Unraveling structural, electronic, and magnetic ambiguities in Pb1-{\delta}CrO3 with an insulating charge-transfer band structure

TL;DR

This study clarifies the crystal structure and electronic properties of PbCrO3 and Pb0.85CrO3, revealing a charge-transfer insulating band structure and higher magnetic ordering temperature in the deficient sample.

Contribution

It provides definitive structural determination and electronic characterization of PbCrO3, challenging previous assumptions and exploring effects of atomic deficiency on magnetic properties.

Findings

PbCrO3 has a pristine Pm-3m symmetry, not previously misassigned structures.

Both samples exhibit a charge-transfer insulating band structure with orbital splitting.

Pb0.85CrO3 shows a higher Néel temperature (~240 K) than PbCrO3 (~200 K).

Abstract

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-{\delta}CrO3 ({\delta} = 0 and 0.15) samples with involving atomic deficiency prepared under pressure. By means of the state-of-the-art diffraction techniques, crystal structure of PbCrO3 is definitively determined to adopt the pristine Pm-3m symmetry, rather than other previously misassigned structures of M2-Pm-3m and Pmnm. The two materials exhibit a similar charge-transfer-type insulating band structure, and the charge-transfer effect splits both Cr2p and Pb4f 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. Besides, Pb0.85CrO3 exhibits an anomalously higher N\'eel temperature of ~240 K than that of PbCrO3 (i.e., ~200 K), likely due to the deficiency-induced enhancements of Cr: 3d-O:2p orbital overlap and magnetic exchange. These findings provide many solid evidences to look into the fundamental properties of this important material system.