Jinliang Ning

First principle study of elastic and thermodynamic properties of FeB4 under high pressure

The elastic properties, elastic anisotropy, and thermodynamic properties of the lately synthesized orthorhombic FeB4 at high pressures are investigated using first-principles density functional calculations. The calculated equilibrium parameters are in good agreement with the available experimental and theoretical data. The obtained normalized volume dependence of high pressure is consistent with the previous experimental data investigated using high-pressure synchrotron x-ray diffraction. The complete elastic tensors and crystal anisotropies of the FeB4 are also determined in the pressure range of 0–100 GPa. By the elastic stability criteria and vibrational frequencies, it is predicted that the orthorhombic FeB4 is stable up to 100 GPa. In addition, the calculated B/G ratio reveals that FeB4 possesses brittle nature in the range of pressure from 0 to 100 GPa. The calculated elastic anisotropic factors suggest that FeB4 is elastically anisotropic. By using quasi-harmonic Debye model, the compressibility, bulk modulus, the coefficient of thermal expansion, the heat capacity, and the Gruneisen parameter of FeB4 are successfully obtained in the present work.

First principle study of elastic and thermodynamic properties of ZrZn2 and HfZn2 under high pressure

A comprehensive investigation of the structural, elastic, and thermodynamic properties for Laves-phases ZrZn2 and HfZn2 are conducted using density functional total energy calculations combined with the quasi-harmonic Debye model. The optimized lattice parameters of ZrZn2 and HfZn2 compare well with available experimental values. We estimated the mechanical behaviors of both compounds under compression, including mechanical stability, Youngs modulus, Poissons ratio, ductility, and anisotropy. Additionally, the thermodynamic properties as a function of pressure and temperature are analyzed and found to be in good agreement with the corresponding experimental data.

Pressure-induced pseudoatom bonding collapse and isosymmetric phase transition in Zr2Cu: First-principles predictions

The structural evolution of tetragonal Zr2Cu has been investigated under high pressures up to 70 GPa by means of density functional theory. Our calculations predict a pressure-induced isosymmetric transition where the tetragonal symmetry (I4/mmm) is retained during the entire compression as well as decompression process while its axial ratio (c/a) undergoes a transition from ~3.5 to ~4.2 at around 35 GPa with a hysteresis width of about 4 GPa accompanied by an obvious volume collapse of 1.8% and anomalous elastic properties such as weak mechanical stability, dramatically high elastic anisotropy, and low Youngs modulus. Crystallographically, the tetragonal axial ratio shift renders this transition analogous to a simple bcc-to-fcc structural transition, which implies it might be densification-driven. Electronically, the ambient Zr2Cu is uncovered with an intriguing pseudo BaFe2As2-type structure, which upon the phase transition undergoes an electron density topological change and collapses to an atomic-sandwich-like structure. The pseudo BaFe2As2-type structure is demonstrated to be shaped by hybridized dxz + yz electronic states below Fermi level, while the high pressure straight Zr-Zr bonding is accommodated by electronic states near Fermi level with dx(2) - y(2) dominant features.

Theoretical prediction of structural stability, electronic and elastic properties of ZrSi2 under pressure

Structural, elastic, electronic and thermodynamic properties of ZrSi2 have been investigated by means of first-principles plane wave pseudopotential calculations combined with the quasi-harmonic Debye model. We find that the orthorhombic base-centered lattice structure (C49) ZrSi2 is mechanically stable up to 80 GPa according to the elastic stability criteria, and there is a transition from brittle to ductile nature at about 56.5 GPa. The calculated elastic anisotropy factors suggest that ZrSi2 is anisotropic and the degree increases with pressure. In addition, the bonding characteristics are discussed by analyzing the energy band structure, charge density distribution and Mulliken populations. The pressure and temperature dependences of the bulk modulus, specific heat, Debye temperature and thermal expansion coefficient are also discussed through the quasiharmonic Debye model.

Anisotropy in elasticity and thermodynamic properties of zirconium tetraboride under high pressure

The recently predicted ZrB4 with an Amm2 orthorhombic structure has great scientific and technical significance owing to its novel B–Zr–B “sandwich” layer bonding and evaluated high hardness. To better understand the performance of Amm2-ZrB4, its elastic and thermodynamic properties under pressure and temperature are studied here by taking advantage of first principles calculations in combination with the quasi-harmonic Debye model. It is found that ZrB4 keeps brittleness and mechanical stability up to 100 GPa, possessing pronounced elastic anisotropy demonstrated by the elastic anisotropy factors, the direction-dependent Youngs modulus, shear modulus and Poissons ratio. The pressure and temperature dependences of the thermodynamics parameters including normalized volume V/V0, bulk modulus, specific heat, Debye temperature, thermal expansion coefficient and Gruneisen parameter in wide temperature (0–1000 K) and pressure (0–50 GPa) ranges are obtained and discussed in detail.