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The electrical conductivity of single crystals of Cr2O3 has been measured as a function of temperature from 600° to 1400°C and as a function of oxygen partial pressure from 1 to 10−6 atm. The results show a high-temperature ``intrinsic'' conductivity that is independent of oxygen pressure, and a low-temperature defect-controlled conductivity that varies with oxygen pressure in a manner which cannot be determined from measurements on single crystals. The very low mobility deduced from the intrinsic conductivity suggests an interpretation in terms of the theory of small polarons. Although the possibility of charge transport in very narrow bands cannot be ruled out on the strength of the experimental data, it seems less likely. The model suggested is that of charge formation and transport in localized 3d levels of the cations.

The dielectric constant and spontaneous polarization of fine-grained BaTiO(3) prepared from powder produced by metalloorganic decomposition technology were studied. The room-temperature dielectric constant of BaTiO(3) was found to increase sharply with increase in grain size, reach a maximum at about 0.4 mum, and decrease with further increase in grain size. Spontaneous polarization continuously decreased with decrease in grain size. A model is proposed to explain the grain size dependence of the dielectric constant.

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Electrical Properties and Defect Structure of Zirconia, I 635 reasonable. If a diffusion couple is formed between Ti and ZrOy, one would expect to find a two-phase region with compositions varying between 100% liquid of composition 1 a t the end facing the Ti source, to 100% solid of composition 4 a t the other end. At any point between, the compositions of liquid and solid and the percentages of each are given by the appropriate tie line and the lever rule. Across the two-phase region, the liquid would vary in composition from that of point 1 to point 3. This would correspond to the black, well-sintered region in Fig. 1. In this work, however, titanium is in contact with vacuum-reduced zirconia, i.e. ZrOz-r. Reoxidation ofThe defect structure of monoclinic zirconia was investigated by measuring the oxygen partial pressure dependence of the electrical conductivity and sample weight. Techniques were developed to calculate the degree of nonstoichiometry and the mobility of the charge carriers from electrical and weight change data. ZrOz was found to be an amphoteric semiconductor at 1000°C with the transition from n-type to p-type conductivity occurring at 10-16 atm. The predominant defect in the oxygen excess region was shown to be completely ionized zirconium vacan-cies. The positive holes arising from the zirconium vacancies were found to have an extremely small mobility.