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In this paper, theoretical investigations of structural, elastic and thermal properties of Zn3P2 material were done using Quantum ESPRESSO code based on density functional theory. The generalized gradient approximation (GGA) exchange correlation-functional helped to model the atomic interaction. First, the structural optimization procedure was carried out, and hence, the optimized structural parameters were utilized to obtain six independent elastic constants C 1 1 , C 1 2 , C 1 3 , C 3 3 , C 4 4 , and C 6 6 for the Zn3P2 tetragonal structure. Accordingly, these elastic constants were used to determine the elastic moduli such as the Bulk modulus, Young's modulus, and shear modulus, as well as other mechanical parameters such as Pugh's ratio, Poisson's ratio, anisotropic ratio, sound velocities and Debye temperature. Calculations of thermodynamic properties such as vibrational energies, vibrational free energies, and fixed volume heat capacities, were performed within the implementation of the Thermo_pw code. Elastic calculations confirmed that this compound is characterized by mechanical stability at zero pressure and 0K temperature, ionic bonding, a high degree of anisotropy, and typical ductility. An observable increase in Debye vibrational energies, entropies and constant volume heat capacities of this compound with increasing temperature was detected throughout the thermodynamic calculations, unlike vibrational free energy which revealed a pronounced decrease as temperature increased. [ABSTRACT FROM AUTHOR]

In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using density functional theory (DFT). The full-potential linearized augmented plane-wave (APW) in the framework of the generalized gradient approximation as used as implemented in the Wien2k package. The temperature dependence of thermal expansion coefficient, bulk modulus and heat capacity in a wide range of temperature (0-1600 K) were investigated. The calculated elastic properties of the compounds show that both intermetallic compounds of AlNi and AlNi3 have surprisingly negative Poisson's ratio (NPR). The results were compared with other experimental and computational data. [ABSTRACT FROM AUTHOR]

Vacancy plays a crucial role in mechanical properties of transition metal borides (TMBs). However, the influence of vacancy on hardness of TMBs is unknown. In this paper, the relationship between boron vacancy and mechanical properties of CrB4 is investigated by first-principle calculations. Two different vacancies including boron monovacancy (MV) and boron bivacancy (BV) are considered. We find that CrB4 with boron MV is more stable than that of boron BV. The removed atom weakens the deformation resistances, and reduces the elastic stiffness and hardness. The calculated shear modulus, Young's modulus and theoretical hardness of boron MV are larger than that of boron BV. The reason is that the removed atom weakens the localized hybridization between B and B atoms, and damages the 3D-network B-B covalent bond. However, the bulk modulus of B is slightly larger than that of perfect CrB4. This reason is attributed to the formation of triangular pyramid bonding in B vacancy. [ABSTRACT FROM AUTHOR]

A comparative study on the structure stability and elastic properties for various types of tungsten tetraboride (4) has been carried out with the generalized gradient approximation (GGA) and local density approximation (LDA) in the framework of density functional theory (DFT). Five types of 4 are considered i.e., orthorhombic Immm, Pnnm, Pmmn, monoclinic C2/m and hexagonal P63/mmc structure. Our calculations indicate that the P63/mmc-4u structure of 4 is unstable at both ambient and pressure conditions, but the other four types of 4 are stable, in agreement with recent theoretical results. By eliminating mechanical calculations, we find that the four types (C2/m, Immm, Pnnm and Pmmn) of 4 are potential candidates to be ultra-incompressible and hard materials. Moreover, the 4 in C2/m type is the most ultra-incompressible among the considered structures due to its superior mechanical properties, and the P63/mmc-2u structure of 4 is not considered to be hard material because of its low hardness. In addition, the calculated B/G ratio exhibits the positive pressure dependence, and four types show brittle nature within 100 GPa. [ABSTRACT FROM AUTHOR]