Large Interplanar Spacing Research Articles

On the phase transition in ethanolic solution of thiourea and KF

The solid phase was obtained as a result of the phase transition process in the bulk of ethanolic solution saturated with thiourea and KF. X-ray powder diffraction diagrams showed large interplanar spacings which are characteristic for a hydrogen-bonded structure. The results indicate the special role of the supporting electrolyte and the solvent in the formation of the condensed phase and may be helpful in studies of the phase transitions at the mercury-solution interface.

Study of charge transfer in FeTi

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.

Intensity and resolution in the time-of-flight method for neutron diffraction

Expressions are derived for the integrated intensities of reflections from powders and single crystals in the time-of-flight method for neutron diffraction. The effect of collimator divergence angle on the intensity and resolution is discussed and it is shown that a fixed Bragg angle of 2 θ = 90° is favored for general applications with powders. Experimental and theoretical values of resolution are compared and contrasted with the resolution obtainable from the double axis spectrometer. It is shown that for comparable measuring times the time-of-flight method gives superior resolution for reflections from large interplanar spacings.