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Synthesis and Water Adsorption Properties of Perovskite-type Oxides Containing Manganese

含锰钙钛矿型氧化物的合成及吸水性能

基本信息

批准号：
63470062
负责人：
NAGAO Mahiko
金额：
$ 3.9万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

Perovskite-type (Ln_<1-x>Ca_x)MnO_3 (Ln: La, Nd, Gd) were synthesized at 1300-1350ﾟC in the flow of pure oxygen gas. X-ray powder diffraction patterns of these manganates were indexed as the perovskite-type structure. At low temperature, manganates are n-type semiconductors and the electrical resistivity follows Mott's T^<-1/4> law, indicating the possible occurrence of variable range hopping of electron due to Anderson localization. Above room temperature, manganates have positive temperature coefficient, and exhibit a metal-insulator transition without any crystallographic change. The magnetic susceptibility measurement suggests that spin state of Mn^<3+> ions change from low to high at the metal-insulator transition temperature. From these results, it is considered that the metal-insulator transition is caused by a change in the spin state of Mn^<3+> ion in (Ln_<1-X> Ca_X)MnO_3.Fine particle (La^<1-x> Ca_x)MnO_3 was synthesized as follows: one is the decomposition of the precursor a … More nd the other is the solid state reaction by using acetates. The precursor was prepared from the co-precipitation method and its formula was found to be (Ca_<0.5> Mn_<0.5>)CO_3.Fine particle (La_<1-X> Ca_X)MnO_3 was synthesized as follows: one is the decomposition of the precursor and the other is the solid state reaction by using acetated. The precursor was prepared from the co-precipitation method and its formula was found to be (Ca_<0.5> Mn_<0.5>)CO_3. Firing this precursor at 950ﾟC, CaMnO_3 was obtained. On the other hand, acetates were weighted and mixed, then fired at 900ﾟC. The particle size of manganates thus obtained was 0.8-0.9 m, and the specific surface area was 3-5 m^2/g. By using these methods, the synthesis temperature of (La_<1-x> Ca_x)MnO_3 was lowered by 300-400ﾟC compared with the conventional solid state reaction.The electrical resistivity of (La_<1-x> Ca_x)MnO_3 under various relative pressure of H_2O vapor was measured. Only the electrical resistivity of CaMnO_3 decreased with increasing vapor pressure of H_2O, and this decrease was assumed to be ascribed to the ionic conductivity of water layer adsorbed on CaMnO_3. Less

在<1-x>1300-1350 ℃纯氧气气氛下合成了钙钛矿型（Ln_ Ca_x）MnO_3（Ln：La，Nd，Gd）。这些锰酸盐的X射线粉末衍射图被索引为钙钛矿型结构。在低温下，锰氧化物为n型半导体，电阻率服从Mott T^<-1/4>定律，表明可能存在由安德森局域化引起的电子变程跳跃。在室温以上，锰酸盐具有正温度系数，并且表现出金属-绝缘体转变而没有任何晶体学变化。磁化率测量表明，在金属-绝缘体转变温度下，Mn^<3+>离子的自旋态由低到高发生变化。根据这些结果，我们认为金属-绝缘体转变是由于（Ln_Ca_x）MnO_3中Mn^<3+>离子的自旋态发生变化而引起<1-X><1-x>的。 ...更多信息另一种是利用醋酸盐的固相反应。采用共沉淀法制备了前驱体，其化学式为（Ca_<0.5>Mn_<0.5>）CO_3。采用<1-X>前驱体分解法和醋酸盐固相反应法合成了（La_ Ca_X）MnO_3。采用共沉淀法制备了前驱体，其化学式为（Ca_<0.5>Mn_<0.5>）CO_3。在950 ℃下焙烧得到CaMnO_3。另一方面，将乙酸盐称重并混合，然后在900 ° C下烧制。由此获得的锰酸盐的粒径为0.8-0.9 μ m，比表面积为3-5 m^2/g。用这些方法合成的（La_<1-x>Ca_x）MnO_3的温度比传统的固相反应降低了300-400 ℃，并测量了（La_<1-x>Ca_x）MnO_3在不同水蒸气相对压力下的电阻率。只有CaMnO_3的电阻率随着H_2O蒸气压的增加而下降，这种下降被认为是由于CaMnO_3上吸附的水层的离子导电性造成的。少