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Title: Composition-Controlled Metal-Nonmetal Transition in La2-xSrxNiO4-δ
Authors: Liu, Chia-Jyi;Mays, M. D.;Cowan, D. O.;Sanchez, M. G.
Contributors: 物理學系
Date: 1991-05
Issue Date: 2012-09-10T06:11:01Z
Publisher: American Chemical Society
Abstract: Materials with the general composition La2,Sr,Ni04-l retain the perovskite-related structure of space
group Nlmmm up to x = 1.50. They undergo a composition-dependent metal-nonmetal transition in
electrical conductivity. The composition parameters x and 6 determine the conductivity type. For x <
1 the materials are nonmetals. For x > 1.1 metallic conductivity is observed that persists to a limit of
at least x = 1.50 if the oxygen deficiency 6 is low. For compositions near the transition the conductivity
type is also dependent on 6. Metallic samples become nonmetals upon heating in flowing Ar at 1000 "C,
which revert to metals upon oxidation in O2 also at 1000 "C. All nonmetal-to-metal transitions are
accompanied by a change in color from black to reddish brown. The Ni average valence u was determined
from the metals composition and iodometric titration data. The 6 value was calculated from u by using
the equation 6 = 0.5~+ (1 - 0.5u), which was derived by using a formal valence convention. Both v and
6 increase monotonically with x in the range 0 5 x I 1.5. A phase diagram is proposed for the metal-nonmetal
transition in which the boundary is given by 6 = 0.5~- 0.51, which corresponds to u i= 3.02. No stoichiometric
214 nickelate (6 = 0) could be prepared in the metallic region, and no superconductive transition was observed
in any material down to -3 K.
Relation: Chemistry of Materials, 3(3): 495-500
Appears in Collections:[物理學系] 期刊論文

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