Spin Gapless Semiconductor Behavior in d∘-d Half-Heusler CrSbSr: Potential Candidate for Spintronic Application

This study was to investigate theoretically the d°-d Half Heusler compound CrSbSr. We have adopted the first-principles full potential linearized augmented plane waves (FP-LAPW) method within GGA and mBJ-GGA potential. The calculated values of formation energy and elastic constants for the d∘-d HH CrSbSr compound support the thermodynamic and mechanical stability. To the best of our knowledge, there are no available data to compare our results. The calculated lattice parameter and magnetic moments are in good agreement with the available works for VSbSr compound. The electronic structure within the GGA scheme indicates that the d∘-d HH CrSbSr compound exhibits a spin gapless semiconductor behavior. This behavior was improved by using the mBJ-GGA potential, thus this compound can be a potential candidate for spintronic applications. We believe that our predictive results can be useful for future studies.

First-Principles Investigation on Type-II Aluminum-Substituted Ternary and Quaternary Clathrate Semiconductors R8Al8Si128 (R = Cs, Rb), Cs8Na16Al24Si112

Structural and vibrational properties of the aluminium-substituted ternary and quaternary clathrates R8Al8Si128 (R = Cs, Rb), Cs8Na16Al24Si112 are investigated. The equilibrium volume of R8Si136 expands when all Si atoms at the 8a crystallographic sites are replaced by Al. Formation of the Al–Si bond is thus anticipated to correlate with decreased guest vibration modes. Underestimation of the predicted lattice phonon conductivity κL (1.15 W m−1 K−1) compared to a previous experiment (1.9 W m−1 K−1) in Cs8Na16Si136 is thought to arise from our evaluation on the phonon mean free path λ using the “scattering centers” model. Accordingly, we expect that the “three-phonon” processes dominate the determination of the phonon relaxation time, leading to a more reasonable λ in the R8Al8Si128 system. Additionally, the “avoided-crossing” effect causes no appreciable difference in the sound speed for acoustic phonons in this framework. Starting with configuration optimization about aluminium arrangements in Cs8Na16Al24Si112, the calculated lattice parameter agrees well quantitatively with the experiment. The reduced Uiso of Cs from this calculation is anticipated to be primarily related to temperature-dependent quartic anharmonicity. Meanwhile, the predicted κL for Cs8Na16Al24Si112 remains not sensitive to the Al arrangement on 96g Wyckoff sites.

First-Principles Investigation on Elastic Constants of TiN under High Pressure

Elastic constants of NaCl-type TiN under pressure were investigated by first-principles calculations within both local density approximation (LDA) and Perdew-Burke-Ernzerhof generalized-gradient approximation (PBE-GGA). At ambient pressure, the calculated lattice parameter, bulk modulus, and elastic constants of NaCl-type TiN are in well agreement with other available values. Under pressure, all elastic constants,C11,C12, andC44, are found to increase with pressure.C11, which is related to the longitudinal distortion, increases rapidly with pressure whileC12andC44which are related to the transverse and shear distortion, respectively, are much less sensitive to pressure.

FIRST-PRINCIPLE STUDY OF STRUCTURAL AND ELECTRONIC PROPERTIES OF CUBIC STRONTIUM TITANATE

We have performed ab-initio investigation of SrTiO3 with cubic structure, and have computed its structural and electronic properties. The calculations are performed using a plane wave expansion within the local density approximation and the pseudopotential approximation. Results are given for the lattice constant, bulk modulus and charge density. The lattice parameter and bulk modulus calculated for SrTiO3within LDA are 3.908 Å and 184.6832 GPa respectively. It is found that the calculated lattice parameter and bulk modulus are in good agreement with the available experimental data. The charge density plots show higher accumulation of charge around the boundary and corners. All these calculations have been carried out using ABINIT computer code.

Thermodynamic Properties of AlNi Intermetallics under High Pressure

The thermodynamic properties of AlNi are investigated by the full-potential linearized muffin-tin orbital (FP-LMTO) scheme within the generalized gradient approximation correction (GGA) in the frame of density functional theory. The calculated lattice parameter and bulk modulus are in excellent agreement with the experimental and other calculated results. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volumeV/V0on pressureP, cell volumeVon temperatureT, linear thermal expansion α and specific heatCVon temperature and pressure are successfully obtained.

Microstructure and Mechanical Properties of Ca-α-Sialon with Low Oxygen Content

Ca-α-sialons with low oxygen content were fabricated at 1800°C by hot pressing. The phase and microstructure were characterized by XRD and SEM. The calculated lattice parameter reveals that 20~30% Ca2+ ions still exist in the grain boundary phase of Ca-α′. A large amount of Ca-containing liquid phase efficiently promotes the anisotropic growth of α′ grains in Ca-rich composition. Reinforced only by elongated α′ grains, the fracture toughness of Ca-α′ can reach 4.96 MPa•m1/2.

The determination of a stress-free lattice parameter within a stressed material using elastic anisotropy

A method for the calculation of a stress-free lattice parameter from the analysis of diffraction data from stressed material is discussed, utilizing the elastic anisotropy of the material. The technique is demonstrated using data obtained during a uniaxial tension test on untextured austenitic (face-centred cubic) steel. The uncertainty in the calculated lattice parameter for various choices of number of diffraction peaks and different number of stress levels available for the calculation is considered. It is shown that when all the data are within the elastic regime, an accurate evaluation of the reference lattice parameter can be made. When some data are in the plastic regime, a more limited evaluation is possible. The use of plots of lattice parameter against Γhkl[= (h2k2+h2l2+k2l2)/(h2+k2+l2)2] as a method for monitoring plasticity as well as freedom from deviatoric stress is demonstrated.