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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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8 results
Now showing 1 - 8 of 8
- 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. - 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 studies on (Y1-xLnx)Ba2Cu3O7, Ln=La,Pr,Tb(01-01-1988)
;Natarajan, S. ;Chandrasekaran, K. ;Thomas, K. A.; ;Subba Rao, G. V. ;Raju, N. P.; Srinivasan, R.Studies on the title compounds show that while La and Pr form complete solid solutions, Tb does not substitute for Y. Superconducting transition temperature (Tc) decreased with increasing x from 91K but pronounced effect is noted for Ln=Pr. PrBa2Cu3O7 exhibits a semiconductor behavior. © 1988 Elsevier Science Publishers B.V. - PublicationEnhancement of thermopower in the high T c superconductor YBa2Cu3O7 and related compounds(01-08-1987)
;Srinivasan, R.; ;Raju, N. P. ;Natarajan, S.; Subba Rao, G. V.The absolute thermopower of single phase YBa2Cu3O7 and Y0.8Er0.2Ba2Cu3O7 has been measured in the range 250 K to the superconducting transition temperature. It is found that these compounds show a large enhancement of thermopower in the range 150 K down to T c. This enhancement shows a steep exponential drop as the temperature increases from the transition temperature. The temperature variation of the enhancement is too steep to be accounted for by electron-phonon or electron-local structural excitation mechanisms. © 1987 Indian Academy of Sciences. - PublicationEffect of chemical substitution on the high-Tc behavior of YBa2Cu3O7(01-01-1987)
; ;Natarajan, S. ;Kumar, T. S.Sampath ;Paranthaman, M. ;Rao, G. V.Subba ;Raju, N. P.Srinivasan, R.The effect of chemical substitution on the high-Tc (91 K) superconducting oxide YBa2Cu3O7, with the distorted perovskite structure, has been studied. Subtle changes in Tc occur when Y is partly replaced by Dy, Ho, Er, Tm, Yb, Lu, Bi and In. The possibility of coexistence of magnetic order and superconductivity or reentrant behavior in these high-Tc compounds will be described and discussed. © 1987.