Mero Rea Divina, Lai Chun-Hao, Du Chao-Hung, Liu Hsiang-Lin
Department of Physics, National Taiwan Normal University Taipei 11677 Taiwan
Department of Physics, Tamkang University Tamsui New Taipei City 25137 Taiwan.
RSC Adv. 2020 Nov 17;10(68):41891-41900. doi: 10.1039/d0ra08200g. eCollection 2020 Nov 11.
Copper metaborate had a unique crystal structure and exhibited noteworthy magnetic phase transitions at 21 and 10 K. The electronic structure and lattice dynamics of copper metaborate CuBO single crystals were investigated and compared with the optical properties of CuBO, to assess the boron isotope effect. The optical absorption spectrum at room temperature revealed two charge-transfer bands at approximately 4.30 and 5.21 eV with an extrapolated direct optical band gap of 3.16 ± 0.07 eV. Compared with the data on CuBO, the electronic transitions were shifted to lower energies upon the replacement of a heavier boron isotope. The band gap was also determined to be lower in CuBO. Anomalies in the temperature dependence of the optical band gap were observed below 21 K. Furthermore, 38 Raman-active phonon modes were identified in the room-temperature Raman scattering spectrum of CuBO, which were also observed in CuBO with a shift to lower frequencies. No broadening caused by isotopic changes was observed. As the temperature decreased, phonon frequencies shifted to higher wavenumbers and the linewidth decreased. Anomalous softening in the Raman peaks below 21 K was also revealed.
偏硼酸铜具有独特的晶体结构，在21K和10K时表现出显著的磁相变。对偏硼酸铜（CuBO）单晶的电子结构和晶格动力学进行了研究，并与CuBO的光学性质进行了比较，以评估硼同位素效应。室温下的光吸收光谱显示在约4.30和5.21eV处有两个电荷转移带，外推直接光学带隙为3.16±0.07eV。与CuBO的数据相比，当较重的硼同位素被取代时，电子跃迁向较低能量移动。还确定CuBO中的带隙较低。在21K以下观察到光学带隙温度依赖性的异常。此外，在CuBO的室温拉曼散射光谱中识别出38种拉曼活性声子模式，在CuBO中也观察到这些模式，且频率向低频移动。未观察到由同位素变化引起的展宽。随着温度降低，声子频率向更高波数移动，线宽减小。在21K以下的拉曼峰中也发现了异常软化现象。
