First principles investigation of lattice dynamical properties of Cu-based chalcopyrite semiconductors and high dielectric constant materials
Küçük Resim Yok
Tarih
2008
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Yayıncı
Bolu Abant İzzet Baysal Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bakır tabanlı üçlü yarıiletkenlerin yapısal, elastik ve örgü dinamiği özelliklerinin basınca bağımlılığı ve çok yüksek genişlikte düşük frekans dielektrik sabitli bazı perovskite yapıların elektronik, yapısal ve dielektrik özelliklerinin temel ilkelerden incelenmesi olarak iki konu çalışmayı planlamıştık.Öncelikle kalkopirit yarı iletkenler CuGaSe2 and CuAlS2'nin hacime bağlı elastik ve örgü dinamiği özellikleri üzerine ab initio hesaplamalar yaptık. Hesaplamalar yerel yoğunluk yaklaşımı çerçevesinde norm korunumlu sanal potansiyeller ve düzlem dalga tabanı kullanılarak gerçekleştirilmiştir. Born etkin yük tensörleri, dielektrik geçirgenlik tensörleri, Brillouin bölge merkezli fonon frekansları ile bunların grüneissen parametreleri, yoğunluk fonksiyonel tedirginme teorisi kullanılarak hesaplandı. Hesaplanan büyüklüklerin grüneissen parametreleri çinkoblende türü yapıların ki ile aynı biçimde olduğu bulundu. Ayrıca hesaplanan elastik-sertlik katsayılarının sanal kübik davranış gösterdiği tespit edildi.Ikinci araştırma konusu olarak, yüksek dielektrik sabitli perovskite türevi oksit Na1/2Bi1/2Cu3Ti4O12 malzemesinin elektronik, dielektrik ve örgü dinamiği özelliklerinin ab initio sonuçlarını rapor ettik. Hesaplamalar yerel spin yoğunluk yaklaşımı, norm korunumlu sanal potansiyeller ve düzlem dalga tabanı kullanılarak yapıldı. Taban durumu direk bant aralıklı antiferromanyetik yarıiletken olarak bulundu. Born etkin yük tensörleri, dielektrik geçirgenlik tensörleri ve Brillouin bölge merkezli fonon frekansları gibi örgü dinamiği özellikleri yerel yoğunluk tedirginme teorisi ile hesaplanarak, daha önce sıklıkla çalışılan CaCu3Ti4O12 ve CdCu3Ti4O12 malzemelerine benzerlik gösterdiği tespit edildi. Hesaplanan elektronik (?o=11.5) ve statik (??=150) dielektrik katsayıları, gözlenen yüksek dielektrik katsayılarının dışsal nedenli olduğunu göstermiştir. Statik dielektrik sabitine temel katkı düşük frekanslı (50 1/cm) yüksek mod etkin yüke sahip kızıl ötesi aktif moddan geldiği bulundu.
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.
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.
Açıklama
Fen Bilimleri Enstitüsü, Fizik Ana Bilim Dalı
Anahtar Kelimeler
Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
