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Relaksör-ferroelektrik malzemeler 1950 li yıllarda keşfedilmiştir, birçok uygulamada kullanılmasına rağmen hala bazı mekanik ve elektrik özellikleri tam olarak anlaşılamamıştır. Özellikle ferroelektrik faz geçişlerindeki, mekanik ve elektriksel davranımlarının sıcaklık bağımlılıklarını tam olarak modelleyebilen bir yaklaşım eksikliği vardır. Bu çalışmada, Landau fenomonolojik teori kullanılarak, Mn katkılı PIN-PMN-PT tek kristal karışım malzemenin ferroelektrik rhombohedral-monoklinik faz geçişinde (TC=112 0C) 512 ve 584 cm-1 Raman modları için; kendiliğinden polarizasyon, dielektrik duyarlık ve gevşeme zamanı sıcaklığa bağlı olarak hesaplanmıştır. Landau fenomonolojik teoriden türetilen dielektrik duyarlık bağıntısı, deneysel veriler ile uyumlu sonuçlar vermiştir. Ayrıca, ferroelektrik rhombohedral fazda farklı sıcaklık aralıkları için aktivasyon enerjileri pseuode-spin fonon ve enerji dalgalanma model yaklaşımları kullanılarak hesaplanmıştır. Her iki model kullanılarak hesaplanan sönümleme sabiti değerlerimiz, gözlemlenen verilerle uyumlu çıkmıştır. Relaxor-ferroelectric materials were discovered in the 1950s, and although they are used in many applications, some of their mechanical and electric properties have not fully understood yet. There haven't been an adequate approach that can precisely model the temperature dependencies of their mechanical and electrical behaviour, especially in ferroelectric phase transitions yet. In this study, using Landau phenomenological theory, Mn-doped PIN-PMN-PT single crystal mixture material ferroelectric rhombohedral-monoclinic phase transition (TC=112 0C) for 512 and 584 cm-1 Raman modes; spontaneous polarization, dielectric sensitivity and relaxation time were calculated based on temperature. The dielectric precision correlation derived from Landau phenomenological theory yielded results consistent with experimental data. Furthermore, activation energies for different temperature ranges in the ferroelectric rhombohedral phase were calculated using pseudospin Phonon and energy fluctuation model approaches. Our damping constant values, which were calculated using both models, were good well consistent with the observed data.

Bridgman tekniği ile büyütülen saf, % 0.1 ve % 0.5 bor katkılı InSe tek kristallerinin morfolojik ve optik soğurma özellikleri araştırıldı. Saf, % 0.1 ve % 0.5 bor katkılı InSe tek kristallerinin morfolojik ve optik soğurma özellikleri AFM, SEM ve UV-Vis spektrofotometre teknikleri ile araştırıldı. SEM analizleri geniş yüzeyli yüksek kalitede InSe tek kristallerinin stokiyometrik eriyikten büyüdüğünü gösterdi. Optik soğurma spektrumlarının analizinden saf ve % 0.1 bor katkılı InSe tek kristallerine oranla % 0.5 bor katkılı InSe tek kristalinin eksiton pikinin genişlediği görüldü. Ayrıca, bor katkısı sonucu soğurma şiddetinin azaldığı ve soğurma kenarının daha uzun dalga boyuna doğru kaydığı görüldü. Optik soğurma ölçümlerinden, hem saf hem de bor katkılı InSe tek kristallerinin direkt yasak enerji bant aralığına sahip olduğu gözlendi. Ayrıca, saf InSe tek kristalinin yasak enerji bant aralığına oranla bor katkılı InSe tek kristallerinin yasak enerji bant aralıklarının katkı oranına bağlı olarak azaldığı görüldü., Morphological and optical absorption properties of undoped, 0.1 at% and 0.5 at% boron doped InSe single crystals grown by Bridgman technique were investigated. Morphological and optical absorption properties of undoped, 0.1 at% and 0.5 at% boron doped InSe single crystals have been investigated by AFM, SEM and UV-Vis spectrophotometer techniques. SEM analysis showed that high quality InSe single crystals with large surface area were grown from the stoichiometric melt. From the analysis of optical absorption spectra showed that the exciton peak in 0.5 at% boron doped InSe single crystal expanded by relative to the undoped and 0.1 at% boron doped InSe single crystals. In addition, it was seen that the intensity of absorption decreased and absorption edge shifted to longer wavelengths as a result of boron doping. Optical absorption measurements showed that both undoped and boron doped InSe single crystals had direct forbidden band energies. Also, energy band gaps in boron doped InSe single crystals decreased with increasing boron concentration relative to the energy band gap of undoped InSe single crystal.

In the present investigation, the temperature dependent measurements of dielectric permittivity for 4-propoxy-biphenyl-4-carbonitrile was reported in the nematic region. Temperature-dependent dielectric characterization was carried out over the frequency range of 1 kHz to 1MHz. The compound shows positive dielectric anisotropy in the nematic phase. The dielectric relaxation frequencies corresponding to the molecular rotation around the long axis were measured as a function of temperature. The activation energy of relaxation process was determined by means of the Arrhenius relation., Bu çalışmada, nematik fazdaki 4-propoxy-biphenyl-4-carbonitrile’in sıcaklığa bağlı dielektrik geçirgenliğinin ölçümleri raporlanmıştır. Bu amaçla 1 kHz ila 1MHz frekans aralığında sıcaklığa bağlı dielektrik karakterizasyonu gerçekleştirilmiştir. Sözü edilen malzeme nematik fazda pozitif dielektrik anizotropik özellik göstermektedir. Ayrıca uzun eksen etrafında molekül rotasyonuna karşılık gelen dielektrik gevşeme frekansları sıcaklığın bir fonksiyonu olarak ölçülmüş ve gevşeme sürecinin aktivasyon enerjisi Arrhenius metodu vasıtasıyla belirlenmiştir.

Beton yapıların hasar değerlendirmelerinde, çatlak yüzeylerindeki kohezif etkileşimi göz önüne alan modeller, güvenilir ve gerçekçi simülasyonlara olanak tanımışlardır. Kohezif modeller, çatlak arayüzeylerinde, çatlak açılma ve kohezif kapanma gerilmeleri arasındaki dengeyi, betonun çekme yumuşaması özelliği ile birlikte göz önüne almaktadır. Bu çalışma, bu kohezif yaklaşımdan kaynaklanarak, kohezif etkileşimin çatlak yüzeylerinde betonun çekme yumuşaması davranışına göre tanımlandığı bir sonlu eleman modeli geliştirmiştir. Nümerik analizler için ABAQUS programı kullanılmıştır. Sunulan kohezif esaslı modelin etkinliğini gösterme amaçlı, diğer simülasyon Genişletilmiş Sonlu Eleman Metodu’nu kullanarak gerçekleştirilmiş ve iki yaklaşımın sonuçları yapısal parametreler bazında karşılaştırılmıştır. İki yaklaşım sonuçları arasındaki yüksek uyum, sunulan kohezif çatlak yaklaşımının doğruluğunu kanıtlamıştır., In the damage evaluation of concrete structures, the models based on the cohesive interaction between crack surfaces enable reliable and realistic simulations. The cohesive models take into account the equilibrium between crack opening and cohesive closing stresses at crack interfaces with the tension softening property of concrete. This study stemmed from this cohesive approach and developed the finite element model with discrete crack approach in which the cohesive interaction was defined along crack surfaces according to the tension softening behaviour of concrete. ABAQUS program was used for numerical analysis. In order to demonstrate the efficiency of proposed cohesive based approach, the other simulation was conducted by using Extended Finite Element Method and results of these two approaches were compared according to the structural parameters. The good agreement between the results of two approaches proved the accuracy of the proposed cohesive crack approach.

Li containing materials have an important place in the development of technology. Therefore, knowledge of the structural and dynamic properties of electronic Li-containing crystals is important. The structural, electronic and lattice dynamic properties of LiAlSi crystal was performed by an ab-initio pseudopotential method and a linear response with the General Gradient Approximation. LiAlSi crystal is in Zincblende structure and the space group is . The lattice parameter of LiAlSi crystal was 6.0306 A. The computed lattice parameter, bulk modulus and first-order pressure derivative of the bulk modulus agree well with the experimental and other theoretical calculations. The electronic band structure and phonon dispersion curve were analyzed by using the Quantum Espresso program. Phonon dispersion curve and phonon density of states were calculated by a density functional perturbation theory. Since the phonon frequency values are positive values, the LiAlSi crystal is stable. Then, electronic band structure and phonon distribution curve under P= 8.892 GPa pressure were examined. LiAlSi crystal showed semiconductor properties at P = 0.0 GPa pressure, whereas P = 8.892 GPa pressure showed semi-metal properties. At this pressure, the phonon frequency values are also positive. In addition, transverse, longitudinal acoustic and transverse, longitudinal optical mode values at high symmetry points Γ, X and L under two different pressures (P = 0.0 GPa and P = 8.892 GPa) are listed. It is thought that the results of this study will contribute to the literature.

Bu çalışmada, yapısında piezoelektrik (PZT) malzemeden yapılmış prizmatikdolgu içeren dikdörtgen kalın plağın bazı elektro-statik problemleri, üçboyutlu elektro-elastisite teorisinin kesin denklemleri ve parçalı homojencisim modeli çerçevesinde matematiksel olarak modellenmiş ve üç boyutlu sonluelemanlar yöntemi yardımıyla sayısal olarak çözülmüştür. Sayısal çözümüngerektirdiği tüm algoritma ve programlar tarafımızdan yapılmıştır. Ele alınan plağın tüm yanal yüzeylerinden basit mesnetli ve PZT malzemeiçeren dış yanal yüzeylerinden elektrik potansiyelin sıfır olduğu ve karşılıklıiki kenarından düzgün yayılı statik çekme kuvvetinin etki ettiği kabuledilmektedir. Ayrıca, PZT dolgu ile çevresindeki matris malzemesi arasındakiara yüzeyde ideal temas koşullarının sağlandığı kabul edilmektedir. Ele alınan PZT dikdörtgen kalınplağın verilen sınır koşulları, temas koşulları ve yükleme durumu için yapısındaoluşan yer değiştirme ve gerilme yayılımlarına, plağa ait çeşitli malzeme vegeometrik parametrelerin etkileri ile elektriksel ve mekaniksel alanlarınkarşılıklı etkileşiminin tesiri incelenmiş ve tartışılmıştır., In this study, some electro-static problems of rectangular thick platecontaining a prismatic inclusion made of piezoelectric (PZT) material aresolved numerically in the framework of the three dimensional linearized exactequations of electro-elasticity theory using piecewise-homogeneous body modelby using three dimensional finite element method. All algorithms and programsrequired for the numerical solution are made by the authors.It is assumed that the plate is simply supported from all lateralsurfaces and also, electric potential is zero and, ideal contact conditions areprovided at the interface surfaces between the PZT inclusion and the matrixmaterial.The effect of materials and geometric parameters as well as the couple interactionbetween the electrical and mechanical fields of the PZT rectangular thick plateunder the uniaxial tensile force in the given boundary conditions isinvestigated and discussed.

Çoğugeleneksel alaşım tek bir element üzerinde kurulmaktadır. Farklı türlerdeki alaşımelementleri bu ana element üzerine özellikleri geliştirmek amacıyla eklenir veböylece tek bir ana element üzerinde dayanan alaşım aileleri oluşturulur.Yüksek entropili alaşımlarda farklı olarak alaşımlar beş veya daha fazla anaelement içerirler. Yüksek entropi kavramı, sadece bir baskın öğeye dayananklasik alaşımlama yaklaşımı ile elde edilemeyen benzersiz özelliklere sahipgelişmiş malzemeler geliştirmenin yeni bir yolunu ortaya koymaktadır. Bumakale, çekirdek etkileri, fazlar ve kristal yapıları, mekanik özellikler,notasyon ve üretim teknikleri de dahil olmak üzere YEA’ların bazı önemliyönlerini açıklamaktadır., Mostconventional alloys are based on one principal element. Different types ofalloying elements are added to the principal element to improve its properties,forming an alloy family based on the principal element. Unlike this,High-entropy alloys (HEAs) are alloys with five or more principal elements. Theconcept of high entropy introduces a new way of developing advanced materialswith unique properties that cannot be achieved by a classical alloying approachbased on one dominant element. This paper describes some important aspects ofHEAs including core effects, phases and crystal structures, mechanicalproperties, notations, process techniques.

In this study, pure and Co (1%, 3% and 5%) doped ZnO nanoparticles were fabricated through mechanical ball milling technique, which is an inexpensive and easy method. X-ray diffraction and synchrotron-based X-ray absorption spectroscopy measurements were used to determine the crystalline properties and local atomic structures of the obtained nanostructured products. A wurtzite structure was observed for all the samples. X-ray absorption spectroscopy results was clearly indicated that the Co2+ ions were successfully substituted into the Zn2+ sites of the ZnO wurtzite lattice without forming any detectable secondary phases. The present study, investigating the structural properties of Co doped ZnO nanoparticles in detail, could make a significant contribution to the potential use of doped ZnO in both spintronic and other nanotechnological applications., Buçalışmada, katkısız ve Co (%1, %3 ve %5 ) katkılı ZnO nanoparçacıkları ucuz vekolay bir yöntem olan mekanik bilyeli öğütme tekniği ile üretildi. Elde edilennanoyapılı ürünlerin kristal özelliklerini ve yerel atomik yapılarınıbelirlemek için X-ışını kırınımı ve sinkrotron-temelli X-ışını soğurmaspektroskopisi ölçümleri kullanıldı. Tüm örnekler için wurtzite yapısıgözlendi. X-ışını soğurma spektroskopisi sonuçları, Co2+ iyonlarınınsaptanabilir herhangi bir ikincil faz oluşturmadan ZnO wurtzite örgüsündeki Zn2+bölgelerine başarıyla geçtiğini açıkça gösterdi. Co katkılı ZnOnanoparçacıkların yapısal özelliklerini detaylı şekilde inceleyen bu çalışma,katkılı ZnO’nun hem spintronik hem de diğer nanoteknolojik uygulamaalanlarındaki potansiyel kullanımına önemli bir katkı oluşturabilir.

Termoelektrik teknolojisi 19. yüzyıl ortalarından beri biliniyor olmasına karşılık yeterince işlevsel bir kullanım alanına ulaşamamıştır. En yoğun kullanım alanı elektrik üretim alanı değil soğutma alanı olmuştur. Otomobillerde kullanılan küçük buzdolaplarının yapımında, bilgisayar işlemcilerinin soğutulmasında, otomobil egzozlarında oluşan ısıyı elektrik enerjisine dönüştürme amacıyla kullanılmaktadır. Termoelektrik üreteç veya termoelektrik jeneratör ısı enerjisini doğrudan elektrik enerjisine dönüştüren cihazdır. Bu dönüşüme Seebeck etki veya daha genel bir ifade ile termoelektrik etki denir. Yapılan bu çalışmada, termoelektrik dönüştürme elemanlarından oluşan bir termoelektrik jeneratör modül kullanımıyla elektrik enerjisinin elde edilmesi ve bu enerji ile ısıl konfor hedeflenmiştir. Kalorifer radyatörünün ve duvarın yüzey sıcaklığını kullanarak sıcaklık farkı elde edilmiş ve bu sıcaklık farkını elektrik enerjisine dönüştüren termoelektrik jeneratörler ile harici bir kaynağa ihtiyaç kalmadan elektrik enerjisi elde edilmiştir. Üretilen enerjiyi faydalı kullanmak için radyatör kanallarındaki fanlar beslenmiştir. Üretilen enerji ile beslenen fanlar kanallardaki sıcak havayı odaya daha hızlı yayarak oda sıcaklığını daha etkin hale getirmiştir. Sıcaklık farkından, termoelektrik jeneratörler ile oda sıcaklığında 3,24 W güce sahip elektrik enerjisi elde edilmiştir. Üretilen enerjiyi faydalı kullanmak için radyatör kanallarındaki fanlar beslenerek normal oda sıcaklığı 8°C artırılmıştır., Although thermoelectric technology has been known since the middle of 19th century, it has not reached its a functional area. The most intensive use area is not the electricity production area but the cooling area. It is used in the invention of small refrigerators used in automobiles, cooling of computer processors, heat generated in automobile exhausts, and converting it into electrical energy. Thermoelectric generator is the device that converts heat energy directly to electrical energy. This formation is called Seebeck effect or, more generally, thermoelectric effect. In this study, it is aimed to obtain electrical energy by using thermoelectric generator modules and thermal comfort with this energy. Temperature difference is obtained by using the surface temperature of the heating radiator and wall, and with the thermoelectric generators that convert this temperature difference into electrical energy, electrical energy is obtained without the need of an external source. The fans in the radiator ducts were supply in order to utilize the energy generated. The fans supply the energy generated ced make room temperature more efficient by spreading the hot air in the ducts to the room faster. From the temperature difference, the electrical energy with thermoelectric generators at room temperature of 3.24 W was obtained. In order to use the generated energy useful, the fans in the radiator channels are supply and the normal room temperature is increased by 8 ° C.

Bu çalışmada, InTe amorf yarıiletken malzemenin, X ışını difraksiyonu, elektriksel iletkenliği, optik ve dielektrik özellikleriaraştırıldı. X-ışını difraksiyon sonuçları InTe numunesinin amorf yapıya sahip olduğunu gösterir. Numunenin elektrikseliletkenliğinin sıcaklığa bağlılığı araştırıldı ve bulunan sonuçlar numunenin bir amorf yarıiletken olduğunu doğrular. InTenumunesi fotoiletkenlik özellik gösterir. Numunenin optik band aralığı ve optik sabitleri geçirgenlik ve yansıma spektrumlarıkullanılarak hesaplandı. Numunede doğrudan optik geçişler meydana geldi. Numunenin kırılma indisi dispersiyon eğrisi tekosilatör modeline uydu. Numunenin dielektrik özellikleri frekansın ve sıcaklığın bir fonsiyonu olarak araştırıldı. Dielektrikparametrelerin sıcaklık ve frekansla değiştiği bulundu. Elektrik modulus eğrileri dielektrik relaksasyon olayını analiz etmek içinkullanıldı., In this study, X-ray diffraction, electrical conductivity, optical and dielectrical properties of the InTe amorphous semiconductormaterial have been investigated. X-ray diffraction results show that InTe sample has an amorphous structure. Temperaturedependence of electrical conductivity of the sample has been investigated and the obtained results confirm that InTe is anamorphous semiconductor. The InTe sample shows photoconductivity behavior. The optical band gap and optical constants ofthe sample were calculated using transmittance and reflectance spectra. In the sample, the direct optical transitions take placeThe refractive index dispersion curve of the sample obeys the single oscillator model. The dielectrical properties of the samplehave been investigated as a function of frequency and temperature. It was found that the dielectrical parameters were changedwith temperature and frequency. The electrical modulus curves were used to analyze the dielectrical relaxation processes.

The magnetocaloric effect of semimagnetic semiconductors in magnetic field is investigated. Analytical expressions for thermodynamic potential and entropy are found. It appears that the change of entropy is the oscillatory and non-oscillatory part. The change of entropy development according to the temperature was investigated., Magnetik alanda yarımagnetikyarıiletkenlerde magnetokalorik etki incelenmiştir. Termodinamik potansiyel veentropi için analitik ifadeler bulunmuştur. Entropi değişiminin osilasyonu olanve olmayan kısmı olduğu görülmüştür. Entropi gelişiminin sıcaklığa göredeğişimi incelenmiştir.

Magnetik alanda yarımagnetikyarıiletkenlerde magnetokalorik etki incelenmiştir. Termodinamik potansiyel veentropi için analitik ifadeler bulunmuştur. Entropi değişiminin osilasyonu olanve olmayan kısmı olduğu görülmüştür. Entropi gelişiminin sıcaklığa göredeğişimi incelenmiştir., The magnetocaloric effect of semimagnetic semiconductors in magnetic field is investigated. Analytical expressions for thermodynamic potential and entropy are found. It appears that the change of entropy is the oscillatory and non-oscillatory part. The change of entropy development according to the temperature was investigated.

WOS: 000403942800008 The structural, elastic, electronic and vibrational properties of Co3Al and Co3Ta alloys with density functional theory have been investigated. The lattice constants, bulk modulus and its pressure derivative are evaluated and compared with the available data. The numerical first principles calculations of the elastic constants were used to calculate C-11, C-12 and C-44 for Co3Al and Co3Ta alloys. The electronic band structure, electronic total and partial densities of states, and total magnetic moment of the Co3Al and Co3Ta alloys are computed and analyzed in comparison with the existing findings. From the electronic calculations made for both alloys, it was found that the alloys were metallic in nature. Phonon-dispersion curves and their corresponding total and projected densities of states have been obtained for the first time using a linear-response in the framework of the density functional perturbation theory. The frequencies of the optical phonon modes of both alloys are calculated and found to be 4.46, 6.095 and 10.35 THz for Co3Al, 4.83, 6.11 and 6.86 THz for Co3Ta. Finally, specific heat capacity at a constant volume versus temperature CV of Co3Al and Co3Ta alloys is calculated and discussed using the quasi harmonic approximation.

Karbon nanotüpler; yüksek mukavemet ve modül, yüksek elektriksel ve ısıl iletkenlik, nispeten yüksek ve düşük sıcaklıklarda stabilite gibi birçok üstün özelliğe sahip olan düşük yoğunluklu ileri malzemelerdir. Bu malzemeler genellikle toz partikül halinde üretilmekle birlikte, dünyada sınırlı sayıda araştırma merkezinde daha özel bir formu olan eğrilebilir karbon nanotüp veya diğer bir ifadeyle karbon nanotüp elyaf halinde de üretilebilmektedir. Eğrilebilir karbon nanotüpler, son derece ince, mukavim ve iletken olmaları yanında doğrudan eğirme işlemiyle %100 karbon nanotüplerden oluşan iplik haline rahatlıkla dönüştürülebilmeleri bakımından özel bir yere sahiptir. Bu liflerden elde edilen karbon nanotüp iplikler, üstün özellikleri sayesinde aktüatörlerden güneş hücrelerine, esnek Li-iyon pilleri için dokunabilir anotlardan süper iletkenlere varıncaya dek çok farklı alanda teknik amaçlı kullanılabilmektedir. Ancak eğrilebilir karbon nanotüpler ve bunlardan eğrilen iplik özellikleri hakkında bilinenler, dünyada olduğu gibi ülkemizde de sınırlıdır. Bu doğrultuda sunulan çalışmayla eğrilebilir karbon nanotüplerin üretimi, bu özel malzemelerin ipliğe dönüştürülme yöntemleri ve elde edilen teknik ipliklerin genel özellikleri incelenmektedir., Carbon nanotubes are highly special materials having low density but high strength and modulus, high electrical and thermal conductivity and stability at relatively low and high temperatures. While these materials are produced in powder particle form generally, there is also few research centers focusing on production of these advanced materials as spinnable nanofiber form, which is a specific form of carbon nanotubes. These materials, that can be named as spinnable carbon nanotubes or carbon nanotube fibers, are special not only for being extremely fine, having high strength and conductivity but also for their easy conversion into yarns that include 100% carbon nanotubes by spinning directly. Owing to their superior properties, once they spun as twisted yarns, then these materials would have many interesting application areas from actuators to solar cells, from weavable anodes for flexible Li-ion batteries to super conductors. However, available information on carbon nanotube fibers and yarns produced from these are limited both in the world and our country. Therefore, production of spinnable carbon nanotubes and conversion of these special materials into technical yarns along with their general properties are investigated in this work.

A van der Waals three body force rigid shell model (VTRSM) developed earlier for NaCl and CsCl structure was expanded by us for zinc blende structure (ZBS). This model includes the effect of three body interactions and van der Waals interactions in the rigid shell model where short-range interactions were considered up to the second neighbor. Our model thus developed was applied to study the phonon dispersion curves, Debye temperature variation, two phonon Raman/IR spectra, and anharmonic elastic properties of ZnS. Our results are in good agreement with the measured data wherever available.

Nanosized zinc ferrite particles, prepared by spray pyrolysis method, were investigated by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, Fe57 Mossbauer spectroscopy, and vibrating sample magnetometer. The cubic crystalline phases were identified in all samples. The lattice parameter (a = 8.446 Å) and the average particle size of all the samples were determined. The particle sizes increased as the annealing temperature increased from 250 °C to 550 °C. The variation in structural parameters and particle size estimated from X-ray diffraction patterns of heat-treated samples suggested that the synthesized sample was in a `metastable' state or a compositionally constrained state. The Mossbauer spectra of the annealed samples showed a single doublet, thereby indicating the presence of superparamagnetism. Magnetic studies using vibrating sample magnetometer also confirm the superparamagnetic nature of the material.

Multiple quantum-well (MQW) electroabsorptive self electro optic-effect devices (SEEDs) are being extensively studied for use in optical switching and computing. The self electro-optic-effect devices which has quantum-well structures is a new optoelectronic technology with capability to obtain both optical inputs and outputs for Gallium-Arsenide/Aluminum Gallium-Arsenide (GaAs/AlGaAs) electronic circuits. The optical inputs and outputs are based on quantum-well absorptive properties. These quantum-well structures consist of many thin layers of semiconductors materials of GaAs/AlGaAs which have emerged some important directions recently. The most important advance in the physics of these materials since the early days has been invention of the heterojunction structures which is based at present on GaAs technology. GaAs/AlGaAs structures present some important advantages to relevant band gap and index of refraction which allow to form the quantum-well structures and also to make semiconductor lasers, dedectors and waveguide optical switches., Çoklu kuantum çukurlu elektroapsorptiv self elektro-optik cihazlar optik anahtarlama ve hesaplamalarında kullanılması için yoğun bir şekilde araştırılmaktadır. Kuantum çukurlu yapılara sahip self elektro-optik cihazlar, galyum-arsenit/aliminyum galyum-arsenit elektronik devrelerine ait giriş ve çıkış işaretlerinin her ikisinin birden optik olarak elde edildiği yeni bir optoelektronik teknolojidir. Optik giriş ve çıkışlar kuantum çukurlu emme özelliklerine dayanır. Bu kuantum çukurlu yapılar, günümüzde yeni boyutlar meydana getirmekte olan GaAs/AlGaAs'li yarıiletken malzemelerle yapılan pek çok ince katmanlardan meydana gelir. İlk günlerden beri bu malzemelerin fiziğinde bulunan en önemli ilerleme şu anda GaAs teknolojisinin dayandığı farklı jonksiyonlu yapıların keşfidir. GaAs/AlGaAs'li yapılar kuantum çukurlu yapıları oluşturmak ve keza yarıiletken laser, dedektör ve optik dalga klavuzlarına ilişkin anahtarlar yapmak için yasak bant ve kırılma indisi ile ilgili bazı önemli avantajlar sunar.

In the active regions of the semiconductor lasers electrons interact with the electromagnetic fields and exchange their energy states and so the atomic energy levels and meanwhile their excess energy is transferred to optical energy. During this exchange the energy states of electrons change. Because the change of the electron energy states affects the threshold current, this energy change is important in the semiconductor laser band engineering. In this work the behaviour of the energy of the electrons and their eigenstates on the heterojunction semiconductor lasers and so the atomic energy levels are investigated., Elektronlar, yarıiletken lazerlerin aktif bölgelerinde elektromanyetik dalga ile etkileşerek enerji seviyelerini değiştirirler. Elektronlar, elektromanyetik alandan aldıkları enerjiyi optik enerjiye dönüştürürler. Bu dönüşüm esnasında elektronların enerji durumları değişir. Yarıiletken lazerlerde enerji durumlarının değişimi, eşik akımını etkilemesi sebebiyle, yarıiletken enerji bant mühendisliğinde önemli bir yer tutar. Bu çalışmada heterojonksiyon yarıiletken lazerlerde elektronların enerji davranışı ve onların öz enerjileri dolayısıyla atomik enerji seviyeleri incelenmektedir.

The effects of deformation temperature and strain rate to the mechanical properties of Aluminum (Al 99.0) were investigated by tensile experiment at different deformation temperatures and strain rate. At the end of investigation; it was determined that, with increasing deformation temperature, yield and tensile strenghts of the material decrease, strain rate and decrease of area increase, when plastic deformation exponent (n) decreases, strain rate accuracy exponent (m) increases. At a fixed temperature an increase in deformation speed increased all mechanical properties., Alüminyum (Al 99.0), çeşitli deformasyon sıcaklığı ve deformasyon hızlarında çekme deneyine tabi tutularak, deformasyon hızı ve deformasyon sıcaklığının bu malzemenin mekanik özelliklerine etkisi incelenmiştir. İnceleme sonucunda; artan deformasyon sıcaklığı ile malzemenin akma ve çekme mukavemeti değerlerinin azaldığı, birim şekil değiştirme ve kopma büzülmesinin arttığı, plastik deformasyon üssü (n)'in azalırken deformasyon hızı duyarlılığı üssü (m)'in arttığı tesbit edilmiştir. Sabit bir sıcaklıkta ise deformasyon hızının artması, tüm mekanik özellik değerlerini arttırmıştır.

In this paper, a new test method to determine biaxial flexural tensile strength of cement based materials is proposed. A mortar triangular plate specimen is supported on three small spherical silver balls and loaded externally on a small spherical silver ball from the center of gravity of specimen. Yield line theory (YLT), which is a kinematic method of plastic analysis, is used to drive a simple equation for biaxial flexural tensile strength of cement based materials. In order to verify the derived equation, lots of triangular and prism mortar specimens were produced and tested according to the proposed model and three-point flexural test, respectively. Moreover, finite element analysis is also used to verify the derived equation and the results obtained from the experimental studies. It was concluded that FE analysis and experimental studies verified the proposed method and the derived closed-form equation for biaxial tensile strength of cement based materials. Experimental results also exhibited that biaxial tensile strength measured by proposed method is about 22% lower than that of the flexural strength obtained from three-point flexural test.

Karbon nanotüpler; yüksek mukavemet ve modül, yüksek elektriksel ve ısıl iletkenlik, nispeten yüksek ve düşük sıcaklıklarda stabilite gibi birçok üstün özelliğe sahip olan düşük yoğunluklu ileri malzemelerdir. Bu malzemeler genellikle toz partikül halinde üretilmekle birlikte, dünyada sınırlı sayıda araştırma merkezinde daha özel bir formu olan eğrilebilir karbon nanotüp veya diğer bir ifadeyle karbon nanotüp elyaf halinde de üretilebilmektedir. Eğrilebilir karbon nanotüpler, son derece ince, mukavim ve iletken olmaları yanında doğrudan eğirme işlemiyle %100 karbon nanotüplerden oluşan iplik haline rahatlıkla dönüştürülebilmeleri bakımından özel bir yere sahiptir. Bu liflerden elde edilen karbon nanotüp iplikler, üstün özellikleri sayesinde aktüatörlerden güneş hücrelerine, esnek Li-iyon pilleri için dokunabilir anotlardan süper iletkenlere varıncaya dek çok farklı alanda teknik amaçlı kullanılabilmektedir. Ancak eğrilebilir karbon nanotüpler ve bunlardan eğrilen iplik özellikleri hakkında bilinenler, dünyada olduğu gibi ülkemizde de sınırlıdır. Bu doğrultuda sunulan çalışmayla eğrilebilir karbon nanotüplerin üretimi, bu özel malzemelerin ipliğe dönüştürülme yöntemleri ve elde edilen teknik ipliklerin genel özellikleri incelenmektedir Carbon nanotubes are highly special materials having low density but high strength and modulus, high electrical and thermal conductivity and stability at relatively low and high temperatures. While these materials are produced in powder particle form generally, there is also few research centers focusing on production of these advanced materials as spinnable nanofiber form, which is a specific form of carbon nanotubes. These materials, that can be named as spinnable carbon nanotubes or carbon nanotube fibers, are special not only for being extremely fine, having high strength and conductivity but also for their easy conversion into yarns that include 100% carbon nanotubes by spinning directly. Owing to their superior properties, once they spun as twisted yarns, then these materials would have many interesting application areas from actuators to solar cells, from weavable anodes for flexible Li-ion batteries to super conductors. However, available information on carbon nanotube fibers and yarns produced from these are limited both in the world and our country. Therefore, production of spinnable carbon nanotubes and conversion of these special materials into technical yarns along with their general properties are investigated in this work

In this study, the electronic energy levels of GaAs/ InxGa1-xAs/GaAs single square quantum well (SQW) have been analytically calculated. The numerical results have clearly illustrated the electronic energy levels dependency to the SQW structure parameters. Such as, In concentration, the barrier height and the width of the well, Elektro-optik sistemler ve bu alandaki ihtiyaçların karşılanabilmesi için kullanılan yarıiletken materyaller arasında en önemlilerinden birisi de InGaAs üçlü alaşımıdır. InxGa1-xAs üçlü alaşımlarının örgü sabiti GaAs ikili bileşiğinin (x=0, bant aralığı 1,42 eV) ve InAs ikili bileşiğinin (x=1, bant aralığı 0,35 eV) örgü sabitlerinin arasında yer alır. Bu alaşımlar ve daha geniş yasak bant aralıklı yarıiletken çoklu yapıları, yüksek performanslı elektronik ve optoelektronik aygıtların geliştirilmesinde ve kuantum sistemlerinin incelenmesinde çok önemli bir rol oynarlar. InGaAs temelli aygıtlar; foto-diyotları, metal-yarıiletken-metal fotodedektörleri, çoklu yapılı lazerleri, yüzeyden-ışımalı dikey-kavite lazerleri (VSCEL) , resonant tünellemeli yapıları, kauntum tel ve noktalarını, modülasyon katkılı alan etkili transistörleri (HEMT) ve heteroeklem bipolar trasnsistörleri içermektedir. GaAs/ InxGa1-xAs kuantum kuyu yapıları, temel araştırma ve aygıt geliştirmesi ile ilgili çalışmalarda büyük bir öneme sahiptir. Kızılötesi lazerlerde, fotodedektörlerde ve entegre optoelektronik sistemlerde önemli uygulamalara sahiptir. Son yıllarda GaAs temelli 1,3-1,55 µm aralığında uzun dalga boylu yarıiletken lazerler, optik fiber iletiminde ilgi çeker duruma gelmiştir. III-V grubu yarıiletkenlerden olan InAs kızıl ötesi bölgede aktif olduğundan dolayı optoelektronik sistemlerde geniş uygulama alanı bulmuştur. Özellikle yarıiletken teknolojisinde InxGa1-xAs gibi alaşımlar, dedektör yapılarında kullanılmaktadır. Yasak enerji aralığı (0,3-0,4eV) aralığında yüksek mobiliteye sahip olması nedeniyle InAs elektronikte önemli bir yere sahiptir. Ayrıca MBE (Molekular Beam Epitaxy) ve MOCVD (Metal Organic Chemical Vapor Deposition) gibi metotlarla elde edilen III-V yarıiletkenlerinin (InxGa1-xAs gibi) manyetik hassasiyetlerinin yüksek olması onların manyetik mikrosensör üretiminde de kullanılmasını sağlamıştır.Bu çalışmada GaAs/InxGa1-xAs oluşan kare kuyudaki elektron enerji düzeyleri hesaplandı. Sayısal sonuçlar, elektronik enerjinin QW yapı parametrelerine oldukça bağlı olduğunu gösterdi. Ayrıca üniversitemizde bulunan MOCVD tek kristal büyütme merkezi sayesinde artık bu yapıları büyütmek mümkün olduğundan sonuçların deneysel olarak kontrol edilme imkânı da doğmuştur.Anahtar Kelimeler: Elektronik Enerji, Kare Kuyu

Study of magnetic non-uniformities in yttrium-iron garnet by the measuring in method of magneto-optical susceptibility in laser beam with the wave length of l = 1.15 m m.

Within the framework of the dielectric continuum model and Loudon's uniaxial crystal model, the full polar optical phonon modes including the quasi-confined (QC) modes, the propagating (PR) modes, the half-space (HS) modes, and the interface optical (IO) modes in a quasi-one-dimensional (Q1D) wurtzite rectangular quantum wire (QWR) structure are deduced and analyzed. The analytical phonon states, their dispersion equations and polar polarization eigenvectors are derived. Numerical calculation of dispersive spectra for these modes is performed on a wurtzite GaN/AlN rectangular QWR. The behavior of the QC mode reducing to the IO mode is observed clearly in the dispersive curves of these modes, which reveals that the present theories of phonon modes are self-consistency and correct for the description of phonon modes in wurtzite Q1D rectangular NW. These observations and results reveal that the confined dimensionality and cross-section shape influence greatly the dispersive properties of phonon modes in wurtzite quantum confined systems.

This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different thicknesses 2000-6800 Å. The transmittance and reflectance of thin films were measured in the wavelength range 500-1000 nm. It was found that the optical band gap increases with film thickness. Variation of refractive index n and extinction coefficient k with thickness have been studied to analyze optical efficiency of the As2Se3 thin films. The dielectric behavior of the films has also been studied and high frequency dielectric constants \varepsilon\infty has been estimated as a function of thickness of films.

We investigated theoretically the change of electronic properties of Si d-doped GaAs layer as a function of temperature. We studied the influence of temperature on the donor concentration for a nonuniform distribution, which is taken as different from the known Gaussian distribution. In order to obtain the electronic structure we have calculated self-consistent Schrödinger - Poisson equations. We have seen that the change of the electronic properties as dependent on temperature is less pronounced at higher doping concentration.

In this study the structure and the magnetic properties of polymer microspheres, filled with magnetite nanoparticles are investigated. Average particle size of magnetite nanoparticles before and after being introduced into polymer microspheres, and the distance between nanoparticles in the polymer microspheres, are measured. Magnetization curve of polymer magnetic microspheres (PMMS) is determined. The magnetic susceptibility of PMMS with various diameters, and the dependence of PMMS magnetic susceptibility on diameter are determined. Magnetization occurs due to the orientation of PMMS as a magnetic moment. The total magnetic moment of PMMS is the sum of magnetic moments of PMMS sections which consist of magnetic moment chains of magnetite nanoparticles lined up along the diameter and lines parallel to the diameter of the PMMS sections. Analysis of results showed that magnetite nanoparticles are uniformly distributed all over the microspheres and do not aggregate during PMMS synthesis. PMMS is superparamagnetic. Analysis of the dependence of PMMS magnetic susceptibility on the diameter shows that for small diameters (d < 300 m m), all magnetite nanoparticles in chains are lined up along the external magnetic field. That is, all magnetite nanoparticles in chains take part in the magnetization. However, for large diameters, some parts of chains in sections are transformed into clusters, this reduces the length of chains and decreases the magnetic susceptibility of PMMS.

CuAlS2 thin films of thicknesses 118 \pm 5 nm were deposited on glass substrates using chemical bath deposition technique. The details of the preparation method are well described. The method is relatively simple and is easily controlled and sufficient to produce large area and good adherence to the substrate films. Effect of annealing temperature Ta on the structure, and optical properties of CuAlS2 films were investigated. The structures of the films were studied by X-ray diffraction and FTIR spectrophotometer. The optical properties of the films were ascertained by UV-VIS spectrophotometer (wavelengths ranging between 300 and 900 nm). The optical transmittance and absorption were utilized to compute the absorption coefficient, band gap energy and optical constant of the films. Nature of the optical transition of the films has been observed in direct allowed with band gap energies between 2.81 eV and 2.4 eV depending on annealing temperatures. The refractive index and extinction coefficient behavior were found to very affect by annealing temperature.

Based on the dielectric continuum model and Loudon's uniaxial crystal model, the interface-optical-propagating (IO-PR) mixing phonon states of a quasi-zero-dimensional (Q0D) wurtzite cylindrical quantum dot (QD) are investigated. It is found that there are two types of IO-PR mixing phonon modes, i.e. r-IO/z-PR mixing modes and the z-IO/r-PR mixing modes coexisting in Q0D wurtzite QDs. Numerical calculation on a wurtzite ZnO QD shows that the dispersion frequencies of the mixing modes are discrete functions of the azimuthal quantum number and axial wave-number. The calculated results agree well with the recent experimental spectra in ZnO QDs. An abnormal electron-phonon coupling strength is observed with the increase of the azimuthal quantum number and the order of phonon modes, which is attributed to the modulation effect of anisotropic dielectric functions of wurtzite ZnO crystal. The analytical Frölich-like Hamiltonian of electron-phonon interaction obtained here is quite useful for further analyzing phonon influence on optoelectronics properties of wurtzite Q0D QD structures. The present results can be reduced naturally to those of wurtzite quantum wires or quantum wells as the height or radius of cylindrical QD approaches infinity. This supports the validity and unity of phonon modes theories in wurtzite low-dimensional quantum systems.

High-temperature superconducting ceramics systems YBaCuO and BiSrCaCuO, both doped by Pb, Sb, Li, K, Na and non-doped, have been produced by the method of solid phase reaction synthesis. The principle of controlled valency by Vervey has been used to characterize high-temperature superconductors. High-temperature superconducting ceramics have been obtained with properties stable in time by single-purpose doping.

Electrons and polar optical phonons and their interactions are considered in the context of semiconductor quantum well devices, with particular reference to real quantum well laser structures. Distinction is made between wide-barrier and narrow-barrier structures and we explore the implications of these regimes for the description of the electron capture process. Special emphasis is made on the significant effects arising from the large effective mass ratio in AlN/GaN structures.

The theory of optical phonons and their confinement in heterostructures is reviewed with analogies made to the theory of acoustic phonons. The dielectric continuum (DC) model is obtained when bulk dispersion is ignored and the hybrid model is found when dispersion is included. The issue of boundary conditions is investigated and the solutions are shown with comparisons made using electron-phonon scattering.

Fe3+ doped CdS nanoparticles using Mercaptoethanol as a capping agent were prepared by colloidal wet-chemical method. UV-VIS spectra show that Fe-doping can effectively tune energy band structure, i.e. a large blue shift (\sim 30 nm) with increasing Fe concentration. PL measurement of doped CdS nanoparticles shows an additional emission band at \sim 532 nm, which can be due to radiative transition of dopant level to ground state. X-ray diffraction patterns studies revealed cubic crystal phase. TEM micrographs show a spherical shape and nearly well distribution with an average particle size of \sim 4 nm.

Subband and shallow donor binding energies are calculated. The emphasis is given on the electric field effects for wires of different shapes. It is shown that the donor binding energy is sensitive to the interplay of the electric field and geometrical effects.

In this paper we first discuss the operating principle of a ferroelectric liquid crystal film in the surface stabilized configuration, and then examine the switching characteristics using optical measurements performed with a polarizing microscope.

Although Trabzon persimmon (Diospyros kaki L.) is a beneficial fruit for both human health and industrial use, it is generally used seasonally, and inadequate attention has been given to its off-season use. This study was designed to determine the best drying method for optimizing the quality of dried Trabzon persimmon (Diospyros kaki 'Fuyu'). Samples treated with sodium metabisulfite prior to drying and dried at 65 °C had the highest L* value (P < 0.05). Rehydration value and ascorbic acid content of samples dried at 50 °C were the highest. Nevertheless, these samples had lower total phenolic content than samples dried at 65 °C and 90 °C. Samples treated with sodium metabisulfite before drying had the highest appearance score; however, these samples were the least liked and had the lowest flavor score. Control samples were the most popular samples in terms of flavor (P < 0.05). During storage, control group samples had the highest increase in total mesophilic aerobic bacteria, while samples treated with sodium metabisulfite prior to drying had the lowest increase in total mesophilic aerobic bacteria, owing largely to the antimicrobial effect of sodium metabisulfite. Although sodium metabisulfite treatment gave the best physical, chemical, and microbiological results, these dried persimmons were given the lowest sensory scores.

An eletrolyte is proposed for the deposition of black cobalt selective absorber coating on copper plate. The influence of the electrolyte composition and operating parameters on the properties of black cobalt coatings including optical properties were studied. The optimum conditions to obtain a high absorptance/emittance ratio are described.

A transition is being observed from an inhomogeneously broadened photoluminescence band under non-resonant excitation of InAs/GaAs Self-Assembled quantum Dots (SAD's) into up to five phonon-assisted emission bands under selective excitation. A similar effect is obtained from photoluminescence excitation experiments (PLE). We interpret the phonon-assisted PL as being due to a giant efficiency of the Fröhlich interaction between an exciton polarized by strain in the SAD and LO-phonons. The model is consistent with the pronounced p-type polarization of the emission observed in our cleaved-side PL-measurements. Further support is obtained from our calculations in which a different localization of the electrons and holes is assumed: The limiting case of this theoretical framework gives a Huang-Rhys factor of \sim 0.1, which is the same order of magnitude as the experimental value.

In this paper we report the composition dependent of dielectric properties in Se100-xPbx (x = 0, 2, 4, 6 and 10) glassy alloys. The temperature and frequency dependence of the dielectric constants and the dielectric losses in the above glassy systems in the frequency range 1 kHz-5 MHz and temperature range 300-340 K have been measured. It has been found that dielectric constant and the dielectric loss both are highly dependent on frequency and temperature and also found to be increased with increasing concentration of Pb in pure amorphous Se. The results have been interpreted in terms of increase in the density of defect states in the incorporation of Pb as a metallic additive in the aforesaid glassy system. Apart from this, the results have been also correlated in terms of a dipolar model which considers the hopping of charge carriers over a potential barrier between charged defect states.

By using the dielectric continuum approximation, the polar optical phonon modes of coaxial cylindrical quantum cables with arbitrary layer-number were studied. In order to describe the vibrating of the longitudinal-optical (LO) phonons, a set of legitimate eigenfunctions for LO phonon modes are constructed and adopted. In order to deal with the interface optical (IO) phonon modes, the transfer matrix method is employed. The quantized LO and IO phonons fields, as well as their corresponding Fröhlich electron-phonon interaction Hamiltonians, are also derived. Numerical calculations on a four-layer GaAs/AlxGa1-xAs QC have been performed. Results reveal that there are six branches of IO phonon modes. When the wave vector kz in the z direction and the azimuthal quantum number m are small, the dispersion frequencies of IO modes sensitively depend on kz and m, and the frequency forbidden behaviors of IO phonon modes were observed and the reason was analyzed. When kz and m are relatively large, with increasing kz and m, the frequency for each mode converges to the limit frequency value of IO mode in a single heterostructure, and the electrostatic potential distribution of each branch of IO mode tends to be more and more localized at some interface; meanwhile, the coupling between the electron-IO phonon becomes weaker and weaker. The calculation also shows that the phonon modes with higher frequencies have more significant contribution to the electron-phonon interaction. At last, it is found that kz and m have analogous influences on the frequencies and the electrostatic potentials of the IO phonons.

Numerical simulation based on FP-LAPW calculations is applied to study the lattice parameters, bulk modulus and band gap energy of zinc blende binaries AlN, GaN and InN under hydrostatic pressure. The results obtained are in a good agreement with experimental and theoretical values.

In this work, the bulk modulus values for liquid alkali metal alloys near melting point are studied in the framework of the Gibbs-Bogoliubov method. We use the local Heine-Abarenkov pseudopotential and Ichimaru-Utsumi screening function in these alloys. The results are compared with experimental and theoretical results.

By employing the method of electrostatic potential expansion, the interface optical (IO) and surface optical (SO) phonon modes and the corresponding Fröhlich-like electron-phonon-interaction Hamiltonian in a Q1D wurtzite cylindrical quantum well wire (QWW) embedded in nonpolar dielectric matrix are derived and studied based on the dielectric continuum model and Loudon's uniaxial crystal model. Numerical calculations for a wurtzite GaN/AlN QWW are mainly focused on the size- and dielectric-dependent IO and SO phonon spectra and electron-IO (SO)phonons coupling functions. Results reveal that, in general, there are two branches of IO phonon modes and one branch of SO mode in the system. The dispersions of the IO and SO modes are obvious only when the radii ratio b and the dielectric constant of nonpolar matrix ed is small. The limiting frequencies of IO and SO modes for very large b have been analyzed in depth from both physical and mathematical viewpoints. The reducing behaviors of some modes have been clearly observed. Via the discussion of electrostatic potential spacial distributions of the IO and SO modes, we find that the QWW structures and dielectric constants of nonpolar matrix have little influence on the low-frequency IO mode, but they can greatly affect the potential distributions of high-frequency IO mode and SO mode. Detailed comparison of the dispersion behaviors of the modes and electron-phonon coupling properties in the Q1D wurtzite QWWs with those in wurtzite QWs and cubic quantum dots has also been made. Furthermore, part of the theoretical results derived in the present paper is consistent with the relatively experimental conclusion.

Electrical properties of GaTe and GaTe:Cu binary compound semiconductors were investigated by Hall effect and resistivity measurements in the 77-320 K temperature range. Donor and acceptor densities, compensation ratios, acceptor ionization energies, valence band effective mass of holes and effective density of states in valence band were determined for the undoped and Cu doped samples using the single donor-single acceptor analysis of the hole concentration. Temperature coefficient of the hole mobility was determined and compared with related theories.

Singlet axial current form factor g0 A is calculated as a function of bag radius in the two flavor chiral solitonic bag model with unequal quark masses. The value of g0 A near 1 fm is sufficiently small.

We present state of art first-principles study on the static and dynamic properties of BaTiO3, a typical ferroelectric material. Here, structure, equation of state, phase stability, and phase transformations of BaTiO3 studied in Generalized Gradient Approximation. Furthermore, properties such as, Born effective charges, optical dielectric constant and phonon spectra are calculated from Density Functional Perturbation Theory.

The first ab-initio calculations were carried out for the electronic and structural properties of BInN boron ternary alloys. The full potential linearized augmented plane wave (FP-LAPW) method was employed within density functional theory (DFT). We have investigated the lattice parameters and band gap energies. The lattice constant a exhibits a small downward bowing. The calculated band gap variation gives a small bowing in good agreement with the experimental reports. We notice a direct to indirect band gap crossover at x = 0.83.

We study the Wigner crystallization in semiconductor quantum wires within the density functional approach. As the density of electrons in quasi-one-dimensional structures is lowered, we find that the system favors the crystalline phase as envisioned by Wigner.

The temperature dependence of spontaneous magnetization and specific heat for a system of magnons are investigated systematically. The correspondence of this system with the Bose-Einstein condensation phenomenon is used. Calculations are performed for both crystalline bulk materials and thin films. The calculated results are consistent with the available experimental data, indicating that our suggested approach is a suitable one for describing the thermodynamic properties for the magnon system. The thermodynamical parameters for magnons system have many similarities with the thermodynamical parameters for boson atomic gas. Results for crystalline bulk material can be used as a zeroth order approximation in any perturbative treatment of thin film. In contrast to a previous study, our method involves only analytic calculations.

We present structural and electronic properties of the cubic structure for different concentrations x of ternary alloy BxGa1-xN. The computational method is based on the full-potential linearised augmented plane wave method (FP-LAPW). The exchange and correlation energy is described in the local density approximation (LDA) and generalized gradient approximation (GGA). We have investigated the effect of composition on the ground state properties, lattice parameters, bulk modulus, pressure derivative and band gap of the zinc blend BN and GaN. The results obtained are in a good agreement with experimental and theoretical values concerning the variation of the gaps and crossover direct, indirect band gap and the bowing parameter. A reasonable agreement is found from the comparison of our results with other theoretical calculations.