Superconducting metal oxides

Another example of the use of neutron diffraction to understand the role of atomic vacancies in producing a superconducting metal oxide phase is work that has been performed on Bao Kq 4fii03. This work demonstrates that at the synthesis temperature (700° C), under the proper conditions, oxygen vacancies are created to allow the formation of the parent phase with bismuth largely in the +3 oxidation state. The presence of the vacancies allows the incorporation of potassium in the... 

Figure 7 Unit cell depiction of the group 2 element containing superconducting metal oxide YBa2Cu307 j...

In 1986, the presence of superconductivity was observed in a metal oxide system (see Electronic Structure of Solids). This ceramic was brittle, not ductile as for metallic samples. Chemical Vapor Deposition is one method for preparing metal oxide compositions. All presently known superconducting metal oxide compositions contain a group 2 element (Figure 7). Owing to the importance of this area to the future development of the inorganic chemistry of the group 2 elements, it is covered in the present context. 

Mixed metal oxides can be addressed as belonging to three main fields, namely superconducting metal oxides (SMOs) (Section V.D.l), transparent conductive oxides (TCOs) (Section V.D.2) and ferroelectric oxides (Section V.D.3). The synthesis procedures for mixed metal oxides include sintering, sol-gel, PLD or laser ablation, sputtering evaporation, MBE, MOVPE (metal-organic vapor-phase epitaxy), OMVPE (organometallic vapor-phase epitaxy) and CVD in particular. 

Deposition of metals and metal oxides by means of metal enolates 1003 TABLE 8. MOCVD of superconducting metal oxides (SMOs)... 

The precursor must be chemically and thermally stable in the region bordered by the evaporation and transport temperatures, even after prolonged use. Early workers in the area of superconducting metal oxide (SMO) CVD were plagued by irreproducible film growth results caused by premature decomposition of source compounds in the bubbler, in transfer lines, and, basically, everywhere, except on the substrate. Such experiences are to be avoided ... 

Superconducting Metal Oxide (SMO) Lattice-Matched Insulators. 294... 

Thallium oxide, TI2O, is an extremely useful material for employment in solar cells and electrical contacts [92]. The interest in thallium oxide has been spurred further by the discovery of thallium-containing superconducting metal oxides [93] (see Chapter 2). Compounds used for the preparation of thallium oxide by CVD include thallium(l) acetylacetonate, (Tl(acac) acac" 6), dimethylthallium acetylacetonate, (CH3)2T1 (acac), and cyclopentadienyl thallium(i), CpTl (13). These precursors decompose in the presence of oxygen at temperatures of 350-400°C to yield TI2O3 [94]. 

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