Unraveling structural, electronic, and magnetic ambiguities in P b1-δCr O3 with an insulating charge-transfer band structure

As a recently identified Mott system, PbCrO3 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 Pb1-δCrO3 (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 PbCrO3 is definitively determined to adopt the pristine Pm3¯m symmetry, rather than other previously misassigned structures of M2-Pm3¯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 Cr4+ and Pb2+ are identified for this oxide system, hence calling into question the validity of recently proposed charge disproportionation mechanisms. In addition, Pb0.85CrO3 exhibits an anomalously higher Néel temperature of ∼240 K than that of PbCrO3 (i.e., ∼200 K), likely due to the deficiency-induced enhancements of Cr3d-O2p orbital overlap and magnetic exchange. These findings provide much solid evidence to look into the fundamental properties of this important material system.