Effect of60Co gamma radiation on La2CuO4
01 Nov 1985-Journal of Radioanalytical and Nuclear Chemistry (Akadémiai Kiadó, co-published with Springer Science+Business Media B.V., Formerly Kluwer Academic Publishers B.V.)-Vol. 96, Iss: 3, pp 301-309
TL;DR: In this article, the effect of 60Co γ-radiation on La2CuO4 solid catalyst prepared by the ceramic method has been studied and the results have been interpreted on the basis of the crystal field model of the structure of La2cuO4.
Abstract: The effect of60Co γ-radiation on La2CuO4 solid catalyst prepared by the ceramic method has been studied. Gamma irradiation of La2CuO4 samples has been found to increase the Cu+ content, electrical conductivities and decrease the magnetic susceptibilities of the catalyst. The results have been interpreted on the basis of the crystal field model of the structure of La2CuO4.
TL;DR: In this article, the authors measured the amount of chemisorbed oxygen in gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride.
Abstract: Chemisorbed oxygen can be determined quantitatively by the measurement of gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride. The amount of chemisorbed oxygen depends on the degree of dispersion during irradiation and also the γ-dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen.
TL;DR: In this paper, the catalytic activity of La2CuO4 for the decomposition of H2O2 was studied in detail and attributed to irradiation generated Cu+ centers on the surface of the catalyst.
Abstract: The catalytic activity of La2CuO4 for the decomposition of H2O2 was studied in detail. La2CuO4 was prepared by the ceramic method in four different ways. Gamma irradiation of the La2CuO4 samples increased their catalytic activity irrespective of the method of preparation. The enhanced catalytic activity is attributed to irradiation generated Cu+ centres on the surface of the catalyst.
TL;DR: It is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions, which makes these oxides attractive models in the study of catalytic chemical conversion.
Abstract: In a time of growing need for catalysts, perovskites have been rediscovered as a family of catalysts of such great diversity that a broad spectrum of scientific disciplines have been brought to bear in their study and application. Because of the wide range of ions and valences which this simple structure can accommodate, the perovskites lend themselves to chemical tailoring. It is relatively simple to synthesize perovskites because of the flexibility of the structure to diverse chemistry. Many of the techniques of ceramic powder preparation are applicable to perovskite catalysts. In their own right, they are therefore of interest as a model system for the correlation of solid-state parameters and catalytic mechanisms. Such correlations [See figure in the PDF file] have recently been found between the rate and selectivity of oxidation-reduction reactions and the thermodynamic and electronic parameters of the solid. For commercial processes such as those mentioned in the introduction, perovskite catalysts have not yet proven to be practical. Much of the initial interest in these catalysts related to their use in automobile exhaust control. Current interest in this field centers on noble metalsubstituted perovskites resistant to S poisoning for single-bed, dual-bed, and three-way catalyst configurations. The formulations commercially tested to date have shown considerable promise, but long-term stability has not yet been achieved. A very large fraction of the elements that make up presently used commercial catalysts can be incorporated in the structure of perovskite oxides. Conversely, it is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions. Even though this expectation is by no means a prediction of commercial success in the face of competition by existing catalyst systems, it makes these oxides attractive models in the study of catalytic chemical conversion. By appropriate formulation many desirable properties can be tailored, including the valence state of transition metal ions, the binding energy and diffusion of O in the lattice, the distance between active sites, and the magnetic and conductive properties of the solid. Only a very small fraction of possible perovskite formulations have been explored as catalysts. It is expected that further investigation will greatly expand the scope of perovskite catalysis, extend the understanding of solid-state parameters in catalysis, and contribute to the development of practical catalytic processes.
TL;DR: Preliminary tests are reported in which lanthanum cobaltite—a semiconducting oxide—has given results comparable to those produced by platinum, and suggestions are made for its development into a practical electrode.
Abstract: THERE is at present great interest in high energy density batteries, especially for use in urban transport1. For this application an electrically rechargeable system would be ideal, and night charging would assist in levelling out the demand for electricity. Metal-air batteries (notably zinc-air) are probably nearest to practical usefulness, but one limitation to their large scale use is the fact that a noble metal catalyst (usually platinum) may need to be used in the air electrodes, which have to reduce oxygen from the air to OH− ions in the concentrated alkali electrolyte and subsequently to act in reverse for recharging. I report here preliminary tests in which lanthanum cobaltite—a semiconducting oxide—has given results comparable to those produced by platinum. The material clearly deserves detailed further attention and, after discussion of the results, suggestions are made for its development into a practical electrode.
TL;DR: The authors examined the structure of La2CuO4 at room temperature and found it to be an orthorhombic distortion of the K2NiF4 structure (a = 5.363 A, b = 4.409 A, c = 13.17 A).
Abstract: We have examined the structure of La2CuO4 at room temperature and found it to be an orthorhombic distortion of the K2NiF4 structure (a = 5.363 A, b = 5.409 A, c = 13.17 A). Refinement of position parameters, based on powder X-ray diffraction data, shows the copper to have two long Cu-0 distances (2.40 A) and four short distances (1.90 A). The orthorhombic unit cell becomes tetragonal at 260°C without any significant change in Cu O distances. The magnetic susceptibility of La2CuO4 is less than 10−6 emu/g from room temperature to 4.2°K and in fields to 17 kOe. We have prepared LaSrV04 by reaction of component oxides in vacuum at 1000°C. The new compound has a tetragonal K2NiF4 structure with a = 3.869 A and c = 12.652 A. Optimization of position parameters gave two longer V O distances (2.09 A) and four shorter (1.94 A).
TL;DR: In this article, the temperature dependence of the resistivity and the thermoelectric power of rare earths have been measured and the tetragonal lattice of La2CuO4 shrinks in the a axis and expands in the c axis.
Abstract: The temperature dependence of the resistivity and the thermoelectric power of Ln2CuO4 (Ln=rare earths) have been measured. The compounds of Gd, Sm, Nd, and Pr are semiconductive, while La2CuO4 shows metallic conductivity. The tetragonal lattice of La2CuO4 shrinks in the a axis and expands in the c axis compared to Pr2CuO4, in spite of the steady expansion of these lattice parameters for the compounds between Gd and Pr. The thermoelectric power of Ln2CuO4, but not La2CuO4, is negative, suggesting an electron-conducting or n-type semiconductor. The resistivity of the Ln2CuO4 at room temperature increases essentially with an increase in the atomic number of Ln. The plots of the thermoelectric power vs. the reciprocal temperature showed a steeper slope for the compounds of the heavier rare earths. The semiconductor-metal transition observed between La2CuO4 and Pr2CuO4 was explained in relation to the structural change (the shrinkage of the a axis and the expansion of the c axis) as being due to the change in ...
TL;DR: In this article, it was shown that conduction occurs via a σ∗ x 2 − y 2 2 band in La2CuO4 and that the conduction band is narrow.
Abstract: X-ray, magnetic susceptibility, and electron paramagnetic resonance measurements have been made on La2CuO4. Magnetic measurements in the range 4.2 – 300 K are consistent with the metallic nature of La2CuO4, and the itinerant - electron susceptibility is estimated to be 239 × 10−6 emu mol−1. The high susceptibility and density of states indicate that the conduction band is narrow. The results are discussed in terms of previous models of the level structure of La2CuO4, and it is concluded that conduction occurs via a σ∗ x 2 − y 2 band. Comparison of La2CuO4 with semiconducting lanthanide cuprates suggests that this compound is on the verge of a semiconductor-to-metal transition.