P 45 Perovskite-like system (Sr, La)(Fe, Ga)O3-delta: structure and ionic transport under oxidizing conditions [] / 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. - V. 150, N 3-4. - С. 229-243. - Bibliogr.: p. 243 (50 ref.) . - ISSN 0167-2738 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): ПЕРОВСКИТЫ -- СМЕШАННЫЕ ПРОВОДНИКИ -- ПРОВОДНИКИ СМЕШАННЫЕ -- ОКИСЛЕНИЕ -- ИОННАЯ ПРОВОДИМОСТЬ -- ПРОВОДИМОСТЬ ИОННАЯ -- КРИСТАЛЛИЧЕСКАЯ СТРУКТУРА -- СТРУКТУРА КРИСТАЛЛИЧЕСКАЯ -- ИОННАЯ ПРОВОДИМОСТЬ -- ПРОВОДИМОСТЬ ИОННАЯ -- Ga -- ГАЛЛИЙ -- Sr -- СТРОНЦИЙ -- ПЕРЕНОС ИОННЫЙ -- ИОННЫЙ ПЕРЕНОС Аннотация: The maximum solid solubility of gallium in the perovskite-type La1-xSrxFe1-yGayO3-delta (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-delta in air decrease with gallium additions. The average thermal expansion coefficients (TECs) are in the range (11.7-16.0) x 10(-6)K(-1) at 300-800 K and (19.3-26.7) x 10(-6)K(-1) at 800-1100 K. At oxygen partial pressures close to atmospheric air, the oxygen permeation fluxes through La1-xSrxFe1-yGayO3-delta (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 g allium concentrations leads to a greater role of the exchange processes. As for many other perovskite systems, the oxygen ionic conductivity of La1-xSrxFe1-yGayO3-delta 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 temperature below 1170 K, and lower activation energy for the ionic transport |
T 82 Transport properties and stability of Ni-containing mixed conductors with perovskite- and K2NiF4-type structure [] = Transport properties and stability of Ni-containing mixed conductors with perovskite- and K2NiF4-type structure / V. V. Kharton, A. A. Yaremchenko, A. L. Shaula, M. V. Patrakeev, E. N. Naumovich, D. I. Logvinovich, J. R. Frade, F. M. B. Marques // Journal of Solid State Chemistry. - 2004. - V. 177, N 1. - С. 26-37. - Bibliogr.: p. 36-37 (43 ref.) . - ISSN 0022-4596 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): НИКЕЛАТ ЛАНТАНА -- ПЕРОВСКИТЫ -- СТРУКТУРА ТИПА K2NiF4 -- ФАЗОВОЕ РАВНОВЕСИЕ -- РАВНОВЕСИЕ ФАЗОВОЕ -- ПРОВОДИМОСТЬ -- КОЭФФИЦИЕНТ СИБЕКА -- СМЕШАННЫЕ ПРОВОДНИКИ -- ПРОВОДНИКИ СМЕШАННЫЕ -- ЭЛЕКТРОННО-ДЫРОЧНЫЙ ПЕРЕНОС -- ПЕРЕНОС ЭЛЕКТРОННО-ДЫРОЧНЫЙ -- КИСЛОРОДНАЯ ПРОНИЦАЕМОСТЬ -- ПРОНИЦАЕМОСТЬ КИСЛОРОДНАЯ -- СТРУКТУРА ТИПА ПЕРОВСКИТА Аннотация: The total conductivity and Seebeck coefficient of a series of Ni-containing phases, including La2Ni1-xMxO4+delta (M = Co, Cu; x = 0.1-0.2) with K2NiF4-type structure and perovskite-like La0.90Sr0.10Ga0.65Mg0.15Ni0.20O3-delta and La0.50Pr0.50Ga0.65Mg0.15Ni0.20O3-delta, were studied in the oxygen partial pressure range from 10(-18) Pa to 50 kPa at 973_1223 K. Within the phase stability domain, the conductivity of layered nickelates is predominantly p-type electronic and occurs via small-polaron mechanism, indicated by temperature-activated hole mobility and p(O2) dependencies of electrical properties. In oxidizing conditions similar behavior is characteristic of Ni-containing perovskites, which exhibit, however, significant ionic contribution to the transport processes. The role of ionic conduction increases with decreasing p(O2) and becomes dominant in reducing atmospheres. All nickelate-based phases decompose at oxygen pressures considerably lower with respect to Ni/NiO boundary. The partial substitution of nickel in La2Ni(M)O4+delta has minor effect on the stability limits, which are similar to that of La0.90Sr0.10Ga0.65Mg0.15Ni0.20O3-delta. On the contrary, praseodymium doping enhances the stability of La0.50Pr0.50Ga0.65Mg0.15Ni0.20O3-delta down to p(O2) values as low as 10(-17)-10(-10) Pa at 1023_1223 K |
H 99 Interfacial effects in electrochemical cells for oxygen ionic conduction measurements. III. Transference numbers vs. grain-boundary resistivity [] / V. V. Kharton, F. M. B. Marques, E. V. Tsipis, A. P. Viskup, N. P. Vyshatko, M. V. Patrakeev, E. N. Naumovich, J. R. Frade // Solid State Ionics. - 2004. - V. 168, N 1-2. - С. 137-151. - Bibliogr.: p. 151 (35 ref.) . - ISSN 0167-2738 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): СМЕШАННЫЕ ПРОВОДНИКИ -- ПРОВОДНИКИ СМЕШАННЫЕ -- ТВЕРДЫЕ ЭЛЕКТРОЛИТЫ -- ЭЛЕКТРОЛИТЫ ТВЕРДЫЕ -- ПИРОХЛОР -- ЭЛЕКТРОХИМИЧЕСКИЕ ЭЛЕМЕНТЫ -- ЭЛЕМЕНТЫ ЭЛЕКТРОХИМИЧЕСКИЕ -- ИОННАЯ ПРОВОДИМОСТЬ -- ПРОВОДИМОСТЬ ИОННАЯ -- ВЗАИМОДЕЙСТВИЕ МЕЖФАЗНОЕ -- МЕЖФАЗНОЕ ВЗАИМОДЕЙСТВИЕ -- КЕРАМИКА Аннотация: Resistive grain boundaries may significantly influence transference numbers of oxygen ion-conducting ceramics due to a distinct blocking effect on the ionic transport with respect to the electronic conduction. This may lead to remarkable uncertainties, particularly in the boundary resistance estimates obtained using impedance spectroscopy without a separation of the ionic and electronic contributions, and in the interpretation of transport parameters determined by DC techniques. The role of grain boundaries was examined by the example of "pure" and SiO2-containing pyrochlore ceramics Gd2-xCaxTi2O7-delta (x = 0.05-0.14), studied at 973-1223 K using impedance spectroscopy, faradaic efficiency and e.m.f. methods. The oxygen ion transference numbers of "pure" materials in air vary in the range 0.95-0.98, increasing when temperature decreases. As expected, minor additions of SiO2 result in segregation of siliceous phase and highly resistive grain boundaries. The total ion transference numbers of silicaenriched ceramics become considerably lower, 0.76-0.89, and increase with increasing temperature due to relatively high activation energy for the boundary resistivity; the bulk transference numbers extracted from the impedance spectroscopy and faradaic efficiency data are similar for all compositions, with and without SiO2 additions. The results, including dependence of the transport properties on oxygen pressure, suggest that a simplified description of the boundaries as a passive transport-limiting barrier is sufficiently adequate |
D 30 Defect interactions in La0.3Sr0.7Fe(M')O3-delta (M' = Al, Ga) perovskites: Atomistic simulations and analysis of p(O2)-T-delta diagrams [] = Defect interactions in La0.3Sr0.7Fe(M')O3-delta (M' = Al, Ga) perovskites: Atomistic simulations and analysis of p(O2)-T-delta diagrams / E. N. Naumovich, M. V. Patrakeev, V. V. Kharton, M. S. Islam, A. A. Yaremchenko, J. R. Frade, F. M. B. Marques // Solid State Ionics. - 2006. - V. 177, N 5-6. - С. 457-470. - Библиогр.: с. 469-470 (39 назв.) . - ISSN 0167-2738 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): КИСЛОРОДНАЯ НЕСТЕХИОМЕТРИЯ -- НЕСТЕХИОМЕТРИЯ КИСЛОРОДНАЯ -- ДЕФЕКТЫ -- ФЕРРИТЫ -- ПЕРОВСКИТЫ -- МОДЕЛИРОВАНИЕ -- ТЕРМОДИНАМИКА -- ОКСИДЫ -- ЛЕГИРОВАНИЕ -- ДОБАВКИ Аннотация: Atomistic modelling showed that a key factor affecting the p(O2) dependencies of point defect chemical potentials in perovskite-type La0.3Sr0.7Fe1-xM'xO3-delta (M' = Ga, Al; x = 0-0.4) under oxidizing conditions, relates to the coulombic repulsion between oxygen vacancies and/or electron holes. The configurations of A- and B-site cations with stable oxidation states have no essential influence on energetics of the mobile charge carriers, whereas the electrons formed due to iron disproportionation are expected to form defect pair clusters with oxygen vacancies. These results were used to develop thermodynamic models, adequately describing the p(O2)-T-delta diagrams of La0.3Sr0.7Fe(M')O3-delta determined by the coulometric titration technique at 923-1223 K in the oxygen partial pressure range from 1 x 10(-5) to 0.5 atm. The thermodynamic functions governing the oxygen intercalation process were found independent of the defect concentration. Doping with aluminum and gallium leads to increasing oxygen deficiency and induces substantial changes in the behavior of iron cations, increasing the tendencies to disproportionation and hole localization. Despite similar oxygen nonstoichiometry in the Al- and Ga-substituted ferrites at a given dopant content, the latter tendency is more pronounced in the case of aluminum-containing perovskites |
M 76 Mixed conductivity, stability and thermomechanical properties of Ni-doped La(Ga, Mg)O3-delta [] = Mixed conductivity, stability and thermomechanical properties of Ni-doped La(Ga, Mg)O3-delta / A. A. Yaremchenko, V. V. Kharton, E. N. Naumovich, D. I. Shestakov, V. F. Chukharev, A. V. Kovalevsky, A. L. Shaula, M. V. Patrakeev, J. R. Frade, F. M. B. Marques // Solid State Ionics. - 2006. - V. 177, N 5-6. - С. 549-558. - Библиогр.: с. 558 (45 назв.) . - ISSN 0167-2738 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): ГАЛЛАТОНИКЕЛАТЫ ЛАНТАНА -- СМЕШАННЫЕ ПРОВОДНИКИ -- ПРОВОДНИКИ СМЕШАННЫЕ -- ПЕРОВСКИТЫ -- РАВНОВЕСИЕ ФАЗОВОЕ -- ФАЗОВОЕ РАВНОВЕСИЕ -- СВОЙСТВА ТЕРМОМЕХАНИЧЕСКИЕ -- ТЕРМОМЕХАНИЧЕСКИЕ СВОЙСТВА Аннотация: Perovskite-type LaGa0.65Mg0.15Ni0.20O3-delta exhibiting oxygen transport comparable to that in K2NiF4-type nickelates was characterized as a model material for ceramic membrane reactors, employing mechanical tests, dilatometry, oxygen permeability and faradaic efficiency measurements, thermogravimetry (TG), and determination of the total conductivity and Seebeck coefficient in the oxygen partial pressure range from 10(-15) Pa to 40 kPa. Within the phase stability domain which is similar to La2NiO4+delta, the defect chemistry of LaGa0.65Mg0.15Ni0.20O3-delta can be adequately described by the ideal solution model with oxygen vacancies and electron holes to be the only mobile defects, assuming that Ni(2+) may provide two energetically equivalent sites for hole location. This assumption is in agreement with the density of states, estimated from thermopower, and the coulometric titration and TG data suggesting Ni(4+) formation in air at T < 1150 K. The hole conductivity prevailing under oxidizing conditions occurs via small-polaron mechanism as indicated by relatively low, temperature-activated mobility. The ionic transport increases with vacancy concentration on reducing p(O2) and becomes dominant at oxygen pressures below 10(-7)-10(-5) Pa. The average thermal expansion coefficients in air are 11.9 x 10(-6) and 18.4 x 10(-6) K(-1) at 370-850 and 850-1270 K, respectively. The chemical strain of LaGa0.65Mg0.15Ni0.20O3-delta ceramics at 1073-1123 K, induced by the oxygen partial pressure variations, is substantially lower compared to perovskite ferrites. The flexural strength determined by 3-point and 4-point bending tests is 167-189 MPa at room temperature and 85-97 MPa at 773-1173 K. The mechanical properties are almost independent of temperature and oxygen pressure at p(O2) = 1-2.1 x 10(4) Pa and 773-1173 K |
O-97 Oxygen nonstoichiometry and mixed conductivity of SrFe1-xMxO3-delta (M = Al, Ga). Effects of beta-site doping [Текст] / M. V. Patrakeev, V. V. Kharton, Yu. A. Bakhteeva, A. L. Shaula, I. A. Leonidov, V. L. Kozhevnikov, E. N. Naumovich, A. A. Yaremchenko, F. M. B. Marques // Solid State Sciences. - 2006. - Vol. 8, № 5. - С. 476-487 Рубрики: ХИМИЧЕСКИЕ НАУКИ |
N 30 Naumovich, E. N. Defect formation in LaGa(Mg,Ni)O3-delta: A statistical thermodynamic analysis validated by mixed conductivity and magnetic susceptibility measurements [Текст] / E. N. Naumovich, V. V. Kharton, A. A. Yaremchenko, M. V. Patrakeev, D. G. Kellerman, D. I. Logvinovich, V. L. Kozhevnikov // Physical Review B: Condensed Matter and Materials Physics. - 2006. - Vol. 74, № 6. - С. 064105/1-064105/12. - Библиогр. : с. 064105/11 (55 назв.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): МАГНИТНАЯ ВОСПРИИМЧИВОСТЬ -- ПРОВОДИМОСТЬ -- ГАЛЛАТ ЛАНТАНА -- ПЕРОВСКИТЫ Аннотация: A statistical thermodynamic approach to analyze defect thermodynamics in strongly nonideal solid solutions was proposed and validated by a case study focused on the oxygen intercalation processes in mixed-conducting LaGa0.65Mg0.15Ni0.20O3−delta perovskite. The oxygen nonstoichiometry of Ni-doped lanthanum gallate, measured by coulometric titration and thermogravimetric analysis at 923–1223 K in the oxygen partial pressure range 5 10−5 to 0.9 atm, indicates the coexistence of Ni2+, Ni3+, and Ni4+ oxidation states. The formation of tetravalent nickel was also confirmed by the magnetic susceptibility data at 77–600 K, and by the analysis of p-type electronic conductivity and Seebeck coefficient as function of the oxygen pressure at 1023–1223 K. The oxygen thermodynamics and the partial ionic and hole conductivities are strongly affected by the pointdefect interactions, primarily the Coulombic repulsion between oxygen vacancies and/or electron holes and the vacancy association with Mg2+ cations. These factors can be analyzed by introducing the defect interaction energy in the concentration-dependent part of defect chemical potentials expressed by the discrete Fermi-Dirac distribution, and taking into account the probabilities of local configurations calculated via binomial distributions Полный текст |
O-97 Oxygen permeability, stability and electrochemical behavior of Pr2NiO4+delta-based materials [Текст] / A. V. Kovalevsky, V. V. Kharton, A. A. Yaremchenko, Y. V. Pivak, E. V. Tsipis, S. O. Yakovlev, A. A. Markov, E. N. Naumovich, J. R. Frade // Journal of Electroceramics. - 2007. - Vol. 18, № 3-4. - С. 205-218 Рубрики: ХИМИЧЕСКИЕ НАУКИ |
O-97 Oxygen non-stoichiometry of Ln4Ni2.7Fe0.3O10-delta (Ln = La, Pr) [Текст] / E. V. Tsipis, M. V. Patrakeev, J. C. Waerenborgh, Y. V. Pivak, A. A. Markov, P. Gaczynski, E. N. Naumovich, V. V. Kharton // Journal of Solid State Chemistry. - 2007. - Vol. 180, № 6. - С. 1902-1910 Рубрики: ХИМИЧЕСКИЕ НАУКИ |
T 44 Thermal and chemical induced expansion of La0.3Sr0.7(Fe,Ga)O3−δ ceramics / V. V. Kharton, A. A. Yaremchenko, M. V. Patrakeev, F. M. B. Marques, E. N. Naumovich // Journal of the European Ceramic Society. - 2003. - Vol. 23, № 9. - P1417-1426 Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): ИНДУЦИРОВАНИЕ |