Variation with oxygen content

Figure 8.8 Variation of the superconducting transition temperature, Tc, with oxygen content ...

In general, a non-stoichiometric compound can be defined as one with variable composition. However, the major structural features are maintained. For example, Figure 6.4 shows the variation in the cubic lattice parameter (a) with oxygen content of Fej 0, which crystallizes with the rock-salt structure. A smooth variation is apparent, gradually reducing as the iron content decreases. 

For a given temperature and a given catalyst, conversion of p-xylene and yield for the para-products increases linear with oxygen content in the educt gas (xqj = 0.04 - 0.2). By variation of the ammonia content in the educt gas we observed a maximum activity at XNH3,Fe d w 0.20 (Fig. 4). 

Figure 3 For YBa Cu Oj variation of oxygen content with temperature and three oxygen partial pressures (100 %, 20%, and 2%) obtained from neutron diffraction study, by Jorgensen et al. (Ref. 12).

Variation in the Structural, Magnetic, and Superconducting Properties of YBa2Cu307 x with Oxygen Content... 

Figure 10.5 Schematic variation of Tc with oxygen content X for YBa2Cu306, x samples prepared by different techniques. (A Cava et al., 1990a, B Namgung et al., 1990) and for Y0 7Ca0 3Ba2Cu306+x (C Legros-Gledel et al., 1991). Reproduced from Allan et al. (1992) with permission of Gordon and Breach Publishers.

Figure 1. Variation of benzene conversion with oxygen content for the methylation of benzene with methane in a batch reactor at 4(X) C and 6.9 MPa pressure for 4 hours [21.22]...

Figure 13.37 The variation of the superconducting transition temperature, Tc, with oxygen content, x, for YBa2Cu30x. Outside of the approximate range of x of 6.95-6.35 the material behaves as a typical insulating ceramic...

Atlas and Schlehman have measured the variation of oxygen content and electrical conductivity with oxygen pressure in the temperature range from 1100 to 16(X)°C (87). From the pressure dependence of the electrical conductivity, they inferred that the defects in Pu02 j are constituted of predominantly interstitial plutonium ions, and discussed the change of the form of defects with temperature. However, measurements by the same authors on the density of the PuOj-j. phases (277) led to the conclusion that oxygen vacancies are the predominant defects in the PUO2 phase. 

The appearance of superconductivity and the magnitude of the superconducting transition temperature are also closely coimected with the composition of these non-stoichiometric solids, which all exhibit considerable variation in oxygen content. The superconducting transition temperature is also affected by external factors such as pressure and crystal elastic strain. 

Figure 8.6 Oxygen stoichiometry in YBa Cuf) (a) the composition of samples annealed at temperatures between 300 and 800°C under 1 bar of oxygen pressure (b) the variation of the superconducting transition temperature with oxygen content...

FIGURE 8.7 Variation of oxygen content with carbon content (Adapted from Berkowitz, N., An Introduction to Coal Technology, Academic Press, New York, 1979.)... 

Absorption. CDs typically show strong optical absorption in the ultraviolet (UV) region, with a tail extending out into the visible range. There may be some absorption shoulders attributed to the n-n transition of the C=C bonds, the n-n transition of C=0 bonds, and/or others. Moreover, CDs prepared via different methods also showed different absorption behaviors and the absorption peak position was also dependent on the preparation method. Besides, the variation of oxygen content was reported to play an important role in deciding the absorption peak position of CDs. 

Figure 4.4 An overlapped plot of the white-hne intensity ratio of Mn L3/L2 and the corresponding chemical composition of o/ Mn as a function of the in situ temperature of the Mn02 specimen based on EELS spectra, showing that the change in Mn valence state is accompanied with the variation in oxygen content...

Figure 10 The variation of Tc with bond length is shown in (a) and in (b) is a schematic representation of the motion of the atoms (i.e., of the charge transfer) as the chemical doping at the Cul site proceeds. Note that this picture applies as well when the oxygen content in the material changes.

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