O.V. Zharikov

Superconductivity and structure of YBa2Cu3O6 single crystals treated in halogen vapours

Abstract Dielectric tetragonal samples of Y-Ba-Cu-O single crystals have been heat treated in an atmosphere of iodine or bromine gas. After halogenation the single crystals exhibited the transition to the superconducting state with T c ≈ 60 K and 85 K, respectively.

Superconductivity and the structure of YBa2Cu3O6 ceramics and single crystals treated in halogen vapours

Abstract Dielectric ceramic and single crystal samples of YBa 2 Cu 3 O 6 were treated in halogen vapours (Cl, Br, I). After halogenation the transition to the superconducting state was observed at 90, 85 and 55 K, respectively.

On the mechanical properties of C60 fullerite crystals

First experimental data on the plasticity, strength and microhardness of C60 fullerite crystals are reported. It is concluded that the mechanical properties of the crystals studied are isotropic, and the values of their breaking point are low. The obtained results are compared with those for other materials (graphite, indium etc.).

129I-Mössbauer study of iodine-doped C60

Abstract 129 I-Mossbauer spectroscopy is applied to study the chemical nature of iodine species in C 60 I 3.64 . Spectra in temperature region 4.2 K – 100 K reveal the presence of two inequivalent sites of iodine with hyperfine parameters related to that of molecular iodine. The two iodine species are attributed to two molecules located at sites with different local symmetry and binding strength as reflected by different quadrupole-interaction tensors and local Debye temperatures. Discussion of the results in the Townes-Dailey formalism show that there is only a small total charge transfer between iodine and C 60 , but a considerable charge redistribution between the two iodine sites.

On the temperature dependence of electrical conductivity of buckytube-containing carbonaceous samples

Abstract We have examined the electrical conductivity, σ(T), from 4.2 to 295 K of samples from a series of buckytube-containing carbonaceous deposits prepared under helium pressures ranging from 20 to 750 Torr. The results show that while absolute values of conductivity are very sample dependent, all temperature variations can be expressed as σ (T) = C exp(AT) where C and A are positive coefficients. We discuss the results in the light of thermally activated tunnelling based on a two level model.

Specific features of NQR and EPR spectra of YBaCuO ceramics doped by iodine and bromine

Abstract Nuclear quadrupole and electron paramagnetic resonance methods have been employed to study samples of YBa 2 Cu 3 O 6 ceramics, treated in iodine or bromine vapours. The sampled singularities may be attributed to the appearance of I or Br ions in Cu(1)-O type planes.

High pressure study of the absorption edge of crystalline C60/C70 mixture

Abstract Absorption spectra of a mixed fullerite crystal C 60 /C 70 have been studied in the energy range 1.5–2.5 eV at pressures up to 20 GPa. It has been found that with growing pressure one can observe an overall enhancement and a strong red shift of the fundamental absorption edge. The magnitude of a mean shift rate has been determined to be 0.08 eV/GPa, that makes it possible to estimate the minimal pressure at which the band gap width could become zero.

Mössbauer study of 129I in a high-Tc superconductor YBa2Cu3O6Ix

Abstract A Mossbauer study of valence states of iodine has been performed in 129 I-doped samples of YBa 2 Cu 3 O 6.1 ceramics, demonstrating the superconducting transition with the onset at T c0 ≈55 K. Iodine is shown to be mainly present in the form of iodide-ion; insignificant quantities of orthoperiodate-ion are also observed. The isomeric shift magnitude suggests that the iodide-ion charge ( Q I ) in this system does not exceed −0.87 Q I

63Cu NQR in superconducting YBa2Cu3O6.1Ix

Abstract YBa2Cu3O6.1 samples, treated in iodine vapours and YBa2Cu3Oy samples with different oxygen content (x = 6.9; 6.5 and 6.1) were studied by 63Cu NQR using a method of spin echo amplitude measurement in a weak magnetic field.

Properties and Structure of Yttrium-Barium Cuprate Treated in Halogen Vapors

The discovery of high-temperature superconductivity in the La-Ba(Sr)-Cu-O system stimulated an avalanche of works with the aim of searching for new compounds with high-Tc values. As a result of these investigations, new complex superconducting oxides of perovskite structure were found, namely, Y-Ba-Cu-O, Ba-K-Bi-O, Bi(Ta)-Ba, (Sr)-Ca-Cu-O, Nd-Ce-Cu-O and their modifications, which exhibit different Tc values. A simple analysis shows that at least two primary elements of the High-Temperaturte Superconductor (HTSC) structure exist in each of these compounds. These are the cuprate planes of the CuO2 type and a rather complicated sublattice of oxygen atoms [7.1,2], Apparently, it is the structure of these elements that plays the decisive role in the charge redistribution and the formation of paired current carriers in these systems.