Perovskite cuprate high-temperature

CUPRATE HIGH-TEMPERATURE SUPERCONDUCTORS 8.6.1 Perovskite-Related Structures and Series... 

Fig. 27.5 (a) A unit cell of perovskite, CaTi03, using a polyhedral representation for the coordination environments of the Ti centres an O atom (red) lies at each vertex of the octahedra, and the Ca ion is shown in grey, (b) Part of a layer of stoichiometry Cu02 which forms a building block in all cuprate high-temperature superconductors colour code Cu, brown O, red. 

Cuprate high-temperature superconductors are copper-containing perovskite-derived oxides. Many of these maintain the superconducting state to temperatures above that of liquid nitrogen (Table 8.1). The stmctures of the superconductors are built up of slices of perovskite type linked by slabs with stmctures (in the main) of the rock salt (NaCl) or fluorite (CaFj) type (Section 4.6). The copper valence in most compounds lies between the formal values of Cu and Cu ". 

Among the high-temperature superconductors one finds various cuprates (i.e., ternary oxides of copper and barium) having a layered structure of the perovskite type, as well as more complicated oxides on the basis of copper oxide which also include oxides of yttrium, calcium, strontium, bismuth, thallium, and/or other metals. Today, all these oxide systems are studied closely by a variety of specialists, including physicists, chemists, physical chemists, and theoreticians attempting to elucidate the essence of this phenomenon. Studies of electrochemical aspects contribute markedly to progress in HTSCs. 

All the high Tc superconductors discovered so far, with one exception, contain weakly coupled copper oxide, Cu02, planes. The highest critical temperatures are found for cuprates containing a Group 2 metal (Ca, Ba, Sr) and a heavy metal such as Tl, Bi, or Hg. The structures of all the cuprate superconductors are based on, or related to, the perovskite structure. The one report (in 2000) of a non-cuprate high T superconductor is of surface superconductivity in Na WOs. The structure of NUxWOs is also based on the perovskite structure. 

The discovery in 1986 of high-temperature superconductivity in ceramic cuprates of perovskite structure started a period of very intensive research of transition metal oxides. Soon afterwards, in 1993, the colossal magnetoresistance effect was discovered in manganite perovskites, again leading to an increasing research activity in the field of magnetic oxides. It is... 

The discovery of high-temperature superconductivity in a lanthanum-based cuprate perovskite material with a transition temperature of Tc = 35 K by Bednorz and Muller... 

The crystal structures of several high-temperature superconductors (HTSC), particularly in the cuprate family, are describable as built of modules of perovskite together... 

Other high-temperature superconductors can be described in similar fashion, e.g. Tl2Ca2Ba2Cu30io (containing Tl, Ca and Ba centres) is composed of layer sequence 27.4. The non-Cu02 oxide layers in the cuprate superconductors are isostructural with layers from an NaCl structure, and so the structures are sometimes described in terms of perovskite and rock salt layers. 

The erystal La2-xBaiCu04 was the first high-temperature superconductor which was discovered in 1986 [1], Since then a whole series of imusual magnetic and transport properties was foimd in lanthanum cuprate perovskites and related compounds. In particular, one of the most interesting features of the inelastic neutron scattering in these crystals is that for hole concentrations x > 0.04, low temperatures and small energy transfers the scattering is peaked at incommensurate momenta (, -5 + ), in the reciprocal lattice units... 

The high-temperature superconductors are a remarkable set of materials that present us with fascinating scientific and technological challenges. The cuprate Ba2YCu307, the first material with a T > 77 K, has a tripled perovskite structure with Cu occupying the small perovskite B site while Ba and Y are ordered on the perovskite A site. Bulk crystals are key to... 

Already in the seminal paper of Bednorz and Muller [1], the guide to look for systems with a high superconductive transition temperature (Tc), has been the presence of strong electron-phonon interactions. Such interaction has been known to exist in a wide class of perovskite type oxides. The authors mention [1] the vibronic Jahn-Teller polaron effect [2] in this context. They also emphasize the fact that the Cu2+-ion is a well-known Jahn-Teller system and this circumstance preserves significance in the physics of cuprate superconductors [3-7]. As a microscopic cause for ferroelectric ordering the interband vibronic hybridisation has been supposed [8-11] enlargening the view on perovskites as Jahn-Teller systems. 

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