HYSTERESIS EFFECTS AND THE STOICHIOMETRY OF PRASEODYMIUM OXIDE
It is demonstrated that water and CO/sub 2/ have a detrimental effect on freshly prepared samples of PrO/sub x/ as far as an infrared interpretation is concerned. X-ray analyses conducted in conventional ways are considered to be subject to some error as a result of atmospheric contamination. The atmospheric contamination of oxide samples is shown to result in the formation of species whose infrared spectra resemble those of praseodymium carbonate and praseodyraium hydroxide. An absorption band at about 15 microns is thought to be a result of the carbonation-hydration effects. The bamd is considered as indicative of a metaloxygen bond. The resistance (R) of praseodymium oxide (in vacuo) is reported over five orders of magnitude as a function of the temperature. It is shown that the resistance of a sample of oxide decreases as the temperature is increased to about 700 deg C, and then increases as the temperature is raised to 920 deg C. At 920 deg C. it is believed that a phase transition takes place, most likely the cubic to hexagonal transformation of Pr/sub 2/O/sub 3/; another phase charge is believed to occur at about 700 deg C. Plots of log R versus 1/T are linear and energies are calculated from the slopes; a change in the sign of the slope at 700 deg C is observed. Association pressures (P/sub B/) between Pr/sub 2/O/sub 3/ and C/sub 2/ are measured; a break in the linear log P/sub B/ versus 1/ T plots occurs at 920 deg C; this evidence is used as additional support for the argument that a phase change occurs at 920 deg C. An additional break is noted in the curve at 745 deg C and is believed to indicate the other phase change found in the resistance studies. The energies of the two transitions are 12 and 20 kcal, respectively. Isotherms are measured from 400 to l000 deg C and from 10/ sup -5/ to 150 mm Hg of oxygen pressure. A quartz beam microbalance provides a continuous monitor of the change of composition with pressure. The isotherms agree with those obtained by a volumetric measuring technique. An analysis of the isotherms shows that hysteresis effects are present between adjacent, apparently stable stoichiometries. The stable stoichiometries have no simple formulas, however. Homologous series are suggested, which qualitatively account for the observed regions of stability. The hysteresis loop at 465 deg C is analyzed and compared with seven theorems proposed in a general theory of hysteresis. A high degree of correspondence is observed between the Pr-O system and the domain system proposed in the theory. An analysis of the interior of the hysteresis loop region at 465 deg C further substantiates the agreement between the theory and the Pr-O system. The correspondence leads to a consideration of the Pr-O system as being composed of domains of PrO/sub x/. A model and mechanism are postulated, which agree qualitatively with experimental observations. (Dissertation Abstr., 22: No. 7, 1962.)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-000177
- OSTI ID:
- 4781052
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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