P M Shirage

Studies on pulse electrodeposition of high Tc superconducting Hg-1212 thin films

The co-deposition of Hg-Ba-Ca-Cu alloyed films was successfully carried out by the pulse electrodeposition technique for the first time. A pulsating potential with 25 Hz frequency and 50% duty cycle was used. Different processing parameters such as deposition potential, current density, deposition time were studied and optimized. These alloyed films were then electrochemically oxidized from 1N KOH solution at room temperature to get superconducting HgBa2CaCu2O6+δ thin films. XRD and microstructural studies were carried out for structural characterization. The films, after electrochemical oxidation, were tested for their electrical properties and were found to show superconducting behavior below Tc = 104.7 K.

Studies on room temperature electrochemical oxidation and its effect on the transport properties of TBCCO films

A novel room temperature electrochemical process for the synthesis of single-phase Tl2Ba2Ca2Cu3O10 (TBCCO/Tl-2223) superconducting films has been developed. Electrochemical parameters were optimized by studying linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry (CA) for the deposition of Tl–Ba–Ca–Cu alloy at room temperature. The superconducting films of the TBCCO were obtained by two oxidation techniques. In the first technique, the electrodeposited Tl–Ba–Ca–Cu alloyed films were oxidized at various temperatures in flowing oxygen atmosphere. In the second technique, stoichiometric electrocrystallization to get Tl2Ba2Ca2Cu3O10 (Tl-2223) was completed by electrochemically intercalating oxygen species into Tl–Ba–Ca–Cu alloy at room temperature for various lengths of time. The oxygen content in the samples was varied by varying the electrochemical oxidation period, and the changes in the crystal structure, superconducting transition temperature (Tc) and critical current density (Jc) were recorded. The high temperature furnace oxidation technique was replaced by the room temperature electrochemical oxidation technique. The dependence of superconducting parameters on oxygen content is correlated with structure–property relations.

Studies on the fabrication of Ag/Hg1Ba2Ca1Cu2O6+δ/CdSe heterostructures using the pulse electrodeposition technique

Metal/superconductor/semiconductor (Ag/Hg1Ba2Ca1Cu2O6+δ (Hg-1212)/CdSe) heterostructures have been successfully fabricated using the pulse electrodeposition technique. The electrochemical parameters are optimized and diffusion free growth of CdSe on to Ag/Hg-1212 was obtained by employing underpotential deposition and by studying nucleation and growth mechanism during deposition. The heterostructures are characterized by x-ray diffraction, scanning electron microscopy studies and low-temperature four-probe electrical resistivity measurements. After the deposition of CdSe, the critical transition temperature of Hg-1212 films was found to be increased from 115 K with Jc (77 K) = 1.7 × 103 A cm−2 to 117.2 K with Jc (77 K) = 1.91 × 103 A cm−2. Tc and Jc (77 K) values were 120.3 K and 3.7 × 103 A cm−2, respectively, when the heterostructure was irradiated with red He–Ne laser. The improvements in superconducting properties of Hg-1212 in Ag/Hg-1212/CdSe heterostructures have been explained at length in this paper.

Electrochemical oxidation of Y1Ba2Cu3 alloyed layers using an alkaline bath

Abstract The electrochemical oxidation of Y 1 Ba 2 Cu 3 alloyed layers using an alkaline bath are reported for the first time. The alloyed Y–Ba–Cu films were electrodeposited onto silver substrates at a deposition potential of −1.75 V with respect to a saturated calomel electrode (SCE) from a dimethyl sulfoxide (DMSO) bath. Intercalation of oxygen species into Y–Ba–Cu alloy films was then carried out at room temperature using the electrochemical technique. The room-temperature electrochemical technique for oxygenation reduces the reaction time and avoids annealing at higher temperatures. The Y 1 Ba 2 Cu 3 O 7−δ thin films were prepared with different oxidation periods and studied for structural, microstructural and electrical properties.

The nucleation and growth mechanism of the electrodeposition of Tl2Ba2Ca2Cu3O10 superconducting thin films on Al-substrate

The present study demonstrates the nucleation and growth mechanism of the Tl2Ba2Ca2Cu3O10 (Tl-2223) superconductor by the electrodeposition technique on low cost aluminum coated glass (ALCG)-substrate at low processing temperature and short synthesis time, which is one of the most important aspects demanded of superconducting materials in practical applications. Superconducting thin films of Tl-2223 have been fabricated by the electrodeposition process on crystalline ALCG-substrate for the first time. The electrodeposition potential was optimized by studying the electrochemical behavior of the precursors by cyclic voltammetry (CV). All the precursor components, including Tl, were deposited at an optimized potential of −3 V with respect to a saturated calomel electrode (SCE) for 5 min followed by the heat treatment at 700 °C for 2 h in flowing oxygen atmosphere. X-ray diffraction (XRD) studies confirmed the presence of the Tl-2223 phase with marked preferential orientation along the c-axis. Atomic force microscopy (AFM) images show uniform and compact morphology with growth of rod-like grains (50–100 nm width) of Tl-2223 along the plane parallel to the ALCG-substrate. The transport measurement for Tl-2223 film showed a superconducting transition temperature Tc of 125 K and a critical current Jc of 0.31 × 106 A cm−2 at 77 K.

Synthesis of single-phase HgBa2Ca2Cu3O8+δ high-Tc superconducting films using the multistep electrolytic process

We report on the use of the multistep electrolytic process for the synthesis of high-Tc single-phase HgBa2Ca2Cu3O8+δ (Hg-1223) superconducting films. The process includes: (i) deposition of BaCaCu precursor alloy; (ii) oxidation of BaCaCu films; (iii) electrolytic intercalation of Hg in precursor Ba2Ca2Cu3Ox films; (iv) electrochemical oxidation and annealing of Hg-intercalated Ba2Ca2Cu3Ox films to convert into Hg-1223. Films were characterized by thermo-gravimetric analysis and differential thermal analysis, x-ray diffraction and scanning electron microscopy. The electrolytic intercalation of Hg in Ba2Ca2Cu3Ox precursor proves to be a novel alternative to the high-temperature–high-pressure mercuration process. The films are single-phase Hg-1223 with Tc = 121.5 K and Jc = 4.3 × 104 A cm−2 at 77 K.

Room temperature electrochemical synthesis of Hg-1212 superconducting thin films

Abstract In the present investigation, the novel two-step electrochemical process of room temperature synthesis of Hg-1212 superconducting films has been developed and reported first time. Electrochemical parameters were optimized by studying cyclic voltammetry, linear sweep voltammetry and chronoamperometry for the deposition of Hg–Ba–Ca–Cu alloy at room temperature. Current time transient showed progressive growth with hemispheriodal granules, which were then revealed by scanning electron microscopy. Stoichiometric electrocrystallization to get Hg 1 Ba 2 Ca 1 Cu 2 O 6+ x (Hg-1212) was completed by electrochemically intercalating oxygen species into Hg–Ba–Ca–Cu alloy at room temperature. The oxygen content in the samples was varied by varying the electrochemical oxidation period and the changes in the crystal structure, microstructure, and superconducting transition temperature ( T c ) and critical current density ( J c ) were recorded. The films oxidized for 28 min showed T c =104.7 K with J c =1.437×10 3 A/cm 2 . The dependence of superconducting parameters on oxygen content is correlated with structure property relations and reported in this paper.

A pathway to high Tc and Jc with the hetero–nano interface of the Tl2Ba2Ca2Cu3O10/Al heterostructure

For the first time, we report on a pathway to high Tc and Jc using the superconducting hetero–nano structures of Tl2Ba2Ca2Cu3O10/Al (Tl-2223/Al). A two-dimensional nano-stripe structure at the interface of Tl-2223/Al was fabricated using the room-temperature electrochemical complexing technique. The confinement of the charge transport along the stripes at the hetero–nano interface was studied at different temperatures ranging from 300 K to 77 K. The high Jc along the interface at different temperatures is explained on the basis of Andreev reflections from the interface followed by confinement of charge transport along the ab-plane (superconducting path) of the Tl-2223 unit cell. The model has been proposed to explain the mechanism of high Tc and Jc observed at the hetero–nano interface. The phenomenon of a pathway to high Tc and Jc using the Tl-2223/Al hetero–nano interface was ascertained as a result of destroying the interface by irradiating the heterostructure.

Electrochemical synthesis of TBCCO films

Abstract Tl–Ba–Ca–Cu alloyed films were electrodeposited at a deposition potential of −1.25 V with respect to saturated calomel electrode (SCE). Intercalation of oxygen species into Tl–Ba–Ca–Cu alloyed films were then carried out at room temperature, the first time using the electrochemical technique. The films oxidized for 20, 25 and 28 min from 1 N KOH electrochemical bath show superconducting behaviour with T c values of the order of 76.5, 103, and 114 K respectively. The room temperature electrochemical technique for oxygenation, reduces the reaction time, avoids annealing at higher temperatures and hence prevents the inhalation of toxic thallous oxide vapours during processing.

Studies on photoinduced effects in Ag/Bi-Sr-Ca-CuO heterojunctions

Polycrystalline films of Bi-Sr-Ca-CuO are deposited on silver substrate using the pulse electrodeposition technique and then electrochemically oxidized at room temperature in 1N KOH solution. Films thus prepared show a resistanceless state below 103 K. Photoinduced effects in heterostructures formed with Bi-based superconducting thin films and Ag (Ag/BSCCO) are studied and reported for the first time. Photovoltages generated across the junction with visible light excitation are found to vary with level of excitation and temperature. The magnitude of the photovoltage is found to decrease linearly with decrease in temperature and dropped down suddenly at 104 K, the superconducting transition temperature of BSCCO present in the junction.