Fluctuation induced conductivity of Cu0.5Tl0.5Ba2Ca2Cu3−ySnyO10−δ superconductors have been studied from the resistivity vs. temperature data. The logarithmic plots of excess conductivity (Δσ) vs. reduced temperatures [ e = ( T − T c mf ) / T c mf ] show two crossover temperatures with three exponents. A distinct cross-over from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations have been observed in all the samples. Another cross over from 2D to 0D fluctuations has also been witnessed. The FIC data fits well with 3D, 2D and 0D fluctuations for lower Sn doping, while it deviates considerably for higher Sn concentration. Also the FIC analysis shows the deterioration in quality of samples (increased ΔTc), increase in anisotropy and decrease in inter-layer coupling strength J with increased Sn content. These factors might be contributing to the suppression of Tc in these samples.

Different regions of fluctuation conductivity in Sn-doped Cu0.5Tl0.5Ba2Ca2Cu3−ySnyO10−δ superconductors

A study of superconducting (Y1-xCax)Ba2Cu3Oy

Positronium formation in (Bi/BiPb)-2212 and -2223 superconductors

Single crystals of Bi 2 Sr 2 CaCu 2 O 8+ x (Bi-2212) with T c of 80 K have been subjected to irradiation with 40 MeV α-particles from a Variable Energy Cyclotron at various doses up to 2 × 10 15 alpha particles/cm 2 . T c decreases after irradiation. From the analysis of excess conductivity, it has been found that the interlayer coupling strength J decreases with the increase of irradiation dose. This decrease is due to a decrease in oxygen concentration.

Alpha irradiation of Bi-2212 superconductor

Radiation damage in Bi-2212 and (Bi 0.92 Pb 0.17 )-2212 superconducting pellets due to irradiation by 40 MeV He ++ -beam has been studied, as these two compounds differ with respect to lattice strain in their Bi–O and (Bi,Pb)–O layers. These samples were prepared with excess oxygen that accounts for their lowered superconducting transition temperature, T c , of 59.5 and 64.5 K, respectively. Irradiation to 8.14×10 15 He ++ /cm 2 raised T c by 4.5 and 5.5 K, respectively, and also their normal state resistivities. Excess conductivity analysis for the unirradiated and irradiated samples showed (i) a transition of the conductivity fluctuation from 2D ( λ =1.0) to 3D ( λ =0.5) behaviour, on cooling across a temperature T 0 , and (ii) also the signature ( λ =3.0) of critical fluctuations in a network of superconducting microregions, for temperatures below T cr , where T cr is seen to be 5 to 10 K lower than T 0 . The rise in T c has been explained from irradiation-induced removal of oxygen taking the hole concentration towards the value for the peak in T c .

Different regions of fluctuation conductivity in unirradiated and alpha-irradiated Bi2Sr2CaCu2O8+δ and (Bi,Pb)2Sr2CaCu2O8+δ superconductors

Increase in critical temperature of Bi2Sr2 CaCu2Ox superconductor due to alpha particle irradiation

SIMS of Y1Ba2Cu3O7-x and (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductors

The superconducting compound YBa2Cu3O7−x (YBCO) and oxides of copper (CuO and mixture of CuO and Cu2O) have been examined by secondary‐ion‐mass spectrometry (SIMS). The results support the fact that two kinds of copper (from the consideration of bonding and valence state) exist in YBCO—one in the basal planes of charge reservoir layers and the other in the conduction layers. The bonding of Cu‐O in the CuO2 conduction layer unit is similar to that in CuO. No Cu+++ secondary ions could be detected in the SIMS spectrum, in agreement with electron spectroscopy for chemical analysis, extended x‐ray‐absorption fine structure, and electron probe microanalysis measurements reported earlier. A plausible explanation has been given for this.

Udayan De

Papers

Increase in critical temperature of Bi2Sr2 CaCu2Ox superconductor due to alpha particle irradiation

SIMS of Y1Ba2Cu3O7-x and (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductors

Studies of bonding and valence states in YBa2Cu3O7−x through secondary‐ion‐mass spectrometry