J. Klamut

Possible antiferromagnetic ordering in Y2Cu2O5. Paramagnetic behaviour of BaCuO2

Abstract The susceptibility anomaly observed at 13 K for Y 2 Cu 2 O 5 strongly suggests the occurrence of antiferromagnetic Cu spin coupling in this compound. Only paramagnetic behaviour was found for BaCuO 2 .

On the magnetic ordering in the R2Cu2O5 systems

Abstract We have investigated the magnetic properties of a large group of compounds with the general formula R2Cu2O5, where R stands either for Sc, In and Lu, or the heavy rare-earth element from Tb to Yb. All compounds investigated are isostructural and crystallize in the orthorhombic Ho2Cu2O5 type of crystal structure and show some magnetic transitions at low temperatures. These transitions are mainly associated with the spins on Cu2+ sites. However, a possible magnetic ordering of the rare-earth moments by these ternary oxides has also been discussed.

Thermal conductivity and electrical resistivity of the high-Tc superconductor YBa2Cu3O9−Δ

Abstract Thermal conductivity and electrical resistivity of single-phase YBa 2 Cu 2 O 9−Δ compound were measured in the superconducting ( T c =89.5 K) and normal states, in the temperature range 5–320 K. The electronic component of the total thermal conductivity was estimated to be 20%. The electrical resistivity changed linearly in the normal state up to highest measured temperature.

AC losses and critical current density of superconducting GdBa2Cu3O7−x

Energy losses occurring in a cylindrical sample of Gd-Ba-Cu-O, subjected to an external AC magnetic field were examined. The loss dependence on the amplitude of the magnetic induction exhibits two stages of flux penetration into the superconductor. Critical current densitities for both stages of penetration were examined and an explanation for such behaviour is proposed. Support for this point of view is obtained by measurements on pulverized sample material. All measurements were performed at a temperature of 4.2 K and in absence of a background field. n nAnalysis of the data provides two critical current densities: an inter-granular critical current density at weak alternating magnetic fields and an intra-granular critical current density at higher magnetic fields. The intra-granular critical current density is at least two orders of magnitude larger than the inter-granular one.

Effect of oxygen atom disordering on Tc OF YBa2Cu3O7 − x

Abstract The effects of oxygen deficiency and temperature-induced oxygen atom disordering on the critical temperature (Tc) of YBa2Cu3O7 − x are presented. Two possible influences are proposed and discussed to explain an extraordinary behaviour of Tc, observed in the oxygen-deficient region of the phase. The first influence is the effect of oxygen disordering on the b-axis Cu-O chains, which results in a state characteristic of a set of mutually perpendicular and inequivalently occupied Cu-O chains, which is possibly more favourable for superconductivity. The second is the influence of the Cu-O planes, which exist between the yttrium and the barium-ion layers, the contribution of which on Tc may exceed that of the Cu-O chains and, starting at a certain oxygen index, it may become dominating. Estimates on the upper value of Tc for 1:2:3 type compounds (165 K) and on the limit of superconductivity in the YBa2Cu3O7 − x phase have been made. They give 6.23, if determined by the oxygen index, or 3 × 10−3 if determined by the orthorombic distortion parameter p.

Low dimensional magnetism in R2Cu2O5 compounds

Abstract High resolution optical absorption spectra of an Er3+ probe in R2Cu2O 5 (Rue5fbY, Lu, Er, Tb) cuprates having the same magnetic structure of the copper subsystem in an ordered state (ferromagnetic CuO planes coupled antiferromagnetically) were measured in a broad temperature range below and above TN. We have found that for all these compounds the splittings Δν of the Er3+ probe spectral lines are nonzero above approximately the same temperature (90 K, much greater than TN). This temperature was shown to correspond to the establishment of 2D magnetic correlations inside the CuO planes.

Hydrogenation and deoxygenation effects on the thermoelectric power of SmBa2Cu3O7

Abstract The normal state thermoelectric power and resistivity of SmBa 2 Cu 3 O 6.92− x H y have been examined in the ranges x =0–0.085 and y =0–0.25. The same effect of hydrogenation and deoxygenation on the thermopower and different ones on the resistivity have been observed. That difference is ascribed to a composition difference between minority intergrain and majority grain areas. The universality of the thermopower behavior of SmBa 2 Cu 3 O 6.92− x H y is also discussed.

On the origin of the 6 K magnetic anomaly in Y2Cu2O5

Abstract This work has been done to explain the origin of the 6 K magnetic anomaly observed in Y 2 Cu 2 O 5 under a very weak external magnetic field. The sensitivity of the anomaly to time- and temperature-dependent treatment is shown. A hypothesis on the possibility of a thermally activated displacement of Cu +2 -ions leading to a creation of new Cuue5f8O coordination polyhedra - trigonal bipyramids is done and proved through X-ray analysis of some chosen samples. The analysis has revealed that the crystal structure of Y 2 Cu 2 O 5 is a specific one and accepts, at least, two equivalent coordination polyhedra for Cu +2 -ions which for the case of selective occupation of any of them by all the Cu 2+ -ions available occur hardly distinguishable through X-ray powder diffraction. Mutual interaction of Cu 2+ -ions, occupying both polyhedra, is the most probable reason for the 6 K anomaly to occur.

The ac susceptibility of Y2Cu2O5

Abstract The temperature dependence of the real and imaginary part of the ac susceptibility was measured for polycrystalline Y 2 Cu 2 O 5 . It was found that apart from the known maximum at 13 K, connected with the antiferromagnetic transition of Cu ions, another maximum appears at about 5.8 K. It is very weak and disappears almost completely for an external magnetic field of above 100 Oe.

Vibrational spectra and internal phonon calculations for the M2Cu2O5 binary oxides (M = In, Sc, Y or from Tb to Lu)

Abstract The room-temperature infrared and Raman scattering spectra of a large group of compounds with the general formula M2Cu2O5 were examined in the polycrystalline state (M is either Sc, In and Y or a heavy rare-earth element from Tb to Lu). The identification of the bands observed for the respective vibrational modes was proposed on the basis of the factor group approach and normal coordinate analysis. The Urey-Bradley force field model and potential energy distribution were applied in the phonon calculations.