Browsing by Author "K.K. Verma"

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Effect of annealing temperature on the structural-microstructural and electrical characteristics of thallium bearing HTSC films prepared by chemical spray pyrolysis technique
(Indian Academy of Sciences, 2005) K.K. Verma; R.S. Tiwari; O.N. Srivastava
In order to get good quality reproducible films of Tl: HTSC system, we have studied the different annealing conditions to finally achieve the optimized annealing condition. In the present investigation, Tl-Ca-Ba-Cu-O superconducting films have been prepared on YSZ (100) and MgO (100) single crystal substrates via precursor route followed by thallination. The post deposition heat treatments of the precursor films were carried out for various annealing temperatures (870°C, 890°C) and durations (1 and 2 min). The optimized thallination procedure occurred at 870°C for 2 min into good quality films with Tc (R = 0) ∼ 103 K for YSZ and Tc (R = 0) ∼ 98 K for MgO substrates, respectively. Further we have correlated the structural/microstructural characteristics of the films. © Indian Academy of Sciences.
Heat ameliorative measures in Murrah buffalo (Bubalus bubalis) heifers during summer: effect on microclimate, thermal comfort, and behavior
(Springer Science and Business Media Deutschland GmbH, 2023) K.K. Verma; M. Singh; U.S. Narwaria; H.C. Joshi; B.H.M. Patel
Water buffalo (Bubalus bubalis) is the mainstay of milk production in Asian countries including India. However, the hot climate of the country remains the biggest bottleneck to exploit the potential of this species. Therefore, a study was conducted to assess the effect of heat ameliorative measures on microclimate, thermal comfort, and behavior of Murrah buffalo heifers during summer. Buffalo heifers (n = 24) between the age of 15 and 20 months with a mean body weight of 363.75 ± 11.27 kg were randomly grouped into four treatments based on their age and body weight. The heifers kept in the shed without any cooling served as CON (control), while the animals of group CJ were tied with a cooling jacket. The buffalo heifers of the CJF group were subjected to the cooling jacket with forced air ventilation, whereas the intermittent (10 min at 2-h intervals) sprinkling followed by forced air ventilation was practiced in group SF between 900 and 1800 h throughout the experiment. The microclimatic variables were low in the sheds of groups CJ, CJF, and SF than the CON. The physiological responses such as rectal temperature, skin temperature, respiration rate, and pulse rate were reduced in groups CJ, CJF, and SF than the CON at 1400 h. The serum cortisol was less in the CJF and SF than those of CON group. The animals of the CJ, CJF, and SF groups spent more time for feeding and rumination with less frequent longer bouts. The extended periods of lying followed by shorter standing and idling were observed in groups CJ, CJF, and SF when compared with the CON. It may be therefore concluded that cooling jacket and intermittent sprinkling in combination with forced air ventilation might be helpful in improving the micro-environment, thermal comfort, and behavior of buffalo heifers particularly under tropical climates during summer. © 2023, The Author(s) under exclusive licence to International Society of Biometeorology.
Optimisation of annealing condition for the prepration of (Bi 5Pb)-Sr-Ca-Cu-O HTSC films by spray pyrolysis technique
(2010) K.K. Verma; R.K. Sinha; R.S. Tiwari; O.N. Srivastava
High temperature superconducting (HTSC) films (Bi1Pb)-Sr-Ca-Cu-O have been prepared by spray pyrolysis technique on MgO (100) single crystal substrate. Annealing steps in regard to oriented nature of the films have been studied in detail which have been confirmed by XRD and SEM results. The optimized film has shown maximum Tc (R=0) of ∼82 K and /c is ∼6×l03 cm-2 at 77 K.
Preparation of high Tc superconducting YBaCuO film by flash evaporation
(1989) K.K. Verma; R.S. Tiwari; O.N. Srivastava
HTSC thin films of YBa2Cu3O7-x have been prepared by flash evaporation technique on MgO substrates. The films processed through optimised annealing treatment under oxygen, exhibited orthorhombic phase which suggested the formation of the HTSC phase. Surface topography monitored by secondary electron imaging shows platelet shaped crystal which have preferential basal orientation. The Tc-onset and Tc-zero for these films have been found to be≈93K and≈80K respectively. © 1989.
Preparation of high-Tc superconducting thin films of Tl-Ca-Ba-Cu-O by the chemical spray pyrolysis technique
(1992) K.K. Verma; A.K. Sexena; A.K. Singh; R.S. Tiwari; O.N. Srivastava
Thin films of the Tl-Ca-Ba-Cu-O system have been prepared on MgO and YSZ single-crystal substrates by a simple chemical process (the spray pyrolysis technique). Since Tl is toxic, the Tl-Ca-Ba-Cu-O films were prepared by a two step process. Firstly, precursor (Ca-Ba-Cu-O) films were prepared followed by diffusion of Tl derived by vaporizing Tl2O3 in a closed system under oxygen flow. A new feature found in the present investigation is that the Tc (R=0) of the Tl-Ca-Ba-Cu-O films has been found to depend upon the microstructural characteristics of the precursor films which can be varied by annealing these films. The Tc (R=0) of the Tl-Ca-Ba-Cu-O HTSCs films prepared from the annealed precursor films has been found to be higher than in the films prepared from the as-deposited precursor films. As, for example, in the case of a film on a MgO substrate, the Tc (R=0) has been enhanced from approximately 90 K to approximately 98 K. The highest T c obtained by the authors for the films synthesized from the annealed precursor films on YSZ substrates corresponds to approximately 103 K. The XRD reveals the biphasic (2223/2122) nature of the films. The microstructural characteristics of the films as monitored by SEM reveals the partially oriented nature of the Tl-Ca-Ba-Cu-O film.
Preparation of Tl-Ca-Ba-Cu-O High-temperature superconducting thin films by flash evaporation
(1990) K.K. Verma; G.D. Verma; R.S. Tiwari; O.N. Srivastava
The Tl-Ca-Ba-Cu-O thin films conforming to 2122 composition have been deposited by a comparatively simple and viable process, the thermal flash evaporation of the Ca-Ba-Cu-O precursor flux followed by diffusion of Tl derived by vapourising Tl2O3. The films have been characterised by R-T monitoring, XRD, SEM and EDAX. The films have been found to have Tc (R=0) of 88 K for ZrO2 and 97 K for MgO substrates. The films have been found to be partially oriented with the c axis perpendicular to the film surface. © 1990 The Japan Society of Applied Physics.
Preparation of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O superconducting films by conventional techniques
(Springer India, 1991) K.K. Verma; A.K. Saxena; S. Rastogi; R.S. Tiwari; O.N. Srivastava
High temperature superconducting films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O have been deposited on different substrates using conventional techniques, like flash evaporation and spray pyrolysis. The microstructural investigation of the films by SEM technique reveals the partially oriented nature of the crystallites. In the case of spray-deposited Bi-Sr-Ca-Cu-O HTSC films it has been found that film/substrate mismatch is not the decisive factor for the superconducting transition temperature T c. © 1991 Indian Academy of Sciences.
Studies on the rf squid effect in tl-ca-ba-cu-o thin films prepared by the spray pyrolysis technique
(1994) N. Khare; A.K. Gupta; A.K. Saxena; K.K. Verma; O. Srivastava
RF SQUID behaviour in thin films of Tl-Ca-Ba-Cu-O has been studied. The films were prepared by the spray pyrolysis technique. Two films (A and B) which have Tc(R=0) values of 85 K and 103 K respectively, were chosen for the RF SQUID studies. Film A consists mainly of 2122 phase with needle-like grains whereas film B mainly consists of 2223 phase with well connected plate-like grains. RF SQUID modulations in film B were observed up to 101 K. The SQUID was also operated in flux-looked-loop mode. The RF SQUID fabricated from film B was found to exhibit better flux noise performance than that fabricated from film A. © 1994 IOP Publishing Ltd.