The sol-gel process is employed to synthesize single-phase lead-doped Bi2Sr2Ca2Cu3O10 ((Bi,Pb)-2223) superconductors. The composition which can yield single-phase (Bi,Pb)-2223 compound is arrived at by varying the calcium and copper concentrations. Samples prepared with the composition Bi1.68 Pb0.32Sr1.75Ca1.8Cu2.8Oy result in the formation of phase pure compound. The mechanism of formation of this compound and the intermediate steps involved during the phase formation are established by X-ray diffraction (XRD) and differential thermal analytical (DTA) studies. It is found that (Bi,Pb)-2223 phase formation occurs through the reaction of (Bi,Pb)-2212 phase with Ca2CuO3 and CuO in the liquid phase obtained from the partial melting calcium rich Bi-2212 phase. The stability region for the (Bi,Pb)-2223 compound is identified as 1118 to 1138 K. Several incongruent melting reactions are identified from XRD and DTA studies during the decomposition of Bi-2223 compound. © 1996 Academic Press, Inc.

Upadhyayula V Varadaraju

Department Of Chemistry

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Solid State Chemistry

Bi-2223 superconductors with silver additions are synthesized by sol-gel process. The effect of silver on the formation of Bi-2223 phase is studied. The addition of silver brings down the reaction temperature as well as annealing time for the formation of Bi-2223 phase. The presence of silver affects the Tc of the Bi-2212 phase. The heat treatment of silver added Bi-2223 samples above 1113 K show poor superconducting properties due to partial melting of Bi-2223 phase. © 1998 Chapman &amp; Hall.

Journal of Materials Science

Effect of silver on the formation of Bi2Sr2Ca2Cu3O10 (Bi-2223) superconductors by sol-gel process

The sol-gel process is a versatile technique generally used to obtain fine, homogeneous powders. The quality of the final product and the kinetics and mechanism by which compound formation takes place through the sol-gel process is dependent on the process parameters, such as pH, water-to-salt molar ratio and temperature of hydrolysis. In the present study, acetates of yttrium, barium and copper were employed to synthesize the high-temperature superconductor YBa2Cu3O7 (123) by the sol-gel process. Differential thermal analysis (DTA), thermogravimetry (TG) and X-ray diffraction (XRD) techniques were employed to study the effect of pH on the kinetics and mechanism of formation of 123. The formation of 123 was found to take place either in a single step or in two steps, depending on the pH of the solution of the starting materials. The formation of 123 occurred in two steps in the samples prepared at pHs 6, 7 and 8, whereas only a single step of formation was observed in the samples prepared at pHs 6.5 and 7.5. To identify intermediate products during the formation of 123, samples were quenched at respective differential thermogravimetry (DTG) peak temperatures and characterized by XRD. Based on the kinetic analysis of the TG data, the mechanism for formation of 123 was identified as nucleation and growth following Avrami's kinetics. Samples prepared at pH 6 resulted in the formation of pure 123 compound, whereas samples prepared at other pHs resulted in impurity phases such as Y2BaCuO5 (211) along with 123. The activation energy for the formation of 123 was evaluated as 223 kJ mol-1. © 1993.

Thermochimica Acta

Thermoanalytical investigation of the formation of YBa2Cu3O6.5

High temperature superconducting YBa2Cu3O7 (123) compounds were synthesized through various sol-gel processes using acetate, nitrate-citrate, acetate-citrate and acrylamide gel routes. The gel samples were characterized using IR, electronic and electron spin resonance (ESR) spectroscopy and scanning electron microscopy and the bonding behaviour in the gels was established and correlated to the phase purity of the 123 compound. Heat-treated gel samples were characterized by X-ray diffraction and superconducting properties were evaluated by resistivity and susceptibility measurements. IR, electronic and ESR spectral studies indicated that gels derived from acetate and acetate-citrate routes contained isolated copper acetate groups, whereas homogeneous heterometal ionic networks were observed in gels derived from nitrate-citrate. The ESR spectrum of acrylamide gels suggested homogeneous distribution of the copper(II) ions in the acrylamide polymeric network giving clearly resolved parallel and perpendicular features characteristic of copper(II). The samples derived from the acrylamide gel route are found to yield single-phase 123 compound with sharp resistive and diamagnetic transitions at 90 K, whereas other gel routes yielded multiphase samples with impurities of either BaCuO2 or Y2BaCuO5 phases. © 1995.

Journal	Journal of Solid State Chemistry
Publisher	Academic Press Inc.
ISSN	00224596
Open Access	No