A.S. Tamhane

PULSED LASER ABLATION : A NEW ROUTE TO SYNTHESIZE NOVEL SUPERCONDUCTING COMPOUNDS AS ORIENTED FILMS

We report here the significance of the pulsed laser ablation technique in stabilizing strained lattices that do not form by the conventional ceramic method and show that the technique offers unique possibilities to probe the structure property relationship in complicated systems. One of such systems is LuBa2Cu3O7−δ; a systematic investigation of structural (in)stability of its superconducting phase is presented here. Our analysis suggests that the system suffers from internal strain due to lower ionic radius of Lu3+; however, the structure can be stabilized only as oriented films on 〈100〉 LaAlO3, 〈100〉 SrTiO3, and 〈100〉 MgO, with excellent superconducting properties (Jc≊5.0×106 A cm−2 at 77 K). We have also investigated similar compounds having their stability close to their crystallographic limit. The important feature of these metastable phases is that they grow only as oriented films. Free energy of epitaxial growth of strained films are investigated and a simple growth model is proposed based on our o...

Superconductivity and valence states of Ce, Pr and Tb in bulk Lu1−xMxBa2Cu3O7−δ (M = Ce, Pr and Tb) systems

Abstract Bulk samples of composition Lu 1− x M x Ba 2 Cu 3 O 7−δ (M=Ce, Pr and Tb) are examined with respect to the formation of 1–2–3 phase and the superconducting properties. Samples with M = Pr and Tb form a superconducting 1–2–3 phase for values of x ≤0.6. We observe that in case of M = Tb, the zero-resistance transition temperature, T c(0) , is 85–86 K and independent of x for 0.1 ≤ x ≤0.3. For M = Pr, a maximum T c(0) of 86 K is observed for x =0.1. T c(0) decreases with increasing x for x > 0.1 and the sample with x =0.6 is observed to be semiconducting down to 12 K. With M = Ce, samples of the composition Lu 1− x − y Ce x Ca y Ba 2 Cu 3 O 7−δ form the superconducting 1–2–3 phase for x , y =0.1 and 0.15. Samples of the compositions Lu 1− x−y Pr x Ca y Ba 2 Cu 3 O 7−δ with x =0.1, 0.2, 0.3 and y =0.1, have lower T c(0) s than samples of a corresponding Pr content without Ca. We infer from our studies that the Pr ions are in the 3+ valence state for 0.1≤ x ≤0.3, the Tb ions are mainly in the 3+ valence state for 0.1≤ x ≤0.3, and the Ce ions are in the 4+ state.

Microstructural and transport properties of laser ablated LuBa2Cu3O7−δ thin films

Abstract High-quality LuBa 2 Cu 3 O 7−δ (LBCO) thin films have been grown on 3 by pulsed laser deposition. Microstructural studies have indicated a high degree of c -axis orientation and an in-plane alignment. Transport measurements carried out on 10 μm wide microbridges of LBCO films have shown high critical current densities in the range 2–5×10 6 A cm -2 at 77 K. Self-field induced flux creep caused by transport currents has also been studied. However, the thickness-dependent effective microwave surface resistance, R eff , measured using a microstrip resonator technique at the X band has shown a minimum at 3000 A indicating film degradation above 3000 A.

Superconductivity in thin films of the composition M0.5Ca0.5Ba2Cu3O7 − δ(M = Lu, Tb, Th)

Abstract We have grown in situ by laser ablation thin films of the composition M0.5Ca0.5Ba2Cu3O7 − δ(M = Lu, Tb, Th). The significance of these investigations is that the compositions MBa2Cu3O7 − δ(M = Lu, Tb, Th) do not form in single phase in bulk form and, in the case of Tb and Th, not even in thin film form. With partial replacement of the M element by Ca, we are able to grow thin films that are highly crystalline and preferentially oriented. Superconducting transition temperature of the films varies from ≌ 12 K to ≌ 45 K. To the best of our knowledge, these are first results reporting superconductivity in a 5f-element-based copper oxide system (in this case, M = Th).

Superconductivity in the system Lu1−xPrxBa2Cu3O7−δ

Abstract Lu1−xPrxBa2Cu3O7−δ compounds were synthesized in steps of x = 0.1 for 0⩽ x⩽ 0.9 by solid-state reactions. Bulk superconductivity was observed in samples with x = 0.1, 0.2 and 0.3, even though the two end members of the series are not superconductors. X-ray diffraction studies show that the samples with x = 0.1 and 0.2 are essentially single-phase 1-2-3 materials, whereas the other compounds contain some impurity phase along with 1-2-3 phase.