The Structure of Interpretations in Family Therapy: A Video-Enhanced Exploration *

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73991/1/j.1545-5300.2000.39204.x.pd

AN EXAFS STUDY OF IRON-LEAD PYROPHOSPHATE GLASS

Lead phosphate glasses are characteristically prone to aqueous attack but become chemically resistant on the addition of iron. We have measured the K-edge EXAFS of Fe and the L-edge EXAFS of Pb in these glasses and find the atomic environments of the two modifiers to be very different. Our results suggest that Fe sites pin the polyphosphate network and so block the percolation of Pb ions thereby increasing the chemical resistance of the whole structure

Structural Studies Of Amorphous Si-Ni-H

It is well know that the transition from an insulator to a metallic conductor may be induced in amorphous semiconductor : metal alloys by increasing the metal concentration above a certain critical limit. However, without a detailed understanding of the changes taking place in the atomic scale structure, it is difficult to ascribe a mechanism to the process. We have investigated the microstructure of one such alloy system, a-Si1-yNiyH, using EXAFS as the principal technique. Thin film samples, prepared by rf co-sputtering, were studied over the composition range 0<y<0.3. Both silicon and nickel K-edge EXAFS results are presented, together with complimentary data from Raman scattering, neutron diffraction and scanning calorimetry experiments. The results indicate that the samples contain two separate amorphous phases: a Ni:Si alloy which is embedded in the surviving, modified a-Si host network. The measured electrical conductivity is discussed in the light of this structural model

The Amplitude Reduction Factor in EXAFS

The amplitude reduction factor so2(k) is usually treated as an empirical parameter in EXAFS data analysis, although a few values have been calculated [1]. We present here the results of a simple model calculation that gives accurate values of so2(k) for all absorption edges of all free atoms. The method is based on the use of Slater orbitals and the Sudden Approximation. We also calculate so2(k) using the Tight-Binding model in order to estimate any variation in the amplitude reduction with chemical environment. We find that so2(k) lies between 0.65 and 0.80 for all edges of use in EXAFS and has a characteristic dependence on atomic number. The calculated values are found to agree with a wide range of experimental data

Comparing Peak Asymmetries in EXAFS using RMC and Cumulant Expansion Data Analysis

EXAFS measurements on RbBr at the Br absorption edge and different ternperature were carried out. Conventional analysis of the data using the Daresbury EXCURV92 code shows with increasing temperature a decrease in nearest neighbour distance. Also large differences are found in the coordination numbers for k and k3 weighted EXAFS with increasing temperature. Using cumulant expansion when fitting the data results in a small increase in nearest neighbour distance with temperature, as expected from thermal data

EXAFS and XANES Study of Structural and Electronic Changes in Y1-xPrxBa2Cu3O7

We present X-ray absorption fine structure (EXAFS) data from Y,Pr,Ba and Cu edges for various concentrations of Pr in Y1-xPrxBa2Cu3O7. Analysis of Y K-edge EXAFS shows no evidence for major changes in interatomic distance or in its mean square variation with composition. The individual Ba-O distances have weak compositional dependence. The Pr-O distance is found to vary linearly with composition. We have interpreted the changes in Pr-O distance to conclude the existence of Pr in a mixture of Pr3+ and Pr4+ States. The Cu-O coordinates at about 2.4 Å (the apical oxygen for Cu) appear to have a compositional dependence. Changes in electronic structure are also discussed besides structural changes along with their correlation