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1.
In an investigation of the resistivity anisotropy of YBa2Cu3O7−x
single crystals with suboptimal oxygen content it is observed that the superconducting transition for the component ρc of the resistivity tensor is shifted to lower temperatures with respect to the transition for the component ρab. A similar shift is also observed for the transition in the temperature dependence of the dynamic magnetic susceptibility.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 309–313 (25 August 1998) 相似文献
2.
Naiping Zhu Longjiang Zhou Yansheng Zhang Tiefan Li Guiwen Qiao Changxu Shi 《Zeitschrift für Physik B Condensed Matter》1988,70(4):409-411
Systematic TGA (Thermogravimetric analysis), magnetic susceptibility measurements and X-ray diffraction investigations have been made on the temperature dependence of oxygen content and phase transition in Y1Ba2Cu3O9–x
compounds. The experimental results show that reversible oxygen relief and absorption appeared during heating and cooling in the temperature range of 400–950°C. A low cooling rate leads to higher oxygen content and quenching can suppress oxygen absorption. The deoxidation process is accompanied by a change of the cell constants,a andb increase whilec decreases with reduced oxygen content while the phase transition from the ortorhombic to the tetragonal system appeares. Nevertheless, this transition is a gradually changing process, no critical point of transition exists. Quenching stress and defects have a pronounced influence on the absorption and relief of oxygen. Maximum rates of oxygen relief and absorption were obtained at about 650°C. Oxygen absorption and desorption can be obtained only in an athermal process. Magnetic susceptibility measurements show that diamagnetic and paramagnetic suceptibilities increase obviously with increasing oxygen content. Deoxidation and oxygen absorption can be restrained by adding Fe to the Y1Ba2Cu3O9–x
phase, which suggests that deoxidation and oxygen absorption are very sensitive to crystal structure and lattice distortions. 相似文献
3.
Positron lifetime and Doppler broadened annihilation radiation lineshape measurements have been carried out in Y1Ba2Cu3O7−x
as a function of temperature in the range of 300 K to 58 K. The positron lifetime and the peak parameter of the annihilation
radiation lineshape are observed to decrease on lowering the temperature without showing any discontinuous change across the
superconducting transition temperature of 90 K as determined by susceptibility measurements. The variation of positron annihilation
parameters with temperature in the superconducting state is significantly larger than that in the normal state. This is qualitatively
explained in terms of the dimerization of oxygen ions in the superconducting state of Y1Ba2Cu3O7−x
. 相似文献
4.
A. P. Gerashchenko K. N. Mikhalev S. V. Verkhovskii Yu. V. Piskunov A. V. Anan’ev K. A. Okulova A. Yu. Yakubovskii L. D. Shustov 《Journal of Experimental and Theoretical Physics》1999,88(3):545-551
Data on the NMR line shifts, the spin-lattice relaxation rate of 63Cu and 17O nuclei, and the spin-spin relaxation rate of 63Cu are obtained for Tl2Ba2CaCu2O8−δ
(T
c
=112 K) in the normal and superconducting states. The hyperfine constants at the copper and oxygen atoms in a CuO2 plane are estimated from an analysis of the temperature dependence of the Knight shift. The temperature-dependent behavior
of the long-and short-wavelength parts of the dynamic spin susceptibility is discussed by modeling an antiferromagnetic Fermi
liquid. The possible relation between the characteristics of the spin-fluctuation spectrum and the superconducting transition
temperature is analyzed for the oxide investigated.
Zh. éksp. Teor. Fiz. 115, 991–1001 (March 1999) 相似文献
5.
We have investigated the superconducting properties of the Bi1.7 Pb0.3Sr2Ca2−xCe
x
Cu3O10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found
to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate
decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T
c (2 : 2 : 2 : 3) phase decreases and low T
c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition
temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent
state in this system; that is, Ca2+ → Ce4+ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T
c of the system. 相似文献
6.
A. A. Blinkin V. V. Derevyanko T. V. Sukhareva V. L. Uvarov V. A. Finkel Yu. N. Shakhov I. N. Shlyakhov 《Physics of the Solid State》2011,53(2):245-255
This paper reports on the results of investigations of the influence of irradiation of the two-band BCS superconductor MgB2 by electrons with an average energy $
\bar {\rm E}
$
\bar {\rm E}
∼ 10 MeV at high doses (0 ≤ ϕt ≤ ∼2.5 × 1018 cm−2) on the temperature and width of the transition to the superconducting state, the temperature dependence of the electrical
resistivity in the normal state, the crystal lattice parameters, and the diffraction line intensity. An increase in the electron
irradiation dose ϕt leads to the following effects: a decrease in the critical temperature T
c
; an increase in the width of the superconducting transition ΔT
c
; and a decrease in the “residual electrical resistivity” ρ273 K/ρ40 K, in the parameters a and c of the hexagonal crystal lattice, and in the ratio between the diffraction line intensities I
110/I
100. From analyzing the results obtained, it has been established that the main type of radiation damages under irradiation of
the BCS superconductor MgB2 by high-energy electrons is the formation of vacancies in the B sublattice, which leads to a narrowing of the large band
gap Δσ on the Fermi surface. 相似文献
7.
The phase transition “triangular lattice-vortex liquid” in layered high-T
c
superconductors in the presence of pinning centers is studied. A two-dimensional system of vortices simulating the superconducting
layers in a high-T
c
Shubnikov phase is calculated by the Monte Carlo method. It was found that in the presence of defects the melting of the
vortex lattice proceeds in two stages: First, the ideal triangular lattice transforms at low temperature (≃3 K)into islands
which are pinned to the pinning centers and rotate around them and then, at a higher temperature (≃8 K for T
c
584 K), the boundaries of the “islands” become smeared and the system transforms into a vortex liquid. As the pinning force
increases, the temperatures of both phase transitions shift: The temperature of the point “triangular lattice-rotating lattice”
decreases slightly (to ≃2 K)and the temperature of the phase transition “rotating lattice-vortex liquid” increases substantially
(≃70 K).
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 269–274 (25 August 1997) 相似文献
8.
V. A. Moshnikov A. V. Moshnikov A. I. Rumyantseva S. A. Nemov R. V. Parfen’ev A. V. Chernyaev 《Physics of the Solid State》1999,41(4):550-555
A reliable technique of local chemical characterization of multicomponent semiconductor solid solutions has been developed,
and the possibility of its application to the SnTe-SnSe quaternary solid solutions doped with 16 at.% In verified. The behavior
of the electrical resistivity of samples of these solid solutions at low temperatures, 0.4–4.2 K, has been studied. The critical
temperature T
c and the second critical magnetic field H
c2 of the superconducting transition and their dependences on the solid-solution composition have been determined. The superconducting
transition at T
c≈2–3 K is due to hole filling of the In-impurity resonance states, and the observed variation of the superconducting transition
parameters with increasing Se content in the solid solution is related to the extrema in the valence band and the In band
of resonance states shifting with respect to one another.
Fiz. Tverd. Tela (St. Petersburg) 41, 612–617 (April 1999) 相似文献
9.
V. F. Gantmakher V. V. Sinitsyn G. É. Tsydynzhapov N. A. Doroshenko V. P. D’yakonov 《JETP Letters》1997,65(6):502-508
An initially nonsuperconducting ceramic sample with the composition NdBa2Cu3O6+x
is brought, by means of pressure and quenching, to a state with a high carrier density and a superconducting transition,
after which it is returned to the initial state by gradual annealing in several steps. The evolution of the magnetoresistance
of the sample showed that even in the most resistive state realized in the experiment the superconducting interaction influences
the resistance of the sample at fields all the way up to 5–6 T. In an 8 T field the change in resistance in this state in
the temperature interval from 0.4 K to 20 K is described well by a logarithmic law ΔR∝ logT.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 6, 475–480 (25 March 1997) 相似文献
10.
Variations in the temperature behavior of resistivity, ρ(T), in the ab plane of the anisotropic single-crystal high-T
c
superconductor BiSrCuO (2201 phase) have been observed at the insulator-metal (IM) transition. At low temperatures, as one
approaches the transition, the Mott relation for two dimensions, ln ρ ∝ T
−1/3, changes to ln ρ ∝ T
−1/2, which corresponds to hopping conduction with a Coulomb gap in the density of states. Negative temperature slopes were revealed
in the samples near the transition. Estimates suggest that superconductivity in these samples sets in from the Anderson insulator
state. The behavior of the width of the superconducting transition and of the temperature of its onset, T
con, at the IM transition has been studied from measurements of the ac magnetic susceptibility. It is shown that in the vicinity
of the IM transition the superconducting transition becomes broader, and the onset of the transition T
con shifts toward higher temperatures. This behavior is attributed to nonuniform superconductivity resulting from formation in
the crystal of superconducting droplets with different values of T
c
, which is caused by fluctuations in the local density of states due to the inherent disorder in the crystal. In these conditions,
superconductivity has a percolation character.
Fiz. Tverd. Tela (St. Petersburg) 40, 1190–1194 (July 1998) 相似文献
11.
I. O. Bashkin M. V. Nefedova V. G. Tissen E. G. Ponyatovskii 《Physics of the Solid State》1998,40(12):1950-1952
The pressure dependence of the superconducting transition temperature in TiD0.74 has been measured up to 30 GPa in a diamond high-pressure chamber. It is found that the deuteride TiD0.74 becomes a superconductor at pressures corresponding to the transition to the high-pressure ζ phase, with a transition temperature that increases from 4.17 to 4.43 K in the interval P=14–30 GPa. The value extrapolated to atmospheric pressure T
c
(0)=4.0 K is significantly lower than the superconducting transition temperature (T
c
=5.0 K) measured earlier in the metastable state obtained by quenching TiD0.74 under pressure. It is assumed that the significant difference of the extrapolated value from the superconducting transition
temperature in the metastable state after quenching under pressure is caused by a phase transition on the path from the stability
region of the ζ phase under pressure to the region of the metastable state at atmospheric pressure.
Fiz. Tverd. Tela (St. Petersburg) 40, 2153–2155 (December 1998) 相似文献
12.
Shengyun Zhu Shennan Zheng Anli Li Hangchen Huang Hongshan Du Honglin Din Donghong Li 《Hyperfine Interactions》1990,62(3):213-218
HighT
c superconductivity in the YBaCuO superconductor has been investigated through the quadrupole interaction of the probe nuclei99Tc. The quadrupole interactions were measured by the TDPAC method from 77 to 296 K. The probe nuclei99Tc were introduced into the YBaCuO superconducting specimen by diffusion. The derived electric quadrupole interaction parameters
show that the probe nuclei are subject to a unique EFG interaction and occupy a substitutional lattice site in the YBaCuO
superconductor. A strong EFG of 1019 V/cm2 was observed. The temperature dependence of the EFG exhibits a linear decrease with temperature increase. Anomalies of both
EFG and ν were found in the superconducting transition temperature region. The role of the oxygen vacancies in the Cu−O chains
is discussed. 相似文献
13.
14.
High-precision x-ray crystallographic studies of YBa2Cu4O8 single crystals (T
c
=70 K) are performed at eight temperatures in the interval 20–295 K. It is found that a number of structural parameters exhibit
anomalous behavior near the superconducting transition of the crystal. A characteristic effect near the phase transition is
the displacement of the O1 bridge atom that joins the Cu1 atom of the cuprate chain to the Cu2 atom of the cuprate plane.
The shift of this oxygen toward the Cu2 atom is indicative of a change in the Cu2-O1 chemical bond and of charge transfer
to the cuprate plane in the process of the transition of the crystal to the superconducting state.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 7, 502–506 (10 October 1997) 相似文献
15.
The temperature dependence of the x-ray absorption spectra above the L
3 absorption edge of bismuth in the superconducting oxide Ba0.6K0.4BiO3 are investigated. It is found that the local structure is different from the simple cubic structure indicated by x-ray and
neutron-diffraction data. It is shown that the oxygen atoms move in an anharmonic double-well potential arising as a result
of the existence of two nonequivalent types of octahedral environments of bismuth. Vibrations in such potential modulate the
Bi-O bond lengths at the low frequency of the rotational (“tilting” type) mode of the oxygen octahedra and thus give rise
to a strong electron-phonon interaction, which explains the quite high superconducting transition temperatures T
c
∼30 K.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 977–982 (25 June 1998) 相似文献
16.
V. N. Krivoruchko 《Journal of Experimental and Theoretical Physics》1997,84(2):300-308
The formation of the superconducting phase in short-period proximity-effect layered superlattices of the superconductor-band-antiferromagnetic-metal
(SC/AF) type is studied. The exact solution of the Usadel equations is used to discuss the possibility of formation in such
structures of a ground state in which the order parameters of the adjacent superconducting layers have opposite signs (the
“π-phase”). The dependence of the superconducting transition temperature and the upper critical field normal to the layers on
the lattice period, the intensity of magnetic interaction in the antiferromagnetic layer, and the state of the interface between
the layers is examined. It is found that there exists a nonlinear dependence of the conditions for the appearance of the superconducting
state in a layered SC/AF system on the system’s parameters. Finally, the conditions for the appearance of the superconducting
phase in proximity-effect superlattices consisting of a superconductor with nonmagnetic, ferromagnetic, and antiferromagnetic
metals are compared.
Zh. éksp. Teor. Fiz. 111, 547–561 (February 1997) 相似文献
17.
The relaxation of the superconducting transition temperature T
c in YBa2Cu3O6.38 is investigated with increasing oxygen order in the CuOx plane under 1 GPa pressure and with decreasing oxygen order after the pressure is relieved. It is established that the oxygen
disordering process is more rapid than the pressure-induced ordering process: The ratio of the relaxation times of T
c in these processes τ
ord/τ
disord≈5. This behavior could be caused by different mechanisms of the pressure-induced increase in the Cu-O chain length and decrease
of this length after pressure relief.
Fiz. Tverd. Tela (St. Petersburg) 40, 1968–1973 (November 1998) 相似文献
18.
Besides the well-known bulk fluctuation contribution to the diamagnetic susceptibility there is an additional surface contribution with the singularity at TSH exceeding the superconducting bulk transition temperature Tc(H). The results obtained allow to explain the anomalous behavior of the diamagnetic susceptibility found by Khaikin and Khlyustikov. 相似文献
19.
The role of anisotropy of the coupling constant in the influence of nonmagnetic impurities on the behavior of the superconducting
transition temperature T
c is investigated in the high-temperature superconductor (HTSC) model, where high values of T
c result from an increase in the density of states near the Fermi surface. It is shown that this model is more sensitive to
impurities than the BCS model; Anderson compensation does not occur in the HTSC model, even for identical distributions of
the densities of states in the superconducting and impurity channels, and the impurity contributions are no longer linear
with respect to the impurity concentration in the vicinity of T
c. Anisotropy of the superconducting gap Δ and the possibility of its disappearance at certain points on the Fermi surface
due to various types of pairing are manifested in the stability of the superconducting phase against the influence of impurities.
Fiz. Tverd. Tela (St. Petersburg) 39, 1940–1942 (November 1997) 相似文献
20.
S. G. Barsov A. L. Getalov V. P. Koptev L. A. Kuzmin S. M. Mikirtychyants G. V. Scherbakov A. A. Vasiljev V. K. Fedotov V. I. Kulakov R. K. Nicolaev N. S. Sidorov Y. M. Mukovskii A. S. Nigmatulin S. E. Strunin 《Hyperfine Interactions》1991,63(1-4):161-167
In this work the magnetic and superconducting properties of YBa2Cu3O6+x
, ceramic samples are studied with regard to there preparations technology and oxygen content. It is shown that at 0.41≤x≤0.45 the magnetic and superconducting states coexist. 相似文献