Trends in bandgap of epitaxial A2B2O7 (A = Sn, Pb; B = Nb, Ta) films fabricated by pulsed laser deposition
Trends in bandgap of epitaxial A2B2O7 (A = Sn, Pb; B = Nb, Ta) films fabricated by pulsed laser deposition
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DOI：
10.1063/5.0089731
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发表时间：
2022-05
期刊：
影响因子：
6.1
通讯作者：
T. Fujita;H. Ito;M. Kawasaki
中科院分区：
文献类型：
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作者：
T. Fujita;H. Ito;M. Kawasaki
焦绿石氧化物A2-B2O7由于其独特的几何结构，成为凝聚态物理研究的重要领域。特别是对A位四面体亚晶格，特别是焦绿石氧化物A2 B2O7(A=SnPb2O7，B=Nb，Ta)，最近的理论研究预测，由于填充的A-n S和O-2p轨道之间的强烈杂化，将出现“准平带”结构。在这项工作中，我们建立了脉冲激光沉积Sn2Nb2O7、Sn2Ta2O7、Pb2Nb2O7和Pb2Ta2O7薄膜的生长条件，以阐明它们的光学性质。直接带隙和间接带隙的吸收边能按Sn2Nb2O7、Sn2Ta2O7、Pb2Nb2O7和Pb2Ta2O7的顺序增加。这种趋势可以通过考虑组成元素的能级来很好地解释。比较了Pb2B2O7的直接带隙和间接带隙，发现Pb2B2O7的价带比Sn2B2O7的价带色散小。我们的发现与理论预测是一致的，并暗示了这类化合物中杂化态的普遍存在。
Pyrochlore oxides A2 B2O7 have been a fruitful playground for condensed matter physics because of the unique geometry in the crystal structure. Especially focusing on the A-site tetrahedral sub-lattice, in particular, pyrochlore oxides A2 B2O7 ( A = Sn, Pb and B = Nb, Ta), recent theoretical studies predict the emergence of the “quasi-flat band” structure as a result of the strong hybridization between filled A-n s and O-2 p orbitals. In this work, we have established the growth conditions of Sn2Nb2O7, Sn2Ta2O7, Pb2Nb2O7, and Pb2Ta2O7 films by pulsed laser deposition on Y-stabilized ZrO2 (111) substrates to elucidate their optical properties. Absorption-edge energies, both for direct and indirect bandgaps, increase in the order of Sn2Nb2O7, Sn2Ta2O7, Pb2Nb2O7, and Pb2Ta2O7. This tendency can be well explained by considering the energy level of the constituent elements. A comparison of the difference between direct and indirect bandgaps reveals that Pb2 B2O7 tends to have a less dispersive valence band than Sn2 B2O7. Our findings are consistent with the theoretical predictions and are suggestive of the common existence of the hybridized states in this class of compounds.