Integrated X-ray intensities of Bragg peaks were observed from single crystals of Zr0.s66Ca0.mOl.s66 and Zr0.Ts6Y0.214Ol.893 in the disordered state. There are displacements of oxygen ions (characterized by A/a ~ 0.05) from the ideal positions of the fluorite structure along (100) directions similar to those that occur on ordering below 1273 K and related to the cubic to tetragonal transition in pure" ZrO 2. These displacements are not related to anharmonicity, at least to fourth-order terms. In addition, there are small displacements of the cations (A/a ~ 0.015) in (111) directions in the yttria-stabilized zirconia. IntroductionZr(Ca)O2_ x and Zr(Y)O2_ x are excellent conductors of 0 2-ions at temperatures above 1173 K, and are, therefore, important solid electrolytes (Etsell & Flengas, 1970;Roth, 1975). These materials have fluorite-type structures, large concentrations of oxygen vacancies, and are stable in the cubic phase over wide ranges of composition and temperature (Etsell & Flengas, 1970). There is, however, a large difference in the reported regions of stability; Carter & Roth (1963, 1968 found that Zr(Ca)O2_ x is stable in the range 0.10 < x < 0.19 at 1673 K. Sardi (1969) indicated that Zr(Y)O2_ x is stable in the range 0.07 < x < 0.29, with this range being almost independent of temperature.There is interest in the order-disorder transformation in these materials (e.g. Carter & Roth, 1963, 1968Steele & Fender, 1974; AUpress & Rossel, 1975;Allpress, Rossel & Scott, 1975; Hudson & Moseley, 1976;Faber, Mueller & Cooper, 1978). Neutron diffraction studies of Zr(Ca)O 2_x in the disordered and ordered states were first reported by Carter & Roth (1963, 1968. They suggested that above the transition (in the disordered state) there is a displacement of the 0567-7394/79/050789-07501.00oxygen ions from the ideal fluorite lattice sites in ( 111 ) directions with the magnitude of displacements reported to be 0.2-0.3 ,/k. The order-disorder transition occurs at ~1273 K and these authors inferred from their measurements that the ordering involved cooperative motions of the oxygen ions in (Ill) directions. In contrast to these results, Steele & Fender (1974) reported that in the disordered state of Zr(Y)Oz-x there is a displacement of oxygen ions along (100) directions. Allpress, Rossel & Scott (1975) have suggested a model for ordered CaZr40 9 (below 1273 K) from Xray measurements with powders, but they could find no evidence for anion displacements from ideal positions. More recently, Faber, Mueller & Cooper (1978) interpreted neutron scattering from ordered single crystals of both Zr(Ca)O1.85 and Zr(Y)O1.91 in terms of internal deformation waves on the oxygen sublattice, with an amplitude of ~0.23 /~; each ion is displaced parallel or anti-parallel to ( 100 ) directions, collectively on { 110} planes.In all the previous studies (except that by Faber, Mueller & Cooper, 1978), powder methods were employed, limiting the accuracy of detecting any displacements, since only a few peaks, often at low sin 0...
Above the 1300 K transition and in the defect fluorite phase, there is diffuse X-ray scattering which is similar for both Ca-and Y-stabilized zirconias. This is largely due to ionic displacements from the average structure, principally oxygen ions displaced locally in (100) directions. It has been proposed that some of this scattering is due to fine precipitates of ZrCaaO 9 or ZrY409. The quantitative analysis of this diffuse scattering reported here does indeed indicate some similarities to this phase; in particular the stabilizing __ ions form rods in the (332) directions similar to those in the precipitate. However, in this compound the stabilizing ion is a second neighbor to an oxygen-ion vacancy, whereas the present results indicate that these tend to be first neighbors. This is the first direct evidence for this association in these materials. This probably occurs to reduce local distortions and to provide local charge balance. It is concluded that the diffuse intensity is from locally ordered regions, not precipitates.
The crystal structure of the title complex was determined by an X-ray diffraction method. The potassium ion is coordinated by six oxygens of a crown ether and two cyano-nitrogens of two TCNQ anion radicals. Both the crown ether dimer and the TCNQ dimer are arranged alternately in the solid.
In VO x (0.8 < x < 1.3), there are large numbers of cation and anion vacancies and interstitial vanadium ions. To determine the local arrangements of these defects, X-ray diffuse scattering was measured in absolute units with single crystals of VO x (x = 0.89, 1.17 and 1.28). For x > 1, the interstitials are present near vacancy clusters, similar to the defect arrays found in the semiconductor FexO. For x < 1, there are few interstitials, but an increased concentration of anion vacancies. The anion and cation vacancies are arranged (so as to minimize the electrostatic energy) in rows along (110) directions with alternating vacancy-rich and vacancy-deficient { 111 } layers. Some portions of this vacancy arrangement resemble that found in metallic TiOx. VO x behaves like a semimetal for x < 1, but a semiconductor for x > 1, and the present results, when compared to the defect structures in TiOx and FexO, show that the nature of the bonding between cations and anions controlling the conduction mechanism is reflected in the defect structure.
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