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The causes of the decrease in electrical conductivity with aging in 11203-stabilized zirconia, an oxygen-ion conductor, were studied. This study was carried out using the dc four-probe technique for measuring electrical conductivity and the activation energy for the migration of oxygen ions. The results show that conductivity decreased with aging below certain temperatures in all specimens. Moreover, it was found that conductivity decreases significantly as the temperature decreases. Samples that were aged at relatively low temperatures exhibited a decrease in conductivity and an increase in activation energy. It was concluded that short range ordering of oxygen ion vacancies toward the zirconium to relax the anistropy of the lattice distortion is the cause of the decrease in electrical conductivity and the increase in activation energy. When aging was carried out at a relatively high temperature, fully stabilized zirconia showed no change in activation energy and only a slight increase in conductivity. This is because oxygen ion vacancies are in the disordered state and the cubic phase is the only phase at this temperature. Short range ordering of oxygen ion vacancies takes such a long time presumably because these oxygen ion vacancies are still able to move even after aging. This was explained using the concept of mean first passage time Infroduction Since Nernst reported Y203-doped Zr03 in 18991 and the

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Microstructural changes in yttria-stabilized zirconia with aging were investigated by X-ray diffraction, high resolution transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy under TEM, and electron diffraction. First, various microstructural changes reported in the literature as the causes of the decrease in conductivity were carefully examined. As a result, almost all of them proved not to be the direct cause. Therefore, the changes with aging were analyzed mainly by calling attention to a characteristically broad area that appears on the left shoulder of the X-ray diffraction peaks as well as the superlattice reflections and diffuse scattering seen on electron diffraction patterns, and the relationship between microstructural changes and conductivity was clarified. It is concluded that various phenomena due to aging at relatively lower temperatures are caused by short range ordering of oxygen ion vacancies, which occurs in order to relax the anisotropy of periodical lattice distortion. We also studied changes in microstructures occurring with changing dopant concentrations and concluded that the changes in microstructures responsible for the decrease in conductivity associated with increasing dopant concentration are caused by short range ordering of oxygen ion vacancies in order to relax the anisotropy in strain fields, similarly to those with aging. InfroductionA number of microstructural studies of stabilized zirconia have been conducted using various methods, including neutron diffraction and scattering,1'6 X-ray diffraction and scattering7-9 electron diffraction,10'14 and transmission electron microscopy (TEM).15"8 Because partially stabilized zirconia is a useful material with incomparably high toughness due to stress-induced phase transformation, many microstructural studies of it have been conducted, examining phase transformations, characterizing lattice defects,

Electrical conduction properties of Sr-doped LaPO 4 and Sr-doped CePO 4 under H 2 O/O 2 and H 2 O/H 2 conditions were investigated with conductivity measurements. Conductivities of 1 mol % Sr-doped LaPO 4 were 10 −5.2 -10 −3.5 S cm −1 at 500-925°C under wet reducing conditions and were close to those under wet oxidizing conditions. It was found from the H/D isotope effect on conductivity that the material showed dominant protonic conduction under wet reducing conditions. As for 1 mol % Sr-doped CePO 4 , conductivities were 10 −2.8 -10 −2.0 S cm −1 at 500-925°C under wet oxidizing conditions and much higher than those of 1 mol % Sr-doped LaPO 4 under the same conditions. Such high conductivities of Sr-doped CePO 4 seemed attributable to electronic conduction due to partial oxidation of Ce 3+ to Ce 4+ caused by substituting Sr 2+ for Ce 3+ . Under wet reducing conditions, however, conductivities of the material decreased to 10 −5.2 -10 −3.4 S cm −1 at 500-925°C, which was almost comparable with those of 1 mol % Sr-doped LaPO 4 . It was concluded that Sr-doped CePO 4 showed mixed protonic and p-type electronic conductions under wet reducing conditions. Based on the results of conductivity measurements, defect structures in Sr-doped LaPO 4 and CePO 4 under wet oxidizing and reducing conditions are discussed.

Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-T c phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5∼10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a=0.537 nm, b=2.682 nm, and c=3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10-6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high-T c phase over the low-T c phase was roughly estimated at 9/1 in volume.

Changes in local structures with aging in yttria-stabilized zirconia were examined by extended x-ray absorption fine structure (EXAFS) and internal friction measurement. An analysis of EXAFS shows that a decrease in the first nearest neighbor coordination number of Zr ions, which means short range ordering of oxygen ion vacancies, a decrease in distance between a Zr ion and its first nearest atoms, and an increase in distance between a Zr ion and its second nearest atoms occurred in aged 8YSZ. Aging caused a noticeable decrease in the relaxation peak of internal friction in 8YSZ. These phenomena are attributed to the short range ordering of oxygen ion vacancies around a Zr ion that results from relaxation in the anisotropy of periodical lattice distortion. Therefore, it is concluded that the trapping of oxygen ion vacancies at Zr ions in order to relax such distortion is responsible for a decrease in conductivity with aging. The relaxation peak of internal friction before aging changed with increasing dopant concentrations, and the behavior of this change from 8YSZ to 1OYSZ was very similar to that when 8YSZ was aged, and that from 1OYSZ to 15YSZ was similar to that when a single crystal of 1OYSZ was aged. This marked similarity indicates that the changes in crystal structure which cause the decrease in conductivity with increasing dopant concentration are caused by the short range ordering of oxygen ion vacancies brought about by relaxation of the distortion, similar to those when conductivity decreases with aging.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35

A novel proton-conducting material based on LaP 3 O 9 was developed and its electrical conduction properties were investigated by measuring conductivities under 0.4-5 kPa of p(H 2 O) and 0.01-100 kPa of p(O 2 ) at 573-973 K. LaP 3 O 9 conducted protons dominantly by partial substitution of Sr for La. Conductivities of the 1 mol % Sr-doped LaP 3 O 9 were 7 ϫ 10 Ϫ7 to 3 ϫ 10 Ϫ4 S cm Ϫ1 at 573-973 K, and were relatively higher than those of other proton-conducting rare earth phosphates such as LaPO 4 and La 7 P 3 O 18 . Conductivities of the Sr-doped LaP 3 O 9 were almost independent of p(H 2 O), suggesting dominant protonic conduction even under low p(H 2 O) conditions. High-temperature protonic conduction has been demonstrated in many solids without protons in the presence of gases containing hydrogen. 1-3 In previous works, acceptor-doped rare earth orthophosphates, LnPO 4 (Ln ϭ La, Ce, Pr, Nd, and Sm with the monoclinic monazite-type structure, and Ln ϭ Y with the tetragonal xenotime-type structure͒, were suggested as interesting candidates for a high-temperature protonic conductor, because of their remarkably predominant protonic conduction and high chemical stability. [4][5][6][7][8][9][10][11][12] In these orthophosphates, protons responsible for conduction are supposed to be introduced as extrinsic positive defects in a following way 5,6,8 1 2where Kröger-Vink notation is used. According to this model, substitution of divalent metals for rare earth metals leads to formation of pyrophosphate ions as intrinsic positive defects, and protons dissolve into the phosphates, forming hydrogen phosphate groups through the equilibrium between the intrinsic positive defects and water vapor in the ambient atmosphere. In brief, it can be said that the formation of pyrophosphate ions at two adjacent orthophosphate ion sites sharing one oxygen, i.e., the condensation of phosphate ions, consequently causes proton dissolution. Assuming the above proton dissolution process via condensation of phosphate ions, similar proton dissolution, and thus protonic conduction, is expected not only in orthophosphates but also in other types of phosphates. From this point of view, we have already examined electrical conduction properties of lanthanum oxophosphate, La 7 P 3 O 18 . 13 As a result, it was found that this oxophosphate became a protonic conductor by partially substituting Sr for La under moisturized conditions although the conductivity of the Sr-doped La 7 P 3 O 18 was lower than that of the Sr-doped LaPO 4 .In this work, lanthanum polyphosphate, LaP 3 O 9 , which is one of six lanthanum phosphate compounds, 14,15 was chosen as the next candidate of proton conducting materials based on phosphates. Samples of LaP 3 O 9 , in which La was partially substituted with Sr, were prepared, and their electrical conduction, particularly protonic conduction, was investigated by using conductivity measurements under various conditions. ExperimentalLaP 3 O 9 and Sr-doped LaP 3 O 9 examined in this work were prepared with solid-state reactions...