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Register a new userThe third-order elastic moduli and pressure derivatives for AlRE (RE=Y, Pr, Nd, Tb, Dy, Ce) intermetallics with B2-structure: A first-principles study
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The third-order elastic moduli and pressure derivatives of the second-order elastic constants of novel B2-type AlRE (RE=Y, Pr, Nd, Tb, Dy, Ce) intermetallics are presented from first-principles calculations. The elastic moduli are obtained from the coefficients of the polynomials from the nonlinear least-squares fitting of the energy-strain functions. The calculated second-order elastic constants of AlRE intermetallics are consistent with the previous calculations. To judge that our computational accuracy is reasonable, the calculated third-order constants of Al are compared with the available experimental data and other theoretical results and found very good agreement. In comparison with the theory of the linear elasticity, the third-order effects are very important with the finite strains are lager than approximately 3.5%. Finally, the pressure derivative has been discussed.
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We have investigated the finite temperature elastic properties of AlRE (RE=Y, Tb, Pr, Nd, Dy) with B2-type structures from first principles. The phonon free energy and thermal expansion is obtained from the quasiharmonic approach based on density-functional perturbation theory. The static volume-dependent elastic constants are obtained from energy-strain functions by using the first-principles total-energy method. The comparison between our predicted results and the ultrasonic experimental data for a benchmark material Al provides excellent agreements. At T = 0K, our calculated values of lattice equilibrium volume and elastic moduli of our calculated AlRE (RE=Y, Tb, Pr, Nd, Dy) intermetallics agree well with the previous theoretical results. The temperature dependent elastic constants exhibit a normal behavior with temperature, i.e., decrease and approach linearity at higher temperature and zero slope around zero temperature. Furthermore, the anisotropy ratio and sound velocities as a function of temperature has also been discussed.
We have performed an ab initio study of the thermodynamical properties of rare-earth-magnesium intermetallic compounds MgRE (RE=Y, Dy, Pr, Tb) with CsCl-type B2-type structures. The calculations have been carried out the density functional theory and density functional perturbation theory in combination with the quasiharmonic approximation. The phonon-dispersion curves and phonon total and partial density of states have been investigated. Our results show that the contribution of RE atoms is dominant in phonon frequency, and this character agrees with the previous discussion by using atomistic simulations. The temperature dependence of various quantities such as the thermal expansions, bulk modulus, and the heat capacity are obtained. The electronic contributions to the specific heat are discussed, and found to be important for the calculated MgRE intermetallics.
The phonon and thermodynamic properties of rare-earth-aluminum intermetallics AlRE (RE=Y, Gd, Pr, Yb) with B2-type structure are investigated by performing density functional theory and density functional perturbation theory within the quasiharmonic approximation. The phonon spectra and phonon density of states, including the phonon partial density of states and total density of states, have been discussed. Our results demonstrate that the density of states is mostly composed of Al states at the high frequency. The temperature dependence of various quantities such as the thermal expansions, the heat capacities at constant volume and constant pressure, the isothermal bulk modulus, and the entropy are obtained. The electronic contribution to the specific heat is discussed, and the presented results show that the thermal electronic excitation affecting the thermal properties is inessential.
First principles calculations of rare earth (RE)-doped LaSi3N5 host lattice are performed to obtain the electronic structure, the band gap (BG), and the character of electronic transitions. Doping with both trivalent and bivalent RE cations is inspected. RE 4f states form two bands of occupied and unoccupied states separated by ~5 eV. In RE3+-doped compounds 4f states are shifted by ~6 eV to more negative energies compared with RE2+-compounds. This stabilization causes that RE3+ 4f bands are in a different position relative to the valence band and the conduction band than RE2+ 4f bands and therefore different electronic transitions apply. BG of RE3+-compounds decreases from ~4.6 eV (Ce) to ~0.5 eV (Eu). Except for Ce3+, exhibiting the 4f-5d transition, other RE3+-compounds show the charge transfer of the p - 4f character. BG of RE2+-compounds increases from ~0.80 eV (Ce, Pr) to ~0.95 eV (Nd, Pm), ~1.43 eV (Sm), and ~3.28 eV (Eu) and the electronic transition is of the 4f-5d character. The energy level scheme constructed from ab initio calculated electronic structures agrees well with the experimental energy level diagram. The agreement demonstrates the reliability of the hybrid functional HSE06 to describe correctly bands of nonbonding RE 4f electrons.
The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe3 family of charge density wave (CDW) compounds via specific heat, magnetization and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe3 indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.
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