This report was prepared a s an account of Government sponsored work. Neither the United .States, nor the Commission, nor any person acting on behalf of the Commission:A. Makes any warranty or representation, expressed o r implied, with respect to the accuracy, completeness, o r usefulness of the information conbined in W s report, o r that the use ' of any information, apparatus, method, o r process disclosed in this report may not infringe privately owned rights; o r B. Assumes any liabilities with respect to'-use of, cir for a m a g e s resulting from the use of any information, apparatus, method, o r process dtsclased in this report.As used in the above, "person actlng on behalf of 'the CommisglonW inclndes any employee o r contractor of the Commission, o r employee of such contractor, to the extent that such employee o r contractor of the Commission, o r employee of such contractor prepares, disseminatee, o r provides access to, any information pursuant to his employment o r contract with the dommiesion, o r his employment with such contractor. Jon avid S c h i e l t z/. An A b s t r a c t of A ~i s s e r t a t i o n Submitted t o t h eGraduate F a c u l t y i n . P a r t i a l F u l f i l l m e n t ofThe Requirements f o r t h e Degree of I n Charge o ?~a~o r Work , Iowa S t a t e U n i v e r s i t y. Ames, Iowa U *rl n *rl m .. . X -r a y . a n a l y s i s and e l e c t r i c a l c o n d u c t i v i t y measurements . . -2yte. -I t s e l e c t r i c a l p r o p e r t i e s a r e v e r y s i m i l a r t o t h o s e of Graduate Faculty i n P a r t i a l F u l f i l l m e n t ofThe.Requirements f o r t h e Degree of . . . 26 INTRODUCTION Conduction Domain Theory Theory of P a r t i a l E l e c t r i c a l Conduction I n t r o d u c t i o n . D e f e c t e q u i l i b r i a and e l e c t r i c a l c o n d u c t i v i t y i n undoped y t t r i a ,Defect e q u i l i b r i a and e l e c t r i c a l c o n d u c t i v i t y i n y t t r i a doped
X-ray analysis and electrical conductivity measurements (800~176 on yttria-hafnia solid solutions between 2 and 20 m/o (mole per cent) Y203 were made to locate the cubic phase and to select the composition best suited as a solid electrolyte. The phase boundary is located near 7 m/o Y203. Total conductivities obtained from the cubic phase solid solutions appear to be ionic. The 8 m/o Y203-HfO2 composition showed the highest conductivity (log ~r ------1.57 at 1000~ and lowest activation energy (16.9 kcal/mole), and was selected as the optimum composition for a solid electrolyte. Open-circuit emf, electrical conductivity, and Wagner d-c polarization measurements between 800 ~ and 1000~ were made to determine the electrolytic domain of the 8 m/o Y203 composition. The electrolytic domain width at 1000~ extends from log Po2(atm) ~ --16.6 to ~-0.4. The 8 m/o yttria-stabilized hafnia composition does appear suitable as a solid electrolyte. Its electrical properties are very similar to those of calcia-stabilized zireonia.
The electrolytic behavior of Y2Oa was investigated. Within the temperature range 700~176there is no electrolytic domain (tion --0.99), however, a small ionic domain (tion ~ 0.5) does exist and is defined within the following boundaries 11,030 log Pe = --15.84 T(~ --35,300 log Pe ---F 15.59 T(~ and Yttrium sesquioxide, Y203, is the only known solid oxide of yttrium. At room temperature and under one atmosphere pressure it possesses the cubic rare earth type C structure (Ia3) (1,2) with 16 sesquioxide formula units per unit cell. The C-type rare earth structure is almost identical to the fluorite structure (3, 4) except that the lattice points are slightly displaced and 1/4 of the anions are missing to balance the trivalent cation charge. These open sites are aligned to form relatively open pathways that could serve as high conductivity paths for oxide ions. Therefore the emf measurements described below were undertaken to determine the log Po2 and 1/T ranges, if any, wherein Y2Oa exhibits predominantly ionic conductivity (5-8).N'oddack and co-workers (9-11) determined the electrical conductivity of yttria, many of the rare earth oxides, and several rare earth oxide binary solid solutions and zirconia-yttria solid solutions. Their results suggested that Y203 is a predominant electronic conductor over the temperature range from 600 ~ to 1200~More carefully controlled conductivity measurements on yttria have been made by Tallan and Vest (12). The electrical conductivity of reportedly very pure, polycrystalline Y203 in controlled Po2 atmospheres and temperatures from 12000 to 1600~ was obtained from guarded (3-probe) measurements with an a-c bridge. The data indicated that yttria is an amphoteric semiconductor over the temperature range 1200~176and oxygen partial pressures from 10 -1-10 -17 arm. Within this region the ratio of ionic to electronic conductivity was determined to be less than 1% by a blocking electrode polarization technique. In the region of predominant hole conduction, the conductivity in ohm -1 cm -1 was expressed by the relationship main. aar = ae = 1.3 • 108 Po28n6 exp (--1.94/kT) [1] where 3/16 power pressure dependence was attributed to fully ionized yttrium vacancies. Polarization effects detected at lower temperatures indicated that the ionic transference number at Po2 = 10-15 atm was about 0.15 at 800~ and about 0.3 at 700~ indicating mixed conduction in yttria below 900~ While investigating the defect structure of ThO~-Y._,O3 solid solutions, Subbarao et al. (13) measured the electrical conductivity of undoped yttria in air between 800 ~ and 1400~The activation energy for conduction agreed quite well with that reported by Tallan and Vest (12).In contrast to the conductivity measurements, galvanic cell emf measurements indicate a much higher ionic transference number for yttria. Such measurements by Schmalzried (6) and Tare and Schmalzried (14) indicate that the ionic domain boundaries for Y203 at 825~ are log Pe(Y203, 825~ = --4.2 [2] log P~(Y203, 825~ = --21.5 [3] These values imply that /:io...
This report was prepared a s an account of Government sponsored work. Neither the United .States, nor the Commission, nor any person acting on behalf of the Commission:A. Makes any warranty or representation, expressed o r implied, with respect to the accuracy, completeness, o r usefulness of the information conbined in W s report, o r that the use ' of any information, apparatus, method, o r process disclosed in this report may not infringe privately owned rights; o r B. Assumes any liabilities with respect to'-use of, cir for a m a g e s resulting from the use of any information, apparatus, method, o r process dtsclased in this report.As used in the above, "person actlng on behalf of 'the CommisglonW inclndes any employee o r contractor of the Commission, o r employee of such contractor, to the extent that such employee o r contractor of the Commission, o r employee of such contractor prepares, disseminatee, o r provides access to, any information pursuant to his employment o r contract with the dommiesion, o r his employment with such contractor. Jon avid S c h i e l t z/. An A b s t r a c t of A ~i s s e r t a t i o n Submitted t o t h eGraduate F a c u l t y i n . P a r t i a l F u l f i l l m e n t ofThe Requirements f o r t h e Degree of I n Charge o ?~a~o r Work , Iowa S t a t e U n i v e r s i t y. Ames, Iowa U *rl n *rl m .. . X -r a y . a n a l y s i s and e l e c t r i c a l c o n d u c t i v i t y measurements . . -2yte. -I t s e l e c t r i c a l p r o p e r t i e s a r e v e r y s i m i l a r t o t h o s e of Graduate Faculty i n P a r t i a l F u l f i l l m e n t ofThe.Requirements f o r t h e Degree of . . . 26 INTRODUCTION Conduction Domain Theory Theory of P a r t i a l E l e c t r i c a l Conduction I n t r o d u c t i o n . D e f e c t e q u i l i b r i a and e l e c t r i c a l c o n d u c t i v i t y i n undoped y t t r i a ,Defect e q u i l i b r i a and e l e c t r i c a l c o n d u c t i v i t y i n y t t r i a doped
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