With pyrochlore structure

Solvothermal crystallization usually produces products with smaller sizes than those obtained by the hydrothermal method. The formation of polymorphs that cannot be obtained by the hydrothermal method is frequently reported PbTiOj with pyrochlore structure/perovskite PbTiOj, cubic BaTiOj/tetragonal-phase BaTiOj, cubic Zr02/tetragonal Zr02. Formation of these phases may be due to the smaller crystallite size of the solvothermal products. 

Xie Y H, Wang J D, Liu R Q and Su X T (2004), Preparation of Lai 9Cao.iZr206 95 with pyrochlore structure and its application in synthesis of ammonia at atmospheric pressure . Solid State Ionics, 168,117-121. 

These electron microscopy results allow a proper rationalization of the OSC values shown in Fig. 2.8 and highlight once more the key influence of the surface on low-temperature OSC measurements. In effect, the decrease in the low-temperature OSC observed for the SR-MO-O1073 sample is due to the deterioration of the pyrochlore-type surface features observed by HRTEM, whereas the increase in low-temperature OSC in the SR-SO-H1123 oxide is due to the appearance at the surface of small nuclei with pyrochlore structure. Likewise, since high-temperature OSC is mainly dominated by thermodynamic factors and the short redox treatments mostly do not modify the bulk structure of the starting oxides, the high-temperature... 

The bixbyite structure of e.g. SC2O3 represents a solution to the problem of filling three quarters of the tetrahedral sites of cubic close-packed Sc with O. It is not the simplest solution that would be the structure obtained by filling the tetrahedral sites not filled in CU2O (i.e. the pyrochlore structure of AgSb03, with Ag, Sb replaced by Sc, cf. Sect. 2.1.1.3). With normal Sc-O bond lengths that structure would have short O... O distances, and so an alternative structure that allows adjustment of the O... O and M... M distances is adopted. 

The effect of a-decay on the pyrochlore structure Gd2Ti207 doped with 244Cm has been investigated in detail (Weber et al. 1998). The material was completely amorphized at a dose of 3.1 x 10 8 a-decays/g. Amorphization is accompanied by volume expansion and increase of dissolution rate (by approximately a factor of... 

Mazzi, F. Munno, R. 1983. Calciobetafite (new mineral of the Pyrochlore Group) and related minerals from Campi Flegrei, Italy crystal structures of polymignite and zirkelite comparison with pyrochlore and zirconolite. American Mineralogist, 68, 262-276. 

Goodenough and co-workers [10] made a detailed study of the solid state chemistry and electrochemistry of ruthenates of general formula Bi(2 2x)P-b2xRu20(7. v) with the pyrochlore structure and reported that the electroreduction of oxygen proceeds at low overpotentials according to the electrokinetic equation... 

Doping of CrF, with Fe(III) or Mg(II), would be expected to result in the formation of solid solutions. However, depending on the Fe(III) concentration, there are two distinct regions, a concentration range from 0 to 41% Fe(III) with the pyrochlore structure and a second range from 65 to 100% Fe with the HTB structure [93], The surface areas of the latter samples are about double those of the former. At about 65% Fe(III) a maximum in the acidity of the samples was observed, acidity decreases with further increase of Fe(III). These phases however, exhibit only average catalytic activity. 

Li et al. reported pyrochlore-structured La2Zr2Q7 prepared by electrospinning technique from PVP/lanthanum nitrate/zirconium oxychloride as precursors, which was then calcinated at 1000 °C for 12 h, with a diameter of 100-500 run (Figure 56) (Li et al., 2006b). The fiber structure shows a low sintering ability, which could be attributed to the random stacking of fiber, resulting in a structure with low contact area between fibers. 

Crystalline pyr-FeFs , a metastable cubic form of FeFs with pyrochlore-related structure, was obtained in a topotactical oxidation reaction of NH4Fe2F6 with Br2 in acetonitrile. At this example, the designation "chimie douce (soft chemistry) for this type of solid-state reaction under low-temperature conditions was propagated in the 1980s. ... 

Exactly as for MgSiOs, high pressure stabihzes a variety of compositions in the compact perovskite structure. Competition with other structures, such as Umenite, defect pyrochlore, and various polytypes of perovskite, as a function of ionic radius, pressure, and temperature has been reviewed. ... 

Other three-dimensionaUy connected oxide structures show ion-exchange chemistry and sorption of small molecules such as water or ammonia. These inclnde oxides with the A2B2O7 pyrochlore structure, KSb03 related phases, and LiNb03. Compositions with these structure types can be exchanged in mineral acids or in molten salts. 

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