Electronic conduction in La-based perovskite-type oxides

Abstract

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm^?1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm^?3 and a small effective mass m? of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1?xSr_xCoO_3±δ and La_1?xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm^?1 for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm^?1 for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1?xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

Electronic conduction in La-based perovskite-type oxides

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm⁻¹ at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm⁻³ and a small effective mass m∗ of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1−xSr_xCoO_3±δ and La_1−xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm⁻¹ for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm⁻¹ for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1−xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

钙钛矿型氧化物混合导体透氧膜材料的选择

在总结文献和实验数据的基础上提出了选择高性能钙钛矿型氧化物混合导体透氧膜材料的策略，应用此策略对几种钙钛矿型透氧膜材料的性能作了合理的解释，并在此基础上开发了具有高透氧量的Ba0.5Sr0.5Co0.8Fe0.2O3-δ材料和具有长期稳定性的BaCo0.4Fe0.4Zr0.2O3-δ材料。     

Ferroelectric Curie points at perovskite-type oxides

The covalent bond energy of the A-O bonding and the enthalpy of formation for perovskite-type oxides ABO₃ were found to show high correlations with Curie points. Perovskite-type titanates with a lower covalent bond energy show higher Curie points, while those with low standard enthalpy of formation show low Curie points, or do not cause displacive transitions. The standard enthalpy of formation of perovskite oxides was inferred to be approximately equal to the sum of that of simple oxides.     

Structural and surface characterization of perovskite-type oxides; influence of A and B substitutions upon oxygen binding energy

Monophasic samples of seven different oxides with perovskite structure, and also -NaAlO2 have been prepared for catalytic applications. They have been characterized by X-ray diffraction and electron microscopy, then by X-ray photoelectron spectroscopy (XPS). The XPS spectra of LaAlO3, La0.9Sr0.1Al0.8Cu0.1Ru0.1O3, La0.8Sr0.2Al0.8Cu0.1Ru0.1O3 and -NaAlO2 contained only one well-defined O 1s peak. The binding energy obtained from the oxygen peak of the perovskites (529.8 eV) was, however, significantly different from that of -NaAlO2 (532.2 eV). The other perovskite oxides, La0.9Ca0.1AlO3, La0.8Ca0.2AlO3, La0.8Sr0.2AlO3 and LaAl0.8Cu0.2O3 had two more or less well-resolved O 1s peaks separated by 2.4 eV. Tentatively, we have interpreted these observations to mean that, in the latter compounds, the surface is reconstructed so that the Al3+ ions have changed their coordination from octahedral to tetrahedral. © 1998 Kluwer Academic Publishers     

Rhenium oxides having an ordered or related perovskite-type structure

Further structural and magnetic observations on compounds of the type A₂BReO₆ (where A = Ca, Sr, Ba; B = Ca, Sr) having the perovskite-related structure were carried out. The thermal decomposition of Ca₅Re₂O₁₂ in vacuo yielded single crystals of a perovskite related phase having the composition Ca₃ReO_5.5. The crystallo-graphic properties for all the derivatives were obtained from powder diffraction studies. Magnetic and electrical results on these phases are reported.     

Effects of B site partial substitutions of perovskite-type La0.6Sr0.4CoO3 on oxygen desorption

Journal of Materials Science Letters -     

Solution and transport of water in oxides

Abstract

First, the dissolution of water into different types of oxides is discussed, including the influence of the water pressure and the oxygen activity. Then the transport of water, i.e. of hydrogen–containing species, in such oxides and its dependence on the water pressure and the oxygen activity is analyzed. Hydrogen–containing species of relevance in this context are water molecules, protons and OH groups. Crystalline and amorphous oxides are considered. Following these more general discussions, some specific experimental observations on the solution and the transport of water and hydrogen–related species in oxides are reviewed and discussed. These observations were made by members of different scientific communities, i.e. by earth scientists, glass scientists, solid state electrochemists, etc. Finally, a few possible consequences of the observations made and of conclusions drawn from them for the high temperature oxidation of alloys in water–containing atmospheres are discussed.     

Curie point of perovskite-type oxides containing bivalent ions of the 4th period in the B-site

The effects of different B-site elements on the Curie points of the PbTiO₃-Pb(M₁/3Nb_2/3)O₃ and 0.99BaTi0₃-0.01Ba(M_1/3Nb_2/3)O₃ series (M = Ca, Mn, Fe, Co, Ni, Cu, Zn), were examined. The Curie point was high when M was copper, while it was low when M was nickel. This was caused by the Jahn-Teller effect in the CuO₆ octahedron keeping the Curie point high. For the 0.99BaTiO₃-0.01 Ba(M_1/3Nb_2/3)O₃ systems, the Curie points were correlated with axial ratioc/a.     

An effect of microstructure on the interface resistance between a perovskite-type oxide electrode and yttria-stabilized zirconia

The electrode characteristics of perovskite-type oxides, La_0.6Sr_0.4CoO₃ and La_0.6Sr_0.4MnO₃, on ceria-based oxide and stabilized zirconia were analysed by the a.c. impedance method. The ionic conductivities of the electrolyte and electrode conductivities from the a.c. impedance analysis agreed with those obtained from the current interruption and d.c. four-probe methods. Two semicircles from the charge transfer and diffusion processes appeared as the electrode resistance. The relative contribution of these two processes to the overall electrode resistance strongly depended on the microstructure of the electrode. The electrode microstructure could be controlled by the dispersion medium used for the electrode slurry. The La_0.6Sr_0.4MnO₃ electrode coated with n-butyl acetate slurry exhibited the smallest electrode resistance.     

A novel method for the synthesis of perovskite-type mixed metal oxides by the inverse microemulsion technique

Nanoparticles of lanthanum-nickel, lanthanum-copper and barium-lead oxalates with the metal molar ratios of 11, 21 and 11, respectively, have been successfully synthesized in inverse microemulsions. These metal oxalate particles of about 20 nm diameter were readily calcined into single-phase perovskite-type LaNiO₃, La₂CuO₄ and BaPbO₃. The calcination temperatures for these metal oxalates were generally 100–250°C lower than those for the metal oxalates prepared by the conventional aqueous solution precipitation method. The substantial reduction in the calcination temperatures is attributed to the formation of uniform, near-spherical nanoparticles of the metal oxalate precursors obtained by the unique inverse microemulsion technique.     

Conductivity measurements on cobalt and nickel oxides in highly-enriched oxygen atmospheres

The pressure dependencies of the conductivities of nickel and cobalt monoxides have been investigated in the range 10^–2 to 7.5 × 10² atmospheres at temperatures in the region of 1000° C. Conductivity saturation occurs in CoO due to the formation of Co₃O₄, and the experimental data correlates well with a model for the separation of the higher phase. NiO exhibits no saturation effect in the pressure range investigated and the p^1/5 dependence of the conductivity at 950° C with this oxide above 0.1 atm is interpreted in terms of the formation of singly ionised vacancies.     

Preparation,magnetic and Mössbauer resonance investigation of some perovskite-type oxides containing iridium +V

New Ir(+V) perovskites of formula MLaMgIrO₆ (M = Ca, Sr, Ba) have been prepared under high oxygen pressure. The stabilization of Ir(+V) thanks to competition between Ir-O and Mg-O bonds is discussed and compared to that observed for La₂LiIrO₆. Magnetic and Mössbauer resonance measurements allow to characterize iridium in the materials, which contain some Ir(+IV).     

High-temperature oxygen nonstoichiometry determination in mixed ionic-electronic conducting oxides

We have developed a new method for determining oxygen nonstoichiometry (3 ? δ) as a continuous function of oxygen partial pressure $\left( {p_{O_2 } } \right)$ at high temperatures in mixed ionic-electronic conducting oxides. A proposed mathematical model allowed us to assess the contribution of the oxygen released from a sample to the oxygen partial pressure at the outlet of a flow reactor after a steplike change of oxygen partial pressure in the incoming gas from 0.2 to 10^?5 atm and to calculate 3 ? δ as a function of $p_{O_2 }$ . The accuracy of the method was demonstrated by comparing our experimental data and data in the literature for the well-studied oxygen-ion-conducting membrane materials SrCo_0.8Fe_0.2O_{3 ? δ} and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_{3 ? δ}