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Structural and mechanical properties of ZnTe in the zincblende phase

Soykan C., Ozdemir Kart S., Cagin T.

Archives of Materials Science and Engineering

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2010

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Vol. 46, nr 2

115-119

EN

Purpose: The aim of this work investigate to the structural and mechanical properties of ZnTe in the B3 structure, using the ab initio method based on Density Functional Theory (DFT). Design/methodology/approach: The Vienna ab initio Simulation Package (VASP) has been used to perform the electronic structure calculations. The projector-augmented wave formalism (PAW) implemented in this package leads to very accurate result comparable to other all-electron methods. The electronic exchange and correlation functions are treated within DFT by using generalized gradient approximation. Findings: The lattice parameter, bulk modulus, it's pressure derivative and the elastic stiffness coefficients are calculated. Our results for the structural parameters and the elastic constants at the equilibrium phase are in good agreement with the available experimental and other theoretical studies. We have also investigated the pressure dependence of mechanical properties for ZnTe in the structure of B3 to see this effect. Research limitations/implications: These compounds are convenient for many technological applications because of they have direct energy band gaps and property of light emitters at room temperature. Practical implications: These compounds used to many technological applications, such as solid state laser devices, photovoltaic devices, solar cells, remote control systems, thin films, transistors, THz emitter, detector and imaging systems etc. Originality/value: In this work, determination of structural and mechanical properties of ZnTe in the B3 structure at high pressures will lead to new technological applications of these materials.

2

First principles studies of SnO at different structures

Erdem I., Hüseyin Kart H., Cagin T.

Archives of Materials Science and Engineering

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2010

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Vol. 45, nr 2

108-113

EN

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.

3

The effects of boron impurity atoms on nickel ∑ 5 (012) grain boundary by first principles calculations

Kart H. H., Cagin T.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 30, nr 2

177-181

EN

Purpose: Impurity atoms in the grain boundary can be responsible for embrittlement or they can strengthen a material. In this work, we have modeled the effect of B impurity on ∑ 5 (012) symmetrical tilt grain boundary in Ni by using first principle quantum-mechanical calculations. The grains can either be pushed apart or pulled together depending on the size of the impurity and nature of the local relaxations. Design/methodology/approach: The calculations were carried out by using the Vienna ab-initio simulation package VASP with the projector augmented wave (PAW) potentials within generalized gradient approximation (GGA). K-space sampling is performed using a 2x2x1 Monkhorst Pack scheme for Brillouin-zone integration in all model systems. The Methfessel-Paxton smearing method with 0.1 eV smearing width is used for the determination of partial occupancies for each wave function. Findings: It is found that the extension of the nickel grain boundary is due to the repulsion of the segregated and neighboring B atoms. Moreover, the effects of tensile strength loaded uniaxially along the (012) direction are analyzed when the impurity atoms of B are substituted into the ∑ 5 (012) symmetrical tilt grain boundary in Ni. Our calculations are compatible with the other first principle calculations. Research limitations/implications: Cohesive energy calculations indicate that interstitial sites are preferred to substitutional sites and that B leads to cohesive enhancement. Originality/value: The effects of boron impurity atoms on nickel ∑ 5 (012) grain boundary by first principles calculations were evaluated.

4

Molecular dynamics study of Cu-Pd ordered alloys

Özdemir Kart S., Erbay A., Kiliç H., Cagin T., Tomak M.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 1

41-46

EN

Purpose: The goal of the paper is to study the molecular dynamics of Cu-Pd ordered alloys. Design/methodology/approach: The thermal and mechanical properties of Cu, Pd pure metals and their ordered intermetallic alloys of Cu3Pd(L12) and CuPd3(L12) are studied by using the molecular dynamics simulation. The melting behavior of the metals considered in this work is studied by utilizing quantum Sutton-Chen (Q-SC) many-body potential. The effects of temperature and concentration on the physical properties of Cu-Pd system are analyzed. Findings: A wide range of properties of Cu, Pd pure metals and their Cu3Pd and CuPd3 ordered intermetallics is presented. It was found that this potential is suitable to give the general characteristics of the melting process in these systems. Practical implications: The simulation results such as cohesive energy, density, elastic constants, bulk modulus, heat capacity, thermal expansion and melting points are in good agreement with the available experimental data and other theoretical calculations. Originality/value: To the best our knowledge this work presents, for the first time, a wide range of physical properties of alloys focusing on Cu-Pd ordered compounds.

5

Mechanical and electronical properties of ZnS under pressure

Bilge M., Özdemir Kart S., Kart H. H., Cagin T.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 1

29-34

EN

Purpose: The wide-gap semiconductor materials are very important for application in the fields of optical device technology. ZnS is wide-gap semiconductor that is attractive material due to the polymorphic structural transformation and it is suitable semiconductor for applications in infrared optics, ultraviolet laser devices, electronic image display, high-density optical memory, solar cell etc. The goal is to evaluate mechanical and electrical properties of ZnS dunder pressure. Design/methodology/approach: We report ab-initio calculations of lattice constants, bulk modulus and elastic constants of the B1 (rocksalt), B3 (zincblende) and B4 (wurtzite) structures of ZnS. Ab-initio calculations are based on the density functional theory (DFT) within generalized gradient approximation (GGA) for the exchange-correlation potential. Findings: Phase transition pressures from B4 phase to B3 phase, from B3 phase to B1 phase and from B4 phase to B1 are predicted from intersection of the enthalpy-pressure data for the three phases. These results are consistent with the experimental and other theoretical calculations. Mechanical properties of ZnS under high pressure are also calculated. It is seen that the mechanical properties of ZnS under high pressure are quite different from those ambient condition. The band structure, density of states (DOS) and energy gaps are also given for B3 structure of ZnS. Research limitations/implications: The results are compared with the previous theoretical and experimental data. Originality/value: Evaluation of mechanic and electronical properties of ZnS under pressure.