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1.
Katsuyoshi Kakinuma Hiroshi Yamamura Hajime Haneda Tooru Atake 《Solid State Ionics》2001,140(3-4):301-306
(Ba1−xLax)2In2O5+x, whose end member is Ba2In2O5, is an oxygen-deficient perovskite oxide showing high oxide-ion conductivity. In order to clarify the reason why the high oxide ion conductivity appeared in this system, the electrical conductivity was measured as a function of temperature and La content. With an increasing La content, the discontinuous jump of ion conductivity in the Arrhenius plot, which is related to the disordering of the oxygen vacancies, disappeared for the sample with x0.2. Above x=0.12, the ion conductivity linearly increased with La content, while the activation energy remained constant with respect to the La content. Moreover, the conductivity for x=0.6 was 0.042 (S/cm) at 1073 K, which exceeded that of 8 mol% yttria-stabilized zirconia. The higher oxide-ion conductivity of this system could be dominated by the amount of mobile oxygen ions. 相似文献
2.
New Scheelite-related solid solutions of the compositions Nax/2Bi1−x/2MoxV1−xO4 (0≤x≤1) and Bi1−x/3 MoxV1−xO4(0≤x≤0.2) have been synthesised by the substitution of Na and Mo at the A and B sites respectively of the ABO4 type ferroelastic BiVO4. The phases were characterised using chemical analysis, powder X-ray diffraction, scanning electron microscopy, EDAX, and Raman spectroscopy. While almost a continuous solid solution is obtained for the series Nax/2Bi1−x/2MoxV1−xO4, the absence of Na at the A-site results only in a narrow stability region for the other series, Bi1−x/3 MoxV1−xO4 where 0≤x≤0.2. Raman spectra of selected samples at room temperature also suggest that vanadium and molybdenum atoms are disordered at the tetrahedral sites. 相似文献
3.
D. M. Bochkov V. V. Kharton A. V. Kovalevsky A. P. Viskup E. N. Naumovich 《Solid State Ionics》1999,120(1-4):281-288
Formation of the La2Cu1−xCoxO4+δ solid solutions with orthorhombic K2NiF4-type structure was found to be in the range of 0≤x≤0.30 at temperatures above 1270 K. Incorporating cobalt into the copper sublattice of lanthanum cuprate leads to increasing oxygen hyperstoichiometry and decreasing electrical conductivity. Thermal expansion coefficients of the La2Cu1−xCoxO4+δ (x=0.02–0.30) ceramics at 470–1100 K were calculated from the dilatometric data to vary in the range (12.2–13.2)×10−6 K−1. Studying the dependence of oxygen permeation fluxes through La2Cu(Co)O4+δ on the membrane thickness demonstrated that the oxygen transport at the thickness values below 1 mm is limited by both surface exchange rate and bulk ionic conductivity. Oxygen permeability of the La2Cu1−xCoxO4+δ solid solutions was ascertained to increase with cobalt concentration at x=0.02–0.10 and to decrease with further dopant additions, indicating a participation of interstitial oxygen in the ionic transport. 相似文献
4.
The perovskite-type oxides were synthesized in the series of Ln1−xSrxCoO3(Ln = Sm, Dy). The formation of solid solutions in Dy1 − xSrxCoO3 was limited, compared with that in Sm1 − xSrxCoO3. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm0.7Sr0.3CoO3. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO3 at 900 °C after 96 h. However, no reaction product between SmCoO3 and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO3 shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples. 相似文献
5.
V. V. Vashook S. P. Tolochko I. I. Yushkevich L. V. Makhnach I. F. Kononyuk H. Altenburg J. Hauck H. Ullmann 《Solid State Ionics》1998,110(3-4):245-253
Oxygen nonstoichiometry and electrical resistance of a series La2−xSrxNiOy solid solutions, where x=0.0, 0.2 and 0.5 in argon flows at oxygen partial pressures 1.5, 10.2, 49.2, 100 and 286 Pa within the temperature range of 20–1050°C were studied. Nickelate oxygen desorption/sorption spectra when heating–cooling at constant rate demonstrated strong dependence of cation composition of the samples. Unlike La1.5Sr0.5NiOy compounds those of La2NiOy and La1.8Sr0.2NiOy have weakly bonded oxygen, capable to exchange reversibly with the gas phase at the temperatures higher than 250°C. The equilibrium values of oxygen nonstoichiometry and specific resistance for the these nickelates were determined at 300–1050°C and pO2=1.5–286 Pa as a functions of temperature versus oxygen partial pressure. All nickelate studied appear to be p-type conductors with metal electric conductivity at equilibrium states. 相似文献
6.
Oxide ion conductivity of the pure and aliovalent ion substituted rare-earth pyrohafnates in the series RE2−xSrxHf2O7 and RE2Hf2−xAlxO7 (RE=Gd and Nd; x=0–0.2) has been explored in the temperature range 400°C–700°C for the first time. It is seen that, conductivity is enhanced by doping 5 atom% Sr at the rare–earth site in these systems. Well defined impedance plots due to grain interior and grain boundary resistances were obtained in the Gd pyrohafnate with Sr substitution. The results of the conductivity variation for the pure, Sr and Al doped phases are explained on the basis of pyrochlore structure. 相似文献
7.
A. N. Petrov O. F. Kononchuk A. V. Andreev V. A. Cherepanov P. Kofstad 《Solid State Ionics》1995,80(3-4):189-199
The crystal structure and properties of La1 − xSrxCoO3 − y with strontium contents ranging from x = 0.1 to x = 0.7 have been studied. The lattice parameters were measured as a function of temperature (4.2–400 K) and the crystal structure was found to change from rhombohedral (at low temperatures and values of x) to cubic. While LaCoO3 is paramagnetic the oxides in the composition range 0.2 < x < 0.6 are soft ferromagnets. The strontium additions are compensated by the formation of Co4+ (cobalt ions with one positive effective charge, CoCo.) and oxygen vacancies (Vo..). From the results it is concluded that the relative importance of oxygen vacancies increases with increasing temperature and decreasing oxygen activity. As a result the concentration of electronic charge carriers — and the resultant electrical conductivity — decrease with increasing temperature. The defect structure is discussed and it is concluded that defect associations — probably between oxygen vacancies and strontium ions — and formation of microdomains of perovskite-related phases are important aspects of the overall structure of these perovskite phases. 相似文献
8.
Z. Tomkowicz 《Physica C: Superconductivity and its Applications》1999,320(3-4):173-182
Pr concentration dependence of the superconducting transition temperature Tc in the Ho1−xPrxBa2Cu3O7−δ system is determined from measurements of DC electrical resistance. This dependence coincides with that for the parallely studied Y1−xPrxBa2Cu3O7−δ reference system. Both systems have the same value of the critical concentration xc=0.58, in accordance with nearly equal ionic radii of Ho3+ and Y3+ ions. It has been shown that the Tc(x) curve can be described with a single mechanism based on a decreasing number of sheet holes trapped by PrIV-ions, if one takes also into account that the number of these ions changes with x. 相似文献
9.
Lithium insertion to distorted ReO3-type metastable solid solution NbxW1−xO3−x/2 (0≤x<0.25) has been studied by chemical and electrochemical methods. In the course of lithium insertion into tetragonal compounds, transition to a cubic phase was found to occur in the region where values of y (in LiyNbxW1−xO3−x/2) fall between 0.2 and 0.3, and the phase transition was found to depend on the conditions of the reaction. Changes in OCV and lattice parameters in tetragonal region (y<0.2) were discussed from the viewpoint of the ordering of lithium ions. Also, the component diffusion coefficient of lithium in tetragonal compounds Li0.1NbxW1−xO3−x/2 (0≤x≤0.23) was found to increase with niobium content when x≤0.10, and to saturate at 4×10−9 cm2/s. 相似文献
10.
E. Goodilin M. Limonov A. Panfilov N. Khasanova A. Oka S. Tajima Y. Shiohara 《Physica C: Superconductivity and its Applications》1998,300(3-4):250-269
On the basis of chemical, thermal analysis and Cu K-edge X-ray absorption measurements, oxygen content in the Nd1+xBa2−xCu3Oz solid solution was determined between 1000°C in air and 400°C in oxygen for x=0.05–0.9 compositions. It has been observed that the oxygen nonstoichiometry Δz of the Nd1+xBa2−xCu3O7+x/2−Δz solid solution decreases 2–2.5 times for a large substitution (Δz≈0.3–0.33 for x=0.9), despite of the acclaimed higher total oxygen content. The difference in nonstoichiometry is explained by a higher average value of the copper oxidation state (ACV), which is vital for the solid solution with large x even at elevated temperatures (ACV≈2–2.05 for x>0.3 at 1000°C, PO2=0.21 atm). On the contrary, the ACV after complete oxygenation is almost constant (about 2.25–2.3) for the whole series. The x-dependence of the oxygen content is not monotonous and structural phase transitions can be observed at x=0.3 and x=0.6, as confirmed by the X-ray diffraction and the Raman scattering spectroscopy. The first well-known transition is connected with the oxygen disorder due to the Nd substitution for Ba at random Ba-sites. In the present work, it is proved by the apical oxygen mode broadening in Raman spectra. Ordering of the Nd and Ba atoms with a subsequent orthorhombic distortion of the lattice may occur even at 1000°C in air due to the second transformation at x≈0.6. The invariable orthorhombicity of the Nd-rich solid solution with x>0.6 is not caused by the oxygen absorption as in the x=0.05 case. Existence of high- and low-temperature orthorhombic modifications of this solid solution has been observed for the first time. Finally, a tentative 3D (z–x–T) diagram is suggested for the Nd1+xBa2−xCu3Oz solid solution up to 1000°C in air, including the new x=0.6–0.9 region. 相似文献
11.
N. Watanabe K. Kuroda K. Abe N. Koshizuka M. Tagami Y. Shiohara 《Physica C: Superconductivity and its Applications》1998,300(3-4):301-308
The polarized Raman spectra of Nd1+xBa2−xCu3O7−δ (−0.023≤x≤0.107) and Pr1+xBa2−xCu3O7−δ (0.01≤x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm−1 in Nd 1:2:3 and 4 cm−1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x(yy)
geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains. 相似文献
12.
V. V. Kharton A. L. Shaulo A. P. Viskup M. Avdeev A. A. Yaremchenko M. V. Patrakeev A. I. Kurbakov E. N. Naumovich F. M. B. Marques 《Solid State Ionics》2002,150(3-4):229-243
The maximum solid solubility of gallium in the perovskite-type La1−xSrxFe1−yGayO3−δ (x=0.40–0.80; y=0–0.60) was found to vary in the approximate range y=0.25–0.45, decreasing when x increases. Crystal lattice of the perovskite phases, formed in atmospheric air, was studied by X-ray diffraction (XRD) and neutron diffraction and identified as cubic. Doping with Ga results in increasing unit cell volume, while the thermal expansion and total conductivity of (La,Sr)(Fe,Ga)O3−δ in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7–16.0)×10−6 K−1 at 300–800 K and (19.3–26.7)×10−6 K−1 at 800–1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La1−xSrxFe1−yGayO3−δ (x=0.7–0.8; y=0.2–0.4) membranes are determined by the bulk ambipolar conductivity; the limiting effect of the oxygen surface exchange was found negligible. Decreasing strontium and gallium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La1−xSrxFe1−yGayO3−δ increases with strontium content up to x=0.70 and decreases on further doping, probably due to association of oxygen vacancies. Incorporation of moderate amounts of gallium into the B sublattice results in increasing structural disorder, higher ionic conductivity at temperatures below 1170 K, and lower activation energy for the ionic transport. 相似文献
13.
Susumu Nakayama Yoshikatsu Higuchi Yuki Kondo Masatomi Sakamoto 《Solid State Ionics》2004,170(3-4):219-223
A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In LaxGe6O12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, Lax(GeO4)6O1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La9(GeO4)6O1.5 (x=9), where the number of cation (La3+) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La9−0.66xSrx(GeO4)6O1.5 (x=0–1), La9−1.33xZrx(GeO4)6O1.5 (x=0–1), La9−xSrx(GeO4)6O1.5−0.5x (x=0–3), La9−xZrx(GeO4)6O1.5+0.5x (x=0–1), Lax(GeO4)3x−21(AsO4)27−3xO1.5 (x=0–3), Lax(GeO4)33−3x(AlO4)3x−27O1.5 (x=0–3), La9(GeO4)6−x (AlO4)xO1.5−0.5x (x=0–3), La9(GeO4)6−x(AsO4)xO1.5+0.5x (x=0–1), La9.33−xSrx(GeO4)6O2−0.5x (x=0–1.2) and Lax(GeO4)4.5(AlO4)1.5O1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La3+and GeO44−of the basic apatite La9(GeO4)6O1.5 with Sr2+ or Zr4+ and AlO45− or AsO43−. Such substitutions lowered the conductivity of La9(GeO4)6O1.5. These results were discussed by the electrostatic interaction between Sr2+, Zr4+, AlO45− or AsO43− and oxide ion as a conductive species. 相似文献
14.
A. A. Yaremchenko V. V. Kharton A. P. Viskup E. N. Naumovich V. N. Tikhonovich N. M. Lapchuk 《Solid State Ionics》1999,120(1-4):65-74
The LaGa1−x−yCoxMgyO3−δ solid solutions with rhombohedrally-distorted perovskite structure were ascertained to form in the concentration range of 0≤y≤0.10 at x=0.60 and 0≤y≤0.20 at x=0.35–0.40. Increasing cobalt content results in increasing electrical conductivity and thermal expansion of the perovskites. Thermal expansion coefficients of the LaGa1−x−yCoxMgyO3−δ ceramics were calculated from the dilatometric data to vary in the range of 12.4–19.8×10−6 K−1 at 300–1100 K. Doping La(Ga,Co)O3−δ solid solutions with magnesium leads to increasing oxygen nonstoichiometry, electronic and oxygen ionic conductivity. Oxygen permeation fluxes through LaGa1−x−yCoxMgyO3−δ membranes were found to be limited by the bulk ionic conduction and to increase with magnesium concentration, being essentially independent of cobalt content. 相似文献
15.
Oxygen tracer diffusion (D*) and surface exchange rate constant (k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La1−xSrxFe0.8Cr0.2O3−δ (x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10−21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV (x=0.2), 1.53 eV (x=0.4) and 1.21 eV (x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10−8 cm2 s−1 for x=0.2 to 10−7 cm2 s−1 for x=0.4 and 0.6. The activation energies determined at constant H2O/H2 ratio are 1.21 eV (x=0.2), 1.59 eV (x=0.4) and 0.82 eV (x=0.6).
The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
16.
The n = 2 Aurivillius phase Bi2 − xPbxSr1 − xNd2O9 was successfully synthesized as a ceramic material over the whole range of simultaneous, charge compensated substitution x = 0–1.0. Structural investigations were performed by Rietveld refinement applying different space groups Fmmm and A21am, and additionally by X-ray absorption spectroscopy (EXAFS) on the Nd LIII-edge, confirming the accommodation of Nd on the atomic sites of Sr, which implies the substitution of Bi3+ by the isoelectronic Pb2+. The ferroelectric transition temperature Tc = 270 °C of the substituted powders with x = 0.4 and 1.0 is distinctly reduced compared to the unsubstituted sample with Tc = 450 °C. In temperature resolved powder X-ray diffraction patterns no structural phase transition could be detected. 相似文献
17.
M. B. Maple R. P. Dickey A. Amann E. J. Freeman C. Sirvent M. C. de Andrade N. R. Dilley 《Physica B: Condensed Matter》2000,280(1-4):347-348
The temperature-composition (T–x) phase diagram and NFL characteristics in the electrical resistivity ρ(T), specific heat C(T), and magnetic susceptibility χ(T) at low temperatures for the systems U1−xMxPd2Al3 (M=Y,Th) are described. The T–x phase diagram, the NFL characteristics, and the underlying mechanism for the NFL behavior are distinctly different for M=Y3+ and Th4+, apparently reflecting the difference in valence of the M atom substituents, and suggesting that U is tetravalent in these two systems. 相似文献
18.
Hiroyuki Shibata Kyoichi Kinoshita Tomoaki Yamada 《Physica C: Superconductivity and its Applications》1990,170(5-6):411-415
Superconductivity and crystallographic properties of La2 − xMxCuO4 − δ (M = Na, K) are studied. In the La2 − xMxCuO4 − δ system, superconductivity is detected for x 0.2. Oxygen content analysis shows that the system has more oxygen vacancies than the La2 − xSrxCuO4 − δ system. These oxygen vacancies may reduce the hole concentration, and high Na-doping is needed to produce superconductivity. In the La2 − xKxCuO4 − δ system, superconductivity is observed for the first time. Resistivity and magnetic susceptibility measurements show that Tc(onset) is 40 K and the Meissner volume fraction is about 4% for x = 0.7. The system changes from orthorhombic to a tetragonal K2NiF4 structure at x ≈ 0.3 and only tetragonal samples show superconductivity. 相似文献
19.
Tracer diffusion of 18O in dense, polycrystalline La1−xSrxCoO3 for x = 0.1 has been measured in the temperature range 400 to 600 °C and at 500 °C for x = 0.2 at an oxygen partial pressure of 1 × 105 Pa. Depth profiles were obtained by secondary ion mass spectrometry. The diffusion coefficient for La0.9Sr0.1CoO3 is given by D = (17–247) exp[(−232 ± 8 kJ/mole)/RT] cm2/s. This value is several orders of magnitude lower than D extrapolated from the results for x = 0.2 measured in the 700–900 °C temperature range. One possible explanation for the discrepancy is that the two measurements reflect different diffusion paths. As expected, La0.8Sr0.2CoO3 exhibits a higher diffusivity at 500 °C than does La0.9Sr0.1CoO3. 相似文献
20.
H. R. Kerchner Yang Ren Sun J. R. Thompson H. R. Khan J. O. Thomson D. K. Christen 《Physica C: Superconductivity and its Applications》1995,250(3-4):331-339
Superconductivity in polycrystalline YBa2AlxCu(3−x)O7−δ materials was characterized by dynamic AC and quasistatic DC magnetometry. Intragranular persistent current density and low-loss intergranular critical current density were deduced using DC and AC techniques, respectively. Addition of aluminum produced modest increases in the intragranular persistent current for x < 0.2, but drastically reduced the intergranular critical current density for x = 0.2. The critical temperature Tc for superconductivity decreased only 4% for Al content up to x = 0.2. 相似文献