[en] A nonsuperconducting La₂Ba₂Cu₄O_9+δ system has been made superconducting by the addition of CaCuO₂, along with rare earth doping at the La site, with the stoichiometric composition La_2-xR_xCa_yBa₂Cu_4+yO_10+δ (R=Nd, Gd, and y=2x). All the samples with 0.0< x<0.5; y=2x were characterized by x-ray diffraction and neutron diffraction measurements for structural properties and by ac susceptibility, dc resistivity, and iodometric analysis for superconducting properties. The x=0.0 sample displays semiconducting behavior. Increasing x increases T_c from less than 15 K for Nd/Gd samples with x=0.1 to ∼78 K for x=0.5 samples. It is interesting to note that the hole concentration and T_c exhibit a strong correlation with increasing dopant concentration. Neutron diffraction studies confirm the occupancy of Ca and Nd ions at the La site with a concomitant displacement of La on to the Ba site. [copyright] 2001 American Institute of Physics

[en] The structural and superconducting properties of (Gd_l-x-yCe_x Ca_y)Ba₂Cu₃O_z (GdCeCaBCO) samples synthesised using ceramic method under identical conditions, are investigated using x-ray diffraction, electrical resistivity, ac susceptibility and oxygen content measurements

[en] We have investigated influence of substitution of La and Ca-La ions on the structural and superconducting properties of (Gd_1-yCa_y)(Ba_2-xLa_x) Cu₃O_z [GdCaBaLaCuO] system by x-ray diffraction, dc resistivity, ac susceptibility and oxygen content measurements. The effect of increasing La concentration in Gd(Ba_2-xLa_x)Cu₃O_z results in suppression of T_c which can be attributed to the hole filling by La. Structural investigations using XRD technique reveal that, increasing La content reduces orthorhombicity and promotes tetragonal structure. The lowering of T_c due to La-doping has been compensated by appropriate hole doping with Ca in (Gd_1-yCa_y) (Ba_2-x La_x)Cu₃O_z. For a particular La concentration (x=0.35), the sample shows nonsuperconducting behaviour, the Ca doping in it helps to revive the superconductivity due to an increase in hole concentration reaching an optimum value for compensated oxide. This simultaneous substitution of Ca-La for GdBa₂Cu₃O_z helps to monitor the oxygen stoichiometry and hole concentration in GdCaBaLaCuO system. The interrelationship between superconducting transition temperature, structural changes, the dopant valencies and variation of oxygen content is discussed in the context of variation in hole concentration in the presently studied GdCaBLaCO system. (author)

[en] The superconducting properties of single phase La_1.5-xCa_x+yBa_1.5-yCu₃O_z, 0.0≤x≤0.60 (LC) and 0.0≤y≤0.70 (CB, compounds with tetragonal triple-perovskite structure are studied, using x-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La_1.5Ca_xBa_1.5Cu₃O_z (LC) samples, 0.15≤x≤0.60, are superconducting with T_c^R=0 between 40 and 74 K. With the increase in x, the oxygen content, hole concentration in the CuO₂ layers as well as the T_c increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa_0.5+yBa_1.5-yCu₃O_z (CB) compounds increase with the increase in y, the T_c^R=O remains nearly constant around 74 K for y=0.0-0.70. A correlation exists between the T_c and the hole concentration for LC and CB compounds. (author)

[en] The structural and superconducting properties of (Gd_1-yCa_y) (Ba_2-xLa_x)Cu₃O_z [GdCaBLaCO] samples with [0.0≤x≤0.5; 0.0≤y≤0.4] have been studied by x-ray diffraction, d.c. resistivity, a.c. susceptibility and oxygen content measurements. The effect of increasing La concentration in Gd(Ba_2-xLa_x)Cu₃O_z results in lowering the hole concentration thereby decreasing T_c which can be attributed to the hole filling by La. Structural investigations using XRD technique reveal that, the increasing La content reduces orthorhombicity and promotes tetragonal structure. The suppression of T_c due to La-doping has been compensated by appropriate hole doping with Ca in (Gd_1-yCa_y) (Ba_2-xLa_x)Cu₃O_z. For a particular La concentration, the samples show non superconducting behaviour, the Ca doping in it helps to revive the superconducting properties with increasing hole concentration reaching optimum value for compensated oxide, where T_c is maximum. This simultaneous substitution of Ca-La for GdBa₂Cu₃O_z(GdBCO) helps to monitor the oxygen stoichiometry and hole concentration in GdCaBLaCO system. The interrelationship between superconducting transition temperature structural changes, the dopant valencies and variation of oxygen content is discussed in the context of hole concentration in the presently studied GdCaBLaCO system. (author)

[en] The structural and superconducting properties of single phase La_2.5-x-y(Ho)_xBa_2.5-yCa_2yCu₅O_z (0.0≤x=y≤0.7) [LHoCaB] series with tetragonal triple perovskite structure are studied using x-ray diffraction, resistivity, a.c. susceptibility and oxygen content measurements. It is observed that samples with 0.2< x=y<0.7 are superconducting. With increasing x=y, both the hole concentration in the Cu₂-O layers (planes) and T_c^R=0 increase to a maximum value of 0.291 and 77K at x=y=0.5, respectively. It is found that, the superconductivity of the LHoCaB series is dependent on the hole concentration of Cu-O layers (planes) but not on the hole concentration of the compound. A correlation between T_c and the hole concentration is studied in the context of hole doping by Ca and turning on of T_c with Ca-concentration in this system. (author)

[en] It has been reported that the addition of equal amounts of CaO and CuO into nonsuperconducting La₃Ba₃Cu₆O_z (La-336) and LaBaCu₂O_z (La-112) resulted in to the occurrence of superconductivity with La₃Ca₁Ba₃ Cu₇O_z(La-3137) and LaCaBaCu₃O_z (La-1113) systems respectively. We report for the first time studies on the superconducting properties of La₂Ca Ba₂Cu₅O_z (La-2125) phase obtained from non superconducting La₂Ba₂ Cu₄O_z (La-224) by addition of CaCuO₂ layers. Also, we present the results of the studies on samples having large La³⁺ ion replaced by smaller rare earth ions like Er³⁺, Gd³⁺ or Yb³⁺ having the stoichiometric compositions (La_2-xR_x)Ba₂(Ca_yCu_4+y)O_z (LRBCaC); (R=Er, Gd or Yb) 0.0 ≤ x ≤ 0.5; y=2x. These results will be discussed in the context of role played by Ca-Cu addition on the revival of superconductivity in non superconducting La-224 and the dependence of T_c on hole concentration. (author)

[en] In order to study the role played by the addition of CaCuO₂ layers in the non superconducting stoichiometric variant La₂Ba₂Cu₄O_z (La-224) of La-336, on the structure and introduction of superconducting behaviour in this system a systematic study was carried out

[en] Lithium ferrite nanoparticles were dispersed in silica matrix to minimize agglomeration. Structural and electrical properties of [Li_0.5Fe_2.5O₄]_1–x[SiO₂]_x (x = 0, 50–90%) nanocomposites synthesized using ultrasonic assisted sol–gel method have been investigated. X–ray diffraction (XRD) measurement confirms phase purity of all the nanocomposites. Crystallite size varies gradually from 29.08 to 17.54 nm with increase in silica content. Higher absorption in dispersed samples compared to pure Lithium ferrite is observed by ultra–violet visible (UV–Vis) measurement. Complex impedance spectroscopy was employed where permittivity and conductivity plots were theoretically fitted using Cole–Cole model and Jonscher's power law, respectively.