Investigation of the Structural, Elastic, Electronic, and Optical Properties of Half-Heusler CaMgZ (Z = C, Si, Ge, Sn, Pb) Compounds

A DFT study of the synthesized MAX phase Zr2SeC has been carried out for the first time to explore its physical properties for possible applications in many sectors. The studied properties are compared with prior known MAX phase Zr2SC. The structural parameters (lattice constants, volume, and atomic positions) are observed to be consistent with earlier results. The band structure and density of states (DOS) are used to explore the metallic conductivity, anisotropic electrical conductivity, and the dominant role of Zr-d states to the electrical conductivity at the Fermi level. Analysis of the peaks in the DOS and charge density mapping (CDM) of Zr2SeC and Zr2SC revealed the possible variation of the mechanical properties and hardness among them. The mechanical stability has been checked using elastic constants. The values of the elastic constants, elastic moduli and hardness parameters of Zr2SeC are found to be lowered than those of Zr2SC. The anisotropic behavior of the mechanical properties has been studied and analyzed. Technologically important thermodynamic properties such as the thermal expansion coefficient (TEC), Debye temperature (ΘD), entropy (S), heat capacity at constant volume (Cv), Gruneisen parameter (γ) along with volume (V) and Gibbs free energy (G) are investigated as a function of both temperature (from 0 to 1600 K) and pressure (from 0 to 50 GPa). Besides, the ΘD, minimum thermal conductivity (Kmin), melting point (Tm), and γ have also been calculated at room temperature and found to be lowered for Zr2SeC compared to Zr2SC owing to their close relationship with the mechanical parameters. The value of the ΘD, Kmin, Tm, and TEC suggest Zr2SeC as a thermal barrier coating material. The optical properties such as dielectric constant (real and imaginary part), refractive index, extinction coefficient, absorption coefficient, photoconductivity, reflectivity, and loss function of Zr2SeC are computed and analyzed to reveal its possible applications.

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Newly synthesized MAX phase Zr2SeC: DFT insights into physical properties towards possible applications

https://escholarship.org/content/qt6vd0f9tp/qt6vd0f9tp.pdf?t=qzd04g

Neighborhood-level COVID-19 hospitalizations and mortality relationships with built environment, active and sedentary travel.

The electronic structure, structural stability, mechanical, phonon, and optical properties of Zr2GaC and Hf2GaC MAX phases have been investigated under high pressure using first-principles calculations. Formation enthalpy of competing phases, elastic constants, and phonon calculations revealed that both compounds are thermodynamically, mechanically, and dynamically stable under pressure. The compressibility of Zr2GaC is higher than that of Hf2GaC along the c-axis, and pressure enhanced the resistance to deformation. The electronic structure calculations reveal that M2GaC is metallic in nature, and the metallicity of Zr2GaC increased more than that of Hf2GaC at higher pressure. The mechanical properties, including elastic constants, elastic moduli, Vickers hardness, Poisson’s ratio anisotropy index, and Debye temperature, are reported with fundamental insights. The elastic constants C11 and C33 increase rapidly compared with other elastic constants with an increase in pressure, and the elastic anisotropy of Hf2GaC is higher than that of the Zr2GaC. The optical properties revealed that Zr2GaC and Hf2GaC MAX phases are suitable for optoelectronic devices in the visible and UV regions and can also be used as a coating material for reducing solar heating at higher pressure up to 50 GPa.

/pdf/ab-initio-predictions-of-structure-and-physical-properties-3m0en76qov.pdf

Ab initio predictions of structure and physical properties of the Zr2GaC and Hf2GaC MAX phases under pressure.

Screen the thermomechanical and optical properties of the new ductile 314 MAX phase boride Zr3CdB4: A DFT insight

The novel ternary carbides and nitrides, known as MAX phase materials with remarkable combined metallic and ceramic properties, offer various engineering and technological applications. Using ab initio calculations based on generalized gradient approximation (GGA), local density approximation (LDA), and the quasiharmonic Debye model; the electronic, structural, elastic, mechanical, and thermodynamic properties of the M2GaC (M = Zr, Hf) MAX phase were investigated. The optimized lattice parameters give the first reference to the upcoming theocratical and experimental studies, while the calculated elastic constants are in excellent agreement with the available data. Moreover, obtained elastic constants revealed that both the Zr2GaC and Hf2GaC MAX phases are brittle. The band structure and density of states analysis showed that these MAX phases are electrical conductors, having strong directional bonding between M-C (M = Zr, Hf) atoms due to M-d and C-p hybridization. Formation and cohesive energies, and phonon calculations showed that Zr2GaC and Hf2GaC MAX phases' compounds are thermodynamically and dynamically stable and can be synthesized experimentally. Finally, the effect of temperature and pressure on volume, heat capacity, Debye temperature, Gruneisen parameter, and thermal expansion coefficient of M2GaC (M = Zr, Hf) are evaluated using the quasiharmonic Debye model from the nonequilibrium Gibbs function in the temperature and pressure range 0-1600 K and 0-50 GPa respectively.

https://www.mdpi.com/1996-1944/13/22/5148/pdf

Structural Stability, Electronic, Mechanical, Phonon, and Thermodynamic Properties of the M2GaC (M = Zr, Hf) MAX Phase: An ab Initio Calculation.

The high-power impulse magnetron sputtering (HiPIMS) technique is widely used owing to the high degree of ionization and the ability to synthesize high-quality coatings with a dense structure and smooth morphology. However, limited efforts have been made in the deposition of MAX phase coatings through HiPIMS compared with direct current magnetron sputtering (DCMS), and tailoring of the coatings’ properties by process parameters such as pulse width and frequency is lacking. In this study, the Cr2AlC MAX phase coatings are deposited through HiPIMS on network structured TiBw/Ti6Al4V composite. A comparative study was made to investigate the effect of average power by varying frequency (1.2–1.6 kHz) and pulse width (20–60 μs) on the deposition rate, microstructure, crystal orientation, and current waveforms of Cr2AlC MAX phase coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to characterize the deposited coatings. The influence of pulse width was more profound than the frequency in increasing the average power of HiPIMS. The XRD results showed that ex situ annealing converted amorphous Cr-Al-C coatings into polycrystalline Cr2AlC MAX phase. It was noticed that the deposition rate, gas temperature, and roughness of Cr2AlC coatings depend on the average power, and the deposition rate increased from 16.5 to 56.3 nm/min. Moreover, the Cr2AlC MAX phase coatings produced by HiPIMS exhibits the improved hardness and modulus of 19.7 GPa and 286 GPa, with excellent fracture toughness and wear resistance because of dense and column-free morphology as the main characteristic.

Guangze Tang

Papers

Ab initio predictions of structure and physical properties of the Zr2GaC and Hf2GaC MAX phases under pressure.

Structural Stability, Electronic, Mechanical, Phonon, and Thermodynamic Properties of the M2GaC (M = Zr, Hf) MAX Phase: An ab Initio Calculation.

Fabrication and Mechanical Properties of Cr2AlC MAX Phase Coatings on TiBw/Ti6Al4V Composite Prepared by HiPIMS.

Ab-initio predictions of phase stability, electronic structure, and optical properties of (0001)-MAX surfaces in M2AC (M = Cr, Zr, Hf; A = Al, Ga)

Theoretical predictive screening of noble-metal-containing M3AuC2 (M = Ti, V, and Cr) MAX phases