Insight into Phase Transition,Electronic, Magnetic,Mechanical, and Thermodynamic Properties of TbTe: a DFT Investigation

Theoretical investigation on TbTe for its structural, electronic, magnetic, and thermodynamic stuffs has been carried within density functional theory (DFT) as implemented in WIEN2K code. TbTe was found stable in ferromagnetic phase. The calculated ground-state parameters were found in a good agreement with the experimental data. The compound was found to have a structural stability in cubic B1 (NaCl-type structure) phase, but under the application of high pressure (at 27 GPa), it undergone to B2 (CsCl-type structure) phase of pressure. The second-order elastic constants and mechanical properties like Young’s modulus, Shear modulus, Poisson ratio, Cauchy pressure (C₁₂–C₄₄), and Pugh’s ratio (B/G) were calculated. The present calculations confirmed the ductile nature of TbTe. Further, the thermodynamic investigations have been carried using quasi-harmonic Debye approximation. We have calculated the pressure and temperature dependence of Debye temperature (??_D), bulk modulus (B), thermal expansion (α), heat capacities (C_V), and entropy (S) in the temperature range of 0 to 1000 K and pressure range of 0 to 25 GPa.     

Influence of Oxygen on the Tribomechanical Properties of Single Crystals of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript>

This paper reports a study on the mechanical and tribological properties of ab- and a (b) c?planes of YBa₂Cu₃O_7?δ single crystals. The single crystals were grown using a CuO-BaO self-flux method. The oxygenation effect on the mechanical and tribological properties of ab- and a (b) c?planes is reported. For the ab- plane, the hardness and elastic modulus were around 6 and 50 GPa, respectively. In this case, significant differences were not observed among the hardness and elastic modulus at different oxygenation states. However, the hardness and elastic modulus for as-grown and oxygenated YBa₂Cu₃O_7?δ single crystals were different from that of the a (b) c?plane, and were observed to be slightly higher for the as-grown than for the oxygenated samples. For as-grown and oxygenated samples, we observed hardness values around 4.7 and 2.0 GPa, respectively. Regarding the elastic modulus, the values were 75 and 40 GPa, respectively. The indentation fracture toughness values on the ab- plane for the as-grown and oxygenated YBa₂Cu₃O_7?δ single crystal were 3.7 ± 1.2 and 2.9 ± 1.2 MPa m^1/2, respectively. For the ab- plane, the scratch resistance of the as-grown sample was higher than that of the oxygenated sample and the scratches under load were deeper for the oxygenated sample. As regards the a (b) c?plane, the scar features were seemingly constant through all the scratch lengths and the scratches under load were deeper and larger for the oxygenated than that for the as-grown sample.     

Ab Initio Study of the Electronic Structure,Elastic Properties,Magnetic Feature and Thermodynamic Properties of the Ba<Subscript>2</Subscript>NiMoO<Subscript>6</Subscript> Material

We report first-principles calculations of the elastic properties, electronic structure and magnetic behavior performed over the Ba₂NiMoO₆ double perovskite. Calculations are carried out through the full-potential linear augmented plane-wave method within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient and Local Density Approximations, including spin polarization. The elastic properties calculated are bulk modulus (B), the elastic constants (C₁₁, C₁₂ and C₄₄), the Zener anisotropy factor (A), the isotropic shear modulus (G), the Young modulus (Y) and the Poisson ratio (υ). Structural parameters, total energies and cohesive properties of the perovskite are studied by means of minimization of internal parameters with the Murnaghan equation, where the structural parameters are in good agreement with experimental data. Furthermore, we have explored different antiferromagnetic configurations in order to describe the magnetic ground state of this compound. The pressure and temperature dependence of specific heat, thermal expansion coefficient, Debye temperature and Grüneisen parameter were calculated by DFT from the state equation using the quasi-harmonic model of Debye. A specific heat behavior C_V?≈?C_P was found at temperatures below T = 400 K, with Dulong–Petit limit values, which is higher than those, reported for simple perovskites.     

Electronic Structure,Phase Stability,and Elastic Properties of Inverse Heusler Compound Mn<Subscript>2</Subscript>RuSi at High Pressure

The structural, magnetic, electronic, and elastic properties of the new Mn-based Heusler alloy Mn₂RuSi at high pressure have been investigated using the first-principles calculations within density functional theory. Present calculations predict that Mn₂RuSi in stable \(F\bar {4}3m\) configuration is a ferrimagnet with an optimized lattice parameter 5.76 Å. The total spin magnetic moment is 2.01 μ _B per formula unit and the partial spin moments of Mn (A) and Mn (B) which mainly contribute to the total magnetic moment are 2.48 and ?0.66 μ _B, respectively. Mn₂RuSi exhibits half metallicity with an energy gap in the spin-down channels. The study of phase stability indicates that the elastic stiffness coefficients of Mn₂RuSi with \(F\bar {4}3m\) structure satisfy the traditional mechanical stability restrictions until up to 100 GPa. In addition, various mechanical properties including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio along with elastic wave velocitieshave also been obtained and discussed in details in the pressure range of 0–100 GPa based on the three principle elastic tensor elements C ₁₁, C ₁₂, and C ₄₄ for the first time.     

Elastic properties of thorium ceramics ThX (X = C,N, O,P, As,Sb, S,Se)

The elastic constants (C ₁₁, C ₁₂, and C ₄₄) of all the known cubic binary phases of thorium with non-metals, ThX (X = C, N, O, P, As, Sb, S, Se), have been calculated using the full-potential linearized augmented plane wave (FLAPW) method with an exchange-correlation potential in the generalized gradient approximation (GGA). Numerical estimates of elastic parameters of the corresponding polycrystalline ceramics (bulk compression modulus, shear modulus, Young’s modulus, Poisson’s ratio, and Lamé’s coefficients) are obtained and analyzed for the first time.     

Vacancies in as-grown CZ silicon crystals observed by low-temperature ultrasonic measurements

By means of the low-temperature ultrasonic measurement, we try to observe the elastic softening due to the vacancies in as-grown silicon crystals grown by the Czochralski (CZ) method. We prepared a high-resistivity CZ silicon crystal ingot comprising the following defect-regions: the void region, the region of ring-like oxidation stacking fault, the Pv-region, the Pi-region, and the region of the dislocation clusters. Both of the elastic constants C ₄₄(T) and [C ₁₁(T) ? C ₁₂(T)]/2 measured for the samples taken from the Pv-region exhibit the softening of the type C _Γ(T) = C _Γ ⁽⁰⁾ [1 ? Δ_JT/(T ? Θ)] which was also found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. No response of the softening to the applied magnetic field is found, as in our previous case of the non-doped FZ silicon. The observed softenings are attributed to the triply degenerate T ₂ states of the vacancy accommodating two electrons with anti parallel spins. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration.     

Measurements of LiNbO<Subscript>3</Subscript> Properties by Multi-parameter Inversion Based on Acoustic Microcopy

This paper expands on a theoretical model between the mechanical and electrical properties with acoustic characteristics to obtain the theoretical dispersion curve for Y-cut LiNbO₃ piezoelectric plate. The experimental dispersion curve of the LiNbO₃ plate is extracted via V(f,z) analysis through defocusing measurements based on an acoustic microscopy and a lens-less line focusing transducer. The objective function of the inversion depends on the experimental dispersion curve. The inversion method adopts a hybrid particle-swarm-based simulated-annealing (PS-B-SA) optimization, which is used for joint inversion of the mechanical and electrical parameters of LiNbO₃. The theoretical dispersion curve will approach the experimental dispersion curve by constantly modifying the mechanical and electrical parameters in the theoretical model: the elastic constants (C₁₁, C₁₂, C₂₂, C₂₃, C₂₅, C₅₅), piezoelectric constants (e₁₁, e₁₂, e₂₆, e₃₃), and dielectric constants (ε₁₁, ε₂₂). The inversed series of constants are those who make the theoretical dispersion curve most fit the experimental ones. The results show that the inversed mechanical and electrical parameters agree well with the reported values, and the stability and accuracy of the inversion is acceptable. This research provides a useful tool to characterize the mechanical and electrical properties of piezoelectric materials simultaneously.     

First-Principles Prediction of Structural,Magnetic, Electronic,and Elastic Properties of Full-Heusler Compounds Co<Subscript>2</Subscript>YIn (Y = Ti,V)

Density functional theory based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, magnetic, electronic, and elastic properties of Heusler alloys Co₂YIn (Y = Ti, V). It is shown that the calculated spin magnetic moments using the local spin-density approximation (LSDA), generalized gradient approximation (GGA), LSDA + U, and Tran–Blaha (TB)-modified Becke–Johnson (mBJ)-local density approximations (LDA) are in good agreement with the Slater–Pauling rule. The obtained results with LSDA, GGA-PBE, and LSDA + U of the density of states illustrate that both compounds have a metal behavior; however, mBJ-LDA predicts Co₂VIn alloy to be a half metal. The band structure obtained with mBJ-LDA has an indirect band gap along the Γ–X symmetry with energy of 0.4 eV for Co₂VIn, and E _F lies in the middle of the gap; the electrons at the Fermi level are fully spin-polarized. The calculation of elastic properties indicates the stability of these compounds, and they have a ductile behavior. The 3D dependences of Young’s modulus exhibit a strong anisotropic character. The high values of the elastic constant C ₁₁ reflect the strength of the bonding Ti (V)–In.     

Study of Half-Metallic Ferromagnetism in Be0.75Ti0.25Y (Y = S,Se, and Te) Using Ab Initio Calculations: Potential Candidate for Spintronic Devices

The structural, elastic, electronic, and magnetic properties of Be_0.75Ti_0.25Y (Y = S, Se, and Te) have been investigated to understand their potential applications in spintonic devices. Crystals of BeS, BeSe, and BeTe, individually doped with Ti with a dopant concentration of x = 0.25, have been evaluated by using full-potential linearized augmented plane-wave plus local orbital method within the framework of density functional theory. We employed the Wu–Cohen generalized gradient approximation for optimizing the crystal structure and evaluating elastic properties. In order improve bandgap values and optical parameters, the modified Becke and Johnson (mBJ) potential has been employed. The theoretical investigation of band structure and density of states confirms the half-metallic ferromagnetic nature of these compounds. The elastic constants are calculated by the charpin method which shows that the compounds under consideration are brittle and anisotropic. Moreover, it is noted that tetrahedral crystal field splits the 3d state of Ti into triple degenerate t_2g and double degenerate e_g states. The exchange splitting energies Δ _x (d) and Δ _x (pd) and exchange constants (N ₀ α) and (N ₀ β) are predicted from triple degenerate t_2g states, and negative values of N ₀ β justify that the nature of effective potential is more attractive in spin down case rather than that in the spin up case. We also find the crystal field splitting (ΔE _crystal = E _t2g?E _eg) energy and reduction of the local magnetic moment of Ti from its free space charge value and creation of small local magnetic moments on the non-magnetic Be, S, Se, and Te sites by p–d hybridization.     

Structural,Elastic, Thermodynamic,Electronic, and Magnetic Investigations of Full-Heusler Compound Ag<Subscript>2</Subscript>CeAl: FP-LAPW Method

Structural, elastic, thermodynamic, electronic, and magnetic properties of the full-Heusler compound Ag₂CeAl were determined using generalized gradient approximation with exchange-correlation functional GGA (PBEsol) with spin-orbit coupling (SOC) correction. The elastic modulus and their pressure dependence are calculated. From the elastic parameter behavior, it is inferred that this compound is elastically stable and ductile in nature. Through the quasi-harmonic Debye model, in which the phononic effect is considered the effect of pressure P (0 to 50) and temperature T (0 to 1000) on the lattice constant, the elastic parameters, bulk modulus B, heat capacity and thermal expansion α, internal energy U, entropy S, Debye temperature ??_D, Helmholtz free energy A, and Gibbs free energy G are investigated. The thermodynamic properties show that the compound Ag₂CeAl is a heavy fermion material. The density of state (DOS), magnetic momentum, and band structure are computed, to investigate the magnetic and metallic characteristics. The calculated polarization of the compound is 77.34%. The obtained results are the first predictions of the physical properties for the rare-earth-based (Ce) full-Heusler Ag₂CeAl.     

First-Principles Study the Electronic and Thermodynamic Properties for CoBi<Subscript>3</Subscript> Superconductor

The electronic, elastic, and thermodynamic properties of CoBi₃ superconductor are investigated by means of first-principles calculations along with the quasi-harmonic Debye model. Our results reveal that the calculated lattice constants are in good agreement with the experimental data. The electronic density of states (DOS) in the vicinity of the Fermi level are dominated by Co- 3d and Bi- 6p states, which are crucial for superconductivity. The elastic constants of CoBi₃ superconductor are calculated, and the bulk modulus, shear modulus, and Young’s modulus have been evaluated. In addition, the ductility behavior is also predicted. Finally, using a quasi-harmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter are obtained.     

Theoretical Study of Structural,Magnetic, Elastic,Phonon, and Thermodynamic Properties of Heusler Alloys Fe<Subscript>2</Subscript>Cr<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = Al,Ga)

First-principle calculations based on generalized gradient approximation and quasi-harmonic Debye model were executed to analyze the structural, magnetic, elastic, phonon, and thermodynamic properties of Fe₂CrX (X = Al, Ga) Heusler alloys. The computed lattice parameters concurred well with available experimental and theoretical data. The calculated elastic constants reveal that the Fe₂CrAl is brittle and Fe₂CrGa is ductile. The phonon dispersion relation of Fe₂CrX (X = Al, Ga) are calculated using finite displacement method with a cutoff radius of 5 Å. We likewise explored the thermodynamic properties by utilizing quasi-harmonic Debye model in which bulk modulus, heat capacity, Debye temperature, Grüneisen parameter, and thermal expansion coefficient are resolved at 0–30 Gpa pressure and 0–900 K temperature from the non-equilibrium Gibbs functions.     

Calculation of thermodynamic properties of SF<Subscript>6</Subscript> including the critical region. Thermal functions and speed of sound

Specific heats C _v and C _p, entropy S, enthalpy H, and speed of sound W have been calculated using a new thermal equation of state with a small number of variable constants, which includes regular and scale contributions with a new transition function. The calculation results correspond to the accuracy level of the modern reference equations of state with a large number of determined parameters in the regular behavioral region of SF₆ properties; in the critical region, these results make it possible to supplement the existing reference data with the related tables, taking into account the scaling-theory advances. The experimental and tabular data on C _v, C _p, S, H, and W have not been used to determine the constants of the calculation equations (except for isochoric specific heat, C _v, in the ideal-gas state). These data have been applied only for comparison of the calculated values with the experimental and tabular values. To calculate the behavior of thermal properties in the critical region, universal critical indices α, β, and γ have been used according to the threedimensional Ising model. The mean error in describing thermal properties of SF₆ does not exceed the error of the existing experimental data. The calculated values coincide with the modern reference data in the regular region in the entire range of gas and liquid states. The discrepancies in the critical region are due to the application of the scale equation of state (in contrast to the regular equations used previously in this region for composing reference tables).     

Kinetics of Competitive Sorption in Decontamination of Materials from Radionuclides

kinetic model of the mass transfer of a microcomponent in the simplest competitive system from the sorbed state (A) into a solution (B) and then into a sorbent (C) in accordance with the scheme A ? B ? C was formulated within the framework of competitive sorption statics. The kinetic equations were solved numerically. The influence exerted by the weight of competing sorbents А and С and by the degree of reversibility of linear reactions on the nonequilibrium decontamination factor K_dec(t) was determined. The time in which the equilibrium decontamination factor is attained for the model of chemical sorption kinetics was estimated from the experimental data on the rate constants of direct and reverse heterogeneous reactions and on the distribution coefficients of Cs(I) in the SiO₂ (A)–CsCl solution (B)–Prussian Blue (C) system.     

Insight into Structural,Electronic, Magnetic,Mechanical, and Thermodynamic Properties of Actinide Perovskite BaPuO<Subscript>3</Subscript>

In this paper, we have performed a systematic investigation on structural, magnetic, electronic, mechanical, and thermodynamic properties of BaPuO₃ perovskite within density functional theory (DFT) using generalized gradient approximations (GGA), onsite coulomb repulsion (GGA + U), and modified Becke-Johnson (mBJ). The calculated structural parameters were found in good agreement with the experimental results. A large value of magnetic moment equal to integer value of 4 μ_B was obtained for the compound. The spin-polarized electronic band structure and density of states present 100% of spin polarization at Fermi level, resulting in half-metallic nature for the compound with spin-up states as metallic and spin- down states as a semiconducting. The elastic and mechanical properties have also been predicted. Moreover, we have calculated thermodynamic properties like Debye temperature (??_D), specific heat (C_V), entropy (S), etc. using quasi-harmonic Debye model.     

Structure and properties of superhard materials based on aluminum dodecaboride α-AlB<Subscript>12</Subscript>

The structures and mechanical properties of materials based on α-AlB12 without additives and with additions of carbon and titanium carbide sintered under high (2 GPa) pressure and by hot pressing (30 MPa) in the contact with hexagonal BN. The light materials were obtained having high hardness, fracture toughness, ultimate strengths at bending, R _bm , and compression. The addition of 17 wt % C to α-AlB₁₂ and sintering at 30 MPa makes possible to achieve fracture toughness K_Ic (49 N) = 5.9 ± 1.4 MPa·m^0.5, hardness H _V (49 N) = 23.6 ± 2.8 GPa, bending R _bm = 310 MPa and compression R _cs = 423 MPa strengths and specific weight was γ = 2.7 g/cm³. The addition of 20 wt % TiC to α-AlB₁₂ and sintering at 30 MPa resulted in the formation of AlB1₂C₂ and TiB₂, increase of the hardness H _V (49 N) = 28.9 ± 1.9 GPa, R _bm = 633 MPa, R _cs = 640 MPa and γ = 3.2 g/cm³, the K_Ic(49 N) = 5.2 ± 1.5 MPa·m^0.5.     

Study of effect of soft inclusion on the mechanical behavior of soilcrete mixtures: experimental and modeling approaches

The influence of the volume fraction and size of soft soil inclusions on the mechanical behavior of soilcretes was experimentally and numerically investigated. Spherical kaolinite chunks with a specific water content and volume were added to the soilcrete samples during the filling phase of the molds. Different mechanical properties such as the effective static elastic modulus (E) and the unconfined compressive strength (UCS) of soilcrete specimens with different volume fraction of inclusions were determined. E and UCS of soilcrete specimens with different volume fraction of inclusions were also determined using 2D (unit cell) and 3D (digital specimens) finite element models. UCS and E decrease considerably as the volume fraction of soft inclusions increases. Experimental results show that these UCS and E drops are, respectively, about 47% and 20% for a volume fraction of inclusions f_v = 9%. A good agreement between the experimental and simulated data was observed, especially for elastic modulus.     

The Influence of Corundum Content and Sintering Temperature on the Mechanical Properties of CaO–ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Ceramic Composites

We have studied the mechanical properties (Vickers microhardness H_V and fracture toughness K_C) of nanostructured CaO–ZrO₂–Al₂O₃ ceramic composites as dependent on the content of corundum (0 ≤ \(C_{Al_{2}O_{3}}\) ≤ 25%) and the temperature of sintering (1250°C ≤ T₁ ≤ 1500°C). Optimum value of the corundum content (\(C_{Al_{2}O_{3}}\) = 5%) and optimum regime (T₁ = 1300°C, 5 min; T₂ = 1200°C, 4 h) of two-stage sintering are established, which favor attaining the best mechanical characteristics of ceramic composites (H_V = 12.25 GPa, K_C = 8.47 MPa m^1/2).     

Study of the Electronic Structure,Magnetic and Elastic Properties and Half-Metallic Stability on Variation of Lattice Constants for CoFeCr<Emphasis Type="Italic">Z</Emphasis> (<Emphasis Type="Italic">Z</Emphasis> = P,As, Sb) Heusler Alloys

Structural, elastic, magnetic and electronic properties of CoFeCrZ (Z = P, As, Sb) Heusler alloys in their YI-type structure have been computed by density functional theory-based WIEN2k code within generalized gradient approximation for exchange correlation functions. Values of formation energy and elastic constants verify the stability of these alloys. True half metallic ferromagnetic behaviour with 100% spin polarization and good band gap in the minority spin are obtained for all the alloys. Magnetic moment of these alloys is 4.00 μ _B , which matches well with the value predicted from Slater-Pauling rule. Half-metallicity is maintained over a wide range of lattice constants making these alloys promising for spintronics device applications.     

Influence of coronene addition on some superconducting properties of bulk MgB<Subscript>2</Subscript>

This study reports the effect of coronene (C₂₄H₁₂) addition on some superconducting properties such as critical temperature (T_c), critical current density (J_c), flux pinning force density (F_p), irreversibility field (H_irr), upper critical magnetic field (H_c2), and activation energy (U₀), of bulk MgB₂ superconductor by means of magnetisation and magnetoresistivity measurements. Disk-shaped polycrystalline MgB₂ samples with varying C₂₄H₁₂ contents of 0, 2, 4, 6, 8, 10 wt%, were produced at 850 °C in Ar atmosphere. The obtained results show an increase in field-J_c values at 10 and 20 K resulting from the strengthened flux pinning, and a decrease in critical temperature (T_c) because of C substitution into MgB₂ lattice, with increasing amount of C₂₄H₁₂ powder. The H_c2(0) and H_irr(0) values are respectively found as 144, 181, 172 kOe, and 128, 161, 145 kOe for pure, 4 wt% and 10 wt% C₂₄H₁₂ added samples. The U₀ depending on the magnetic field curves were plotted using thermally activated flux flow model. The maximum U₀ values are respectively obtained as 0.20, 0.23 and 0.12 eV at 30 kOe for pure, 4 wt% and 10 wt% C₂₄H₁₂ added samples. As a result, the superconducting properties of bulk MgB₂ at high fields was improved using C₂₄H₁₂, active carbon source addition, because of the presence of uniformly dispersed C particles with nanometer order of magnitude, and acting as effective pinning centres in MgB₂ structure.