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Journal ArticleDOI

Enhancement and degradation of Tc in Bi-HTSC due to Li3+ irradiations

Abstract: Radiation damage in Bi2Sr2CaCu2O8+δ or Bi(2 2 1 2) by 55 MeV Li3+-beam has been studied from electrical resistivity and X-ray diffraction characterizations. This irradiation increases electrical resistivity and broadens X-ray diffraction lines by generating defects in all samples. But superconducting critical temperature, Tc, is seen to increase for Bi(2 2 1 2) with excess oxygen and decrease for Bi(2 2 1 2) with O-content less than the optimum, that gives maximum Tc. This increase of the superconducting critical temperature on Li-irradiation of O-rich Bi(2 2 1 2) as well as the decrease for low-O Bi(2 2 1 2) is due to O-displacement. This is in agreement with our earlier He-irradiation results.
Topics: Electrical resistivity and conductivity (54%), Superconductivity (52%), Radiation damage (50%), Irradiation (50%)
Citations
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Journal ArticleDOI
Abstract: In this short topical review, a brief account of the evolution of defects due to controlled changes in polycrystalline zinc oxide has been presented. X-ray diffraction, Positron annihilation spectroscopy and optical absorption spectroscopy has been employed to understand various defective states of ZnO. Thermogravimetric analysis, room temperature resistivity and photoluminescence measurements (just mentioned) have been used to throw more light on this topic. A coherent scenario in the light of previous works in this field has been discussed. At the end discussion on the magnetic studies on ZnO-based systems has been added in short.

263 citations


Journal ArticleDOI
Abstract: A highly resistive nanocrystalline thin film of Li0.25Mg0.5Mn0.1Fe2.15O4, deposited by RF magnetron sputtering technique on Si(1 0 0) substrate, is irradiated with 190 MeV Au14+ ions. To probe the swift heavy ion induced modifications in the electrical properties in the film an in situ measurement of electrical resistance using two-probe method is carried out. We observe the value of resistivity comes down drastically from 1.5 × 108 to 1 × 105 Ω cm after irradiation at the fluence of 1 × 1013 ions/cm2. In XRD spectra after irradiation no previous spinel peaks are observed. No loss in oxygen content with fluence is observed. We have presented the observed phenomenon as an effect of formation of amorphized latent tracks on the basis of thermal spike model.

19 citations


Journal ArticleDOI
Abstract: Nanocrystalline Li0.25Mg0.5Mn0.1Fe2.15O4 ferrite thin films, prepared by R.F. magnetron sputtering technique, are irradiated with 190 MeV Au14+ ions. The significant behavioural changes in magnetic and electrical properties of thin films after swift heavy ion irradiation confirm the formation of stable defects. A transformation from ferrimagnetic to superparamagnetic behaviour is observed from CEMS (conversion electron Mossbauer spectroscopy) with increase in fluence from 2.5 × 1012 to 1 × 1013 ions/cm2. The resistivity initially increases after irradiation till the fluence reaches 1 × 1012 ions/cm2 and then reduces with further increase in fluence. We have also studied the X-ray diffraction pattern with fluence variation. A possible explanation of the above results on the basis of thermal spike model is presented. These effects are mainly due to amorphized latent tracks and variation in the cation distribution due to heavy ion irradiation.

13 citations


Journal ArticleDOI
Abstract: 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 .

8 citations


Journal ArticleDOI
Abstract: Present report deals with the effect of disorder on Bi-2212 type high Tc superconducting and LCMO type CMR oxide materials. Ion irradiation (50 MeV Li3+ beam) creates high level of disorder in the superconducting system and as a result increase of room temperature resistivity (ρ300) has been observed. Radiation induced point defects cause an increased dρ/dT in the metal-like regime of Bi-2212. Similar increase of dρ/dT in the FM (ferromagnetic and metal-like) state has also been found in LCMO system. Enhancement of metal-like behavior is unusual in the sense that a simultaneous decrease of Tmi (metal–insulator transition temperature for LCMO) or Tc (superconducting transition temperature for Bi-2212) due to irradiation has also been observed. Effect of the defects incorporated by other means like variation of heat treatment and ion irradiation has been investigated for a better understanding on the electrical transport in these complex materials. Results have been discussed in the light of their intrinsic granular nature.

4 citations


References
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Journal ArticleDOI
Abstract: The static magnetic susceptibility of Bi 2 Sr 2 CaCu 2 O 8+ y and Tl 2 Ba 2 CuO 6+ y is studied as a function of oxygen content y over the temperature range 2–900 K. With increasing oxygen (hole) content the superconducting transition temperature T c ( y ) passes through a maximum for the Bi-compound and falls monotonically for the Tl-system, reaching a maximal value of c ≅92 K in both systems. As the oxygen content is varied, a correlation is observed between the magnitude of T c ( y ) and the temperature dependence of the normal-state magnetic susceptibility. The fact that this same correlation can also be seen in the published data on La 2- x Sr x CuO 4 and YBa 2 Cu 2 O 6+ y implies that it may be a universal property of hole-doped oxide superconductors.

82 citations


Journal ArticleDOI
Abstract: Tl-based superconducting copper oxides Tl 2 Ba 2 CaCu 2 O 8 , TlBa 2 Ca 2 Cu 3 O 9 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 were irradiated at 140 K by 3.6 GeV Xe ions and the resistance measured in situ as a function of the fluence. The results confirm that electronic stopping of GeV heavy ions plays a major role in the defect creation mechanism. Critical current densities were obtained from magnetization measurements on samples irradiated by 5.8 GeV Xe ions at fluences up to 2x10 12 cm -2 and magnetic field orientations parallel and normal to the heavy ions tracks. Large enhancements of flux pinning and J c are observed, in particular at low fluences, without significant change of the T c 's.

36 citations


Journal ArticleDOI
Abstract: A substantial increase in the transition temperature has been noted in Bi 2 Sr 2 CaCu 2 O x superconductor after irradiation with 20 MeV alpha particles. This is probably due to oxygen removal from an oxygen rich superconducting phase.

15 citations


Journal ArticleDOI
21 Aug 1995-Physics Letters A
Abstract: Positron annihilation lifetime (PAL) measurements on well-characterized pellets of Bi-2212, (Bi,Pb)-2212 and (Bi,Pb)-2223 superconductors indicate the presence of a very long (around 1500 ps) third lifetime. This τ 3 is attributed to positronium formation in voids even in these conducting oxides and subsequent o-Ps to p-Ps conversion. Ignoring τ 3 in the fit leads to altered values of τ 1 and τ 2 .

14 citations