Surface electrical properties of Gd-doped PbZrO3

Work function (WF) of undoped and Gd-doped PbZrO₃ (PZG) was determined during isothermal oxidation and reduction experiments at 400 and 500 °C in the P(O₂) range between 10 and 2.1×10⁴ Pa. The obtained results are discussed in terms of two competitive effects, such as (i) an acceptor-type effect due to oxygen chemisorption and its subsequent incorporation into the oxide lattice and (ii) donor-type effect due to p(O₂)-induced structural transitions, such as decomposition of PbZrO₃ resulting in the formation of a surface layer composed of PbO and ZrO₂. Both effects have different rates of appearence and the effect on electrical potential. It was found that oxidation results in irreproducible changes of surface properties involving the formation of a low-dimensional surface layer.     

Thermoelectric power of mixed electronic-ionic conductors III. Case of calcium titanate

The primary purpose of the present work is the determination of the thermopower component related to electronic charge carriers for undoped calcium titanate. The second purpose of this work is establishment of the relationship between this thermopower component and the electronic component of electrical conductivity. An essential part of the present study includes the determination of the thermopower components corresponding to different charge carriers (electrons, electron holes and ions). The determination procedures are based on the following three models:

Symmetrical model. This model assumes consistency between thermopower and electrical conuctivity in terms of the n-p transition (this model assumes that minimum of electrical conductivity corresponds to the electronic component of the thermopower equal zero). It was shown that this model does not apply for CaTiO₃.

The Heikes model. This model is based on Heikes formula and also hopping mechanism of the transport of electrons. It was shown that thermopower of CaTiO₃ cannot be described by this model and, consequently, thermopower vs. electrical conductivity cannot be considered within the Jonker formalism.

General model. This model is based on a general thermopower equation for mixed conductors without any simplifying assumptions. Application of this model indicates that the electronic component of thermopower is not consistent with the minimum of electrical conductivity.

     

Interactions of oxygen with yttria-stabilized zirconia at room temperature

This paper reports the results of work function and EPR studies of yttria-stabilized zirconia (10Y-ZrO₂). The experimental data are considered in terms of the formation of oxygen chemisorbed species and subsequent oxygen incorporation as well as related charge transfer. It is concluded that oxygen chemisorption on 10Y-ZrO₂ at room temperature in its initial stage results in the formation of O ₂ ⁻ species. These species are then transformed into O ₂ ²⁻ , O⁻ species and, finally, are slowly incorporated into the oxide lattice. These processes take place without presence of Pt or any other electrode material.     

Defect chemistry and electrical properties of La1−xSrxCoO3−δ III. Oxygen nonstoichiometry

This paper concerns verification of the defect chemistry models of La_1−xSr_xCoO_3−δ (LSC), involving the random defect model and the cluster defect model, against empirical data of oxygen nonstoichiometry. It appears that the experimental data may well be explained within the random defect model.     

Room-temperature phosphorescence of anilinonaphthalenesulfonate “fluorescence probe” compounds

2,6-anilinonaphthalenesulfonate (2,6-ANS) and 2,6-toluidinonaphthalenesulfonate (2,6-TNS) exhibit room-temperature phosphorescence when absorbed on filter paper, but the corresponding 1,8-isomers (1,8-ANS and 1,8-TNS) do not. The phosphorescence of the 2,6-isomers and nonphosphorescence of the 1,8-isomers is also found to hold in rigid glass at 77 K. No phosphorescence was detectable from N-phenyl-1-napthylamine at room temperature or 77 K, indicating that intramolecular hydrogen bonding in the 1,8-isomers isomers is not an essential feature inhibiting phosphorescence. Very effective heavy-atom enhancement of the phosphorescences of 2,6-ANS and 2,6-TNS by sodium iodide is observed.     

DFT Study of Methanol Adsorption on Defect-Free CeO2 Low-Index Surfaces

Methanol decomposition is a promising method for hydrogen production. However, the performance of current catalysts for this process is not sufficient for commercial applications. In this work, methanol adsorption on the CeO₂ low-index surfaces is studied by density functional theory (DFT). The results show that methanol always dissociates spontaneously on the (100) surface, whereas dissociation on the (110) surface is site-selective; dissociation does not occur at all on the (111) surface, where only weak physisorption is found. The results confirm that surfaces with higher energies are more catalytically active. Analysis of the surface geometries shows that the dominant factors for the dissociation of methanol are the degree of undercoordination and the charges of the surface ions. The adsorption energy of each methanol molecule decreases with increasing coverage and there is a transition threshold between dissociative and associative adsorption. The present work indicates that a strategy to design catalysts with high activity is to maximize exposure of surfaces on which the ions have a high degree of undercoordination and a strong tendency to donate/accept electrons. The results demonstrate the importance of appropriately selecting and controlling exposed facets and particle morphology for optimizing catalyst performance.