Oxygen nonstoichiometry and valence of copper in the Cu-1222 superconductor

Extremely Overdoped Superconducting Cuprates via High Pressure Oxygenation Methods

“…The effects on bonding and antibonding potential wells in the ab-plane could impact the oxygen absorption potential of the compound; our analysis indicates a higher aptitude for oxygen overdoping among the Sr samples. Other effects of the choice of A-site species are charge balance; e.g., substitution by europium [58] adds charge flexibility to the layer by tolerating both oxidation states 2+ and 3+.…”

“…Low-pressure oxygenation (LPO) methods are taken to include the use of O 2 atmosphere under ambient pressure synthesis [45,58,69,70], but also pressurized treatments in gas phase, e.g., in an autoclave [23,47,52,54,56] at pressures up to ca. 25 MPa.…”

“…Variants of the solid-state method are the nitrate route [40,51,67] and sol-gel route [30,32,68], in which the primary precursors are initially mixed by dissolution, followed by drying and annealing with intermediate grinding. Low-pressure oxygenation (LPO) methods are taken to include the use of O2 atmosphere under ambient pressure synthesis [45,58,69,70], but also pressurized treatments in gas phase, e.g., in an autoclave [23,47,52,54,56] at pressures up to ca. 25 MPa.…”

“…KCl can be washed away, at the expense of risking sample degradation, while Ag residues are practically inseparable from the cuprate product. An external oxidizer can be used in HPO synthesis [50,58,73,74], but is more often employed in HPO treatment of pre-formed but oxygen-deficient products The HP sample assembly preferred by the principal author: the sample is encased in a gold capsule (1); which fits into a boronitride sleeve including caps (2); which in turn fits into a graphite tube (3) that functions as a resistance-heating furnace; which is capped with Mo and steel plates (4 and 5) that electrically connect the graphite furnace to the anvils via how the heating current is connected, as the entire assembly is fit into the pyrophyllite gasket (6) that acts as a solid pressure-transfer medium. Preference-based variations in sample assembly exist.…”

“…KCl can be washed away, at the expense of risking sample degradation, while Ag residues are practically inseparable from the cuprate product. An external oxidizer can be used in HPO synthesis [50,58,73,74], but is more often employed in HPO treatment of pre-formed but oxygen-deficient products [23,55,57,58,60,61]. Intermediate APO steps are commonly used to minimize the amount of oxidizer needed at the HPO step, thus minimizing residue and maximizing the often very limited amount of the HPO sample [30,50,56,57,61,75].…”