2 research outputs found
Melting of Pb Charge Glass and Simultaneous PbāCr Charge Transfer in PbCrO<sub>3</sub> as the Origin of Volume Collapse
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 PbCrO<sub>3</sub>, which has been known for
almost 50 years, without any obvious inhomogeneity or triangular arrangement
in the charge system. PbCrO<sub>3</sub> has a valence state of Pb<sup>2+</sup><sub>0.5</sub>Pb<sup>4+</sup><sub>0.5</sub>Cr<sup>3+</sup>O<sub>3</sub> with Pb<sup>2+</sup>āPb<sup>4+</sup> correlation
length of three lattice-spacings at ambient condition. A pressure
induced melting of charge glass and simultaneous PbāCr charge
transfer causes an insulator to metal transition and ā¼10% volume
collapse
AāSite and BāSite Charge Orderings in an <i>sād</i> Level Controlled Perovskite Oxide PbCoO<sub>3</sub>
Perovskite PbCoO<sub>3</sub> synthesized
at 12 GPa was found to have an unusual charge distribution of Pb<sup>2+</sup>Pb<sup>4+</sup><sub>3</sub>Co<sup>2+</sup><sub>2</sub>Co<sup>3+</sup><sub>2</sub>O<sub>12</sub> with charge orderings in both
the A and B sites of perovskite ABO<sub>3</sub>. Comprehensive studies
using density functional theory (DFT) calculation, electron diffraction
(ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction
(NPD), hard X-ray photoemission spectroscopy (HAXPES), soft X-ray
absorption spectroscopy (XAS), and measurements of specific heat as
well as magnetic and electrical properties provide evidence of lead
ion and cobalt ion charge ordering leading to Pb<sup>2+</sup>Pb<sup>4+</sup><sub>3</sub>Co<sup>2+</sup><sub>2</sub>Co<sup>3+</sup><sub>2</sub>O<sub>12</sub> quadruple perovskite structure. It is shown
that the average valence distribution of Pb<sup>3.5+</sup>Co<sup>2.5+</sup>O<sub>3</sub> between Pb<sup>3+</sup>Cr<sup>3+</sup>O<sub>3</sub> and Pb<sup>4+</sup>Ni<sup>2+</sup>O<sub>3</sub> can be stabilized
by tuning the energy levels of Pb 6<i>s</i> and transition
metal 3<i>d</i> orbitals