ORALS
SESSION:
SolidStateChemistryTuePM2-R4
| Poeppelmeier International Symposium(3rd Intl Symp on Solid State Chemistry for Applications & Sustainable Development) |
| Tue. 28 Nov. 2023 / Room: Dreams 4 | |
| Session Chairs: Alexander Norquist; Session Monitor: TBA |
16:50: [SolidStateChemistryTuePM211] OS
SYSTEMATIC CHARGE DISTRIBUTION CHANGES IN BI, PB-3D TRANSITION METAL PEROVSKITE OXIDES Masaki Azuma1 ;
1Tokyo Inst. of Technology, Yokohama, Japan;
Paper Id: 512
[Abstract] Bismuth and lead are main group elements, but these have charge degree of freedom stemming from 6s2 (Bi3+ and Pb2+) and 6s0 (Bi5+ and Pb4+) electronic configurations. Stereochemical 6s2 lone pairs of Bi3+ and Pb2+ induce polar distortions as typically observed in PbTiO3 and BiFeO3. These are coupled with charge variation and magnetism of transition metals resulting in various functionalities. From left to right in the periodic table, BiCrO3 to BiCoO3 are all Bi3+M3+O3. However, BiNiO3 has an unusual Bi3+0.5Bi5+0.5Ni2+O3 charge distribution. An intermetallic charge transfer between Bi5+ and Ni2+ takes place under pressure leading to the Bi3+Ni3+O3 high-pressure phase. BiNiO3 decomposes on heating at 500 K, but La substitution for Bi or Fe substitution for Ni destabilizes the Bi charge disproportionation and (Bi,La)3+(Ni,Fe)3+O3 appears on heating at an ambient pressure. Because of the contraction of Ni-O bond owing to the oxidation of Ni2+ to Ni3+, negative thermal expansion, shrinkage of volume on heating, is observed.Similar charge distribution changes are observed three times in PbMO3. PbVO3 is Pb2+V4+O3 like Pb2+Ti4+O3, but PbCrO3, PbMnO3 and PbFeO3 were found to be Pb2+0.5Pb4+0.5M3+O3. PbCoO3 has turned out to be Pb2+Pb4+3Co2+2Co3+2O12. PbNiO3 has a valence distribution of Pb4+Ni2+O3. Namely, PbMO3 changes from Pb2+M4+O3 to Pb2+0.5Pb4+0.5Cr3+O3 (average valence state of Pb3+M3+O3) to Pb2+0.25Pb4+0.75Co2+0.5Co3+0.5O3 (Pb3.5+Co2.5+O3) and to Pb4+M4+O3 according to the order in the periodic table and the depth of d level.Among these compounds, BiCoO3 and PbVO3 have PbTiO3-type polar structures with enhanced c/a ratios exceeding 1.2 because of the stereochemical activities of 6s2 one pairs of Bi3+ and Pb2+ and dxy orbital ordering of Co3+ and V4+. Giant negative thermal expansions in PbVO3 derivatives will also be discussed.
References:
[1] M. Azuma et al., Annu. Rev. Mater. Res., 51, 329 (2021).
SESSION:
SolidStateChemistryWedPM1-R4
| Poeppelmeier International Symposium(3rd Intl Symp on Solid State Chemistry for Applications & Sustainable Development) |
| Wed. 29 Nov. 2023 / Room: Dreams 4 | |
| Session Chairs: Paul Salvador; Session Monitor: TBA |
14:30: [SolidStateChemistryWedPM106] OS
UNUSUAL CHARGE DISTRIBUTION AND PHYSICAL PROPERTIES INDUCED BY BI,PB 6S ELECTRONS Takumi Nishikubo
1 ; Yuki Sakai
1 ;
Masaki Azuma2 ;
1Kanagawa Institute of Industrial Science and Technology, Ebina, Japan;
2Tokyo Inst. of Technology, Yokohama, Japan;
Paper Id: 150
[Abstract] Bi and Pb have a unique 6s0 and 6s2 electron configuration that creates charge degrees of freedom. Due to the lack of this 6s1 electron configuration, a property called valence skipper, Bi takes 3+ and 5+ and Pb takes 2+ and 4+. In particular, for perovskite compounds containing Bi or Pb at the A site, the valence state changes according to the depth of the d-orbitals of the transition metal ions corresponding to the order in the periodic table of the elements due to the close relationship between the 6s level of Pb or Bi and the 3d level of the 3d transition metal ions. For BiMO3, M= Cr, Mn, Fe, Co, the state is Bi3+M3+O3, while BiNiO3 has a specific valence state of Bi3+0.5Bi5+0.5Ni2+O3. PbMO3 has Pb2+0.5Pb4+0.5MO3 for M= Ti and V, Pb2+0.5Pb4+0.5M3+O3 for M= Cr and Fe, PbCoO3 has Pb2+0.25Pb4+0.75Co2+0.5Co3+0.5O3, PbNiO3 has Pb4+Ni2+O3. In BiNiO3 and PbMO3 (M = Cr, Fe and Co), Bi and Pb become charge disproportionated in the 6s0 and 6s2 states, and temperature- and pressure-induced elimination of charge disproportionation and charge transfer phase transitions occur. These charge transfer phase transition causes leads to unique physical properties such as negative thermal expansion.
