【摘要】 运用X射线衍射和内耗测量技术研究了La1-xCaxMnO3(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TCO,切变模量出现明显软化.在T<TCO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△G/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,△G/G在x=0.75时达到最大值.内耗研究表明,对应于TCO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Qmax-1/Qmin-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 La1-xCaxMnO3 (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 △G/G varies with the Ca2+ concentration, and reaches the largest value at x-0.75. An internal friction peak appears at TCO, 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 Qmax-1/Qmin-1=a×f-b.更多还原