Oxygen parameters

Recognizing the impracticability of determining the positions of the oxygen atoms from X-ray data, we have predicted a set of values for the oxygen parameters with the use of assumed minimum interatomic distances which is found to account satisfactorily for tbe observed intensities of a large number of reflections and which also leads to a structure which is physically reasonable. 

The point symmetry of the octahedral sites in the spinel-structure is Dsd- While the octahedra are perfect for an oxygen parameter u of 3/8, they are compressed along a threefold axis for u < 3/8, and expanded for u > 3/8. In the case of MgCr204 ( a0,385) and MgAl204 (21 = 0,387) ( normal spinels with Mg + in tetrahedral and Cr +, Al + in octahedral sites), the expansion is of the magnitude of about 4 to 5%. The corresponding splitting effects of the second absorption band in the remission spectra of the mixed-crystal powders (Mg)( > (Cr jAL-x) O4 (13) are about... 

Titanium dioxide, TiOa (rutile), In the structures so far considered, all the atoms have occupied very special positions in the unit cell there were no continuously variable parameters to be determined. The structure of rutile, now to be considered, is a simple example of a structure in which there is one parameter. This structure has been described on p. 226, where it was introduced in connexion with the calculation of structure amplitudes. The general arrangement of the atoms was assumed, and the effect of the variation of the oxygen parameter on the structure amplitudes of the reflections was demonstrated (Fig. 123). Here we shall consider the evidence which leads to a knowledge of the general arrangement of the atoms. 

Together with biochemical reactions catalyzed by enzymes of yeasts and bacteria, chemical reactions also occur between molecules already present in the must, those gradually extracted from the grape solids during fermentation, those derived from metabolism and, possibly, also those released by the wood. For many of them, the temperature and dissolved oxygen parameters related to technological operations of the winery can have dramatic effects and the quality of the final wine depends on the type and intensity of reactions taking place. 

The fact that Mn3+ or Cu2+ ions occupying more than a critical fraction of the spinel B sites produce distortions from cubic to tetragonal (c/a > 1) symmetry has been well established, as can be seen from Table XV. In fact Satomi (552) has measured the oxygen parameters in M113O4 to demonstrate directly that it is the octahedral sites that are distorted that the tetrahedral sites resist the distortion. 

Figure 2 The B(4 )OA3(6 ) coordination—A, B open and dotted circles, respectively—in a fragment of the spinel structure (A2(6)B(4)04, with ideal oxygen parameter one A06 octahedron is indicated).

Figure 12 Changes in pulmonary hemodynamic and oxygenation parameters for an ARDS patient before and after aerosolized DETA/NO administration (a) pulmonary vascular resistance (PVR) index, (b) mean pulmonary arterial pressure (PAP), (c) intrapulmonary shunting, and (d) alveolar-arterial oxygen partial pressure gradient (A-aDC>2). The 20-min period of DETA/NO aerosol administration is indicated by ( ). [Adapted from Reference 27 with permission.]...

G. Strangman, M. A. Franceschini, and D. A. Boas, Factors Affecting the Accuracy of Near-Infrared Spectroscopy Concentration Calculations for Focal Changes in Oxygenation Parameters, Neuroimage, 18,865 (2003). 

For the interactions the distances Me-O and Me-O-Me play an important role, ten triangular configurations of Me-O-Me are illustrated in Figure2, where the shortest distance is shown as p and other distances are given by q, r, s and t these distances are also given in Tabled, as a function of the variable 8 = u - 3/8 that 8 is oxygen parameter [11]. 

From the lattice parameters of samples listed in Table 4.2, it is seen that the lattice parameters decrease with the increase of x in the Fei xO. The reason may be that the oxygen parameter reduces with the increase of iron ion defect in the rock salt cubic lattice by the dense accumulation of ions of Fei xO crystals. The R values of all wiistite catalyst are consistent with this scope. When Fe-O system is rapidly cooled down to room temperature (rapid crystallization) metastable wiistite can be obtained. 

Wendschuh-Josties M, O Neill HSC, Bente K, Brey G (1995) Lattice and oxygen parameters of ZnGa204 as a function of equilibriation temperature. Neus Jahrbuch Mineralogie 1995 (6) 273-280... 

Dukhovskaya EL, Saksonov YG, Titova AG (1973) Oxygen parameters of certain compounds with the garnet structure. Izvestiya Akad Nauk SSSR Neorganicheskie Mater 9 809-813... 

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