Semiconductive and semimetallic components in superconducting oxides: effect of oxidation

doi:10.1016/0022-3697(89)90412-5

Journal of Physics and Chemistry of Solids

Volume 50, Issue 2, 1989, Pages 153-161

https://doi.org/10.1016/0022-3697(89)90412-5 Get rights and content

Abstract

Some of the diverse variations of conductivities vs temperature for the superconducting oxides are described quantitatively by a single equation containing two components: a semiconductor and a semimetal coexisting as a microcomposite. Least squares resolutions of the conductivities for YBa₂Cu₃O_7−δ, YBa₂[Fe_xCu_1−x]₃O_7−δ, La_1.85Sr_0.15 CaO_4−δ, and BaPb_0.8Bi_0.2O₃ into these components give the parameters: (1) scattering exponent (0.8—3): (2) the Fermi energy (4−11 × 10⁻⁴ eV); and (3) the gap energy (0.1–2.8 · 10⁻²eV). In general, the superconducting temperature increases with increasing gap energy and scattering exponent. The resolution into the semiconductive and semimetallic components and the structures of the oxides resemble the model of composites treated by Allender, Bray and Bardeen (Phys. Rev. B7, 1020, 1975) and suggests a role for the excitation mechanism in the superconductive state and a correlation between the superconducting temperature and the ABB depth of penetration of electrons with energies in the semiconductive gap.

References (25)

A.W. Sleight et al.
Solid St. Commun.
(1975)
R.J. Thorn
J. Phys. Chem. Solids
(1987)
R.J. Thorn
J.G. Bednorz et al.
Z. Phys. B; Cond. Mat.
(1986)
M.K. Wu et al.
Phys. Rev. Lett.
(1987)
L.J. Sham et al.
E. Abraham
Phys. Rev.
(1954)
D. Pines
M. Kaveh et al.
Adv. Phys.
(1984)
N. Karl et al.
Molec. Cryst. Liq. Cryst.
(1985)
P.D. Hale et al.
J. chem. Phys.
(1985)
K. Fueki et al.

A.M. Kini et al.

Inorg. Chem.

(1987)

H. Takagi et al.

Jap. J. appl. Phys.

(1987)

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Carrier-charge measurement test for the existence of large bipolarons in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>z</inf>
1993, Physica C: Superconductivity and its applications
The carrier-charge determination method suggested by Emin in the case of large bipolarons using simultaneous Seebeck coefficient and resistivity measurements in the semiconducting parents of the high-temperature superconductors has been used in the case of YBa₂Cu₃O_z. It is shown that this method can only be applied in a limited composition range around z=6.2 and at temperatures higher than 600 K. In this range the carrier-charge is likely to be equal to one elementary charge.
The role of hydrostatic pressure in the conductivity vs temperature of κ -(BEDT-TTF)<inf>2</inf>CuN(CN)<inf>2</inf>Br
1993, Journal of Physics and Chemistry of Solids
The application of hydrostatic pressure to k-(BEDT-TTF)₂CuN(CN)₂Br causes the resistance vs temperature to change, in a systematic way, from an R(T), with a maximum, to an R(T) which increases monotonically as occurs with a metal [Sushko Yu.V., Bondarenko V.A., Petrosov R.A., Kushch N.D. and Yagubskii E. B., J. Phys. I France1, 1375 (1991)]. This systematic variation can be interpreted in terms of two models: (1) a phenomenological one in which the density of states is zero between the Fermi energy and the energy at the bottom of the valence band and is constant otherwise; and (2) the small polaron model of Holstein [Holstein T., Ann. Phys.8, 325, 342 (1959)]. The results show that the primary feature associated with the systematic variation is the chemical potential of the electron involved in chemical equilibria among mixed valent cations and anions: C^c+A^a− = C^(c−1)+A^(a−1)−.
Conductivity, chemical equilibria and small polaron in oxide superconductor: YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf>
1992, Physica C: Superconductivity and its applications
An investigation of the structures of the thermal variations of the conductivities, σ(T,δ)'s, and an examination of the chemical equilibria in YBa₂Cu₃O_7−δ indicate the existence of a small polaron in the normal state. The overall structures of σ (T),δ)'s can be analyzed in terms of delocalized and localized (thermally activated) carriers with narrow band tunneling (Fermi energy of order of 10⁻⁴ eV) and hopping (activation energy of the order of 10⁻²eV), respectively. The rapidly increasing σ(T) observed in some cases at low decreasing temperatures corresponds to the heretofore unrecognized narrow band tunneling in the small polaron theory: as a consequence of the chemical equilibria which must be recognized in any mechanism of conductivity in the normal state, thermodynamic equilibria can be associated with small polarons in which charge is transported through the time rate of change in the dipole moments. A precondition for the onset of the superconducting state is the co-existence of the two mechanisms and some relation between their two parameters such as the one derived by Allender, Bray and Bardeen (Phys. Rev. B 7 (1973) 1020). The superconducting state appears to be a bipolaronic state.
Temperature dependence of conductivity of κ(BEDTTTF)<inf>2</inf>Cu(SCN)<inf>2</inf>; Resolution into two components; Small polaron
1990, Solid State Communications
The variation of resistance with temperature of κ(BEDTTTF)₂Cu(NCS)₂ displays a maximum or a suppressed maximum near 90 K. These unusual variations can be interpreted in terms of a model which resolves the variation into metal-like and thermally activated components. The resolution suggests the applicability of the small polaron model of Böttger and Bryksin with tunneling and hopping conductivities (Hopping Conduction in Solids, VCH Verlagsgesellchaft, 1985).
Resistivity of a superconductor: A search for the origin of superconductivity
2001, Journal of Physical Chemistry B

^☆: Work performed under the auspices of the Office of Basic Energy Sciences, Division of Material Science, USDOE under contract number W-31-109-ENG-38 and contract number DE-AC02-76CH00016.

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Semiconductive and semimetallic components in superconducting oxides: effect of oxidation☆

Abstract

Solid St. Commun.

J. Phys. Chem. Solids

Z. Phys. B; Cond. Mat.

Phys. Rev. Lett.

Phys. Rev.

Adv. Phys.

Molec. Cryst. Liq. Cryst.

J. chem. Phys.

Inorg. Chem.

Jap. J. appl. Phys.