煅烧温度对Ca1-xPrxMnO3粉体结构与导电性能的影响

Effects of calcination temperature on the structure and electrical property of Ca1-xPrxMnO3 powders

摘要:

为改善CaMnO₃粉体的导电性能,采用溶胶-凝胶自蔓延法在不同温度下合成Ca1-xPr_xMnO₃(0≤x≤0.3)粉体,并研究煅烧温度对Ca1-xPr_xMnO₃粉体结构及导电性能的影响．结果表明,随着煅烧温度的升高,电阻率呈现先降低后升高的变化趋势,且在1 000 ℃时电阻率最低．XRD分析结果表明,Ca1-xPr_xMnO₃粉体的特征衍射峰均向小角度方向偏移,且强度随着煅烧温度的升高而增强．XRD计算结果表明,Ca1-xPr_xMnO₃粉体的晶胞参数受烧结温度影响,是导致电阻率变化的原因之一,煅烧温度为1 000 ℃时,粉体的晶格畸变程度相对较大．SEM分析结果表明,Ca0.75Pr0.25MnO₃粉体的晶粒尺寸随温度的升高不断增大,合适的粒度有利于粉体电阻率的降低．在煅烧温度为1 000 ℃的Ca1-xPr_xMnO₃粉体中Mn的平均价态最低．晶界效应、粒度和Mn的价态3个因素共同作用导致了Ca1-xPr_xMnO₃粉体的电阻率随温度升高而呈现先减小后增大的变化趋势．

Abstract:

To improve the electrical properties of CaMnO₃ powders, the modified Ca1-xPr_xMnO₃(0≤x≤0.3) powders were prepared by the sol-gel auto-combustion route at different calcination temperatures and the effects of calcination temperature on the structure and electrical conductivity of the powders were characterized. It was indicated that the resistivity of modified powders represented the typical V type variation of firstly decreased and then increased with the increasing of calcination temperatures, and the resistivity was the lowest when the calcination temperature was at 1 000 ℃. The XRD analysis illustrated that with the increasing of calcination temperatures, the diffraction peaks of Ca1-xPr_xMnO₃ powders were moved to the small angles with the strengthening in intensity. The crystallography data calculated from XRD illustrated that the cell parameters which related to the resistivity of Ca1-xPr_xMnO₃ powders were affected by the calcination temperatures. When the calcination temperature was at 1 000 ℃, the crystal distortion was most distinct. The SEM analysis illustrated that the higher calcination temperature led to the larger size of grains, and the suitable grain size was good at decreasing the resistivity of Ca1-xPr_xMnO₃ powders. Moreover, the quantivalency of Mn was the lowest when the Ca1-xPr_xMnO₃ powders were calcined at 1 000 ℃. The grain boundary, grain size and the quantivalency of Mn together lead to the decreasing then increasing type variation of the resistivity of Ca1-xPr_xMnO₃ powders calcined at different temperatures.