arXiv subjects

Anurag Gupta

Publications and source records attributed to Anurag Gupta.

58 records · Page 4Linked to original sources

arXiv2004

Systematic induction of superconductivity in Y1-xCaxBa2Cu3O6.3 system

Compounds of series YBa2Cu3O7-d (d = 0.7), being synthesized by solid-state synthesis route with x = 0.0, 0.10, 0.15 and 0.20, crystallize in single-phase form with tetragonal structure (space group P4/mmm). The c-lattice parameter increases with increasing x, indicating successful substitution of Y3+ by bigger Ca2+ ion. Resistance versus temperature (R vs. T) measurements show that pristine sample (x = 0.0) is semiconducting down to 5 K. Induction of superconductivity is seen with an increase in x. The x = 0.10 sample exhibit the onset of superconducting transition (Tconset) at around 42 K without attaining zero resistance superconducting transition temperature (TcR=0) state down to 5 K. For x = 0.15 and 0.20 samples TcR=0 is observed at 25 K and 35 K with Tconset of 52 K and 61 K respectively. Thermo-electric power (S) measurements in temperature range of 5 - 300 K, exhibited TcS=0 at around 25 K and 35 K respectively for x = 0.15 and 0.20 samples. Further a sign change in S from +ve to -ve is observed at low temperatures for x = 0.0 sample. Room temperature +ve S value decreases with increase in x, indicating enhanced number of mobile holes. The Magneto-transport measurements under applied magnet ic fields of 3 and 6 Tesla show the broadening of superconducting transition for x = 0.15, and 0.20 samples. For x = 0.10 sample the superconducting transition is suppressed in applied fields of 3 and 6 Tesla. Our results will help in constructing the complete phase diagram of Y1-xCaxBa2Cu3O7-d compounds with various x and d.

cond-mat.supr-con↗

arXiv2003

Effect of Sr substitution on the stability of CuO chains in oxygen and nitrogen annealed YBa2-xSrxCu3O(x = 0.0, 0.50, 1.0) superconducting system

Samples of YBa2-xSrxCu3O7-d (x = 0.0, 0.50, 1.0) series were synthesized by solid-state reaction and first annealed in flowing O2 gas. All samples crystallized in orthorhombic structure, where orthorhombic distortion was found to decrease with an increase in x. Four probe resistivity measurements showed that superconducting transition temperature (Tc) decreases monotonically with x at a rate of dTc/dx = 1.3 K/at%. The sample with x=0 had a Tc = 91 K. The samples were further annealed in flowing N2 gas at 450 0C. The Tc of all samples decreased by nitrogen annealing. Interestingly, the decrease in Tc(x) became nearly three times larger at a rate of dTc/dx = 3.7 K/at%. The sample with x=0 had a Tc = 42 K. We discuss possible reasons and implications of the Tc(x) suppression vis stability of CuO chains. Key words: Y-123, Sr substitution, Superconducting transition

cond-mat.supr-con↗

arXiv2003

Comparison of the superconducting critical transition temperature of LaBaCaCu3O7-d and NdBaCaCu3O7-d

LaBaCaCu3O7 (La:1113) and NdBaCaCu3O7 (Nd:1113) compounds are synthesized by solid state reaction route. Both compounds crystallize in tetragonal structure. Four probe resistivity measurements showed that superconducting transition temperature (Tc) is 73 K and 41 K respectively for La:1113 and Nd:1113 compounds. Considering the fact that for RE:123 (REBa2Cu3O7) compounds the Tc hardly depends upon the choice of RE (Rare earth, except Ce, Pr and Tb), the current nearly two fold increase in Tc of La:1113 when compared to Nd:1113, warrants serious discussion.

cond-mat.supr-con↗

arXiv2003

Structural and magnetic properties of MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds with M = Fe and Co

MSr2Y1.5Ce0.5Cu2Oz (M-1222) compounds, with M = Fe and Co, have been synthesized through a solid-state reaction route. Both compounds crystallize in a tetragonal structure (space group I4/mmm). A Rietveld structural refinement of room-temperature neutron diffraction data for Fe-1222 reveals that nearly half the Fe remains at the M site, while the other half goes to the Cu site in the CuO2 planes. Existence of Fe at two different lattice sites, is also confirmed by 57Fe Mossbauer spectroscopy from which it is inferred that nearly 50% of the total Fe occupies the Cu site in the CuO2 planes as Fe3+, whereas the other 50 % is located at the M site with nearly 40 % as Fe4+ and around 10% as Fe3+. For the M = Co compound, nearly 84 % of Co remains at its designated M site, while the rest occupies the Cu site in the CuO2 planes. The oxygen content, z, based on oxygen occupancies refined from the neutron diffraction data, comes close to 9.0 for both the samples The ZFC and FC magnetization curves as a function of temperature show a complex behavior for both Fe-1222 and Co-1222 compounds.

cond-mat.str-el↗