O-Mn bond angle of MnO₆ octahedron. Structural analysis is of great importance to further study the transport and magnetic properties of these hole-doped manganese oxides.Electrical measurements of La_0.67Sr_0.18â–¡_0.15MnO_3-δ show that all of the samples exhibit a metallic-semiconducting transition, and the effect of the magnetic field is to lower the value of the resistivity and make T_MI shift to higher temperature. The transport results also show that every sample is metallic because of single magneton scattering in low temperature, on the other hand every sample is an insulator because of small polar hopping model in high temperature. The two transport properties of small polaron and single magneton scattering coexist at the temperature rang of phase transition. The resistivity of samples sintered in oxygen or annealed in oxygen is lower than that sintered in air.