Vs. oxygen stoichiometry

Figure 3. Lattice constants and unit cell volume vs. oxygen stoichiometry x for YBa2Cu307 x ((a) - a and b (b) - c and unit cell volume)...

Figure 5. Superconducting transition temperature Tc vs. oxygen stoichiometry x for YBa2Cu307 x, as determined from Faraday Magnetometer Meissner effect measurements in Figure 4. The (50%) midpoints of the transitions (O, ) and temperatures at which the samples attained 10% of the maximum diamagnetism ( , ), are indicated. Also shown are additional corresponding data ( ,A) from the VSM. The arrows denote temperatures above which no superconductivity was observed.

Oxygen Nonstoichiometry. Samples quenched from oxygen at 750C and air at 950C have been studied. A value near 6.5 for the oxygen stoichiometry is expected for both of these samples (10). The samples are found to be semiconducting by measurement of their resistance vs temperatures curves. The reflectance spectrum of the air quenched sample has been taken to directly determine the value of the optical band gap in these materials. The reflectance spectrum in the infrared is presented in Figure 1. As in... 

The half-wave potentials of these steps are approximately -0.1 and -0.9 V (vs. the saturated calomel electrode). The exact stoichiometry of these steps is dependent on the medium. The large background current accrued from this stepwise oxygen reduction interferes with the measurement of many reducible... 

Pressed pellets of BaTiC>3 were sintered in a platinum dish for six hours at 900°C in a controlled partial pressure of oxygen. The samples were quenched to room temperature, and the spectra recorded on a four-slit double-monochromator Raman spectrophotometer. An Ar+ laser with excitation at 514.5 nm was the source. The spectra were recorded at room temperature. Figure 4-30 shows the spectrum of BaTiC>3 whose Ba/Ti ratio is equal to 0.9999. The Raman spectrum is sensitive to the Ba/Ti ratio and theoxygen non-stoichiometry. The half-band width is variable as well as the intensity ratio of the 525 and 713 cm-1 bands. The ratio (I525/713) is at a minimum at the composition of 0.9999, and this can be observed in Fig. 4-31, which shows a plot of the intensity ratio (I525//713) vs. the Ba/Ti composition. 

Magnitude of Response vs. That for HC Oxidation and Stoichiometry. The response of the NO-NH3 interaction in the presence of excess oxygen and that of the highly reactive 1-butene oxidation were compared at 390°C at flow rates of 1.0 and 2.3 ft3/hr. On a C vs. N basis, the C/N relative response was 1.27 at 1.0 ft3/hr and 0.90 at 2.2 ft3/hr. Response for HC s less reactive than butenes (e.g. butanes) was much less. The interaction of NO and NH3 in the presence of oxygen apparently releases about the same heat and is more rapid than 1-butene oxidation. Reactions 6 and 7 both qualify in heat effect and ratio of NH3/NO utilized. It seems probable that both reactions are involved. For our purposes, it was not necessary to make the distinction. 

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