Calcium oxide, superconductors

The one-meter-long conductor, based on a bismuth-strontium-calcium-copper oxide superconductor, carries over 2300 amps of direct current at liquid nitrogen temperatures (77 K). This is more than twice the current-carrying capability of conventional copper cables. 

In addition to the above, preparation in w/o microemulsions of nanoparticles of various other types of compounds, viz. silica-coated iron oxide, Fe203-Ag nanocomposite, oxides of ytrium, erbium, neodymium, vanadium and cobalt, titanates of barium and lead, ferrites of barium, strontium, manganese, cobalt and zinc, oxide superconductors, aluminates, zirconium silicate, barium tungstate, phosphates of calcium, aluminium and zinc, carbonates of calcium and barium, sulphides of molybdenum and sodium, selenides of cadmium and silver etc. have been reported. Preparative sources and related elaboration can be found in [24]. 

Fransaer J., Roos I.R., Delaey L., Van der Biest O., Arkens O., Cells J.P. Sol-gel preparation ofhigh-Tc bismuth calcium strontium coppo oxide and yttrium barium copper oxide superconductors. J. Appl. Phys. 1989 65 3277-3279... 

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. 

Neither the calcium nor the strontium compound is a superconductor. A possible reason may be that the oxidation state of copper is equal, or very close, to 2+. 

Oxides containing bismuth oxygen atom double layers include the bismuth calcium copper oxide series of superconductors exemplified by Bi2Sr2CaCu20g (Bi-2212) and the beta phase oxide ion conductors based on the composition Sr Big j 0(2 j)/2. While the details of these two stmcture types are quite different, they have the common feature of containing BiMT double layers that are only weakly bonded. In Bi-2212, the bismuth atoms are four + one coordinated by oxygen atoms whereas, in Srj Bi9 j 0(2 j)/2 they are three + one coordinated and form square and hexagonal layers of Bi-O bonds. Both classes of compounds and be intercalated by iodine atoms that are inserted between the Bi-O double layers. 

The system 8a La Cu Q chosen by Bednorz and Muller (1) for their first investigation of superconductivity was connected to the existence of metallic properties of the oxide BaLa CusOis+s recently isolated in Caen (2). However the method used for the synthesis did not lead to the expected oxide but to a mixture of phases. Fortunately, one of these latter phases was found to be at the origin of superconductivity. In fact the concerned oxide is a M liF -type oxide, La2-xBaxCu04-y, isolated and studied for its electron transport properties several years before in Caen (3-4). It was then shown by several authors (5-9) that the strontium isostructural oxide La2-xSrxCu04-y (10-11) and the calcium compound (3-4) were also superconductors with Tc values ranging form 20K to 40K. 

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