Application of high-pressure techniques: stabilization and oxidation-state control of novel superconductive and related multi-layered copper oxides

Abstract

Copper oxide superconductors possess multi-layered structures with a layer sequence of -CuO2 -(Q-CuO2 )n -1 -AO-(MO1± )m -AO- or -CuO2 -B-(O2 -B)s -1 -CuO2 -AO-(MO1± )m -AO- along the elongated c axis. Based on this layer sequence, the known copper oxide structures are categorized as members of the homologous series, Mm Ar Qn -1 Cun Om +r +2n ± (M-mr (n -1)n ; category A) or Mm A2k Bs Cu1+k Om +4k +2s ± (M-m (2k )s (1+k ); category B). Stabilization of such structures especially in the case of high values of the n /s parameter, i.e. the higher members of the homologous series, has been demonstrated to be apparently promoted under high pressures and/or strongly oxidizing conditions. Consequently, techniques for applying both high oxygen gas pressures (10-2000 atm) and ultra-high solid-medium pressures (2-8 GPa) have been advantageously utilized in synthesizing various superconductive copper oxide phases. Especially the ultra-high solid-medium pressure synthesis carried out in the so-called cubic-anvil/belt-type apparatus has proven to be extremely successful in synthesizing novel superconductive phases. In order to achieve high partial pressures of oxygen in the solid-medium environment, `external' oxygen-generating oxides such as KClO4 , KClO3 and Ag2 O2 are commonly added to the precursor mixtures. It is emphasized that in some cases it is possible to utilize `internal' oxidizing agents alone, i.e. highly oxidized precursors such as BaCuO2+ and Ba2 Cu3 O5+ containing metal constituents common with the desired copper oxide phase only. In the present paper, the potential and applications of high-pressure techniques in synthesizing multi-layered copper oxides and related structures are reviewed and discussed with emphasis on the important `historical' discoveries of novel phases and the present status of controlled production of high-quality samples of such phases.

Oxygen Absorption Capability of YBaCo4O7+δ

“…4 In the present work, we employed two different HP approaches, i.e. gas-medium (10-100 atm O 2 ) and solidmedium (1-5Á10 4 atm plus KClO 3 as an oxygen generator) treatments.…”

Study of layered superconductors in the theory of an electron - phonon coupling mechanism

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The influence of doping with Ca and Mg in YBa2Cu3O7-δceramic

“…It is also realized that the superconducting transition temperature, Tc, sensitively depends on both the hole concentration in the CuO 2 planes and the relative electric charge of the oxygen within the planes [3,4]. The level of this charge can be controlled either by manipulating the oxygen stoichiometry in the Cu-O chains, by application of pressure or by ionic substitution [5,6].…”