Lattice Dynamics of Mixed Divalent Metal Fluorides

Density functional perturbation theory is used to study the lattice dynamics of CaxCd1-xF2, CaxSr1-xF2 and CaxMg1-xF2 where x=0, 0.25, 0.50, 0.75 and 1.The result obtained for the dielectric constants of the alloys ranges from 2.157 to 2.609. The calculated Borneffective charges of the cations (Ca, Cd, Mg and Sr) and anions (F) of the alloys whenthe atoms of the alloys are displaced in the presence of an electric field deviate from thenominal ionic values (+2 and -1 respectively). The anions’ values range from -0.810 to-0.986 except for Ca0.25Cd0.75F2 in which Z = -1, while the cations’ values range from+2.354 to +2.566. The deviation is because the ionic bond in the alloyshas a certain amount of covalent character, indicating a mixed ionic-covalent nature ofthe bond. They are weak ionic compounds. The dielectric constants calculations showed that the alloys are dielectricmaterials that can be used in designing capacitors and optical fibres.