Nonstoichiometric Cerium Dioxide Research Articles

A thermodynamic and electrical conductivity study of nonstoichiometric cerium dioxide

Thermodynamic and dc electrical conductivity measurements were performed on nonstoichiometric CeO 2− x to characterize the electrical behavior and defect structure in the vicinity of the n to p transition. Using the mass action approach, activation energies of 2.57, 1.15 and 0.63 eV were obtained for the electron, hole and ionic partial conductivities respectively (600–1000°C, 1< P o 2 <10 −4 atm). Thermodynamic measurements of 99.99%CeO 2- x by electrochemical coulometric titration yielded expressions for point defect concentrations per cm 3 and nonstoichiometry in the impurity dominated region at 800°C as follows: [Ce′ Ce]=7.08×10 16P − 1 4 O 2 cm −3;[ h ̇ ]=9.26×10 18P + 1 4 O 2 cm −3;x=2.03×10 −2 3(7.08×10 16P − 1 4 O 2 −9.26×10 18P + 1 4 O 2 ) . Thermodynamic constant composition measurements revealed a decrease in the partial molar enthalpy (from - 10 eV) with decreasing stoichiometry for x<10 −2.8. This decrease is attributed to defect reaction involving both holes and electrons.

Electrical conductivity in nonstoichiometric cerium dioxide

The essential features of the electronic contribution to the electrical conductivity of non stoichiometric cerium dioxide, i.e. strong composition and temperature dependence of the mobility and of the activation energy may easily be understood in the frame of a simple model, taking into account long range Coulomb interactions associated with short range interactions. Energy parameters have been deduced from a purely thermodynamic analysis. Particularly, it has been shown that these interactions are the cause of the failure of mass action law to explain the puzzling rapid change of mobility in nearly stoichiometric oxide.

Solid-state oxygen meter equipped with CeO 2− x thick-film electrode: determination of composition of Co/Co 2 gas mixtures

The properties of a thick film of non-stoichiometric cerium dioxide, used as an oxygen electrode in a high-temperature solid-state oxygen meter, have been investigated. Experiments were carried out in a wide range of temperature (650 – 1000 °C) and CO/CO 2 gas mixture composition (75% - 9% CO). Results are reported and compared with those obtained, in the same conditions, with a porous platinum electrode made from Hanovia 6082 platinum paste.

Thermodynamic and conductivity studies of nonstoichiometric cerium dioxide by coulometric titration: A simultaneous measurement

Simultaneous measurements of thermodynamic properties (Δ H̄ o2 and Δ S̄ o2) and electrical conductivity (σ) for constant compositions in nonstoichiometric cerium dioxide (CeO 2− x ) were carried out by coulometric titration in the temperature range 800–945°C and oxygen-partial-pressure range 10 −10 to 10 −21 atm. The thermodynamic quantities, Δ H̄ o2 and Δ S̄ o2 were calculated in the regime 1.86 × 10 −3 ⩽ x ⩽ 3.16 × 10 −2. In previous studies of metal oxides (e.g., CeO 2− x ), the electron mobility (μ) has been determined by combining separate experimental measurement of x and σ. In this study, the electrochemical, constant-composition technique is used as a fast and direct method for obtaining thermodynamic data and simultaneous measurements of the electrical conductivity.

Oxygen Association Pressure Measurements on Nonstoichiometric Cerium Dioxide

The data that were obtained by using a capacitance manometer system to measure the deviation from stoichiometry in nonstoichiometric cerium dioxide as a function of oxygen partial pressure at 800°C were analyzed along with existing data obtained at other temperatures. It was determined that, for values of log less than −2.4, the observed −1/5 dependence of the deviation from stoichiometry upon the oxygen partial pressure is due to the existence of doubly ionized nonstoichiometric vacancies along with the presence of charge compensating doubly ionized vacancies that are caused by Ca impurities. The mass action constants that were calculated for the defect reaction at various temperatures were then used to analyze the conductivity data that exists at corresponding temperatures. It was determined that the −1/5 dependence of the conductivity upon the oxygen partial pressure is also due to the presence of doubly ionized nonstoichiometric vacancies along with the existence of charge compensating doubly ionized vacancies caused by Ca impurities. Finally, it was also shown that, for values of log less than −2.4, not only is the mobility a function of temperature only, but also that the oxygen partial molal enthalpy change is independent of both temperature and composition.

Small-polaron mobility in nonstoichiometric cerium dioxide

The high temperature drift mobility (μ d ) of charge carriers in nonstoichiometric cerium dioxide (CeO 2−x) has been calculated by combining the electrical conductivity and nonstoichiometry data on the basis of the oxygen vacancy model with correct ionization state. The electrical conductivity was measured by a four-probe d.c. technique and the nonstoichiometry by thermogravimetric analysis. The dilute solution model of the point defects is valid up to x = 0.03. From the magnitude of μ d and its temperature dependence, the charge carriers in CeO 2−x, are proposed to be small-polarons formed by localization of electrons at cerium sites and the charge transport process is proposed to occur by a hopping mechanism. The observed temperature dependence of μ d is in accord with that derived by Holstein and Friedman for small-polaron transport by the hopping mechanism. The activation energy of mobility is found to increase with increasing x as expected for the hopping model.

The electrical conductivity and thermodynamic behavior of SrO-doped nonstoichiometric cerium dioxide

Electrical conductivity and thermogravimetric measurements were made on SrO-doped nonstoichiometric cerium dioxide (i.e., Ce 1− y Sr y O 2− y− x ) as a function of temperature (∼700–1500°C) and oxygen partial pressure (∼1 to 10 −21 atm). Assuming limiting case defect models the ionic, σ i , and electronic, σ e , conductivities were calculated from this data. In the region where y ⪢ x (i.e., at low temperatures and high oxygen pressures) the conductivity is independent of P O 2 and up to approximately 3 mole% SrO, it is proportional to mole% SrO. The equation for ionic conductivity, σ i ⋍ [4.5 ± 0.5] [m/o SrO]exp(−0.58/kT) , was obtained by fitting the conductivity data in this region to an expression derived on the basis of an oxygen vacancy model. In the composition region between approximately x = 10 −3 and x = 10 −2, both the thermodynamic behavior and the electrical conductivity was shown to be consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies and electrons localized on normal cerium sites. In this region the electronic conductivity varies linearly with x and the electronic mobility decreases with increasing SrO content.

A thermodynamic study on CaO-doped nonstoichiometric cerium dioxide

Thermogravimetric measurements were performed on CaO-doped nonstoichiometric cerium dioxide (i.e. Ce 1− y Ca y O 2− y− x ) in the temperature range 800–1500°C and from oxygen pressures of 10 −1–10 −21 atm. Fr data the deviation from stoichiometry x = x( T, P O 2 ) y was determined for values of y = 0.01, 0.045, 0.07, 0.10 and 0.14. The thermodynamic quantities Δ H O 2 ; and ΔS O 2 were calculated in the region 0.001 ⩽ x ⩽ 0.2 and found to be independent of temperature with the exception of those for 14 mole % CaO at large deviations from stoichiometry. p]In the composition region near stoichiometry (i.e. for x between approximately 10 −3 and 10 −2), the variation of Δ S O 2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies and electrons localized on normal cerium sites. The range of nonstoichiometry with which this defect model fits the experimental results increases with increasing CaO content. In this same region ΔH̄ O 2 exhibits a slight dependence on x for y = 0.01 and 0.045 and is essentially independent of x for y = 0.7,0.10 and 0.14. The experimental observation that x α P − 1 4 O 2 is rationalized on the basis of the above model for the case where y > x. At large deviations from stoichiometry the dependence of x = x( T, P O 2 ) y is similar to the nonstoichiometric behavior of “pure” CeO 2− x when y = 0.01 or 0.045. The dependence of ΔH O 2 ; and ΔS O 2 on x is also similar. for y = 0.10 and 0.14 the nonstoichiometric behavior and the dependence of ΔH O 2 on x differs significantly from the behavior of “pure” CeO 2− x .

X-ray and neutron diffraction study of intermediate phases in nonstoichiometric cerium dioxide

Powder samples of reduced ceria, CeO 2− x , of known compositions in the range 0 < x < 0.3 have been examined by X-ray and neutron diffraction techniques in order to determine which intermediate phases belonging to the homologous series Ce n O 2 n−2 (with n = integer) truly exist. Through the appearance of superlattice lines in the neutron diffraction patterns, the existence of four distinct phases, corresponding to n = 7, 9, 10 and 11 was established. Aside from the phase Ce 7O 12, the structures of these phases cannot be accounted for with rhombohedral cells based on 〈111〉 vacancy strings, but indicate lower (monoclinic or triclinic) symmetry. The structure of Ce 9O 16 and Ce 10O 18 do not agree with structures proposed for the analogous Pr n O 2 n−2 compounds.

A thermodynamic study of nonstoichiometric cerium dioxide

Thermogravimetric measurements were performed on nonstoichiometric CeO 2−x in the temperature range 750–1500°C and from oxygen pressures of 10 −2 to 10 −26 atm. From this data the deviation from stoichiometry x = x( T, P o 2 ) was determined. The thermodynamic quantities Δ H o 2 and Δ S o 2 were calculated in the region 0.001⩽ x ⩽ 0.3 and found to be independent of temperature. In the composition region 0.001< x < 0.006, the variation of Δ S o 2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental P o 2 - 1 5 dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δ H o 2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δ H o 2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed. In the composition region 0.006 < x < 0.1, x ∝ P o 2 − 1 n with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ P o 2 − 1 n with n increasing rapidly with x to n≅ 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO 1·72 and CeO 1·70 was not observed in this study at temperatures between 1300° and 1500°C.

A thermodynamic study on CaO- doped nonstoichiometric cerium dioxide

A thermodynamic study on CaO- doped nonstoichiometric cerium dioxide

The electrical conductivity and thermodynamic behavior of SrO-doped nonstoichiometric cerium dioxide: R. N. Blumenthal and J. E. Garnier. Metallurgy and Materials Science, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233

The electrical conductivity and thermodynamic behavior of SrO-doped nonstoichiometric cerium dioxide: R. N. Blumenthal and J. E. Garnier. Metallurgy and Materials Science, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233

X ray and neutron diffraction study of intermediate phases in nonstoichiometric cerium dioxide: S. P. Ray and A. S. Nowick. Henry Krumb School of Mines, Columbia University, New York, New York 10027. And D. E. Cox, Physics Department, Brookhaven National Laboratory, Upton, New York 11973

X ray and neutron diffraction study of intermediate phases in nonstoichiometric cerium dioxide: S. P. Ray and A. S. Nowick. Henry Krumb School of Mines, Columbia University, New York, New York 10027. And D. E. Cox, Physics Department, Brookhaven National Laboratory, Upton, New York 11973

A thermodynamic study of non-stoichiometric cerium dioxide

A thermodynamic study of non-stoichiometric cerium dioxide

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO 2− x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10 −22 atm). The isothermal compositional dependence of the electrical conductivity of CeO 2− x was determined by combining recently obtained thermodynamic data, x = x( P O 2 , T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression σ=410[x]e −(0.158+x) kT ( ohm cm) −1 over the temperature range 750–1500°C and from x = 0.001 to x = 0.1. This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration n ce′ ce= 8x a 0 3 where n Ce′ Ce is the number of Ce′ Ce per cm 3 and a 0 is the lattice parameter and (b) the electron mobility μ=5.2(10 −2)e −(0.158+x) kT ( cm 2/ V sec) .

Electronic conductivity in nonstoichiometric cerium dioxide: R. N. Blumenthal and R. K. Sharma. Metallurgy and Materials Science, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233

Electronic conductivity in nonstoichiometric cerium dioxide: R. N. Blumenthal and R. K. Sharma. Metallurgy and Materials Science, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233

ChemInform Abstract: THE ELECTRICAL CONDACTIVITY OF CAO‐DOPED NONSTOICHIOMETRIC CERIUM DIOXIDE FROM 700 DEGREES TO 1500 DEGREES

Chemischer InformationsdienstVolume 4, Issue 49 Physical Inorganic Chemistry ChemInform Abstract: THE ELECTRICAL CONDACTIVITY OF CAO-DOPED NONSTOICHIOMETRIC CERIUM DIOXIDE FROM 700 DEGREES TO 1500 DEGREES R. N. BLUMENTHAL, R. N. BLUMENTHALSearch for more papers by this authorF. S. BRUGNER, F. S. BRUGNERSearch for more papers by this authorJ. E. GARNIER, J. E. GARNIERSearch for more papers by this author R. N. BLUMENTHAL, R. N. BLUMENTHALSearch for more papers by this authorF. S. BRUGNER, F. S. BRUGNERSearch for more papers by this authorJ. E. GARNIER, J. E. GARNIERSearch for more papers by this author First published: December 4, 1973 https://doi.org/10.1002/chin.197349012AboutPDF 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. Volume4, Issue49December 4, 1973 RelatedInformation

The Electrical Conductivity of CaO ‐ Doped Nonstoichiometric Cerium Dioxide from 700° to 1500°C

The electrical conductivity of sintered specimens of was measured over the temperature range 700°–1500°C and from 1 to 10−22 atm of oxygen. All specimens of exhibited mixed conduction. Two limiting case regions were observed. At low temperatures and high oxygen pressures, the conductivity is predominantly ionic. In this region the conductivity is independent of and between approximately 1 and 8 m/o is proportional to mole per cent . The following equation for ionic conductivity was obtained by fitting the conductivity data in this region to an expression derived on the basis of an oxygen vacancy model. An approximate expression for the diffusion coefficient for oxygen vacancies was calculated from the above expression and the Nernst‐Einstein relation. At high temperatures and low oxygen partial pressures and for lower contents the conductivity is predominantly electronic. In this region the magnitude and dependence of σ is similar to “pure” . A thermodynamic argument is also presented which favors oxygen vacancies as the nonstoichiometric defect in both pure and .

Studies of the Defect Structure of Nonstoichiometric Cerium Dioxide

The electrical conductivity of sintered specimens of was measured over the temperature range 800°‐1500°C and from 1 to 10−21 atm of oxygen. Based on the agreement between these experimental data and theoretically derived relations obtained using the law of mass action, the nonstoichiometric defect structure of was interpreted in terms of a defect structure consisting of triply and quadruply ionized cerium interstitials and localized electrons. The standard enthalpies of formation for the following defect reactions in were determined

Electron mobility in nonstoichiometric cerium dioxide at high temperatures

Electron mobility in nonstoichiometric cerium dioxide at high temperatures