Unraveling structural, electronic, and magnetic ambiguities in Pb 1−𝛿 CrO 3 with an insulating charge-transfer band structure
As a recently identified Mott system, PbCrO 3 remains largely unexplored, especially for its band structure, leading to many contentious issues on its structural, electronic, and magnetic properties. Here we present a comprehensive study of two different Pb 1−𝛿 CrO 3 (δ = 0 and 0.15) samples involving atomic deficiency prepared under pressure. By means of state-of-the-art diffraction techniques, the crystal structure of PbCrO 3 is definitively determined to adopt the pristine 𝑃𝑚$\overline{3}$𝑚 symmetry, rather than other previously misassigned structures of M2-Pm$\overline{3}$𝑚 and Pmnm. The two materials exhibit a similar charge-transfer-type insulating band structure, and the charge-transfer effect splits both Cr 2𝑝 and Pb 4𝑓 orbitals, rationalizing doublet splitting of the associated spectral lines. Nearly identical nominal cationic valence states of Cr 4+ and Pb 2+ are identified for this oxide system, hence calling into question the validity of recently proposed charge disproportionation mechanisms. In addition, Pb 0.85 CrO 3 exhibits an anomalously higher Néel temperature of ∼240 K than that of PbCrO 3 (i.e., ∼200 K), likely due to the deficiency-induced enhancements of Cr3𝑑–O2𝑝 orbital overlap and magnetic exchange. In conclusion, these findings provide much solid evidence to look into the fundamental properties of this important material system.