Pressure-driven evolution of structural, mechanical and thermodynamic properties of Zr2GeN and Zr2GeF: a first-principles investigation

The MAX phase has attracted much attention due to its unique properties combined with the merits of both metal and ceramic, including the low density, high electrical conductivity and good oxidation resistance, which makes it significant for possible applications in various high temperature or other environments. There is a lot of research work on Ti2AlX (X=C, N). However little research about thermodynamic properties at high pressure is carried out. So we study the structural, mechanical and thermodynamic properties of Ti2AlC and Ti2AlN at various pressures and temperatures. The first-principles calculations based on electronic density-functional theory framework are used to investigate the properties at various pressures. The cut-off energy is 350 eV. Converged results are achieved with 10102 special K-point meshes. The self-consistent convergence of total energy is set to be 5.010-6 eV/atom. According to the calculated structural parameters at various pressures, we can find that the ratios V/V0 (V0 denotes the system volume at 0 GPa) of Ti2AlX are reduced by 20.59% and 18.93%, respectively, so the compressibility of the system is strong. As the internal pressure increases, the curves of V/V0 become gentle. Then we calculate elastic constants at pressures ranging from 0 to 50 GPa in steps of 10 GPa. It is obvious that the Ti2AlX is mechanically stable because all of the elastic constants satisfy the Born stability criteria. The bulk modulus, shear modulus and Young's modulus linearly increase with internal pressure increasing, implying that the pressure can improve the resistance to volume deformation. The ductility and brittleness can be judged according to Pugh's criterion (ratio of bulk modulus to shear modulus B/G), and the brittle nature turns into ductile nature in a pressure range of 40-50 GPa for the Ti2AlX since the value of B/G exceeds 1.75. Finally, we study the thermodynamic properties at various pressures and temperatures based on the quasi-harmonic Debye approximation theory, including the bulk modulus, heat capacity and thermal expansion coefficient. The bulk modulus decreases with temperature increasing but increases with pressure increasing. The heat capacity at constant volume Cv and the heat capacity at constant pressure Cp have the same variation tendency, while Cv obeys the Dulong-Petit limit. It is easy to see that temperature and pressure have opposite influences on heat capacity and the effect of temperature is more significant than that of pressure. The effects of temperature and pressure on linear expansion coefficient mainly occur at low temperature and the effect of pressure is not so considerable when the pressure exceeds 30 GPa. Above all, the effects of temperature and pressure on thermodynamic properties are inverse.

In order to find a kind of MAX phase material suited for thermal barrier coating (TBC) field, the structural properties, mechanical properties, electronic structure, and thermal properties of Nb2AN (A = Si, Ge, and Sn) MAX phase compounds were studied by density functional theory. The results of cohesive energy, formation enthalpy, elastic constants, and lattice dynamics show that the Nb2AN (A = Si, Ge, and Sn) possess good structural stability, mechanical stability, and dynamical stability. Especially in Nb2SnN phase, although its calculated melting point is not the largest one among them, it possesses the best thermal shock resistance. Its coefficient of thermal expansion fits most suitably to the Ni‐based alloy in 300–1452 K and lowest lattice thermal conductivity force it to be an application prospect TBC material. Its mechanical performance is also good for its own smallest deformation of octahedron structure, highest ductileness, and lowest anisotropy. Electronic structure analysis shows that its lowest Debye temperature comes from its highest ionic degree and lowest covalency. Thus, our research provides a deep theoretical basis for the development of new MAX phase materials.

Study of the structural, mechanical and thermodynamic properties of the new MAX phase compounds (Zr1-xTix)3AlC2

First-principles calculations of the structural, electronic, mechanical and thermodynamic properties of MAX phase Mon+1GeCn (n = 1–3) compounds

Electronic packages are frequently exposed to thermal cycling during their service life between low to high temperature extreme. Similar phenomena can be observed in solder joints during the characterization of thermal-mechanical fatigue behavior. This variation in temperature causes the evolution of mechanical and microstructural behavior of solder joints. Also, dwelling at high temperature extreme causes the mechanical properties reduction of solder joints due to thermal aging phenomena which eventually leads to the change in microstructure. In literature, the effect of thermal aging on the mechanical behavior evolution has been reported by several research groups, but the evolution of mechanical and microstructural properties under different thermal cycling exposure is limited. In our prior study, reduction of mechanical properties of SAC305 lead-free solder material under different thermal cycling exposures have been reported for up to 5 days of thermal cycling. It was found that thermal cycling with long ramp period and dwell time has severe effect on mechanical properties reduction. In our present study, previous study has been extended up to 100 days along with the mechanical behavior evolution of solder joints under stress free condition at different thermal cyclic loading. Particularly, the evolutions of mechanical behavior in both bulk SAC305 miniature solder bar samples and small SAC305 solder balls under stress free condition have been investigated for several thermal cycling profiles, and then the results were compared. Reflow solidification technique with a controlled temperature profile has been used to prepare bulk solder specimens for uniaxial tensile testing. Optical microscopy has been used to figure out the single grain BGA solder balls after grounding and polishing to avoid grain orientation effect during nanoindentation technique. Then, both bulk solder bars and solder balls were thermally cycled between −40 C to +125 °C under a stress-free condition (no load) in a thermal chamber. Several thermal loading were adopted such as (1) 150 minutes cycles with 45 minutes ramps and 30 minutes dwells, (2) air-to-air thermal shock exposures with 30 minutes dwells and near instantaneous ramps, (3) 90 minute cycles with 45 minutes ramps and 0 minutes dwells (thermal ramp only), and (4) Isothermal aging at high temperature extreme (no cycle). After each thermal cycling exposure, mechanical properties evolution of both solder bars and solder balls were recorded in terms of effective elastic modulus (E), hardness (H), yield strength (YS), and ultimate tensile strength (UTS). For the BGA solder balls, the evolution of mechanical properties was measured using nanoindentation. Moreover, mechanical properties evolution of both specimens was compared in terms of normalized properties with respect to elapsed time under different thermal cycling exposures. Finally, the microstructural evolution of bulk solder bars was observed under slow thermal cycling exposures with elapsed time.

An intensive study on structural, electronic mechanical and optical properties of bulk Niobium Dichalcogenides NbX2 (X=S, Se) was carried out using the first principle. The structural parameters such as Equilibrium Lattice Parameters, Volume, Bulk Modulus, and FirstDerivative Modulus were calculated to determine if the materials are energetically stable. Elastic constants were further obtained from which mechanical properties i.e. bulk, Young's and shear moduli and consequently Poisson's ratio were obtained. Based on the well-known Born stability conditions Bulk-NbS2 is most likely mechanically anisotropic ductile material. While Bulk-NbSe2 for the predicted B/G ratio in all three methods is less than a critical value of 1.75, hence this shows that NbSe2 is a brittle material exploring its electronic and optical properties whose motivation was to find out the most stable phase and ascertain if these materials could be used in various fields that suit their mechanical and optical properties. Furthermore, from the calculated optical spectra, plasma frequencies were analyzed which indicated the possibility of applying the material in plasmonic-related fields.

Pressure-induced elastic, mechanical and opto-electronic response of RbCdF3: A comprehensive computational approach

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

MAX phase compounds, combining metallic and ceramic properties, are ideal for high-pressure environments due to their excellent electrical and thermal conductivity, corrosion and oxidation resistance, and damage tolerance. This study investigates the structural, mechanical, electronic, thermal, and optical properties of M4AlC3 (M = Ti, Zr) under hydrostatic pressure. Negative formation energies and positive phonon dispersion confirm thermodynamic and dynamic stability, while mechanical stability aligns with Born's criteria. Increasing stiffness constants and moduli (bulk, shear, Young's), along with Poisson's and Pugh's ratios, suggest enhanced mechanical performance. Ti4AlC3 and Zr4AlC3 are brittle below 60 GPa and 40 GPa, respectively, but become ductile above these pressures. A rising machinability index with pressure supports industrial applicability. Anisotropy is confirmed via 3D plots, and DOS analysis reveals metallic nature. Strong UV absorption and conductivity highlight their potential in UV-optical devices. Reflectivity above 60% and high IR reflectance suggest use in thermal coatings and solar heat management. Increasing Debye and melting temperatures under pressure further indicate their suitability for high-temperature applications. These findings support their use in extreme conditions such as aerospace, deep-sea exploration, and ultra-hard ceramic development.

The structural, mechanical, lattice-dynamic, anisotropic, electronic and thermal properties of M2SX (M=Sc, Y; X=B, C, N) are investigated based on density functional theory. The calculated results indicate that all the phases satisfy the thermodynamic, mechanical and dynamic stability criteria. The mechanical properties are in good agreement with the reported values, and the results show that Sc2SN exhibits the highest bulk modulus B (145.7 GPa), shear modulus (103.0 GPa) and Young’s modulus E (250.0 GPa) with brittle behavior. The elastic anisotropy of M2SX indicates that Sc2SC is the most isotropic among the 6 phases. The electronic structure reveals that Sc2SC and Y2SC are indirect-bandgap semiconductors with 0.927 eV and 1.260 eV bandgap, and the other phases exhibit metallic characteristics. The Debye temperature, lattice thermal conductivity, minimum thermal conductivity, heat capacity and entropy have also been calculated for M2SX phases. The tendency for lattice thermal conductivity in high temperature: K lat (M2SN) > K lat (M2SC) > K lat (M2SB). All the present calculated data will provide useful guidance for development and research on the novel S-based MAX phases in the future.

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, Grüneisen 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.

Prediction of a new Sn-based MAX phases for nuclear industry applications: DFT calculations

First principle calculation of mechanical stability, opto-electronic and thermo-electric properties of TaIrGe1-xSnx(0 ≤ x ≤ 1) Half-Heusler alloy

The widespread implementation of the hydrogen economy demands access to materials with a high weight percentage of hydrogen. Mg-based hydrogen storage alloys have become a research hot-spot in recent years owing to their high hydrogen storage capacity, good reversibility of hydrogen absorption/desorption, low cost, and abundant resources. However, high decomposition temperature of Mg-based hydrideslimits their practical usage. Hydrogen is lightest of all elements, typically it need large volumes or high pressures to store appreciable amount of hydrogen.To overcome these challenges research activities are currently going on metal hydrides and complex hydrides based on transition metal. The main challenges come when endothermic decomposition enthalpy is considered. It becomes difficult to release the hydrogen at ambient thermodynamic conditions. On the other hand, the meta-stable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favourable under the ambient conditions. The good kinetics along with evolution of hydrogen around the room temperature possessed by these materials offer much promise for underground storage and it can be used as a grid energy.The present research specifically focus on transition metal based complex hydrides such as NaMgMnH6 and NaMgFeH6 for hydrogen storage and especially predicted the crystal structure of the same using VASP simulation package. ABCX6 and AB2X6 were taken as reference composition A,B,C and X were substituted with Na, Mg, transition metals(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) and H, respectively.From the ICSD database search the corresponding structural variants were considered as trial structure to predict the ground state structure of these newly designed compounds. using the predicted ground state structure for these compounds, important properties like formation energy, hydrogen site energy, partial density of states(pDOS), electron density(ED), Mulliken effective charge(MEC), Bader electron charge(BEC), Born effective charge, ELF and COHP were calculated. the calculated properties of these compounds were compared with the well known reference compounds. We found that both NaMgMnH6 and NaMgFeH6 are stable with negative formation energy and als othey are semiconductors with the band gap value of 0.51eV and 1.01 eV, respectively. from the calculated electronic structure we found that both these materials are having indirect band behaviour. Analysing the electronic density of states, charge density and various charges mentioned above the chemical bonding behaviour was established as iono-covalent in nature. from the force as well as stress minimisation considering 53 structural variants as input the ground state structure, its space group, equilibrium lattice parameters and atom positions are listed. Also from the energy vs. volume curve for the ground state structure, the equilibrium volume, bulk modulus and pressure derivatives were found out. Among NaMgMnH6 and NaMgFeH6 our spin polarised calculation show that NaMgMnH6 is possesing spontaneous magnetic polarisation with substantial magnetic moment at the Mn site. Among the considered paramagnetic, ferromagnetic, as well as A-, C-,and G- antiferromagnetic configurations the G type antiferromagnetic configuration is found to be the ground state for NaMgMnH6.

First-principles insights into structural stability, elastic anisotropies, mechanical and thermodynamic properties of the Hf[formula omitted]Ge[formula omitted] ([formula omitted], N, and B) 211 MAX phases