Impeding conduction by breaking the charge carrier hopping in charge-ordered perovskite BaBiO3 (BaBi0.53+Bi0.55+O3): Experimental and theoretical electronic structural correlations

$\text{BaBi}{O}_3$ (BBO), a charge-ordered perovskite with mixed-valent states of Bi (Bi³⁺ and Bi⁵⁺), is known for its charge density wave (CDW) semiconducting and topological insulating properties. BBO has been extensively investigated for its superconducting, electrical, and photocatalytic properties. The present study aims to understand the alterations in the CDW and electronic properties of $\text{Ba}{\text{Bi}}_{0.5}^{3+}{\text{Bi}}_{0.5}^{5+}{O}_3$ by valence-selective substitution of Bi³⁺ and Bi⁵⁺ with La³⁺ and Nb⁵⁺, respectively, in the solid solutions $\text{Ba}{\text{Bi}}_{0.5-x}^{3+}{{\text{La}}_x\text{Bi}}_{0.5}^{5+}{O}_3$ and $\text{Ba}{\text{Bi}}_{0.5}^{3+}{\text{Bi}}_{0.5-y}^{5+}{\text{Nb}}_y{O}_3$ (x = y = 0.0, 0.1, 0.3, and 0.5). The samples synthesized via high-temperature solid-state reaction method were characterized by powder X-ray diffraction and various spectroscopic techniques (FT-IR, Laser Raman, EPR, XPS, and UPS). Impedance analysis revealed an upsurge in total impedance with the substitution of Bi³⁺/Bi⁵⁺ by La³⁺/Nb⁵⁺ indicating the blocking of electron/hole hopping by disruption of the charge ordering of redox pair Bi³⁺ and Bi⁵⁺. The valence-selective substitution of Bi³⁺/Bi⁵⁺ in BaBiO₃ resulted in an alteration of the electronic structure and changes in the bandwidth of $\text{Ba}{\text{Bi}}_{0.5-x}^{3+}{{\text{La}}_x\text{Bi}}_{0.5}^{5+}{O}_3$ and $\text{Ba}{\text{Bi}}_{0.5}^{3+}{\text{Bi}}_{0.5-y}^{5+}{\text{Nb}}_y{O}_3$ (x = y = 0.0, 0.1, 0.3, and 0.5) solid solutions, which were confirmed by both theoretical density of states (DOS) calculations and experimental ultraviolet photoelectron spectroscopic (UPS) studies.