Vacancy calcium

Anion Vacancies If the cation of the host structure has a higher charge than the replacing cation, electroneutrality may be maintained by introducing vacancies into the anion sublattice. The best-known examples of anion vacancies occur in the stabilized zirconia, such as calcium- or yttrium-stabilized zirconia. The high-temperature... 

Recently, nanocomposites of calcium and bismuth mixed oxides obtained by flame synthesis were used for the degradation of organic dyes under visible light, with good activity due to the formation of relatively high surface area materials and oxygen vacancy formation in the flame process [119]. 

Jeanjean, J., McGrellis, S., Rouchard, J. C., Fedoroff, M., Rondeau, A., Perochf.au, S. Dub is, A. 1996. A crystallographic study of the sorption of cadmium on calcium hydroxyapatites incidence of cationic vacancies. Journal of Solid State Chemistry, 126, 195-201. 

Ca2+ ions ([Ar]). One electron can be accommodated in the single vacancy of a Cl atom ([Ne]3s23p5) to form a Cl ion ([Ne]3s23p6). To achieve an electrically neutral substance, two Cl- ions are needed for each Ca2+ ion so the chemical formula of calcium chloride is CaCl2. 

However a lack of calcium is observed and the correlation between the amounts of fluoride ions and carbonate ions is not rigorous. This is due to the existence of a second type of substitution as originally proposed by LABARTHE (4-5). According to this author, the substitution of a PO ions by a C0- ion is accompanied by the formation of vacancies in an oxygen site and also in the Ca + and F" sites of the channel which are the closest to the missing oxygen. The B-type carbonated fluorapatite can be described by the formula ... 

TCP, Ca3(PC>4)2, exists in two crystal forms, viz. a-TCP and p-TCP. Both forms can only be prepared by calcination at high temperature (>800 °C).70 a-TCP is meta stable at room temperature and is more soluble than p-TCP in water. The crystal structure of a-TCP shows that there are 16 inequivalent phosphorus sites.110 Its 31P MAS spectrum contains only 14 peaks, where the chemical shifts range from —3 to 5 ppm.111 Although there are only three crystallographically inequivalent phosphorus sites for (3-TCP,112,113 there are as many as 16 resolved peaks in the 31P MAS spectrum because of the presence of some calcium vacancies.114 The 31P chemical shifts of (S-TCP are in the same range as reported for a-TCP, but the overall patterns of their 31P MAS spectra are quite different. In addition, it has also been found that even a minor substitution of Ca2+ by Na+, Mg21 or Zn2+ ions will perturb the 31P MAS spectrum, revealing the substantial effect of the counter ions near the phosphorus sites.114,115... 

About 3%Au/hydroxyapatite (a type of calcium phosphate) gave >90% conversion at 573 K, with little deactivation, and no formation of methane up to 653 K.44 This result is of interest because creation of anion vacancies in the support is very unlikely to occur. 

In the case of calcium, anion vacancies are formed and charge compensation occurs. Substitution by addition of tantalum results in considerable changes in ionic diffusivity and electrical conductivity. 

Figure 8.12. Orbital population of calcium unoccupied orbitals in cluster models in Fig. 4(A) ft 4(C). (A) No vacancy (without surface relaxation),...

Calcium fluoride, Cap2, is fluorite itself Hence, similar to CSZ, F can conduct through vacancies (Vp) generated by the partial replacement of Ca + with a monovalent cation such as Na+. Thus Cap2 l%NaF has a conductivity of 10 S cm at 400 °C, which is several orders of magnitude larger than that of CSZ at the same temperature. 

Fig. 2 Crystallographic structure of CHA-B [23]. Hydroxyl groups are located at the c-axis inside triangles formed by calcium. In this scheme, four tetrahedral phosphate oxygen sites, labelled I, II and III, are occupied by three oxygens of a carbonate ion, while the site IIT is vacant. Note the calcium and hydroxyl vacancies in the neighbourhood of the carbonate ion...

A free hole is represented by h and a defect electron by e. For example, an oxygen vacancy is denoted V", an oxygen interstitial O", and a calcium on a lanthanum site, Cai a-... 

Serret A, Cabanas MV, Vallet-Regi M (2000) Stabilization of calcium oxyapatites with lanthanum(lll)-created anionic vacancies. Chem Mater 12 3836-3841 Seiy A, Manceau A, Greaves GN (1996) Chemical state of Cd in apatite phosphate ores as determined by EXAFS spectroscopy. Am Mineral 81 864-873... 

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