RELATION BETWEEN STRUCTURE AND DOPING IN LA2-XSRXCUO4+DELTA - A NEUTRON-DIFFRACTION STUDY ON SINGLE-CRYSTALS
RELATION BETWEEN STRUCTURE AND DOPING IN LA2-XSRXCUO4+DELTA - A NEUTRON-DIFFRACTION STUDY ON SINGLE-CRYSTALS
复制标题
DOI：
10.1016/0921-4534(94)91284-x
复制
发表时间：
1994-04-10
期刊：
影响因子：
1.7
通讯作者：
KOJIMA, H
中科院分区：
文献类型：
--
作者：
BRADEN, M;SCHWEISS, P;KOJIMA, H
本文报道了La2-xSrCuO4+ δ单晶在540 ~ 22 K温度下的中子衍射实验结果。la9多面体的尺寸与CuO6八面体的尺寸存在内在的不匹配，这似乎导致了从高温四方相（HTT）到低温正交相（LTO）的结构转变。在这个不适合的模型中，可以解释http - lto跃迁的几乎整个现象。电子结构通过Cu-O键的长度与相变有关。转变对结构的影响之一是延长了这些Cu-O键，从而改变了电子能带结构。通过掺杂引入的额外电荷导致平衡Cu-O距离的减小，从而减少了错配。这样，载流子浓度决定了结构转变。我们总是观察到强各向异性的热参数，这证实了La2-xSrCuO4结构在CuO6八面体绕任何轴旋转时的不稳定性。在未掺杂晶体（x=0.0）的情况下，我们发现实验均方位移与基于已知声子色散曲线的晶格动力学模型的结果之间有很好的一致性。在掺杂（x=0.13）和超导晶体中，与结构转变相关的非调和效应导致热参数的温度依赖性发生显著变化。
We present the results of neutron-diffraction experiments on a series of La2-xSrCuO4+delta single crystals at temperatures between 540 K and 22 K. There is an intrinsic misfit between the size of the LaO9 polyhedra and the CuO6 octahedra, which seems to cause the structural transition from the high-temperature tetragonal (HTT) to the low-temperature orthorhombic (LTO) phase. Within this misfit model it is possible to explain almost the entire phenomenology of the HTT-LTO transition. The electronic structure is related to this phase transition via the length of the Cu-O bonds. One of the effects of the transition on the structure is to lengthen these Cu-O bonds and hence to alter the electronic band structure. The introduction of additional charge by doping leads to a decrease of the equilibrium Cu-O distances, and hence to a reduction of the misfit. In this way the, charge-carrier concentration determines the structural transition. We always observe strongly anisotropic thermal parameters, which confirm the instability of the La2-xSrCuO4 structure against a rotation of the CuO6 octahedra around any axis. In the case of an undoped crystal (x=0.0), we find a good agreement between the experimental mean square displacements and the results of a lattice dynamics model which is based on the known phonon dispersion curves. In a doped (x=0.13) and superconducting crystal, the anharmonic effects related to the structural transition lead to significant changes in the temperature dependence of the thermal parameters.