La_(0.67)Ca_(0.33-0.5x)Li_xMnO_3多晶陶瓷结构及电学性能研究  

Structure and Electrical Properties of La_(0.67)Ca_(0.33-0.5x)Li_xMnO_3 Polycrystalline Ceramic

作　　者：李迪 陈清明[1] 陈晓慧 李之昱 张亚林 张辉[1] LI Di;CHEN Qingming;CHEN Xiaohui;LI Zhiyu;ZHANG Yalin;ZHANG Hui(College of Materials Science and Engineering,Kunming University of Science and Technology,Kunming 690093)

机构地区：[1]昆明理工大学材料科学与工程学院,昆明650093

出　　处：《材料导报》2018年第2期184-188,共5页Materials Reports

基　　金：国家自然科学基金(11564021)

摘　　要：用溶胶-凝胶法制备La_(0.67)Ca_(0.33-0.5x)Li_xMnO_3(x=0.00,0.05,0.10,0.20)多晶陶瓷,用XRD分析多晶陶瓷的晶体结构,用SEM对多晶陶瓷的微观形貌进行分析,用标准四探针法测量电阻率-温度关系。结果表明,随着Li掺杂量的增加,所有样品均为斜方晶系,晶胞体积不断减小,金属-绝缘体转变温度(TP)降低,电阻率不断增加,电阻率温度系数(TCR)不断减小。低温区域(T<TP)的电阻率数据可以用ρ(T)=ρ0+ρ_2T^2+ρ_(4.5)T^(4.5)进行拟合;高温区域(T>TP)的电阻率数据可以用小极化子跃迁(SPH)模型和变程跳跃(VRH)模型进行拟合。整个温度区域(100~300K)可以使用渗透模型对电阻率进行拟合。从拟合数据可知极化子激活能Ea随Li掺杂量的增加而增大,这是由于Li的加入减小了Mn^(3+)-O^(2-)-Mn^(4+)的键角,增大了有效带宽的间隙,因此也减弱了双交换作用,增大了电阻率。A series of La 0.67 Ca 0.33-0.5 x Li x MnO 3 ceramic(x=0.00,0.05,0.10,0.15,0.20)were prepared by sol-gel technique.The crystal structures were analyzed by X-ray diffraction(XRD),the surface morphology and grain boundaries were investigated by scanning electron microscope(SEM),and the temperature dependence of the resistivity(R-T)of the bulk samples were studied by the standard four-probe method.It can be indexed with an orthorhombic structure for all of La 0.67 Ca 0.33-0.5 x Li x MnO 3 polycrystalline ceramics.The results showed that with the increase of the content of Li element,the unit cell volume decrease and the resistance increases.The insulator-metal transition temperature T P shifts to lower temperature and the temperature coefficient of resistivity(TCR)decrease continually.The data of resistivity on low-temperature(T<T P)have been fitted with the relationρ(T)=ρ0+ρ2T 2+ρ4.5 T 4.5,the high-temperature(T>T P)resistivity data were explained using small-polaron hopping(SPH)and variable-range hopping(VRH)models.The resistivity data in whole temperature range(100-300 K)can be fitted by percolation model.Polaron activation energy E a is found to increases with increasing the contant of Li(x),which suggests that Li doping decrease bond angle of Mn 3+-O 2--Mn 4+,thereby the increase of effective band gap and the decrease of double exchange coupling,this is the reason of the increase of resistivity.

关 键 词：LA0.67 Ca0.33-0.5x Lix MnO3多晶 电阻率拟合 金属-绝缘体转变 

分 类 号：TQ174[化学工程—陶瓷工业]