• H K Singh

      Articles written in Bulletin of Materials Science

    • Investigations on Tl-2223 thin films fabricated through ultrasonic spray pyrolysis under oxygen deficient conditions

      H K Singh O N Srivastava

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      In this paper we have shown that polycrystalline films corresponding to Tl-2223 phase can be grown by employing high thalliation temperatures and short thalliation times. Ultrasonically deposited precursor films corresponding to Ba2Ca2.2Cu3.3Ox(Agy) have been thalliated under high vacuum (∼ 10-5 torr) at 890°C to obtain single phase Tl-2223 films. An off-stoichiometric and unreacted pellet of composition Tl2.05Ba2Ca2Cu3Oz has been used as source of Tl. We have shown that oxygen ambient is not necessary for the growth of Tl-2223 phase. The as-thalliated films have Tc’s in the range 123 K ±0.70 K. TheTc has been found to be independent of the addition of AgNO3 to the precursor. The zero field transportJc has been observed to be > 1.2 X 105 A/cm2 at 77 K. NearTc (110 K-122 K),Jc has been observed to follow the power lawJc ∞ (1-T/Tc)p,p 2. A power law withp tt 1.4 has been observed for the temperature range 70 K-110 K. An optimum doping of Ag has been observed to induce about 25% increase inJc and it also leads to uniform and enlarged grain growth. The surface morphology of Ag free samples contains plate like grains having arbitrary shapes. In contrast to this 0.35 Ag doped sample exhibits nearly rectangular plate like grains

    • Effect of cationic size in Hg(Tl/Bi)Ba2Ca2Cu3O8+𝛿 on superconducting and microstructural characteristics

      Rajiv Giri H K Singh R S Tiwari O N Srivastava

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      In this paper we have reported investigations on the effect of simultaneous substitution of Bi and Tl at the H𝑔 site in the oxygen deficient H𝑔O𝛿 layer of H𝑔Ba2Ca2Cu3O8+𝛿 cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown H𝑔Bi0.2–𝑥Tl𝑥Ba2Ca2Cu3O8+𝛿 (with 𝑥 = 0.00, 0.05, 0.10, 0.15, 0.20) corresponds to the 1223 phase. It has been found that the 𝑇c varies with the average cationic size $\langle R_d \rangle$ of the dopantcations. The optimum 𝑇c of ∼ 131 K has been found for the composition H𝑔Bi0.15Tl0.05Ba2Ca2Cu3O8+𝛿. This composition leads to the average dopant cation size of ∼ 1.108 Å which is very close to the size of H𝑔2+ (∼ 1.11 Å). The microstructure for H𝑔Bi0.15Tl0.05Ba2Ca2Cu3O8+𝛿 has been found to be most dense and this phase exhibits the highest stability. The 𝐽c of the optimum material H𝑔Bi0.15Tl0.05Ba2Ca2Cu3O8+𝛿 is found to be ∼ 1.29 × 103 A/cm2 at 77 K.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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