Structural changes in HgBa2Ca2Cu3O8+δ under high pressure

Core-level photoemission spectra of Mo0.3Cu0.7Sr2ErCu2Oy, a superconducting perovskite derivative. Unconventional structure–property relationships

“…The compounds with square coordination have not been doped successfully but those with copper in octahedral coordination have been over-doped. 25,[51][52][53][54] Therefore, shortening the apical oxygen distance in the oxygenated superconducting (Mo,Cu)-1212 samples could worsen the hole transfer (charge transfer) from the copper chain site. On the other hand, in the T′-phase superconductor where copper is square planar coordinated, the pressure coefficient of T C is negligibly small.…”

“…51,52 We can recall that HgBa 2 Ca 2 Cu 3 O 8+δ shows the largest T C having a large apical distance and an almost flat copper plane. 25,[51][52][53][54] Therefore, shortening the apical oxygen distance in the oxygenated superconducting (Mo,Cu)-1212 samples could worsen the hole transfer (charge transfer) from the copper chain site. Nevertheless, our TEP measurements show that the hole concentration in the CuO 2 plane increases after oxygenation in the present materials.…”

“…12,13,16 Moreover, the structural refinement of the as-prepared (non-superconducting) and oxidized (superconducting) phases for the first four members of the homologous series (Cu 0.75 Mo 0.25 )Sr 2 (Ce,Y) s -Cu 2 O 5+2s+δ by Grigoraviciute et al 17 showed that, besides the 1212 compound, the 1222 and 1232 molybdo-cuprate compounds also show the trend of shortening apical oxygen dis-tances after oxygenation. 25 High-temperature superconductors have been widely studied by photoemission spectroscopy; 26 X-ray photoelectron spectroscopy (XPS) is a powerful tool for studying the doping of the 3d element in the Cu site and can study the electronic structure of the system. 25 High-temperature superconductors have been widely studied by photoemission spectroscopy; 26 X-ray photoelectron spectroscopy (XPS) is a powerful tool for studying the doping of the 3d element in the Cu site and can study the electronic structure of the system.…”

“…At the same time, in these compounds, 12,13,16 the out-of-plane buckling angle 24 increases with oxygenation in disagreement with the common belief that maximum T C 's are achieved when perfectly flat CuO 2 planes are present, as exemplified by mercury cuprate. 25 High-temperature superconductors have been widely studied by photoemission spectroscopy; 26 X-ray photoelectron spectroscopy (XPS) is a powerful tool for studying the doping of the 3d element in the Cu site and can study the electronic structure of the system. Core-level measurements provide information on the electronic states of the compounds, such as oxidation states and doping-induced chemical potential shifts and, in the case of the highly correlated Cu cations, charge-transfer mechanisms and multiplet splitting.…”

THE STUDY ON THE SPIN GAP PHENOMENON IN OXYGEN DEFICIENT YBa2Cu3O6+δ AND Ca-DOPED Y1-xCaxBa2Cu3O6+δ SUPERCONDUCTORS

“…Many reports demonstrated that the apical oxygen atom approaches the copper ion in the CuO 2 plane much faster than that expected from the contraction along the c direction under high pressure. [12][13][14][15] The structure within the space between the CuO 2 planes can be considered as a charge reservoir, whose important role is to fix the charge carriers in the CuO 2 planes with a certain density. According to the pressure-induced charge transfer (PICT) model, 16 the T c variation is ascribed to the charge transfer from the charge reservoir to the CuO 2 plane.…”