High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.
J Phys Chem Lett. 2023 Feb 23;14(7):1762-1768. doi: 10.1021/acs.jpclett.3c00020. Epub 2023 Feb 10.
We report diffuse reflectivity measurements in InNbO, ScNbO, YNbO, and eight rare-earth niobates. A comparison with established values of the bandgap of InNbO and ScNbO shows that Tauc plot analysis gives erroneous estimates of the bandgap energy. Conversely, accurate results are obtained considering excitonic contributions using the Elliot-Toyozawa model. The bandgaps are 3.25 eV for CeNbO, 4.35 eV for LaNbO, 4.5 eV for YNbO, and 4.73-4.93 eV for SmNbO, EuNbO, GdNbO, DyNbO, HoNbO, and YbNbO. The fact that the bandgap energy is affected little by the rare-earth substitution from SmNbO to YbNbO and the fact that they have the largest bandgap are a consequence of the fact that the band structure near the Fermi level originates mainly from Nb 4d and O 2p orbitals. YNbO, CeVO, and LaNbO have smaller bandgaps because of the contribution from rare-earth atom 4d, 5d, or 4f orbitals to the states near the Fermi level.
我们报告了 InNbO、ScNbO、YNbO 和八种稀土铌酸盐的漫反射率测量结果。与 InNbO 和 ScNbO 带隙的已有值进行比较表明，Tauc 图分析给出了带隙能量的错误估计。相反，考虑到使用 Elliot-Toyozawa 模型的激子贡献，可以得到准确的结果。CeNbO 的带隙为 3.25 eV，LaNbO 的带隙为 4.35 eV，YNbO 的带隙为 4.5 eV，SmNbO、EuNbO、GdNbO、DyNbO、HoNbO 和 YbNbO 的带隙为 4.73-4.93 eV。从 SmNbO 到 YbNbO 的稀土取代对带隙能量的影响很小，并且它们具有最大的带隙，这是由于费米能级附近的能带结构主要源于 Nb 4d 和 O 2p 轨道的事实。由于来自稀土原子 4d、5d 或 4f 轨道的贡献，YNbO、CeVO 和 LaNbO 的带隙较小。
