Thermo-elastic and optical properties of molybdenum nitride

2016 ◽  
Vol 94 (9) ◽  
pp. 902-912 ◽  
Author(s):  
Zainab N. Jaf ◽  
Zhong-Tao Jiang ◽  
Hussein A. Miran ◽  
Mohammednoor Altarawneh
Keyword(s):  
Mechanical Properties ◽  
Bulk Modulus ◽  
Hexagonal Phase ◽  
Harmonic Approximation ◽  
Elastic Stiffness ◽  
Hexagonal Structure ◽  
Cubic Phase ◽  
Slight Variation ◽  
Molybdenum Nitride ◽  
Thermal And Mechanical Properties

This contribution aims to investigate volume-dependent thermal and mechanical properties of the two most studied phases of molybdenum nitride (c-MoN and h-MoN) by means of the quasi-harmonic approximation approach (QHA) via first-principles calculations up to their melting point and a pressure of 12 GPa. Lattice constants, band gaps, and bulk modulus at 0 K match corresponding experimental measurements well. Calculated Bader’s charges indicate that Mo–N bonds exhibit a more ionic nature in the cubic MoN phase. Based on estimated Gibbs free energies, the cubic phase presents thermodynamic stability higher than that detected for hexagonl, with no phase transition observed in the selected T–P conditions as detected experimentally. The elastic stiffness coefficients of MoN in hexagonal structure revealed that it is stable elastically; in contrast to the cubic structure. The temperature dependence on the bulk modulus is more profound on the dense cubic phase than on the hexagonal phase. Overall, the two considered structures of molybdenum nitride display very minimal harmonic effects, evidenced by the slight variation of thermal and mechanical properties with the increase of pressure and temperature. The optical conductivity of both phases near a zero photon energy coincides well with their metallic character inferred by their corresponding DOS curves. It is expected that the thermo-elastic properties of saturated molybdenum nitrides reported in this study will aid in the continuous pursuit to enhance their catalytic and mechanical utilizations.

scholarly journals Systematic Study of the Thermal Properties of Zeolitic Frameworks

2021 ◽  
Author(s):  
Maxime Ducamp ◽  
François-Xavier Coudert
Keyword(s):  
Mechanical Properties ◽  
Thermal Expansion ◽  
Bulk Modulus ◽  
Systematic Study ◽  
Harmonic Approximation ◽  
Negative Thermal Expansion ◽  
Great Influence ◽  
Physical Property ◽  
Thermal And Mechanical Properties ◽  
Wide Range

<div> <div> <div> <p>We report a systematic study of the thermal and mechanical properties of 134 pure SiO2 zeolites through DFT-based calculations by making use of the quasi-harmonic approximation (out of a total of 242 known fully ordered zeolitic frameworks). The comparison of our results with reported experimental data for several zeolites revealed a very good accuracy and validated our simulation methodology. We observe a wide range of thermal expansion coefficients (from −5 to −35 MK−1), highlighting the great influence of the framework topology over this physical property, while demonstrating that all pure-silica zeolites exhibit negative thermal expansion (NTE). Our simulations also provide a path for the computation of the bulk modulus for each structure, as well as its pressure and temperature dependence. Results revealed a large gamut of bulk modulus values (from 8 to 134 GPa), showing that most frameworks display pressure-induced softening — but not all! Finally, this study provides some hints to the open question of experimental feasibility of zeolitic frameworks, showing that the experimentally synthesized structures appear to have a distinct distribution of thermal and mechanical properties. </p> </div> </div> </div>

scholarly journals Systematic Study of the Thermal Properties of Zeolitic Frameworks

2021 ◽  
Author(s):  
Maxime Ducamp ◽  
François-Xavier Coudert
Keyword(s):  
Mechanical Properties ◽  
Thermal Expansion ◽  
Bulk Modulus ◽  
Systematic Study ◽  
Harmonic Approximation ◽  
Negative Thermal Expansion ◽  
Great Influence ◽  
Physical Property ◽  
Thermal And Mechanical Properties ◽  
Wide Range

<div> <div> <div> <p>We report a systematic study of the thermal and mechanical properties of 134 pure SiO2 zeolites through DFT-based calculations by making use of the quasi-harmonic approximation (out of a total of 242 known fully ordered zeolitic frameworks). The comparison of our results with reported experimental data for several zeolites revealed a very good accuracy and validated our simulation methodology. We observe a wide range of thermal expansion coefficients (from −5 to −35 MK−1), highlighting the great influence of the framework topology over this physical property, while demonstrating that all pure-silica zeolites exhibit negative thermal expansion (NTE). Our simulations also provide a path for the computation of the bulk modulus for each structure, as well as its pressure and temperature dependence. Results revealed a large gamut of bulk modulus values (from 8 to 134 GPa), showing that most frameworks display pressure-induced softening — but not all! Finally, this study provides some hints to the open question of experimental feasibility of zeolitic frameworks, showing that the experimentally synthesized structures appear to have a distinct distribution of thermal and mechanical properties. </p> </div> </div> </div>

Observation of Hexagonal AiGaAs Grown by OMCVD

1990 ◽  
Vol 209 ◽  
Author(s):  
D. M. Hwang ◽  
T. S. Ravi ◽  
R. Bhat ◽  
S. Simhony ◽  
C. Y. Chen ◽  
...  
Keyword(s):  
High Resolution ◽  
Quantum Wire ◽  
Gaas Substrate ◽  
Hexagonal Phase ◽  
Stacking Faults ◽  
Hexagonal Structure ◽  
Cubic Phase ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Cladding Layers

ABSTRACTExtended regions of hexagonal zinc sulfide (wurtzite) structure are found to exist in AlGaAs grown by low-pressure OMCVD at 750°C. The specimen was prepared on a (001) GaAs substrate patterned with [110]-orientedV-grooves, intended for a quantum wire laser structure. A high density of planar faults was observed to originate in theAl0.66Ga0.34As cladding layers near the inner corners of the V-grooves and propagate towards the surface along the {111} planes. Many of these faults are stacking faults and microtwins. However, there also exhibit extended regions of hexagonal structure, revealed in electron diffraction patterns and high resolution lattice images. The hexagonal phase shares the same close-packed layers with the cubic phase, i.e., (0001)hexagonal // {111}cubic. The mechanism for the formation of hexagonal structure in this specimen is not yet fully understood.

Transmission electron microscopy studies of boron nitride thin films produced by pulsed laser deposition

1993 ◽  
Vol 51 ◽  
pp. 732-733
Author(s):  
D.L. Medlin ◽  
T.A. Friedmann ◽  
P. B. Mirkarimi ◽  
K.F. McCarty ◽  
M.J. Mills
Keyword(s):  
Boron Nitride ◽  
Phase Distribution ◽  
Hexagonal Phase ◽  
Pulsed Laser ◽  
Hexagonal Structure ◽  
Film Deposition ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Energy Beam ◽  
Deposition Conditions

We are synthesizing boron nitride films by pulsed laser ablation in order to study the deposition conditions necessary to produce the cubic phase (cBN) which has a number of useful applications as a hard coating, semiconductor, and optical material. The yield of cubic material is controlled in part by the simultaneous irradiation of the growing film with a low energy beam of N2 and Arions. In order to understand how this transformation process occurs, we are using TEM to investigate how the microstructure and phase distribution varies with film deposition conditions.In many ways analogous to carbon, boron nitride forms both sp3- and sp2-bonded phases. The cubic phase (cBN), which is sp3 bonded, has the zinc blende structure, and in addition, BN can also form an sp3 bonded hexagonal phase with the wurtzite structure (wBN). An sp2-bonded hexagonal structure (hBN) is the stable room temperature phase, but like its analog, graphite, the sp2-bonded material can also exist in a highly disordered state, often referred to as turbostratic (tBN).

Amorphous Alloys Atomic Structure Investigation by Means of Electron Microscopy and Diffraction

2021 ◽  
Vol 887 ◽  
pp. 254-261
Author(s):  
Evgenii V. Pustovalov ◽  
Aleksandr N. Fedorets ◽  
Vladimir V. Tkachev
Keyword(s):  
Electron Microscopy ◽  
Atomic Structure ◽  
Hexagonal Phase ◽  
Hexagonal Structure ◽  
Electrolytic Deposition ◽  
Cubic Phase ◽  
Total System ◽  
Atomic Order ◽  
Coordination Spheres ◽  
Fourth Coordination

In the paper, the atomic structure of amorphous and nanocrystalline alloys of the electrolytically obtained CoP, NiP, CoNiP, CoW, and CoNiW systems has been studied. The structure was investigated by electron microscopy and diffraction using a Libra 200 HR FE transmission electron microscope at an accelerating voltage of 200 kV within a temperature range of 50-35 °C. The obtained radial atom distribution function and the coordination sphere radii are in good agreement with the data for the cobalt structure in the cubic and hexagonal modifications. The high coordination numbers of the third and fourth coordination spheres allow suggesting a predominantly cubic structure of the local atom environment in CoP samples but somewhat lower, which is explained by the presence of free volume and phosphorus atoms distorting the local structure. When heating, the near atomic order also corresponds to the cubic phase of cobalt, and the ordering occurs in the second, third, and fourth coordination spheres. The data obtained for CoNiP alloys indicate that by configuration, the local atomic environment is closer to the hexagonal structure of nickel. In general, the structure of the CoP-CoNiP system alloy films obtained by electrolytic deposition is already in one of the local minima of the total system energy, which is confirmed by the near atomic order similar to the cubic phase of cobalt or hexagonal phase of nickel. This determines the good stability of the structure and properties during thermal exposure.

Ab initio study of the structural, vibrational and thermal properties of Ge2Sb2Te5

2015 ◽  
Vol 04 (02) ◽  
pp. 1550009
Author(s):  
Henry Odhiambo ◽  
Herick Othieno
Keyword(s):  
Thermal Properties ◽  
Phonon Dispersion ◽  
Hexagonal Phase ◽  
Harmonic Approximation ◽  
Experimental Studies ◽  
Energy Functional ◽  
Residual Entropy ◽  
Cubic Phase ◽  
Phonon Dispersion Curves ◽  
Valence States

The structural, vibrational and thermal properties of hexagonal as well as cubic Ge 2 Sb 2 Te 5 (GST) have been calculated from first principles. The relative stability of the possible stacking sequences of hexagonal GST has been confirmed to depend on the choice for the exchange-correlation (XC) energy functional. It is apparent that without the inclusion of the Te 4d orbitals in the valence states, the lattice parameters can be underestimated by as much as 3.9% compared to experiment and all-electron calculations. From phonon dispersion curves, it has been confirmed that the hexagonal phase is, indeed, stable whereas the cubic phase is metastable. In particular, calculations based on the quasi-harmonic approximation (QHA) reveal an extra heat capacity beyond the Dulong–Petit limit at high temperatures for both hexagonal and cubic GST. Moreover, cubic GST exhibits a residual entropy at 0 K, in agreement with experimental studies which attribute this phenomenon to substitutional disorder on the Sb / Ge / v sublattice.

Mechanical Properties of Nanostructured Hard Coating of ZrO2

2009 ◽  
Vol 1224 ◽  
Author(s):  
Renat F. Sabirianov ◽  
Fereydoon Namavar ◽  
Xiao Cheng Zeng ◽  
Jaeil Bai ◽  
Wai-Ning Mei
Keyword(s):  
Mechanical Properties ◽  
Bulk Modulus ◽  
Physical Vapor Deposition ◽  
Ion Beam ◽  
High Vacuum ◽  
Cubic Phase ◽  
Energetic Ions ◽  
Nano Crystalline ◽  
Crystalline Films ◽  
Strong Adhesion

AbstractNano-crystalline films of pure cubic ZrO2 have been produced by ion beam assisted deposition (IBAD) processes which combine physical vapor deposition with the concurrent ion beam bombardment in a high vacuum environment and exhibit superior properties and strong adhesion to the substrate. Oxygen and argon gases are used as source materials to generate energetic ions to produce these coatings with differential nanoscale (7 to 70 nm grain size) characteristics that affect the wettability, roughness, mechanical and optical properties of the coating. The nanostructurally stabilized chemically pure cubic phase has been shown to possess hardness as high as 16 GPa and a bulk modulus of 235 GPa. We examine the mechanical properties and the phase stability in zirconia nanoparticles using first principle electronic structure method. The elastic constants of the bulk systems were calculated for monoclinic, tetragonal and cubic phases. We find that calculated bulk modulus of cubic phase (237GPa) agrees well with the measured values, while that of monoclinic (189GPa) or tetragonal (155GPa) are considerably lower. We observe considerable relaxation of lattice in the monoclinic phase near the surface. This effect combined with surface tension and possibly vacancies in nanostructures are sources of stability of cubic zirconia at nanoscale.

Atomic structure of interface of intermetallic compound TiAl and nitride Ti2AIN using HREM and image processing

1991 ◽  
Vol 49 ◽  
pp. 570-571
Author(s):  
E. Sukedai ◽  
H. Mabuchi ◽  
H. Hashimoto ◽  
Y. Nakayama
Keyword(s):  
Mechanical Properties ◽  
Image Processing ◽  
Composite Material ◽  
Intermetallic Compound ◽  
Side Surface ◽  
High Resolution Electron Microscopy ◽  
Hexagonal Structure ◽  
Second Phase ◽  
Resolution Electron ◽  
Compound Tial

In order to improve the mechanical properties of an intermetal1ic compound TiAl, a composite material of TiAl involving a second phase Ti2AIN was prepared by a new combustion reaction method. It is found that Ti2AIN (hexagonal structure) is a rod shape as shown in Fig.1 and its side surface is almost parallel to the basal plane, and this composite material has distinguished strength at elevated temperature and considerable toughness at room temperature comparing with TiAl single phase material. Since the property of the interface of composite materials has strong influences to their mechanical properties, the structure of the interface of intermetallic compound and nitride on the areas corresponding to 2, 3 and 4 as shown in Fig.1 was investigated using high resolution electron microscopy and image processing.

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