Heat Capacity and Chemical Bond Strength of Fluoride Crystals and Glasses

Abstract

Heat capacity of several fluoride crystals and glasses has been m easured at various temperatures from 100 to 350 K by using differential scanning calorimetry (DSC). The temperature dependence of the heat capacity has been analyzed in terms of 3-band theory, which was proposed by the present authors previously, in order to examine bonding characteristics in these materials. For the fluoride crystals, the characteristic temperaturesθ₁, and θ₃, which correspond to interatomic vibration between a cation and its nearby anion and intermoleculartype vibration, respectively, are almost identical with each other. Also, for the present fluoride crystals as well as the, oxide crystals reported previously, there exists a proportional relationship between the value ofθ₁, and the bond strength which is estimated from reduced mass and average interatomic separation by assuming electrostatic potential between ions. This fact indicates thatθ₁is a good parameter for evaluation of the interatomic bond strength in fluoride crystals as well as in oxide crystals. On the other hand, θ₁, =θ₃ holds for all of the present fluoride glasses. This fact implies that structure of the present fluoride glasses is describable in terms of random packing of fluoride ions.