Electrolytic Behavior of Yttria

Abstract

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...

Improving the Physicochemical Properties of Fe–25Cr Ferritic Steel for SOFC Interconnects via Y-Implantation and Y2O3-Deposition

“…15). This is related to the high electrical resistance of the Y 2 O 3 layer [58][59][60][61][62] found in the scale (Figs. 5c, 7c).…”

“…Numerous works dedicated to the research of point defect structure and electrical conductivity of pure and doped mono-and polycrystalline yttrium oxide have reported that regardless of the type of dopant and its concentration, Y 2 O 3 is p-type semiconductor at high temperatures and for high oxygen partial pressures. [60][61][62] The conductivity of this oxide is predominantly determined by the ionic component. [60][61][62] Due to the large discrepancies in the values of conductivity and activation energy it is difficult to clearly determine which of the Y 2 O 3 sublattices controls the ionic conductivity of this compound.…”

“…[60][61][62] The conductivity of this oxide is predominantly determined by the ionic component. [60][61][62] Due to the large discrepancies in the values of conductivity and activation energy it is difficult to clearly determine which of the Y 2 O 3 sublattices controls the ionic conductivity of this compound. [60][61][62] The ASR of the Fe-25Cr/scale system obtained after the oxidation of pure steel in air and the ASR of the Fe-25Cr/Y 2 O 3 steel pre-oxidized in both atmospheres exceed the acceptable ASR level of 0.1 X cm 2 over the entire investigated temperature range.…”

“…[60][61][62] Due to the large discrepancies in the values of conductivity and activation energy it is difficult to clearly determine which of the Y 2 O 3 sublattices controls the ionic conductivity of this compound. [60][61][62] The ASR of the Fe-25Cr/scale system obtained after the oxidation of pure steel in air and the ASR of the Fe-25Cr/Y 2 O 3 steel pre-oxidized in both atmospheres exceed the acceptable ASR level of 0.1 X cm 2 over the entire investigated temperature range. The reason for the deterioration in the electrical properties of the Fe-25Cr/scale system is poor adhesion of the scale to the metal substrate (Figs.…”