CRYSTAL GROWTH AND ELECTRONIC STATES OF CaB_2C_2

CaB_2C_2 的晶体生长和电子态

• 批准号: 13640358
• 负责人: SUZUKI Kazuya
• 金额: $ 2.3万
• 依托单位: YOKOHAMA NATIONAL UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640358/
• 关键词: HIGH TEMPERATURE FERRQMAGNETISM; BOROCARBIDES; CRYSTAL GROWTH; CRYSTAL STRUCTURE; OPTICAL REFLECTIVITY; HIGH TEMPERATURE FERRQMAGNETISM; BOROCARBIDES; CRYSTAL GROWTH; CRYSTAL STRUCTURE; OPTICAL REFLECTIVITY

Since the discovery of high-temperature ferromagnetism in La-doped CaB_6, the electronic states of this series of borides have been studied very extensively. In order to elucidate the mechanism of the high-temperature ferromagnetism, it is very important to study the electronic structure of the analogous compounds CaB_2C_2.We have succeeded in preparing single crystals of CaB_2C_2 using self-flux method. At the first stage of this study, we found spontaneous magnetization developing below 600 K and 450 K, however, by removing contaminations of the ferromagnetic impurities, the susceptibility of CaB_2C_2 becomes diamagnetic. We performed structure analyzes on powders and single crystals by X-ray and neutron diffraction method, respectively. The structure is determined as follows ; tetragonal I4/mcm (140), a=5.367A, c=7.398A, V=213.1A^3 Z=4. In the four-membered rings in boron-carbon network, the bond angle BCB is smaller than that of CBC so the four-membered rings are distorted as the boron-boron distance becomes closer. This result indicates the Semiconducting behavior in CaB_2C_2 in consideration of the band structure of this compound with the I4/mcm structure. We also measured the optical reflectivity of CaB_2C_2 and found that this compound is a semiconductor with very narrow band gap.

自从在LA掺杂的CAB_6中发现高温铁磁性以来，已经对这一系列硼化物的电子状态进行了广泛的研究。为了阐明高温铁磁学的机制，研究类似化合物的电子结构CAB_2C_2.我们成功地使用self-flux方法来准备CAB_2C_2的单晶。在这项研究的第一阶段，我们发现自发性磁化强化在600 K和450 K以下的发展，但是，通过消除铁磁杂质的污染，CAB_2C_2的易感性变为磁性。我们分别通过X射线和中子衍射法对粉末和单晶进行了结构分析。结构被确定为如下；四方I4/MCM（140），A = 5.367a，C = 7.398a，V = 213.1a^3 z = 4。在硼 - 碳网络中的四元环中，键角BCB小于CBC，因此随着硼隆距离变得更近，四元环会变形。该结果表明CAB_2C_2中的半导体行为是考虑到该化合物的带有I4/MCM结构的频带结构的。我们还测量了CAB_2C_2的光学反射率，并发现该化合物是具有非常狭窄的带隙的半导体。