Rietveld analysis and superconductivity of compounds

Abstract

A series of single-phase La 3−x Ca 2x Ba 3−x Cu 6 O y (0 ≤ x ≤ 0.75) compounds with tetragonal triple-perovskite structure is studied by Rietveld analysis. For x ≤ 0.43, all of the Ca 2+ ions enter the centre site: the Y 3+ site of the tetragonal YBa 2 Cu 3 O y phase. For 0.43 < x ≤ 0.75, a maximum of about 1/2 of the Y 3+ sites are occupied by Ca 2+ ions and the extra Ca 2+ ions enter the Ba 2+ site. Double plateaux are found between T c and OF (the difference between the occupancy factor of Ca 2+ ions at the Y 3+ site and that of La 3+ ions at the Ba 2+ site). It is suggested that T c of the La-Ca-Ba-Cu-O compounds containing 50 mol% copper atoms with tetragonal triple-perovskite structure can be predicted from the correlation of T c versus OF.

Prediction of inorganic superconductors with quasi-one-dimensional crystal structure

“…Copper ions in Cu1O6 octahedra can be left or substituted by Hg 2+ , Tl 3+ , or Pb 2+,4+ . All the above substitutions were successfully performed in high-T c cuprates (see, for example, [88][89][90]). The composition of these hypothetical superconductors can be as follows: (Ba 0.4 A 0.6 ) 4 (A 0.6 Ca 0.4 )Cu 4 BO 13−δ (where A = Tl 3+ , La, Y; B = Tl 3+ , Cu, (Hg 1−x Tl x ), (Hg 1−x Cu x )) and (Sr 0.4 Y 0.6 ) 4 (Y 0.6 Ca 0.4 )Cu 4 BO 13−δ (where B = Cu, (Tl 1−x Pb x )).…”

Superconducting properties of the Sr substituted La3Ca1−xSrxBa3Cu7Oysystem

“…Neutron diffraction studies confirm the occupancy of Ca at the La site (the Y site of the tetragonal Y-123 phase) with a concomitant displacement of La on to Ba site for the La 3 Ca x Ba 3 Cu 6+x O y system [13,[15][16][17]. It is interesting to know that Ca substitutes for both La and Ba sites with a corresponding amount of La substituting at the Ba site [15,16]. We suppose that, in La-3137, nearly 60% of Ca occupies the usual La site, while the remaining 40% and a corresponding amount of La occupy the Ba site.…”

“…This may mainly be due to the site occupancies of the dopants in the La 3 Ca 1−x Sr x Ba 3 Cu 7 O y compounds. Neutron diffraction studies confirm the occupancy of Ca at the La site (the Y site of the tetragonal Y-123 phase) with a concomitant displacement of La on to Ba site for the La 3 Ca x Ba 3 Cu 6+x O y system [13,[15][16][17]. It is interesting to know that Ca substitutes for both La and Ba sites with a corresponding amount of La substituting at the Ba site [15,16].…”