Tran Thanh Trung

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Bi1-xLaxNiO3????????X?????
12pRB-3

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Physical properties of RNiO3
RNiO3 typical bandwidth-controlled
metal-insulator transition system
tolerance factor t
R La paramagnetic metal R Pr, Nd TMI TN
R Sm, TMI gt TN
J. B. Torrance et al., PRB 45, 8209 (1992).
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Physical properties of BiNiO3
Electrical resitivity
Magnetic susceptibility
S 1
Insulating behavior
BiNiO3 A-site (Bi) charge disproportionationr(B
i3) gt r(La3) ? metallic ? No!
S. Ishiwata et al., J. Mater. Chem. 12, 3733
(2002).
Bi31/2Bi51/2Ni2O3 Ni2 (S 1) Bi3Ni3O3
Ni3 (S 1/2)
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Physical properties of Bi1-xLaxNiO3
Electrical resistivities
x 0 ? insulating x 0.05, 0.1 ? jump of
resistivity (broad hysterisis) x 0.2, 0.5 ?
metallic

• Suppression of charge disproportionation at Bi
  site
• Ni2 (BiNiO3) ? Ni3 (LaNiO3)

From XAS and XPS
Composition dependence Valances of Ni and
Bi Valance band
S. Ishiwata et al., submitted to PRB.
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Experimental

• Polycrystals of Bi1-xLaxNiO3 (x 0, 0.05, 0.1,
  0.2, 0.5)
• Photon Factory (PF) BL-2C with SCIENTA SES-100
  analyzer
• hn 600 1100 eV
• DE 200 600 meV
• T R. T.
• SCIENTA SES-100 analyzer
• hn 21.2 eV (He I), 40.8 eV (He II)
• DE 10 meV (He I), 50 meV (He II)
• scraping in situ

XPS XAS
Photon Factory (PF)
UPS
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Core levels
O 1s Single peak ? clean surface Ni 2p Almost
no composition dependence. Bi 4f O 1s shift
of binding energy ? change in average valence
of Bi ?
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Shifts of core levels
Difference of binding energies of O1s and Bi 4f
higher valence
lower valence
O 1s - Bi 4f valence of Bi 0 x 0.1
Average valence of Bi remains almost constant
(average 4). x 0.2 Valance of Bi
increases. ? Holes are doped into Bi site.
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Ni 2p XAS
B
A
Ni3
Ni2
M. Medarde et al., PRB 46, 14975 (1992).
x 0 similar to NiO ? Ni2 x gt 0
combination of Ni2 and Ni3 (gradual increase of
the valence of Ni) Even at x 0.5, considerable
amount of Ni2 exists.
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Valence of Ni
Estimation of the valences of Ni and Bi
After subtraction of La 3d5/2
Ni
Bi
0 x 0.1 Valence of Ni remains almost 2.
x 0.2 Amount of Ni3 gradually
increases. (Holes are doped into Bi site,
too.) La doping donates holes to this system.
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Valence band
Valence band
Near EF
Three structures (A - C) and satellite
structure. The intensity at EF increases with
increasing x. ? Fermi edge at x 0.05.
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Valence band (hn dependence)
PrNiO3
T. Mizokawa et al., PRB 52, 13865 (1995).
Photoionization cross section (J. J. Yeh and I.
Lindau)
Three structures (A - C) were observed. A ? -1.6
-1.7 eV, B ? -3.2 -3.3 eV, C ? -6 eV A Ni
3d dominant, C O 2p dominant ? consistent with
other Ni oxides (e.g. PrNiO3)
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Summary

• We measured photoemission and x-ray absorption
  spectra of
• Bi1-xLaxNiO3 polycrystals.

Valences of Ni and Bi

• The valence of Ni increases with x, but
  considerable amount of Ni2 exists even at x
  0.5.
• The average valence of Bi increases at x 0.2.

Increasing metallicity
Valence band

• Three structures (A - C) were observed in the
  valence band.
• Fermi edges were observed at x 0.05.

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O 1s XAS
M. Medarde et al., PRB 46, 14975 (1992).