S. Rolandson’s research while affiliated with Chalmers University of Technology and other places

Phonon dispersion relations in RbI have been obtained by inelastic scattering of thermal neutrons. Measurements were performed in the crystallographic symmetry directions Δ, Σ, A, and Z at 80 °K and some selected zone boundary phonons were also measured at 300 °K. A simplified version of the generalized shell model, involving a variable number of parameters was fitted to the experimental dispersion curves. From an eleven parameter model the frequency spectrum, the Debye temperature and other physical quantities have been calculated.Die Phononendispersionsbeziehungen in RbI wurden durch inelastische Streuung thermischer Neutronen erhalten. Die Messungen wurden in den kristallographischen Symmetrierichtungen Δ, Σ, A und Z bei 80 °K durchgeführt. Einige ausgewhlte Zonengrenzen-Phononen wurden auch bei 300 ° K untersucht. Mit einer vereinfachten Version des verallgemeinerten Schalenmodells, das eine variable Anzahl von Parametern enthielt, wurden die experimentellen Dispersionskurven angepaßt. Mittels eines Elf-Parameter-Modells wurden das Frequenzspektrum, die Debye-Temperatur und andere physikalische Größen berechnet.

Phonon frequencies in RbBr at 80 K have been obtained by inelastic scattering of thermal neutrons. The measurements were performed in the symmetry directions Delta , Sigma and Lambda and along the line Z. Some zone boundary phonons were also measured at 300 K. Four versions of the shell model were fitted to the experimental frequencies, and the elastic and dielectric constants were calculated from the model parameters. From an eleven parameter model the authors have also calculated the phonon frequency spectrum and the temperature variation of the Debye temperature.

Phonon dispersion relations have been obtained in the Delta , Sigma and Lambda symmetry directions using inelastic scattering of thermal neutrons. The results are used to calculate effective charges and effective compressibilities from the relations derived by Szigeti (1949 and 1950). Elastic constants are calculated from the slopes of the dispersion curves for small wave vectors and compared to those obtained in ultrasonic work. The dispersion curves are compared with calculations by Karo using the deformed-dipole-next-nearest- neighbours model. The Lyddane-Sachs-Teller (1941) relation is found to be satisfied in all instances except in RbCl at 80 K. Results from earlier work on NaCl and KCl are included for comparison.

Phonons propagating in the symmetry directions Δ, ∑, and A in K0.5Rb0.5I are obtained by inelastic scattering of thermal neutrons at 300 K. The acoustic phonons are well defined and no anomalous broadening is observed, but the transverse zone centre phonon, the only observed optic phonon, has a width about twice the instrumental resolution. The phonon frequencies in the mixed crystal are generally below the averaged frequency values of KI and RbI. The softening of modes is more prominent near the zone boundaries. The results are analysed in terms of the shell model and the rigid ion model for ionic crystals, and compared with similar calculations for KI end RbI. The elastic constants obtained from the eleven parameter shell model in units of 1011 dyn/cm2 are C11 = 3.04, C12 = 0.12, and C44 = 0.50. Phononen in K0,5Rb0,5J, die sich in Symmetrierichtungen Δ, ∑ und A ausbreiten, werden durch inelastische Streuung thermischer Neutronen bei 300 K gemessen. Die akustischen Phononen sind genau definiert, und es wird keine anomale Verbreiterung beobachtet, aber das transversale Zonenzentrum-Phonon bei Γ, das einzige beobachtete optische Phonon, hat eine Breite, die doppelt so groß ist wie die experimentelle Auflösung. Die Phononenfrequenzen der gemischten Kristalle liegen im allgemeinen tiefer als die gemittelten Frequenzwerte von KJ and RbJ. Die Weichheit der Moden ist in der Nähe der Zonengrenzen stärker. Die Ergebnisse werden mit Hilfe des Schalenmodells und des starren Ionenmodells für ionische Kristalle interpretiert und mit ähnlichen Rechnungen für KJ und RbJ verglichen. Folgende elastische Konstanten werden mit Hilfe des elf-parametrigen Schalenmodelles bestimmt: C11 = 3,04, C12 = 0,12 und C44 = 0,50 (in 1011 dyn/cm2).

The neutron diffraction pattern of powdered KCl has been measured using the triple-axis spectrometer both in the double-axis and the triple-axis modes. The thermal diffuse scattering (TDS) correction, which is very important in the double-axis pattern, is essentially eliminated in the triple-axis mode. Theoretical calculations are presented which give the relative TDS correction for the two cases by calculating the energy distribution of TDS. The Debye-Waller coefficient B using the triple-axis data is found to be (2.17 ± 0.16 Å2), which is in agreement with the TDS-corrected values of other workers.

A brief review of attempts made during the last 50 years to determine the structure and size of the cell unit of cellulose is followed by a description of an experimental investigation which was carried out in order to clarify the discrepancy regarding the unit cell dimensions as given in the literature. The triple axis neutron spectrometer used in this study is described. Details of neutron diffraction measurement are tabulated and some neutron diffraction patterns included. A thorough discussion is concluded with a statement that low-angle neutron diffraction studies provide information about the structure of cellulose I that has been lacking in the x-ray studies. The results for cellulose I (cotton crystallites) are in general agreement with the findings of Honjo and Watanabe based on electron diffraction studies of cellulose I (Valonia ventricosa) that 'a' and 'c' axes are about twice as long as those proposed by Meyer and Misch on the basis of x-ray diffraction studies of cellulose I.

Phonon frequencies of copper have been measured at 80 K with a neutron crystal spectrometer at a large number of points—mainly in off-symmetry directions. The frequency distribution is calculated, and also the Debye temperature in the interval 0-300 K. The agreement with calorimetric measurements is very satisfactory. Several Born-von Kármán models were fitted to the experimental frequencies. The best fit was obtained using a model with general forces extending to eighth nearest neighbors. The conditions for axial symmetry of the interatomic forces are much better fulfilled in copper than, for instance, in aluminum. However, a general force model is preferable also for copper when a good fit in the whole zone is wanted.

The phonon dispersion relations in cesium fluoride have been measured by inelastic neutron scattering in the symmetry directions Δ Σ, and A. The measurements were performed at 80 and 300 K using a three-axis spectrometer. The experimental results are compared with theoretical calculations based on various models of the interionic interactions in alkali halides. A satisfactory fit was obtained by a seven-parameter model with only the cesium ion polarizable, and the fit was only slightly improved by using more complicated models with a larger number of adjustable parameters. The frequency distribution has been calculated using an eleven-parameter shell model with both ions polarizable, and compared with similar calculations based on data from macroscopic measurements. Die Phononendispsion in Cäsiumfluorid wurde durch inelastische Neutronenstreuung in den Symmetrierichtungen Δ, Σ und A gemessen. Die Messungen wurden mit einem dreiachsigen Spektrometer bei 80 und 300 K durchgeführt. Die Meßresultate werden mit theoretischen Berechnungen verglichen, denen verschiedene Ionenwechselwirkungsmodelle in Alkalihalogeniden zugrunde liegen. Es wurde zufriedenstellende Übereinstimmung mit einem Sieben-Parameter-Modell gefunden, in welchem nur das Cäsium-Ion als polarisierbar angenommen wurde. Kompliziertere Modelle konnten die Übereinstimmung nur wenig verbessern. Für die Berechnung der Frequenzverteilung wurde ein Elf-Parameter-Schalen-modell verwendet, in dem die Polarisierbarkeit beider Ionen berücksichtigt wurde. Die Ergebnisse werden mit ähnlichen Berechnungen verglichen, die sich auf Daten makroskopischer Messungen stützen.

The phonon dispersion curves of cesium bromide have been observed by inelastic neutron scattering in the symmetry directions Δ, Σ, and Λ and along the symmetry line T. The measurements were performed at 80 and 300 K using a three-axis crystal spectrometer. The observations have been fitted to various versions of the shell model, and the frequency distribution and the temperature dependence of the Debye temperature have been calculated from the model which gives the best fit to the experimental frequencies.