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Upadhyayula V Varadaraju
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Upadhyayula V Varadaraju
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Upadhyayula V Varadaraju
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Varadaraju, Upadhyayula V.
Varadaraju, Upadhyayula
Varadaraju, U. V.
Varadaraju, Upadhyayula Venkata
Varadaraju, Upadhayayula V.
Varadaraju, U.
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17 results
Now showing 1 - 10 of 17
- PublicationSuperconductivity Studies on the High Tc Phase in the Y–Ba–Cu–O System(01-01-1987)
;Rao, G. V.Subba; ;Thomas, K. A. ;Vijayashree, R. ;Raju, N. P. ;Srinivasan, R. ;De, U. ;Janaki, J.Radhakrishnan, T. S.Synthesis, characterization and superconducting behavior of the phases (i) Y2-xBaxCu2O5 (0\leqslantx\leqslant1.6) and (ii) YBa2Cu3CxO7Cy (0\leqslantx\leqslant2.0) are reported. The composition YBa2Cu4O7Cy shows a Tc (zero resistance) of 94K. © 1987 The Japan Society of Applied Physics. - PublicationLithium insertion into phases with NZP structure(01-12-1987)
; ;Thomas, K. Antony ;Sivasankar, BommasamudramRao, G. V.SubbaInsertion of Li into the vacant sites (channels) of certain NZP phases (ATi2P3O12, A = Li, Na, and NbTiP 3O12) using BunLi at room temperature has been established; the preparation and preliminary structural and i.r. data of the phases are described. - PublicationMetal atom incorporation studies on the phases with NZP structure: â–¡NbTiP3O12(01-01-1987)
;Rao, G. V.Subba; ;Thomas, K. A.Sivasankar, B.A wide variety of electropositive elements of the periodic table can be inserted into the vacant sites in the host framework structure of hexagonal NbTiP3O12 (an analog of nasicon) to give rise to isostructural phases. Synthesis, characterization, and preliminary data on the structure, IR spectra, and electrical resistivity are presented. Possible areas for further exploration are delineated. © 1987 Academic Press, Inc. All rights reserved. - PublicationOxygen-enrichment of YBa2Cu3 YBa2Cu3O7-δ using the fluidization techniqueusing the fluidization technique(01-03-1989)
; ;Subba Rao, G. V. ;Chandrasekaran, K. D. ;Baradarajan, A. ;Krishnaiah, K. ;Agarwala, Mukesh ;Achutharaman, V. S. ;Venugopal, P. ;Padmanabhan, K. A. ;Vaidyanathan, L. S.Rangarajan, G.The oxygen-deficient phase of the high T c superconductor, YBa2Cu3O7, was oxygen-enriched using the fluidization technique to give good superconducting properties. The normal method of oxygen treatment at 900°C for 24 h and at 600°C for 24 h has been reduced to just one treatment at 600°C for 12 h by the fluidization technique to achieve almost the same strength of superconducting signal for the YBa2Cu3O7 powder, which establishes the attractiveness of the latter route for the large-scale preparation of superconducting material. The particle sizes were in the range 0-90, 90-180 and 180-420 μm. The fluidized particles were crystalline with orthorhombic distortion. T c onset, estimated using the a.c. magnetic susceptibility method, was 91·3 K. The volume fraction of superconducting material in the product was 83·7-85·3%, one of the highest values reported so far for YBa2Cu3O7. © 1989 Indian Academy of Sciences. - PublicationResistivity, Thermopower And Single-Particle Tunneling Studies On Some Zinc-Doped Yttrium Barium Copper Oxide Superconductors(01-11-1989)
;Srinivasan, R.; ;Subramaniam, C. K. ;Rajam, Prakash Fortunata; ;Radhakrishnan, Vijayashree ;Krishnan, H.; Subba Rao, G. V.Resistance and thermopower measurements have been made on a series of compounds, YBa2Cu3-xZnx07_Yl, with x - 0.025, 0.05, 0.1, 0.15 and 0.2. The superconducting transition temperature decreases as the zinc concentration increases. In a range of temperatures below TM, the mid point of the transition, the resistance shows an exponential temperature dependence fitting the phenomenological formula proposed by Ausloos et ai From the plot of logarithm of resistivity vs. (TM- T)1/2/T, one deduces a value of the average dimension of the Josephson junction to be a few tens of A, suggesting the microtwin boundaries to be the location of the junctions. The thermopower shows a peak always just above Tc. This conclusively shows that phonon drag is not the cause of the peak. The temperature dependence of the thermopower appears to resemble closely the earlier observations of Srinivasan et al. on yttrium barium copper oxide. Single-particle tunneling measurements carried out for two concentrations, x = 0 and 0.05, appear to indicate that the energy gap parameter scales with Tc, and 2Δ/kTchas an approximate value of 5.5. © 1989, Taylor & Francis Group, LLC. All rights reserved. - PublicationHIGH-T//c SUPERCONDUCTIVITY IN Ln//2// minus //xBa//xCu//2O//5 (1. 0 less than equivalent to x less than equivalent to 1. 6) AND LnBa//2Cu//3O//7 (Ln equals Dy, Er, Tm, Yb AND Y) COMPOUNDS.(01-12-1987)
;Subba Rao, G. V.; ;Vijayashree, R. ;Padmanabhan, K. ;Balakrishnan, R. ;Mary, T. A. ;Raju, N. P. ;Srinivasan, R. ;De, U. ;Janaki, J.Radhakrishnan, T. S.Structure and T//c data on LnBa//2Cu//3O//7 (Ln equals Dy, Ho, Er, Tm, Yb and Y) compounds are reported and discussed. No reentrant behavior has been noted in these high-T//c superconductors for Ln equals Er and Yb until 4. 2 K. Four-probe resistivity was measured in the range 77-300 K employing ultrasonically soldered In-contacts. An inductance bridge with carrier-frequency amplifier was used to quickly check the samples for superconductivity at and above 77 K. A calibrated test set-up was employed to measure the superconductivity transition by the magnetic susceptibility technique. - PublicationHigh-Tc superconductivity in Ln2-xBaxCu2O5 (1.0≤x≤1.6) and LnBa2Cu3O7 (Ln=Dy, Er, Tm, Yb and Y) compounds(01-01-1987)
;Rao, G. V.Subra; ;Vijayashree, R. ;Padmanabhan, K. ;Balakrishnan, R. ;Mary, T. A. ;Raju, N. P. ;Srinivasan, R. ;De, U. ;Janaki, J.Radhakrishnan, T. S.Structure and Tc data on LnBa2Cu3O7 (Ln=Dy, Ho, Er, Tm, Yb, and Y) compounds are reported and discussed. No reentrant behavior has been noted in these high-Tc superconductors for Ln=Er and Yb till 4.2 K. © 1987. - PublicationSpecific heat of praseodymium doped yttrium barium copper oxide(01-01-1988)
;Sankar, N.; ;Vaidhyanathan, L. S. ;Rangarajan, G. ;Srinivasan, R. ;Thomas, K. A.; Subba Rao, G. V.The specific heat of samples of Y1-xPrxBa2Cu3O7-y for x = 0.1 to 0.5 has been measured from 4.5 to 65 K using a quasi-adiabatic calorimeter. A plot of C/T vs T2 shows a linear behavior below 20 K. The excess specific heat due to praseodymium in all the compounds is obtained by subtracting the specific heat of YBa2Cu3O7-x from the that of doped compound. The excess specific heat shows a peak near 19 K and its height decreases with increase in x. The excess specific heat could be interpreted on the basis of Schottky anomalies due to Pr3+ and Pr4+ ions, the peak at 19 K arising from the former. The fraction of Pr3+ ion obtained from a fit to the specific heat curves decreases from 0.30 for x = 0.1 to 0.05 for x = 0.5. © 1988. - PublicationSuperconductivity behaviour in screen-printed YBa2Cu3O7 films(01-01-1988)
; ;Rao, G. V.Subba ;Chandrasekaran, K. D.Baradarajan, A.We have fabricated films of the high Tc superconducting oxide YBa2Cu3O7 by screen printing on alumina, calcia-stabilized zirconia, yttria-stabilized zirconia, SrTiO3 and La2CuO4 substrates. Alumina was found to be a suitable substrate for screen printing. La2CuO4 and SrTiO3 substrates can be used with shorter annealing times. Superconducting transition temperatures in the vicinity of 85 K have been established in some of the films. © 1980. - PublicationEffect of oxide additives on the properties of high temperature superconductor, YBa2Cu3O7(01-03-1989)
;Chandrasekaran, K. D.; ;Baradarajan, A.Subba Rao, G. V.The effect of oxide additives-CuO, SiO2, Y2O3, Bi2O3 and ZnO in 1-10 mol% on the sintering and superconducting properties of YBa2Cu3O7 was studied. SEM studies indicated improvement of grain size and interconnectivity due to the additives, the best results being obtained with Bi2O3, SiO2 and Y2O3. The superconducting transition temperature is unaffected (92±2 K) even with 10 mol % of the additives. ZnO, however, decreases the T c as expected. © 1989 Indian Academy of Sciences.