Melting of Pb Charge Glass and Simultaneous Pb–Cr Charge Transfer in PbCrO₃ as the Origin of Volume Collapse

Abstract

A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. We report that the charge glass state is realized in a perovskite compound PbCrO3, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system. PbCrO3 has a valence state of Pb(2+)(0.5)Pb(4+)(0.5)Cr(3+)O3 with Pb(2+)-Pb(4+) correlation length of three lattice-spacings at ambient condition. A pressure induced melting of charge glass and simultaneous Pb-Cr charge transfer causes an insulator to metal transition and ∼10% volume collapse.

Unusual Mott transition in multiferroic PbCrO 3

“…It has come to our attention that the phase-transition mechanism of PbCrO 3 was reported by Cheng et al (29) and Yu et al (30) during the submission of this article. However, in their work, either a charge disproportionation mechanism (i.e., 3Cr 4+ = 2Cr 3+ + Cr 6+ ) or a charge transfer process between Pb and Cr were proposed for α-PbCrO 3 based on a distorted cubic structure (29) or a low-symmetry orthorhombic structure (30). Such proposed structures would lead to the presence of 100 peak in neutron diffraction patterns, which is contrary to our experimental observations (Fig.…”

Charge Disproportionation, Mixed Valence, and Janus Effect in Multiorbital Systems: A Tale of Two Insulators

“…Note that Eq. (20) ensures that all the g(E Γ ) components of a given multiplet with energy E Γ have the same probability |Φ(E Γ )| 2 , ruling out any possible spin or orbital ordering. Here, g(E Γ ) = g(n, L, S) = (2L + 1)(2S + 1)…”

Valence State of Pb in Transition Metal Perovskites PbTMO3 (TM = Ti, Ni) Determined From X‐Ray Absorption Near‐Edge Spectroscopy

“…Starting from the left end of the periodic table, PbTiO 3 is expected to have charge state Pb 2+ /Ti 4+ , while to the right end, PbNiO 3 is expected to have the Pb 4+ /Ni 2+ charge state . In between, for TM = Cr, Fe and Co a mixed valence state 6s 2 (Pb 2+ )/6s 0 (Pb 4+ ) has been inferred from the valence determination on the TM ions or the Pb core‐level X‐ray photoemission spectroscopy . PbMnO 3 (P4 mmm −1 ) is special with the claim of Pb 2+ Mn 4+ O 3 (6s 2 ), which requires further confirmation with spectroscopic methods.…”