Phonon features of some PbFCl-type compounds

Abstract The low temperature specific heat of BaFCl, BaFBr and BaFI shows a behaviour typical for insulators with a T 3 temperature variation in the lowest temperature range. The obtained Debye temperatures, θ D (0), follow the Lindemann relation yielding predictions for other compounds of the matlockite family without experimental data. The effective Debye temperature θ D (T) has been determined as a function of temperature, whereas the experimental θ D (0) values do not fit with theoretical estimations based on elastic constants. Finally, for increasing temperature, deviations from the T 3 law appear and this may be due to the layered tetragonal structure of PbFCl-type of these compounds.