Erdem, İsa
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Erdem, Isa Erdem I., Erdem, I.
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ierdem@pau.edu.tr
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17.03. Physics
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| Journal | Count |
|---|---|
| Archives of Materials Science and Engineering | 2 |
| Journal of Alloys and Compounds | 2 |
| Current Applied Physics | 1 |
| Materials Science in Semiconductor Processing | 1 |
| Vacuum | 1 |
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Doctoral Thesis Sn bazlı yarı iletken malzemelerin ilk prensipler yöntemi ile fiziksel özelliklerinin incelenmesi(Pamukkale Üniversitesi Fen Bilimleri Enstitüsü, 2015) Erdem, İsa; Hasan Hüseyin KartBu çalışmada Sn (kalay) bazlı yarı iletken malzemelerin fiziksel özellikleri ab initio simülasyon yöntemi ile incelenmiştir. İlk prensipler yoğunluk fonksiyonel teorisi (DFT) hesapları, PAW (GGA) potansiyellerinin PBE tipi ve US (LDA) potansiyelleri kullanılarak yapılmıştır. SnO2 malzemesinin gözlemlenen altı yapısal fazı vardır. Bütün fazların elastik sabitleri ve bunların basınç ile değişimleri hesaplanmıştır. Hesaplanan yapısal parametreler ve elastik sabitleri elde edilebilen diğer teorik ve deneysel sonuçlar ile uyumludur. Fazlar mekanik olarak kararlıdırlar. GGA ve LDA fonksiyonelleri ile hesaplanan SnO2 rutil fazı enerji band aralığı beklenildiği gibi küçük hesaplanmıştır. SnO2 rutil (tetragonal) fazının fonon dispersiyonları polarizasyondan kaynaklanan frekans kaymaları (LO/TO kayma) dahil edilecek şekilde örgü dinamiği hesapları ile elde edilmiştir. Deney sonuçlarından sapma % 10 mertebelerinde veya daha azdır. Bu sonuçlar örgü dinamiği hesaplamalarında DFT’ nin başarısıdır ve güvenilir olduğunun göstergesidir. Mod frekanslarının basınç davranışları 10 GPa basınca kadar hesaplanmıştır. B1g modunda sonraki yapıya ferroelastik faz geçişinin bir işareti olarak değerlendirilen yumuşama görülmüştür. Kuazi-harmonik yaklaşım yapılarak Gibbs serbest enerjisi, hacim modülü, termal genleşme gibi fiziksel özelliklerin sıcaklık ile değişimleri elde edilmiştir. Gözlemlenen fazların dispersiyonları hesaplanmıştır, bu fazlar termodinamik kararlılık göstermektedirler. Farklı basınçlardaki SnO2 florit yapı dispersiyonları termodinamik olarak kararsızlık göstermektedirler. Sonuç olarak, bazı teorik çalışmaların tersine, florit yapının SnO2’ nin bir fazı olması mümkün görünmemektedir. Physical properties of Sn (tin) based semiconductor materials have been invesitgated via ab initio simulation techniques in this study. First principles DFT calculations have been performed by employing PBE type of PAW (GGA) and US (LDA) potentials. SnO2 has six polymorphs observed. Elastic constants of polymorphs of SnO2 and pressure behavior of them have been calculated. Calculated structural parameters and elastic constants are in good agreement with other available theoretical and experimental studies. These polmorphs are stable mechanically. Calculated band gap energy values of rutile phase of SnO2 using GGA and LDA functionals are underestimated as expected. Phonon dispersions of rutile (tetragonal) structured SnO2 are obtained through lattice dynamics calculations including frequency shifts (LO/TO splitting) due to polarization. Deviations from experimental results are in the rate of 10 % or less. These results indicate that lattice dynamics calculations by DFT are successful and reliable. Pressure behavior of mode frequencies up to 10 GPa pressure are also calculated. Softening of B1g mode has been detected which can be interprated as a sign of ferroelastic phase transition to the following structural phase. Temperature dependences of some physical properties such as Gibbs free energy, bulk modulus, thermal expansivity are obtained by applying quasi-harmonic approximation. The dispersions of polymorphs of SnO2 observed are calculated and they show thermodynamical stability. However, dispersions of florite structure of SnO2 at different pressures show thermodynamical instability. Hence, contrary to some theoretical studies, it seems impossible for florite structure to be a phase of SnO2.Article Citation - WoS: 5Citation - Scopus: 5Point defects in Dirac semimetal BeN4 monolayer and their interaction with gas molecules(Elsevier Ltd, 2024-04) Erdem, Isa; Bilican, Fuat; Kart, Hasan Huseyin; Kart, Sevgi Ozdemir; Ersan, FatihPoint defects in materials may occur during the fabrication process of monolayer materials, or these defects can be created via electron beam irradiation to the perfect crystals. Recently, a triclinic phase of beryllium tetranitride BeN4 was synthesized from elements at ∼85 GPa pressure and can become a monolayer under ambient conditions. In this study, we have introduced various point defects into the BeN4 monolayer such as Be or N mono vacancy (Bevac, Nvac), Be[sbnd]N divacancy (Be[sbnd]Nvac), antisite defect of Be[sbnd]N atomic positions and Stone–Wales (SW) defect, and investigated electronic and magnetic changes in the material. It is found that with the Be vacancy, the Dirac cone of the BeN4 monolayer disappears and the Bevac monolayer shows semi-metallic properties with overlapping valence and conduction bands. N vacancy induces local magnetic moment (0.797 μB) to the structure, and the Nvac monolayer has a direct band gap value of 0.172 eV. While the Be[sbnd]N divacancy turns the structure to metal, the antisite-defected BeN4 monolayer turns into a non-magnetic semiconductor with a band gap value of 0.256 eV. Furthermore, we have introduced bare and defected BeN4 monolayers with CO, CO2, H2, H2O and O2 gas molecules and found that these molecules give rise to crucial effects on the electronic and magnetic properties of the materials. While the considered molecules are physisorbed on the bare BeN4 monolayer, the H2O molecule dissociated to OH and H on the Nvac structure, and O2 molecule strongly binds on Nvac and antisite BeN4 monolayers. Furthermore, we have reported that the antisite BeN4 monolayer may be a good candidate material for hydrogen storage devices with an adsorption energy of 0.355 eV of the H2 molecule. We believe that our theoretical findings will be beneficial for further experimental and theoretical studies on BeN4 structure. © 2024 Elsevier LtdArticle Citation - Scopus: 10First principles studies of SnO at different structures(2010) Erdem, İsa; Kart, H.H.; Cagin, T.Purpose: Structural and mechanical properties of the Sn (tin) based oxides SnO and SnO2 are investigated. The aim of this study to determine in which structural phase SnO is found and to calculate its elastic constants at different pressures. Design/methodology/approach: Calculations have been made for three different structures of SnO by density functional theory (DFT). The behavior of structural parameters (lattice constants, internal parameters) and bulk modulus under different pressures, and elastic constants are calculated by using ab initio calculations. Generalized Gradient Approximation (GGA) and Perdew-Burke-Ernzerhof (PBE) parameterization is used. Findings: All of six elastic constants of litharge SnO and three elastic constants of rocksalt structure of SnO are calculated for the first time in this study. Among three structures of SnO, namely, rocksalt, cesium chloride and tetragonal litharge, the most energetically favorable one is the litharge structure at ambient conditions. The calculation of enthalpies with respect to pressure shows that any phase transition from litharge to rocksalt structure does not occur by applying the pressures of up to 5 GPa to the systems. Equilibrium volume, energy and bulk modulus of rutile SnO2 are also calculated. Our results are compared with other available experimental data and theoretical results. Research limitations/implications: Computer calculation speeds and its information storage area are limitations, it will be possible to reach experimental results as near as in condition that they are improved. Practical implications: It is very difficult to measure elastic constants especially under high pressure experimentally. However, they are calculated by first principles calculations. Originality/value: Behavior of elastic constants and structural parameters under high pressures are determined for the first time in this study. Simulations can lead experimentalist to find new applications of these technologically important materials. © International OCSCO World Press. All rights reserved. 2010.Article Citation - WoS: 27Citation - Scopus: 29High pressure phase transitions in SnO2 polymorphs by first-principles calculations(Elsevier Ltd, 2014-02) Erdem, I.; Kart, H. H.; Cagin, T.The structural and mechanical properties of SnO2 polymorphs are investigated by the calculations of first-principles density functional theory (DFT) which employs Generalized Gradient Approximation (GGA) parameterized by Perdew-Burke-Ernzerhof (PBE). Structural parameters are in good agreement with experimental and other theoretical results. Pressure induced phase transitions have occurred in the following sequence: the rutile-type › the CaCl 2-type at 7.59 GPa, the CaCl2-type › the ?-PbO2-type at 11.50 GPa, the ?-PbO2-type › the pyrite-type at 18.70 GPa, the pyrite-type › the ZrO 2-type at 25.69 GPa, the ZrO2-type › the cotunnite-type at 32.71 GPa, the cotunnite-type › the fluorite-type at 19.70 GPa. The mechanical properties of these polymorphs such as bulk modulus B0 and its first derivative B0' and the elastic stiffness constants of them are calculated. It is shown that the results determined in this study are compatible with the experimental and other theoretical calculations. © 2013 Elsevier B.V. All rights reserved.Article Citation - Scopus: 20First principles investigations of hgx (X=S, Se and Te)(International OCSCO World Press, 2016-05-01) I., Düz; I., Erdem; S., Ozdemir Kart; V., KuzucuPurpose: The aim of this study is to determine the structural, and mechanical properties of Hg chalcogenide materials (HgX; X=S, Se, Te) in the zinc-blende structure which are presented as promising candidates for modern optoelectronic and spintronic applications. The dependence of elastic constants of pressure for three materials are evaluated. Moreover, isotropic mechanical properties such as bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are obtained. Design/methodology/approach: First principles calculations based on Density Functional Theory are performed by employing Projector Augmented Waves potentials. The electronic exchange and correlation function is treated by using Generalized Gradient Approximation parametrized by Perdew, Burke and Ernzerhof (PBE96). Findings: Calculated results of structural and mechanical properties are in good agreement with those of experimental and other theoretical studies. This three materials in zinc-blende structure are mechanically stable. İsotropic mechanical properties are also obtained. Resistance against both linear strain and shear strain and ductility decrease as we go into the sequence of HgS?>HgSe?>HgTe. The wave velocities and Debye temperatures calculated for this materials. Debye temperatures are founded for HgS, HgSe and HgTe as 306.21 K, 264.30 K and 240.19 K, respectively Research limitations/implications: Calculation speeds of the computers and data storage are some limitations. Also, the lack of experimental data hinder for the comparison of our results. Practical implications: Obtaining high pressure elastic constants by calculations is preferable since it is very difficult or even impossible to measure them by experimentally. Originality/value: There are only restricted number of investigation of elastic constants of mercury chalcogenides both theoretically and experimentally. © International OCSCO World Press. All rights reserved. 2016.Master Thesis Spin-1/2 ısing modelinin creutz cellular automaton programının incelenmesi(Pamukkale Üniversitesi Fen Bilimleri Enstitüsü, 2006) Erdem, İsa; Mestan KalayDoğrusal boyutu L=10, 12 olan örgülerde en yakın komşu spin etkileşmelerini içeren beş boyutlu Ising modelinin Creutz ''cellular automaton'' ında simülasyonlar yapılmaktadır. Daha önce yapılan beş boyutta Ising modelinin Creutz ''cellular automaton'' simülasyonlarından farklı olarak demon sayısı artırılmış ve simülasyonların bir kısmı da dış manyetik alanın varlığında gerçekleştirilmiştir. Bunları yapabilmek için simülasyon programı detaylı bir şekilde incelenmiş ve gerekli değişiklikler yapılmıştır. Dış manyetik alanın varlığında üç bitli ve dört bitli demonlar kullanılarak elde edilen sıcaklık değerleri ve bu sıcaklık değerlerine karşılık gelen manyetizasyon değerleri hesaplanmış ve sonucun ortalama alan teorilerinin öngördüğü şekilde olduğu ve artık H=0' ın Tc kritik sıcaklığında faz geçişi olmadığı görülmüştür. İkinci olarakta yine L=10, 12 örgü uzunlukları için simülasyonlar demon sayısı dörde artırılarak yapılmıştır. Sıcaklığa karşı manyetizasyon, Binder parametresi, öz ısı ve manyetik alınganlık grafikleri çizilmiştir. Binder parametresi L=10 ve L=12 eğrilerinin kesişme noktasından kritik sıcaklık Tc=8,7797(9) olarak bulunmuş ve bunun da daha önce yapılan beş boyutlu çalışmalarla uyumlu olduğu gözlenmiştir.Article Citation - WoS: 10Citation - Scopus: 10DFT study on phase transition behavior and mechanical properties of HgSe polymorphs under high pressure(Elsevier B.V., 2018-04) Duz, I.; Kart, S. Ozdemir; Erdem, I.; Kuzucu, V.Total energy calculations based on density functional theory are performed for HgSe in the ambient and pressure induced phases. The electronic exchange and correlation effects are described by employing the generalized gradient approximation together with the projector augmented wave potentials. The equation of state parameters and the phase transition paths are obtained from the energy-volume landscape and enthalpy versus pressure data, correspondingly. The observed phase transition sequence of HgSe as ZB › Cinnabar › RS › Cmcm and the final transition from Cmcm to CsCl structure predicted by the other theoretical study are confirmed by our calculations. The pressure dependence of elastic constants of the structures considered in this study is reported. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Debye temperature as isotropic mechanical properties are evaluated for HgSe polymorphs. Our calculations of energy band structure reveal the inverted band structure evoking that HgSe in ZB phase is a semimetal. © 2018 Elsevier B.V.Article Citation - WoS: 4Citation - Scopus: 5Density functional theory study of tin and titanium dioxides: Structural and mechanical properties in the tetragonal rutile phase(Elsevier Ltd, 2014-12) Erdem, I.; Kart, H. H.Structural and mechanical properties in rutile (tetragonal) phases of SnO 2 and TiO 2 are investigated by performing first-principle density functional theory (DFT) calculations. Generalized Gradient Approximation (GGA) potentials of electronic exchange and correlation part parameterized by Perdew-Burke-Ernzerhof (PBE) are used. Second order elastic stiffness constants, bulk modulus, first-derivative of bulk modulus, and pressure behavior of these mechanical properties are studied up to pressure of 10 GPa. Structural properties and elastic constants of SnO 2 and TiO 2 calculated in this study are compatible with experimental and other available theoretical studies. Electronic band gap energies of these semiconductors are also calculated. As expected, the calculated values by standard DFT calculations are underestimated in comparison to experimental values. © 2014 Elsevier Ltd. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 8First principles lattice dynamics study of SnO2 polymorphs(Elsevier Ltd, 2015-06) Erdem, I.; Kart, H. H.; Cagin, T.The structural properties of SnO2 polymorphs in the sequential order of observed phases in experiments are determined by the density functional theory (DFT) calculations based on local density approximation (LDA) of ultra soft pseudo potentials (US-PPs). Phonon dispersion relations are calculated by the lattice dynamics calculations. Shifts in the infrared (IR) active optical modes due to polarization (LO/TO splitting) are also calculated. Moreover, softening of B1g mode at the rutile-CaCl2 second-order ferroelastic phase transition is confirmed. Thermal properties, such as temperature behavior of bulk modulus and thermal expansion in the rutile phase are obtained by employing quasiharmonic approximation (QHA). They are in good agreement with the available experimental results. Dynamic stabilities of SnO2 polymorphs except for the rutile phase are checked for the first time by using phonon dispersions. The rutile, CaCl2, pyrite, ZrO2 and cotunnite type structures have shown thermodynamical stability. The cause of ?-PbO2 phase showing nearly stability is discussed in the light of experimental studies. However, the fluorite type structure is definitely instable even at different pressures. It may not be one of SnO2 polymorphs. © 2015 Elsevier B.V. All rights reserved.