Sune Pettersson

Calculation of the thermal conductivity of alkali halide crystals

The thermal conductivities of 17 alkali halides with the sodium chloride structure have been calculated in the medium- and high-temperature ranges. Dispersion relations throughout the whole Brillouin zone have been obtained from a deformation dipole model and low-temperature input data. The linearised Boltzmann equation is solved by a variational method with two different trial functions proportional to the wave-vector and the group velocity, respectively. The results differ significantly and optic branches are found to be very important.

The Influence of Group Work Discussion on Scores of the Force Concept Inventory in Lao PDR

In this study, we investigated if freshman students participation in small group discussions in the tutorial sessions would influence their score of the Lao version of the Force Concept Inventory ...

On the role of optic phonons in the thermal conductivity of alkali halides

The thermal conductivity of 17 alkali halides has been calculated with a variational method. The calculations confirm previous results from relaxation-time calculations on NaCl and KCl that optic phonons are important in both the heat current and the scattering processes. It is found that the relative contributions to the scattering integral from different combinations of branches are strongly correlated to the mass ratio of the two constituent ions. On the other hand the amount of heat carried by optic phonons is more dependent on the ratio of the static and optic dielectric constants, epsilon 0/ epsilon infinity , than on the mass ratio. The theory of mirror pairs has been applied in an analysis of the thermal conductivity data. It is shown that experiments on Li and LiBr would be a critical test of the variational calculations.