Electrical Properties and Defect Structure of Zirconia: I, Monoclinic Phase

Abstract

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.

Doping in the Valley of Hydrogen Solubility: A Route to Designing Hydrogen-Resistant Zirconium Alloys

“…For this material, we present in Fig. 1(a) [48,49] and oxide off-stoichiometry [50] of MZrO 2 exhibit a slope of −1=6 with log 10 P O 2 at low values of P O 2 and at temperatures as high as 1200 K. The forgone conclusion based on these experiments is that the −1=6 slope at low P O 2 is due to the equilibrium established between free electrons and V •• O . Our theoretical predictions are in accordance with this conclusion.…”

“…The experiments of Refs. [48,50] show a slope of 1=5, which is interpreted as an equilibrium between holes and V 0000 Zr . On the other hand, a slope of 1=4 is found in the electrical conductivity measurements of Ref.…”

“…Electron transport is expected to be slowest in the oxygen-rich part of the oxide [48,49], corresponding also to the oxide surface where the reduction of protons takes place. Electron transport is quantified by the electronic conductivity σ, and in an insulator σ is proportional to the concentration of electrons in the conduction band, n c .…”

Radiolysis in the adsorbed state. II. N2O adsorbed on silica gel and zirconia

“…for the thermal decomposition of N,O on doped nickel oxides, particularly since zirconia may be a p-type semiconductor at oxygen pressures greater than atmosphere (8,20,21). In this case SF6 would not lower the nitrogen yield since its electron affinity is higher than that of an oxygen atom (22,23).…”

The Interaction of Zirconia with Oxygen and Its Defect Structure

“…Numerous studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] have been devoted to the investigation of possible forms of lattice defects of zirconia; the results of these studies may disagree with one another and, what is most important, they fail to produce a complete correlated pattern of manifestations of nonstoichiometry of this oxide. As a rule, these studies involved the determination by some method or preassignment of the correlation x ~ p(O 2 ) q between the value of deviations x (from the stoichiometric ratio O/Zr = 2) and p(O 2 ).…”