By Professor Dr. Bernard Raveau, Professor Dr. Claude Michel, Professor Dr. Maryvonne Hervieu, Professor Dr. Daniel Groult (auth.)
The fresh discovery of high-temperature superconductivity in copper dependent oxides is an occasion of significant significance not just with appreciate to the actual phenomenon itself but additionally since it certainly exhibits that stable nation chemistry, and particularly the crystal chemistry of oxides, has a very important position within the synthesis and figuring out of recent fabrics for destiny appli cations. the various papers released within the box of excessive Tc supercon ductors within the final 5 years exhibit that the nice complexity of those fabrics necessitates an in depth collaboration among physicists and stable country chemists. This e-book is predicated to a wide quantity on our adventure of the crystal chemistry of copper oxides, which we've got been learning within the laboratory for greater than twelve years, however it additionally summarizes the most effects that have been bought for those compounds within the final 5 years when it comes to their dazzling superconducting houses. we've curious about the struc ture, chemical bonding and nonstoichiometry of those fabrics, taking into consideration that redox reactions are the main to the optimization in their supercon ducting houses, because of the significance of the combined valence of copper and its Jahn-Teller impact. we have now additionally drawn on reviews of prolonged defects by means of high-resolution electron microscopy and on their construction by way of ir radiation effects.
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Extra resources for Crystal Chemistry of High-Tc Superconducting Copper Oxides
Annealing the same samples at the same temperature for longer periods (24h) in air allows pure phases to be prepared with the same structure, but with a greater amount of Cu(III). 21. xSrxCuO•. 2 ····~~2Cu04 ...... 2 x oxygen pressure will also influence the Cu(III)/Cu(lI) ratios. Heating, for example, some Cu(III) samples at a low temperature under vacuum produces a decrease of Cu(III) without destroying the structure. In the same way, reaction in an oxygen flow allows the Cu(III) to be increased.
27. e. taking place without variation of composition, or does it result from an oxygen loss? 45-48] answer the question. 27) from the orthorhombic one only in the positions of some oxygen atoms, and by the oxygen content. One observes again triple layers of corner-sharing CuO n polyhedra, whose cohesion is ensured by a plane of yttrium cations. The ordering of the yttrium and barium planes of the type "1-2", along c remains unchanged. 2A). The Cu04 groups of the orthorhombic phase corresponding to the Cu(l) atoms at z = 0 are replaced by "ClI06 octahedra".
56 A The A2 sites correspond to the metal atoms located in the SrO-type layers. e. 33A). 90A). The distribution of the La3 + and Sr2+ or Ca2+ cations over the A 1 and A2 sites is remarkable. A preferential occupancy of the A2 sites of SrO-type layers by lanthanum is observed: 70%-90% of these sites contain La3 + . Moreover, the occupancy factor of these sites by La3 + is much greater for calcium oxides (90%) than for strontium compounds (70%-75%). This greater tendency to ordering in the case of calcium is easily understood because calcium is 29 smaller than lanthanum, whereas strontium and lanthanum have similar sizes.