Temel ilkelerle bakır tabanlı kalkopirit yarı iletkenler ve yüksek dielektrik sabitli malzemelerin örgü dimamiği özelliklerinin incelenmesi

We have planned to study two subjects: First principle investigation of hydrostatic pressure dependence of structural, elastic and lattice dynamical properties of Cu-based ternary semiconductors and electronic, dielectric and lattice dynamical properties of some perovskite structures that have very large low frequency dielectric constants.Firstly we have performed an ab initio study of volume dependence of elastic and lattice dynamical properties of chalcopyrite semiconductor CuGaSe2 and CuAlS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permitivity tensors, the phonon frequencies at the Brillouin zone center and their Grüneisen parameters are calculated using density functional perturbation theory. We compare the Grüneisen parameters of the calculated quantities with those of zinc-blende type materials and found similar trends. Calculated elastic stiffness constants show pseudocubic behavior.As a second research topic, we report the results of an ab initio study of electronic, dielectric and lattice dynamical properties of high dielectric constant perovskite-derived oxide Na1/2Bi1/2Cu3Ti4O12. The calculations have been carried out within the local spin density functional approximation using normconserving pseudopotentials and a plane-wave basis. The ground state is found to be antiferromagnetic direct-band gap semiconductor. Lattice dynamical properties, such as Born effective charge tensors, dielectric permittivity tensors, and phonon frequencies at the Brillouin zone center were calculated using density functional perturbation theory and found to be similar to more studied CaCu3Ti4O12 and CdCu3Ti4O12 compounds. The calculated electronic (?o=11.5) and static (??=150) dielectric constants indicate that the observed high dielectric constant is extrinsic in origin. The main contribution to the static dielectric constant is found to be due to a low frequency (50 1/cm) infrared-active mode which has a large mode effective charge.