N-type Electronic Conductivity Research Articles

Effect of ion implantation doping on electrical properties of yttria-stabilized zirconia thin films

The change in conductivity of Fe and Ti implanted rf-sputtered layers of yttria-stabilized zirconia (YSZ) was studied as a function of the temperature (400–800°C) and oxygen partial pressure. In an oxidized state and in the temperature range of 400–600°C, the conductivity of the Fe implanted YSZ film (15keV, 8×10 16 at.cm −2) was dominated by the n-type electronic conductivity of a thin Fe 2O 3 layer with an estimated thickness of less than 2 nm on top of the YSZ thin film. Due to the incorporation of a part of the implanted Fe atoms in the yttria-stabilized zirconia lattice, the ionic conductivity was somewhat decreased. In a reducing atmosphere this electronic conduction was no longer observed. In an oxidized state, the conductivity of the YSZ film was not influenced by the implantation of Ti (15keV, 8×10 16at.cm −2). After reduction in a H 2 atmosphere, an increase in the conductivity of the sputtered film with 2–3 orders of magnitude was observed. This has been ascribed to the presence of nonstoichiometric TiO 2− x , which is an semiconductor.

Determination of electronic conductivity limits of mullite and ZrO2-9 mol% MgO solid electrolytes

A coulometric titration technique was used for the determination of the parameterPϑ, defined as the oxygen partial pressure at which the ionic conductivity and n-type electronic conductivity of the electrolyte are equal, for mullite and 9 mol% MgO stabilized zirconia electrolytes in the temperature range 1674–1921 K. The results ofPϑ for mullite and ZrO2-9 mol% MgO were log(Pϑ/101 325 Pa)=54.32−137000/T and log (Pϑ/101 325 Pa)=27.16–75500/T, respectively. The results for low oxygen activities in liquid iron are discussed on the basis of the present results forPϑ values.

Oxygen permeability in ZrO 2TiO 2Y 2O 3 system

The oxygen permeability of yttria-stabilized zirconia containing 7.5 and 10 mol% TiO 2 was measured under low oxygen partial pressure and at high temperatures up to 1500°C. The measured oxygen permeability increases with decreasing oxygen partial pressure according to P −1/6 O 2 . This proportionality indicates that the n-type electronic conduction in the yttria-stabilized zirconia containing TiO 2 is due to the electron hopping between Ti 4+ and Ti 3+ ions. The activation energy of 1.9 eV is obtained for the electronic conduction. At 1000°C, the contribution of the electronic conduction is negligibly small even under low oxygen partial pressure. From these results, ZrO 2TiO 2Y 2O 3 system is not so promising materials for electrode in SOFC. As this system is stable and has a high oxygen permeability at high temperatures up to 2000°C, it is the promising material as a membrane for a direct water splitting at high temperatures to produce hydrogen.

Determination of mixed ionic and electronic conduction in commercial-grade magnesia-stabilized zirconia electrolyte

The extent of mixed ionic and n-type electronic conduction in commerical-grade zirconia electrolyte has been determined by employing coulometric titration and open-circuit e.m.f. measurements. Impurities such as Al2O3, TiO2 and Fe2O3 did not seriously affect the electronic conduction.

Ionic conduction and microstructure of the ceria-strontia system

Ionic conduction of oxygen in the ceria-strontia system, (CeO 2) 1- x (SrO) x , was investigated as a function of temperature, partial pressure of oxygen, and oxide composition, together with its crystal structure, density and microstructure. Undoped ceria and its solid solution of strontia have the cubic fluorite structure. Samples above the solubility limit of strontia ( x>0.08) were mixtures of 0.92CeO 2·0.08SrO and SrCeO 3. The ionic conductivity was greatly enhanced with an addition of small amount of strontia to ceria. The conductivity of ceria-strontia system at 0.05⩽ x⩽0.40 was much higher than that of calcia-stabilized zirconia. At this composition range, the ionic transference number was nearly unity even at 600°C. It was found that the excellent ionic conductivity was little affected by the presence of the second phase of SrCeO 3 at 0.1< x<0.4. Further increase in strontia content leads to a decrease in conductivity at x=0.5. The (CeO 2) 0.90(SrO) 0.10 sample is regarded as a pure ionic conductor at P O 2 >10 −11 atm (900°C), where the conductivity is a constant versus P O 2 . The n-type electronic conductivity increased with a decrease in P O 2 and became dominant below P O 2 =10 −11 atm.

Electrical transport properties of gadolinium scandium gallium garnet

Electrical conductivity and thermoelectric power are measured on a single crystal of Gd 3.0Sc 1.8Ga 3.2O 12 (GSGG) between 1273 and 1673 K. The measurements are made both in air and in controlled atmospheres, and P O 2 varies from 10 −1.68 to 10 −5.6 MPa. The data indicate GSGG may well be a mixed conductor in this temperature and P O 2 range, with n-type electronic conductivity and ionic transport on the oxygen sublattice. Changes in temperature induce long-lived disequilibrium in electrical conductivity of GSGG (over 30 h at T < 1373 K) that can be explained by temperature dependent cation redistribution. The effective activation energy for equilibrium electrical conductivity is E a = 2.40 ± 0.05 eV, as opposed to values of E a between 1.8 and 2.2 eV during actual temperature changes. An additional contribution in the equilibrium E a, due to thermally activated cation redistribution, can account for the higher value seen.

IONIC CONDUCTION AND ELECTRONIC CONOLUCTION IN THE HIGH IONIC CONDUCTOR OF THE SYSTEM Bi2O3-Y2O3

The ionic electrical conduction in sintered Bi2O3-Y2O3 system for samples containing 20-30 mol% Y2O3 was investigated by means of measurement of ac conductivity and the emf of oxygen gas concentration cell using the specimen tablet as electrolyte. The experimental po2 range from 1 to 10-21 atm for ionic electrical conduction measurement-These materials showed high oxygen ionic conduction, the conductivities for samples containing 22.5-30mol% Y2O3 are many times higher than those of stabilized zirconia ZrO based solid electrolyte at corresponding temperatures. When these materials are used to construct an oxygen concentration cell, the E/E0 is equal to 1 or approaches 1. These values show that the samples containing 22.5 to 30 mol% Y2O3 are nearly pure ionic conductors. The p-type hole conductivity is very small at higher po2 values, so it is negligible. The n-type electronic conduction was investigated by means of coulomb titration technique for Y2O3 27.5 mol% sample We obtained that lg pe＇=-767000/T +665. The pe＇ is equal to 2.6×10-61 atm at 800℃. The n-type electronic conduction is vary small, so that it is also negligible.These materials are proved to be good high ionic conductors.

Measurements of the Parameter, &lt;I&gt;P&lt;/I&gt;&lt;SUB&gt;\ominus&lt;/SUB&gt;, for the Determinations of Mixed Ionic and N-Type Electronic Conduction in Commercial Zirconia Electrolytes

Measurements of the Parameter, &lt;I&gt;P&lt;/I&gt;&lt;SUB&gt;\ominus&lt;/SUB&gt;, for the Determinations of Mixed Ionic and N-Type Electronic Conduction in Commercial Zirconia Electrolytes

Defects and charge transport in stabilized α-Ta2O5

Abstract The high temperature form of tantalum oxide, α-Ta2O5, stabilized by the addition of several mol% SC2O3, has been shown to be an excellent oxygen conductor. Lattice oxygen transport is comparable to that found in calcia stabilized zirconia in the temperature range 500-950° and is 1 -2 orders of magnitude greater than found for low (β) Ta2O5 at these temperatures. Electrical conductivity is characterized by a dominant ionic component with an activation energy, in air, ∼1 eV. n-type electronic conduction, characterized by a po2 −1/4 dependence, becomes important at highly reduced oxygen partial pressures and high temperatures. Transport properties have been characterized using complex impedance measurements within the kinetically stable range of α-Ta2O5, at 500 po 2>10−20 atm; and within the thermodynamically stable temperature range, T>1360°. Frequency range of measurement was 10 Hz-2 MHz. Galvanic cell measurement of ionic transference number was used to confirm oxygen vacancies as the d...

Evaluation of electrochemical oxygen probes for use in steelmaking

The electrochemical behaviour of oxygen sensors equipped with an Mo+MoO2 reference electrode is discussed with regard to n-type electronic conduction in the solid electrolyte and the resulting transport of oxygen through the cell.

Galvanic-cell investigations with a CaF 2 solid electrolyte at elevated temperatures

Recent results from our laboratory indicate that CaF 2 can be used to measure oxygen and sulfur chemical potentials in the temperature range of 500–900°C. A theoretical explanation of the manner in which the CaF 2 electrolyte functions as either an oxygen or a sulfur sensor is presented. It is concluded that CaF 2 is a useful electrolyte for the measurement of extremely low oxygen chemical potentials, possibly even in regions where zirconia-based and thoria-based oxide electrolytes exhibit n-type electronic conductivity. The CaF 2 electrolyte is also suitable for the measurement of sulfur chemical potentials in solids and gas mixtures.

Report on the U.S.-Japan joint seminar on Transport in Non-Stoichiometric Compounds

From October 10-12, 1979, a U.S.-Japan joint seminar, "Transport in Non-Stoichiometric Compounds" was held at the East-West Center in Honolulu, Hawaii under the sponsorship of the Japan Society for Promotion of Science and the U.S. National Science Foundation. This was a follow-up seminar to the earlier "Defects and Diffusion in Solids" seminar held in Tokyo, October 4-6, 1976. The purpose of this seminar, at which there were eight Japanese participants, eight U.S. participants, and one U.S. observer, was to bring together scientists from the two countries for discussions of transport in nonmetallic solids including oxidation and sulfidation reactions of metals, the role of defects in nonmetallic solids and transport in solid electrolytes. The research papers were not published as a symposium proceedings but each author was free to submit his paper to the journal of his choice. A brief summary of the highlights of the program is presented here to acquaint readers with recent developments and the discussions of papers. The sessions were divided into three areas. These were (1) Synthesis, Properties, and Application of Solid Electrolytes; (2) High-Temperature Corrosion; and (3) Defects and Transport Properties of High Temperature Materials. T. Takahashi reported on his extensive research on high oxide ion conduction in sintered oxides. Some perovskite-type oxides of general formula, ABO3 were found to be oxygen ion conductors when A or B was substituted with a cation of lower valency. Such materials were accompanied by p-type electronic conductivity under high partial pressure of oxygen and a small n-type electronic conduction under low oxygen partial pressures. The oxygen ion conduction is via anion vacancies. Examples of such oxides were CaTio.7Alo.303_~, CaTio.sAlo.503_~, CaTio.95Mgo.0503_~. These *Center for Solid State Science, and Department of Physics, Arizona State University, Tempe, Arizona 85281. 501

Mixed ionic and n-type electronic conduction in commercial ZrO2+11mol%CaO solid electrolyte.

Parameter, Pθ, at which the ionic and n-type electronic conductivities are equal, was measured for commercial ZrO2+11mol% CaO by means of Swinkels' coulometric titration technique. The results obtained were log(Pθ/atm)=-66300(T/K)-1+20.6(±0.5) at 1100° to 1400°C.

Thermal efficiency of solid electrolyte fuel cells with mixed conduction

The effect of mixed anionic and n-type electronic conduction in solid electrolytes on the thermal efficiency of a fuel cell system was analyzed quantitatively. The mixed conduction observed when electrolytes based on ceria are used in H 2/air fuel cell applications lowers the maximum attainable cell thermal efficiency to below 40%. Neither the zirconia nor the ceria based solid oxide electrolytes studied to date can be used in a low temperature (700 °C) system that meets simultaneously the requirements of power density and thermal efficiency for electric utility power plants. The material properties required for an advanced fuel cell power plant solid electrolyte were derived in terms of the ionic conductivity and the Schmalzried parameters P⊕ and P⊖ : σ ion > 0.033 (ω-cm) −1, P⊕ > 10 3 atm., P⊖ < 10 −23 atm. at 700 °C.

Thermal efficiency of solid electrolyte fuel cells with mixed conduction

The effect of mixed anionic and n-type electronic conduction in solid electrolytes on the thermal efficiency of a fuel cell system was analyzed quantitatively. The mixed conduction observed when electrolytes based on ceria are used in H 2/air fuel cell applications lowers the maximum attainable cell thermal efficiency to below 40%. Neither the zirconia nor the ceria based solid oxide electrolytes studied to date can be used in a low temperature (700 °C) system that meets simultaneously the requirements of power density and thermal efficiency for electric utility power plants. The material properties required for an advanced fuel cell power plant solid electrolyte were derived in terms of the ionic conductivity and the Schmalzried parameters P⊕ and P⊖ : σ ion > 0.033 (Ω-cm) −1, P⊕ > 10 3 atm., P⊖ < 10 −23 atm. at 700 °C.

Electronic conductivities of commercial ZrO2 + 3 to 4 wt pct CaO electrolytes

Potentiostatic electrochemical experiments with liquid metal electrodes have been analyzed to provide values for the mixed electrical conduction parameters (PMion, ooo, Oo , Po,Po, and E O,C.) associated with commercial-grade ZrO2 + 3 to 4 wt pct CaO electrolytes. Good agreement between experimental and calculated values for the open-circuit cell voltage,E o. c., for relatively high oxygen concentrations in the melt demonstrates that the currently accepted interpretation of electronic conduction in solid electrolytes is valid. In addition, these results provide an experimental verification that n-type electronic conductivity is proportional toPo2-1/4.

The electrical conductivity of zirconium dioxide films at intermediate temperatures

The a.c. electrical conductivity of zirconia has been measured as a function of temperature for various electrode materials. Reproducible results were obtained after the removal of surface conduction effects by heating specimens to a temperature of 180°C. An activation energy of 0·56 ev was found for the conduction process in the temperagure range 250-300°C. Results obtained using an indium electrode may be interpreted in terms of an n-type electronic conduction process. The anomalous results obtained with a silver electrode are explained in terms of the diffusion of silver along grain boundaries.

Electrical Properties and Defect Structure of Zirconia: II, Tetragonal Phase and Inversion

The defect structure of tetragonal zirconia was investigated by measuring the temperature and oxygen partial pressure dependence of the electrical conductivity and the electronic transference number. Tetragonal zirconia was a mixed electronic and ionic conductor under all conditions studied. The n-type electronic conductivity observed at high temperatures and low oxygen partial pressures was interpreted on the basis of a defect model involving fully ionized oxygen vacancies. The conductivity change associated with the monoclinic ⇒ tetragonal phase transformation was isothermal, but the rate of change was a function of the thermal history and the method of preparation of the sample.