Nonstoichiometric Rutile Research Articles

Defect Structure and Related Thermodynamic Properties of Nonstoichiometric Rutile (TiO2-X) and Nb2O5Doped Rutile

Defect Structure and Related Thermodynamic Properties of Nonstoichiometric Rutile (TiO_2-X) and Nb₂O₅Doped Rutile

Low temperature parahydrogen enrichment on nonstoichiometric rutile

The reduction of rutile by vacuum outgassing between 450–825°C, or by hydrogen or carbon monoxide at 350°C, yields active catalysts for low temperature parahydrogen enrichment due to the presence of surface Ti3+ ions. Since the kinetics indicate saturation of these active sites, the absolute rate of enrichment at 77 K and 1.3 × 103 N m–2 can be taken as a direct measure of the extent of surface non-stoichiometry. Poisoning experiments with oxygen indicate Ti3+ ions are not limited to the surface layer alone, but are distributed between surface and sub-surface layers, and are effectively mobile at temperatures considerably below the Tammann temperature. The activity for parahydrogen enrichment arising from oxygen molecules physically adsorbed on fully oxidised rutile has been used to derive an equation, which is used to estimate the concentration of Ti3+ ions in reduced surfaces. This did not exceed ∼8.0 × 1016 ion m–2 for the most active surface studied.

Studies of the Defect Structure of Nonstoichiometric Rutile, TiO2 − x

The electrical conductivity of single crystals of rutile was measured in the “c” and “a” directions over the temperature range 1000°–1500°C and from 1 to 10−15 atm of oxygen. Based on the excellent fit observed between the theoretically derived relation and the experimental conductivity data, the nonstoichiometric defect structure of rutile was rationalized in terms of quasi‐free electrons and both triply and quadruply ionized titanium interstitials. In addition, this equation satisfies a contribution due to impurity conduction where is proportional to a temperature dependent concentration of ionized impurities or a contribution due to intrinsic conduction where is proportional to a temperature dependent concentration of holes in the valance band.The standard enthalpy of formation for the following defect reactions in rutile were determined from the temperature dependence of , , and obtained from the above relation and from the experimental expression for the temperature dependence of electron mobility. The values of , , and are in agreement, within experimental error, with those obtained in an earlier investigation based on conductivity measurements in the c direction only. If impurity conduction is involved, is equal to the standard enthalpy of formation for the ionization of an impurity. If intrinsic conduction is involved, is equal to the band gap energy which is thought to be between 3 and 4 ev for rutile. The ratio of electrical conductivities for the c and a direction is essentially independent of oxygen pressure above 1100°C; but at the lower temperatures, 1000° and 1100°C, the ratio is dependent on pressure in contradiction to the initial assumption that mobility is a function of temperature only.

Thermodynamic Study of Nonstoichiometric Rutile (TiO2‐x)

Journal of the American Ceramic SocietyVolume 48, Issue 7 p. 384-384 Thermodynamic Study of Nonstoichiometric Rutile (TiO2-x) J. B. MOSER, J. B. MOSERSearch for more papers by this authorR. N. BLUMENTHAL, R. N. BLUMENTHALSearch for more papers by this authorD. H. WHITMORE, D. H. WHITMORESearch for more papers by this author J. B. MOSER, J. B. MOSERSearch for more papers by this authorR. N. BLUMENTHAL, R. N. BLUMENTHALSearch for more papers by this authorD. H. WHITMORE, D. H. WHITMORESearch for more papers by this author First published: July 1965 https://doi.org/10.1111/j.1151-2916.1965.tb14769.xCitations: 55 I'resented at the Sixty-Sixth Annual Meeting, The American Ceramic Society, Chicago, Ill., April 22, 1964 (Basic Science Division, No. 35-B-64). This work was supported by Materials Central, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio. At the time this work was done J. B. Moser and R. N. Blumen-thal were research associates, Department of Materials Science, Northwestern University, Evanston, Ill. D. H. Whitmore is professor, Department of Materials Science, Northwestern University. J. B. Moser is now associate ceramist at Argonne National Laboratory, Argonne, Ill, and R. N. Blumenthal is associate professor of materials science, College of Engineering, Marquette University, Milwaukee, Wis. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume48, Issue7July 1965Pages 384-384 RelatedInformation

A note on the transformation in non-stoichiometric rutile

Abstract Intersecting, nearly orthogonal faults on {131} planes are formed when rutile is annealed in a reducing atmosphere. These faults have been observed to become aligned at high temperatures and this phenomenon appears to be associated with a mechanism of rutile transformation. It is tentatively coricludetl that the transformation is related to an instability of the rutile lattice containing a high point defect concentration.

Phase Transformation Studies in TiO2 Supporting Different Defect Mechanisms in Vacuum-Reduced and Hydrogen-Reduced Rutile

Studies of the anatase-rutile transformation show that the rate of transformation is accelerated in hydrogen atmospheres and retarded in vacuum. This information, interpreted in terms of the defect structure of TiO2, supports data obtained by other investigators indicating that the mechanism by which nonstoichiometric rutile is formed depends upon the atmosphere in which reduction occurs.

Point-Defect Relaxation in Rutile Single Crystals

The existence of a well-defined relaxation process was established in internal friction studies of nonstoichiometric rutile, TiO2, crystals. The peak was observed only in crystals which were vacuum reduced to a room-temperature-resistivity value of 21 Ω-cm or less and oriented so that the principle vibrational strain coincided with an ``a'' crystallographic axis. All resistivity measurements were made with the current flowing parallel to the longitudinal specimen axis. For measurements in the frequency range 3 to 10 cps, the peak temperature varied from ≃60 to 85°C and exhibited a dependence on the degree of reduction, i.e., the peak temperature increased with increasing reduction. The average activation energy for the process obtained from peak shift and peak shape determinations was 24 kcal/mole. Crystallographic considerations coupled with the orientation dependence of the peak suggest that the nonstoichiometric defect in vacuum-reduced rutile is the titanium interstitial.