Unravelling a new many-body large-hole polaron in a transition metal oxide that promotes high photocatalytic activity

A many-body large polaron, which is important for both fundamental physics and technological applications, has been predicted to occur in bismuth vanadate (BiVO₄). Herein, using a combination of high-resolution spectroscopic ellipsometry, X-ray absorption spectroscopy at the V L3,2 and O K-edges, and high-resolution X-ray diffraction supported by theoretical calculations, we reveal a new many-body large-hole polaron in W-doped BiVO₄ films and the interplay of the large-hole polaron and indirect bandgap when determining the photocatalytic activity. With various W doping concentrations and temperatures, anomalous spectral weight transfers in the complex dielectric function are observed, revealing electronic correlations, particularly the on-site Coulomb interactions of Op (Upp) and Vd (Udd), and screening in BiVO₄. Due to the distortion of BiO₆ dodecahedra and Udd, Bi 6s is lifted to the top of the valence band, which results in the formation of an indirect bandgap and a large-hole polaron. The large-hole polaron is found to form as a localized midgap state, consisting of O p hybridized with the V d and Bi sp orbitals, and this is important when determining the high photocatalytic activity of BiVO₄. Our results show the importance of the interplay among the charge, orbital, and lattice degrees of freedom in forming the many-body large-hole polaron, which improves the conductivity and results in a transition metal oxide with high photocatalytic activity.

Xiao Chi, Lily Mandal, Cuibo Liu, Angga Dito Fauzi, Anindita Chaudhuri, Thomas J. Whitcher, Hariom Kirit Jani, Zhongxin Chen, Shibo Xi, Caozheng Diao, Muhammad Avicenna Naradipa, Xiaojiang Yu, Ping Yang, Antonio Helio Castro-Neto, Mark B. H. Breese, Kian Ping Loh, Thirumalai Venky Venkatesan, Andrivo Rusydi