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Öğe Computational investigations of mechanic, electronic and lattice dynamic properties of yttrium based compounds(World Scientific Publ Co Pte Ltd, 2018) Yildiz, Gokcen Dikici; Yildiz, Yasin Gokturk; Selgin, A. L.; Iyigor, Ahmet; Arikan, NihatElectronic, mechanic and lattice dynamic properties of yttrium-based compounds, X3Y, where X = Pd, Pt and Rh were investigated using the density functional theory. The electronic band calculations demonstrated that X3Y compounds are metallic at the cubic crystal structures. The calculated elastic constants using the energy-strain method indicate that the three materials are mechanically stable. The calculated bulk modulus and Young's modulus values suggest that the Pt3Y is stiffer than that of the other two. The type of bonding and ductility in the X3Y compounds were also evaluated based on their B/G ratios, Cauchy pressures (C-12-C-44) and band structure calculations. These compounds were found to be ductile in nature. The density functional perturbation theory was used to derive full phonon frequencies and total and projected phonon density of states. The computed full phonon spectra for X3Y compounds show that these compounds in the L1(2) phase are dynamically stable. Debye temperature and specific heat of these compounds were also calculated and evaluated using quasi harmonic approximation.Öğe Electronic, Elastic, Vibrational and Thermodynamic Properties of HfIrX (X = As, Sb and Bi) Compounds: Insights from DFT-Based Computer Simulation(SPRINGER, 2020) Arikan, Nihat; Dikici Yildiz, Gokcen; Yildiz, Yasin Gokturk; Iyigor, AhmetAb-initio calculations were performed to reveal and thoroughly understand the structural, electronic, elastic, thermodynamic and vibrational properties of HfIrX (X = As, Sb and Bi) compounds in the C1(b) phase. Basic physical characteristics, such as bulk modulus, pressure derivative of bulk modulus, anisotropy factor, shear modulus, Poisson's ratio, Cauchy pressure, elastic constants and Young's modulus were obtained and some of them were compared with those in the literature. Electronic band structure, the density of states and phonon dispersion curves were obtained and compared with current theoretical calculations. It was concluded according to current band structure calculations that the HfIrAs and HfIrBi compounds showed semimetal characteristics, while the HfIrSb compound behaves as a semiconductor. It was determined based on phonon calculations that all three compounds were dynamically stable. Various thermodynamic properties, such as heat capacity, thermal expansion coefficient values and Gruneisen parameter were calculated under constant volume and constant pressure by using Gibbs2 code within the Quasi-harmonic approach, and these results are discussed.Öğe First-Principles Study on PdMnSn and PtMnSn Compounds inC1(b)Structure(PLEIADES PUBLISHING INC, 2020) Arikan, Nihat; Yildiz, Yasin Gokturk; Yildiz, Gokcen DikiciThe phase stability, the electronic, mechanic and lattice dynamical properties ofC1(b)-type PdMnSn and PtMnSn compounds were investigated using first principles density functional calculations within the generalized gradient approximation. The computed lattice constants of PdMnSn and PtMnSn compounds were in line with the experimental and theoretical data in the published literature. The elastic constants in theC1(b)structure for PdMnSn and PtMnSn compounds were carried out using the energy-strain method. The computed values of three independent elastic constants, both compounds are mechanically stable in theC1-type crystal structure and met the stability criteria. The electronic structure, total and partial density values of states, and total magnetic moment of these compounds were calculated and the evaluations were carried out by comparing with the existing results. Dynamic properties of PdMnSn and PtMnSn compounds were obtained using the density functional perturbation theory. Both of the compounds were dynamically stable due to the absence of the imaginary phonon frequencies. In addition, it was found that the compounds had a rapid rise in specific heat capacities from 0 to 300 K.Öğe Investigation of the Mechanical, Electronic and Phonon Properties of X2ScAl (X = Ir, Os, and Pt) Heusler Compounds(KOREAN PHYSICAL SOC, 2020) Arikan, Nihat; Ocak, Hamza Yasar; Yildiz, Gokcen Dikici; Yildiz, Yasin Gokturk; Unal, RahmiIn the present study, the second-order elastic constants and the electronic band structures of the X2ScAl (x= Ir, Os, and Pt) compounds crystallized in the L2(1)phase were calculated separately by using theab-initiodensity functional theory. According to the results for the second-order elastic constants, these compounds met the Born mechanical stability criteria. Also, according to the Pugh criteria, they were found to have a ductile structure and to show anisotropic behavior. The microhardneses of the compounds were between 2 and 14 GPa, and the highest hardness was found in the Ir2ScAl (14.290 GPa) compound. In addition, the energy band structures of these compounds were calculated, and the crystals were found to have a metallic bond structure. All the computed data were compared with previously calculated results obtained with different methods. According to the findings obtained in the present study, in terms of its mechanical and electronic behaviors, Ir2ScAl was found to have better physical properties than Os2ScAl and Pt2ScAl. The phonon dispersion curves and their corresponding total and projected densities of states were investigated for the first time by using a linear-response approach in the context of density functional perturbation theory. The frequencies of the optical phonon modes of all compounds at the Gamma point were 4.767, 7.504 and 9.271 THz for Ir2ScAl, 2.761, 7.985 and 9.184 THz for Os2ScAl and 2.012, 5.6952 and 8.118 THz for Pt2ScAl. The heat capacityC(v)at constant volume versus temperature was calculated using a quasi-harmonic approach and the results are discussed.
