【作者】 周华伟；

【导师】 马欣新；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 硕士

【摘要】 本文采用溶胶-凝胶方法制备La 1-x Sr x MnO（3x=0.0,0.2,0.3,0.33,0.375,0.4,0.5）系列及La 0.67-y Ce y Sr 0.33 MnO3（y=0.0,0.1,0.15,0.2,0.25）系列粉体,并经过压制成型,最后对块体进行烧结。通过改变掺杂元素含量以及烧结工艺来研究块体样品的结构和电阻率-温度关系。XRD对样品相结构进行分析;SEM对粉体、块体样品形貌进行观察和分析;EDS对样品的成分进行检测;使用标准四引线法测量样品的电阻率-温度关系;用德国耐驰STA449C综合热分析仪对粉体的前驱体进行热分析,以检测溶胶-凝胶工艺的合理性。TG-DSC曲线分析表明,溶胶-凝胶制备粉体工艺设计合理,XRD分析粉体（900℃）为菱面体钙钛矿结构;粉体形貌观察表明,1000℃,烧结4小时后粉体形貌变规则,颗粒尺寸增大,发现由900℃平均～50nm增大到～60nm。所制粉体压制成圆片状并在不同工艺下进行烧结,进行SEM观察,发现随着烧结温度提高,时间延长,材料致密度提高,颗粒明显长大。而且LSMO块体样品平均晶粒尺寸随着Sr掺杂含量增加而减小;LCSMO块体样品平均晶粒尺寸随着Ce含量增加缓慢增加。XRD检测发现:LSMO样品为菱面体钙钛矿结构;LCSMO样品为菱面体钙钛矿相与CeO2相,并随着掺杂Ce含量提高CeO 2含量增加。成分分析结果表明制备样品纯度高。采用标准四引线法表征块体样品电阻率随温度的变化关系,研究结果表明,LSMO和LCSMO样品都出现金属-绝缘体转变,1000℃,4h烧结LSMO样品随着掺杂Sr含量增加金属-绝缘体转变温度（TMI）先升高后降低,并且La 0.7 Sr 0.3 MnO3的TMI最大（269K）,而电阻率随着Sr掺杂含量增加逐渐降低。LCSMO样品（1000℃,4h）电阻率-温度关系曲线表明掺杂Ce后显著降低T MI ,从248K（La 0.67 Sr 0.33 MnO 3 ）降低到133K(La_0.57Ce_0.2Sr_0.33MnO₃)。对LSMO掺杂Sr含量为0.3、0.33、0.4的样品及LCSMO样品Ce掺杂含量为0.1的样品进行不同烧结工艺处理,研究表明,随着烧结温度提高样品TMI明显提高,电阻率下降,在1200℃烧结后,T MI普遍在室温以上。La_0.67Sr_0.33MnO₃样品在1100℃,8h烧结工艺下T MI在室温27℃。更多还原

【Abstract】 The polycrystalline powder La 1-x Sr x MnO3（x=0.0,0.2,0.3,0.33,0.375,0.4,0.5）and La 0.67-y Ce y Sr 0.33 MnO3（y=0.0,0.1,0.15,0.2,0.25）were prepared by sol-gel method, then compressed into pellets and sintered. The structure and the temperature dependence of resistivity of polycrystalline samples were studied by changing content of doped elements or sintering technologies.The phase structure of samples were studied by X-ray diffraction; the morphology of powder and ceramics samples were studied by scanning electron microscope; the compositions were detected by EDS; the temperature dependence of resistivity of samples was measured using the standard four-probe method;the thermoanalysis of powder precursor was measured by STA449C General Thermoanalysis Apparatus that made from Germany. The rationality of sol-gel method was checked by analyzing thermogravimetric curve.The analysed result of TG-DSC curve shows that the sol-gel technology was reasonable. The structure of powder was studied by XRD and it shows the rhombohedral perovskite. The powder morphologies indicate that they’ll be regular and grain coarsening after sinter 4 hours at 1000℃. The average grain size of LSMO powder is increased from～50nm at 900℃to～60nm at 1000℃. The resultant powder was pressed into disks, which were then sintered at different technologies. It shows that the grain size clearly coarsed and the density increased at the higher sintered temperature or longer sintered time. The average grain size of LSMO bulk samples decrease with doped Sr content. And the current grain size of LCSMO increases slowly as doped Ce content. The structure of bulk samples were analysed by XRD. The results indicate that LSMO samples has the rhombohedral structure and LCSMO samples are composed by rhombohedral perovskite and CeO 2 . The CeO2 phase increases as doped Ce content. The samples are pure from the results of EDS.The temperature dependence of resistivity of bulk samples was measured using the standard four-probe method. It indicates that the bulk samples of LSMO and LCSMO show metal-insulator transition. When adding the content of doped Sr in LSMO samples that sintered 4 hours at 1000℃, the T MI first rise and then fall. The T MI of composite La 0.7 Sr 0.3 MnO3 comes to maximal value （269K）. The resistivity reduces as the content of doped Sr. The curve between temperature and resistivity of LCSMO that sintered at 1000℃for 4 hours indicate that the TMI decreases distinctly when adding the content of doped Ce , from 248K （La 0.67 Sr 0.33 MnO 3 ） to 133K(La_0.57Ce_0.2Sr_0.33MnO₃).The samples of LSMO （x=0.3, 0.33,0.4） and LCSMO （x=0.1） were carried on different sinter technologies, the results show that the TMI increasing and the resistivity decreasing as the sinter temperature improved. The TMI of bulk samples is above room temperature when sintered at 1200℃. The T MI of La_0.57Ce_0.2Sr_0.33MnO₃ sintered 8 hours at 1100℃is 27℃.更多还原