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C. N. R. RAO,G. V. SUBBARAO,AND S. RAMDAS
and naeso-NaDMGA, the change is caused only by the effect of substituents (or by the effect of solvents), since the conformation is found to be fixed over all degrees of neutralization. I n the case of isotactic P (NaMA) , however, we were unable to decide between the two possibilities, since the vicinal coupling constants are not known, It is a t least probable, however, that the effect of the substituent should be most important for the change in . I n any case, it is certain that the effect of the substituent or the
solvent should be carefully examined when assigning the nmr peaks or calculating the tacticity of polymers.
Acknowledgment. Most of the measurements were carried out by a Varian HA-100 spectrometer of Toyo Rayon Co. We wish to thank this company for its aid and particularly Dr. Kenkichi Nukada for his interest and advice in this work. We also wish to thank Mr. Y. Kawaguchi, who prepared the sample of isotactic P (AA) .
Phase Transformations and Electrical Properties of Bismuth Sesquioxide
by C. N. R. Rae,' G. V. Subba Rao, and S. Ramdas Department of Chemistry, Indiun Institute of Technology, Kanpur, India
(Receiued June 10, 1068)
Phase transformations of BieOs have been studied by differentialthermal analysis. The enthalpy and activation energy of the monoclinic-cubic transformation are 8.8 and 110 kcal mol-', respectively. The enthalpies of the cubic-tetragonal and tetragonal-monoclinic transformations are estimated to be 6.7 and 2.1 kea1 mol-'. The electrical conductivity of BiiOs shows marked changes in conductivity at temperatures where the phase transformations occur. In addition, Bi203 shows a change in slope in the log a-l/T curve due to a change from p-type to n-type behavior; this observation is supported by the change in sign of the Seebeck coefficient, p , around the same temperature. /3 changes sign at lower temperatures as the oxygen partial pressure is reduced. The band model seems to be applicable in the case of BieOa.
Introduction Bismuth sesquioxide, Bi&, is an important solidstate material which finds uses in glass technology and electronics. The phase transformations of BizOs have been examined by X-ray diff raction2 and differential thermal analysis3 and it appears certain that there is structural hysteresis in the reversible crystal structure transformation. Biz03 changes from a monoclinic (pseudoorthorhombic) structure to a cubic structure on heating to -730" (and then melts a t 4 3 2 5 " ) ; on cooling, the cubic form reverts back to the monoclinic form through a metastable tetragonal phase. There seems to be some uncertainty in the enthalpy of the monoclinic-cubic transformation"* and there are no data in the literature on the enthalpies of the reverse transformations. Electrical properties of Biz03 have been studied by a few worker^.^-^ Biz03 behaves like a p-type semiconductor up to -650" at moderate pressures of oxygen and there are some indications that it changes over to n-type behavior at relatively low temperatures (3, indicated the only extracting species were the molecular adduct TBP. HzO and the hydronium ion species clod-, an ion pair, where 0 Ip I 1.5. I n this study even more dilute TBP solutions 3TBP.H30f.pHz0 in CCl, were examined, and a two-TBP acid complex, in addition to the three-TBP complex,was found. In the isooctane system either a two- or three-TBP acid complex, depending upon TBP concentration, was found to predominate. With 1,2-dichloroethane-TBP and at the organic-phase acid concentrations examined, only a dissociated three-TBP complex was found. In addition to an anion effect, it is suggested solvent effects upon both TBP and the extraction complex are changing, to a greater or lesser extent, the TBP coordination number of the extracted hydronium ion from three to two.
-. 0
Introduction A previous study of HC104 extraction by dilute solutions of tributyl phosphate (TBP) in CCL indicated that the proton was coordinated with three TBP molecules in the organic phase.z This study also showed that at least one water molecule was always coextracted. From these two results a model for the extracted species was suggested; the complex has a hydronium ion core to which the three TBP molecules are coordinated. It was also suggested that this model could have general application as a guide for understanding acid extraction by dilute solutions of other weakly basic organic extractants as well as by other TBP-diluent systems.
To test the validity of this proposed model the extraction of HC104 by TBP in other diluents was investigated. I n this paper, the first of a two-part study, the use of isooctane and of 1,Zdichloroethane as diluents was investigated. Isooctane was chosen to illustrate the extraction process in a solvent which possesses relatively weak solvating properties and so can be considered relatively “inert.” This system will be used as a reference against which the other TBPdiluent systems can be compared. The solvent 1,2-di(1) This work was done under the auspices of the U.S. Atomic Energy Commission. (2) D. C. Whitney and R. M. Diamond, J . Phys. Chem., 67, 209 (1903). Volume ‘73,Number 9 March lB50
