Intergranular flux pinning in underdoped and overdoped R1−xCaxBa2Cu3Oz (R=Y, Gd; x=0, 0.2) samples

The tetragonal FeSe phase is an intensively investigated iron based superconductor. In this study we examined the influence of Ag addition on the superconducting properties of selenium deficient polycrystalline FeSe 0.94 . The samples were obtained by solid state reaction and melting methods. XRD analysis shows the presence of tetragonal phase and EDX analysis establishes inhomogeneous Ag distribution in the grains. The superconducting properties were investigated by fundamental and third harmonic AC magnetic susceptibility. The intergranular critical current determined from AC magnetic susceptibility in the Ag doped sample is several times higher than that in the undoped one, obtained by melting at approximately the same temperatures. Intragranular current is field independent up to almost 1000 Oe. Using the temperature dependence of third harmonic AC magnetic susceptibility at different DC magnetic fields, the irreversibility lines were obtained for all samples. It is found that Ag addition increased the irreversibility field in comparison with undoped melted and powder sintered samples. All results show that the Ag addition in selenium deficient (FeSe 0.94 ) samples leads to improvement of inter-and intra-granular properties: screening ability, pinning, activation energy and critical current and improves the irreversibility line.

Section: Frequency Dependence Of Ac Magnetic Susceptibilitymentioning

confidence: 99%

The Effect of Ag Addition on the Superconducting Properties of FeSe0.94

Nazarova

Buchkov

Terzieva

et al. 2014

“…Although Ca substitution at the Y site has been used to improve the J c of Y:123 superconducting systems [1][2][3][4][5], it also leads to oxygen loss from Cu-O 2 planes, and consequently, T c is decreased [6][7][8][9]. However, introduction of Ca contents at the Y site may lead to oxygen loss from Cu-O 2 planes as a result of the difference of coordination number between Y (8-fold) and Ca (6-fold) [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Mechanical and Transport Properties of Argon Annealed Y1 − x Ca x :123 Superconductors

Sedky

2016

We report here the effects of argon heat treatment at 450 • C for 12 h on two similar sets of oxygenated Y 1 − x Ca x :123 superconducting samples prepared by two different heat treatments and oxygen purity as reported by Sedky and Abu-Ziad (Physica C 470, 659; 2010). The oxygenated samples are called ssqHp, sssHp, ssqLp, and sssLp, and the Ar annealed samples are called ssqHpAr, sssHpAr, ssqLpAr, and sssLpAr. It is found that the c parameter of annealed samples is gradually increased with Ca addition for all samples, while orthorhombic distortion (OD) is decreased. It is also noted that Ar heat treatment decreased the link between superconducting grains for all samples, and a linear decrease in microhardness (Vickers hardness number (VHN)) with Ca addition is obtained. But the rate of increase/decrease of the c parameter, OD, and VHN against Ca content is different in ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples. Interestingly, the sssHpAr and ssqLpAr samples show a considerable loss of oxygen and small decrease in T c . While the ssqHpAr and sssLpAr samples show much smaller loss of oxygen and a gradual increase in T c up to 16 and 17 K, respectively. These A. Sedky results are discussed in terms of the mechanism of oxygen loss by Ca in addition to ssqHpAr and sssLpAr samples as compared to sssHpAr and ssqLpAr samples.

“…flux flow motion plays an important role in its AC loss [7,[14][15][16]. In addition, Ca-doped YBCO has similar behavior [17]. However, study on the A-site and B-site co-doped YBCO has not been made so much because 2-site doping YBCO is too difficult.…”

Section: Introductionmentioning

confidence: 99%

Field-dependent Behavior of AC Susceptibility in [Y 0.8 Ca 0.2](Ba 0.5 Sr 0.5)2 Cu 3 O 7−δ

Lee

Seo

Valladares

et al. 2015

The AC susceptibility of [Y 0.8 Ca 0.2 ](Ba 0.5 Sr 0.5 ) 2 Cu 3 O 7−δ was investigated as a function of frequency and amplitude of AC magnetic field. The susceptibilities of the sample display the field amplitude dependence. The peak temperature (T p ) of its imaginary part shows not frequency dependence but field amplitude dependence. The frequency effect on AC susceptibility was negligible. As the field amplitude increases, T p shifts to lower temperature.