Svend Erik Rasmussen

Structures and Phase Transitions of Na2SO4

Sodium sulfate, Na2SO4, has been reported to exist in five polymorphous forms labelled I–V. Structure analysis has been reported on three of the polymorphs and thermal analysis on all of them. The system has been reinvestigated by differential scanning calorimetry (DSC) and by X-ray powder diffraction at several temperatures in order to examine the Na2SO4 system with the same batch of material in the same laboratory by two independent methods. The X-ray results confirm the existence of the crystalline phases labelled I, II, III and V but not IV. The DSC results do not entirely rule out the existence of five phases. The structure of phase II has been determined and the structures of all phases have been refined by the Rietveld method.

A versatile spectrometer for secondary x-ray fluorescence excitation

Abstract Inexpensive research equipment for secondary x-ray fluorescence excitation is described. The primary beam from a high-powered x-ray tube is collimated onto the targets, six of which may be easily and safely interchanged. A collimator system ensures that the detector receives radiation from well defined areas of the sample. The geometry minimizes radiation from Compton scattering, the twice-scattered continuum radiation from the x-ray tube, and the characteristic lines from the secondary target. The unit is designed for use with standard x-ray tubes and generators, and is part of an energy-dispersive spectrometer used for multielement analysis. The performance of the system with a variety of samples is described.

Crystal Data for Pb7Bi3, a Superconducting ε-Phase in the Pb-Bi System

The e-phase is hexagonal, space group P6 3 /mmc. For the composition Pb 7 Bi 3 the following data were determined, a = 3.5058(1) A c = 5.7959(5) A, Vol. = 61.687 A 3 (5), D c = 11.17 Mg m −3 . Filings from single crystal material were used to obtain powder data by the Guinier method and the X-ray results were in accordance with single crystal neutron diffraction data. Transition to the superconducting state took place in the interval 8.3 K–8.55 K.

New Crystal Data for Mo .63 Ru .37 (Mo 5 Ru 3 ) A Superconducting Sigma Phase

New crystal data for the intermetallic sigma phase in the Mo-Ru-system are reported and the indexing of the pattern given in the Powder Diffraction File has been extended. The material is tetragonal, P4 2 /mnm (No. 136) with a = 9.5652(4) A; c = 4.9362(3) A; Vol = 451.63(7) A 3 , D c = 10.79 Mg m −3 for the composition Mo .63 Ru .37 , and a = 9.5569(21) A; c = 4.9418(20) A; Vol = 451.35(38) A 3 , D c = 10.75 Mg m −3 for Mo .70 Ru .30 . Powder data were obtained by the Guinier method and the indexing was corroborated by single crystal data. Transition to the superconducting state took place in the interval 6.8 K – 8.8 K.

Growth of chromium silicide, Cr3Si, crystals

Trichromium silicide, Cr3Si, was prepared by floating zone melting, and single crystals having the size of 1–15 cm3 were obtained by repeated zone passes. The crystals were examined by X-ray and neutron diffraction.

Composition of pigments of Santorini frescoes: The Rietveld method as an aid in qualitative phase analysis

Ten fragments of bronze age frescoes from the Greek group of volcanic islands known as Santorini have been examined by powder X-ray diffraction. A qualitative phase analysis based on line positions only was supplemented by the Rietveld method which uses complete diffraction profiles to increase the credibility of the phase analysis.

Crystal data for CaNa-iminodisulphonate, trihydrate

Calcium sodium iminodisulphonate trihydrate was first described by Divers and Haga [J. Chem. Soc. 943–968, (1892)]. It has recently been found as one of several crystalline products resulting from the removal of sulphur dioxide from flue gas. It has not so far been included in the ICCD powder diffraction file.

Growth of Mo3Ir single crystals

Abstract Mo 3 Ir was prepared by floating zone melting and single crystals of up to 10 mm 3 were obtained. The crystals were examined by X-ray, μ-ray and neutron diffraction, and by measurement of critical temperature for superconductivity.

A monochromator for single-crystal X-ray crystallography

The President of the Union, Professor A.Guinier , together with the Chairman of the Commission on Journals, the General Secretaly, the Treasurer, employees of the Union and guests, attended a luncheon in Chester on 7 January to mark the opening of the new Union office. This office, incorporating the office of the Technical Editor and the office of the Executive Secretary, is at 13 White Friars, Chester CH1 1NZ, England. All correspondence for the Technical Editor, Mr S.A.Bryant , and the Executive Secretary, Dr J .N .King , should be sent to this address. Dr King has now taken over the day-to-day business of the Union from the General Secretary and the Treasurer.

Precision of determination ofd-spacings using a Guinier camera

The precision of determination of lattice spacings using a commercial triple Guinier camera and a precision comparator is evaluated. Determination of lattice constants on germanium, tungsten and various samples of mullite are given. It is found thatd-spacings can be routinely determined with uncertainties of the order of 1 part in 10000 in the analytically most useful Bragg angle range from 0 to 45‡ in theta.