【作者】 唐奡男； 杨洋； 汪伟； 郑仁奎； 李广； 李晓光； 魏建宁； 水嘉鹏；

【Author】 TANG Aonan YANG Yang WANG Wei ZHENG Renkui LI Guang LI Xiaoguang Structure Research Laboratory,Department of Materials Science and Engineering,University of Science and Technology of China,Hefei 230026 WEI Jianning,SHUI diapeng Key Laboratory of Materials Physics,Institute of Solid State Physics,The Chinese Academy of Sciences,Hefei 230031

【机构】 中国科学技术大学材料科学与工程系结构分析重点实验室； 中国科学院固体物理研究所材料物理重点实验室；

【摘要】 运用 X 射线衍射和内耗测量技术研究了 La_1-xCa_xMnO₃（0．50≤x≤0．85）在电荷有序态下的合作 Jahn-Teller 晶格畸变．随着温度从高温降至电荷有序相变温度 T_CO,切变模量出现明显软化．在 T＜T_CO时,由于合作 Jahn-Teller 晶格畸变的形成导致切变模量出现大的硬化,而切变模量的相对硬化程度ΔG/G 随 Ca²⁺离子掺杂量的变化而变化,反映了电荷有序态下的合作 Jahn-Teller 晶格畸变的大小随 Ca²⁺离子掺杂量的变化而变化,ΔG/G 在 x=0．75时达到最大值．内耗研究表明,对应于 T_CO时出现相变内耗峰,其高度随着测量频率增大而减小,峰的位置不随测量频率变化,表现出典型的结构相变特征．电荷有序相变的内耗行为与测量频率呈非线性关系,此非线性关系可以通过公式 Q_max^-1/Q_min^-1=a×f^-b进行拟合．更多还原

【Abstract】 The cooperative Jahn-Teller lattice distortion in the charge ordered（CO）state for La_1-xCa_xMnO₃（0.50≤x≤0.85）was studied using the powder XRD and the internal friction.With decreasing temperature from the high temperature to the charge ordering transition temperature Tco, the shear modulus softens conspicuously;nevertheless,when the temperature is cooled below Tco, dramatic stiffening of the shear modulus driven by the development of the cooperative Jahn-Teller distortion was observed.The relative stiffening of the shear modulus ΔG/G varies with the Ca²⁺ concentration,and reaches the largest value at x=0.75.An internal friction peak appears at T_CO, its height decreases with increasing measuring frequency and its position is frequency independent, showing a typical structural phase transition.The non-linear frequency dependence of the peak height can be fitted using the equation Q_max^-1/Q_min^-1=a×f^-b.更多还原