Re-examination of the room temperature crystal structure of ? by x-ray diffraction experiments: observation of new superlattice reflections
Re-examination of the room temperature crystal structure of ? by x-ray diffraction experiments: observation of new superlattice reflections
复制标题
重新检查室温晶体结构？
DOI：
10.1088/0953-8984/9/4/003
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
J. Akimitsu
中科院分区：
文献类型：
--
作者：
M. Hidaka;M. Hatae;I. Yamada;M. Nishi;J. Akimitsu
最近的一项电子顺磁共振 (EPR) 研究揭示了该化合物中 c 轴上的 Cu 自旋之间存在反对称交换相互作用 (Yamada I、Nishi M 和 Akimitsu J 1996 J. Phys.: Condens. Matter 8 2625)。为了允许这种相互作用，晶体结构必须在相关铜位点之间没有反转中心。然而，Vollenkle 等人针对该化合物提出的空间群 Pbmm 结构并已被接受，该结构不允许这种相互作用，因为它在 c 轴上最近邻 Cu 位点之间的中点有一个反转中心。 EPR研究中指出了这一冲突，并被认为表明该结构与Pbmm的不一致。为了找到正确的晶体结构，在室温下对样品进行了 X 射线衍射实验，这些样品的质量显着提高，因为它们是通过对浮区法生长的单晶进行退火和缓慢冷却而生产的。结果，检测到了迄今为止尚未报道的新的超晶格反射。空间群和晶胞分别确定为 和 ，其中 是 Vollenkle 等人提出的伪晶胞。新发现的结构允许上述反对称相互作用。讨论了新结构与为什么会发生导致铜自旋二聚化的结构转变的问题之间可能的联系。
A recent electron paramagnetic resonance (EPR) study of revealed the existence of an antisymmetric exchange interaction, , between Cu spins on the c-axis in this compound (Yamada I, Nishi M and Akimitsu J 1996 J. Phys.: Condens. Matter 8 2625). To allow this interaction, the crystal structure must have no inversion centre halfway between relevant Cu sites. However, the structure with the space group Pbmm , which was proposed for this compound by Vollenkle et al and has been accepted so far, does not allow this interaction because it has an inversion centre at the midpoint between nearest-neighbour Cu sites on the c-axis. This conflict was pointed out in the EPR study and was taken to indicate the inconsistency of the structure with Pbmm. To find the correct crystal structure of , x-ray diffraction experiments are performed at room temperature on samples which are markedly improved in their quality because they are produced by the annealing and slow cooling of single crystals grown by the floating-zone method. As a result, new superlattice reflections which had not been reported so far are detected. The space group and the unit cell are determined to be and , respectively, where is the pseudo-unit cell proposed by Vollenkle et al. The newly found structure allows the antisymmetric interaction mentioned above. Possible connections between the new structure and the question of why the structural transition, which brings about the dimerization of Cu spins, occurs in are discussed.