La_(0.8-x)Ca_(0.2)MnO_3钙钛矿氧化物居里温度研究

Study on Curie temperature of polycrystalline La_(0.8-x)Ca_(0.2)MnO_3 oxides

来用溶胶－凝胶法制备了系列 Ｌａ_(０．８－ｘ)Ｃａ_０．２ＭｎＯ_３钙钛矿多晶样品，用Ｘ射线衍射分析确定了样品的钙钛矿结构，用透射电子显微镜观察了样品的形貌并估算了颗粒度及粒径分布情况，用 ＰＡＲ１５５型振动样品磁强计测量了样品磁性并确定各样品的居里温度。结果表明，随焙烧温度的提高，样品的平均粒径略有增大，但居里温度的变化没有明显的规律性，对于不同温度焙烧的样品居里温度Ｔｃ随Ｌａ３＋离子空位浓度ｘ的变化表现出相似的规律性，当ｘ＞０．０３时Ｔｃ随ｘ变化不大，当ｘ＜０．０３时，Ｔｃ随ｘ的增大有明显的提高。

Series of polycrystalline La0.8-xCa0.2 MnO3 (x= 0, 0.01, 0.03, 0.05, 0.08, 0.1 ) was prepared by sol-gel method. XRD pat- terns show that all the samples are single perovskite-type phase. The average size of the particles and the size distribution were inves- tigated by TEM photograph. The magnetic properties of the samples with different magnetic field and different temperature were measured using PAR155 type vibration sample, magnetization(VSM) and the Curie temperature was then determined. The results show that with the increase of sintering temperature, the average size of the particles inereases slightly but the vary of Curie tempera- ture show no clear regulation, for the samples sintered at different temperatures, the dependence of Curie temperature on La3+ vacu- um concentration show very similar regulations. Curie temperature changes slowly with the increase of x in the range 0. 08>x>0. 03; but when x<0. 03, Curie temperature increases dramaticly with the increase of x.