用固相反应法制备La4/5Sr1/5MnO3及在其A位分别掺K、Ag系列样品,通过X射线衍射（XRD）谱,电阻率-温度（ρ～T）曲线,磁电阻-温度（MR～T）曲线,研究了在A位同时掺入一价、二价元素而保持Mn3＋/Mn4＋比值（摩尔比n（A）/n（B））不变的钙钛矿锰氧化物体系A位离子半径及A位离子的无序度σ2对电输运性质及磁电阻的影响.结果表明：A位离子的无序度σ2对电输运性质的影响比A位平均离子半径对电输运性质的影响大;电阻率曲线出现双峰是由于表面相电阻率与体相电阻率竞争的结果;MR的温度稳定性是本征磁电阻与隧穿磁电阻竞争的结果;掺K样品在253～175K温区MR从8.1%缓慢上升到9.5%,掺Ag样品在260K以下温区MR都在7.4%以上,纯的La4/5Sr1/5MnO3样品在318～259K温区MR都在7.0%以上,在如此宽温区MR几乎不变有利于MR的实际应用.
La4/5 Srl/5 MnO3 and its doped samples with respective doping of K and Ag at A-site were prepared by the solid-state reaction method. The influences of the radius 〈rA〉 and disorder degree a2 of A-site ions on electric transport property and magnetoresistance of the perovskite manganite system with unchanged value of Mn3＋/Mn4＋ ratio through the introduction of both univalent and bivalent elements at A-site have been studied through the measurements of X-ray diffraction （XRD） patterns, resistivity-temperature （MR-T） curves, and magnetoresistance-temperature （MR-T） curves. The results indicate that： the influence of the disorder degreea2 of A-site ions on electric transport property is larger than that of the average radius 〈rA 〉 of A-site ions; the resistivity curves exhibit the double-peak phenomenon, which is the result of the competition between the resistivity of surface phase and that of body phase; the temperature stability of MR is the result of the competition between intrinsic magnetoresistance and tunneling magnetoresistance; MR of the sample with K doping increases slowly from 8. 1 ~ to 9.5 % in the tempera- ture range of 253-175 K, MR of the sample with Ag doping is above 7. 4% in the temperature range below 260 K, and MR of the pure sample La4/5 Sr1/5 MnO3 is above 7.0% in the temperature range of 318-259 K; MR almost keeps the same in such wide temperature range, which is beneficial to its practical application.
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