Mechanical properties of zirconium alloys and zirconium hydrides predicted from density functional perturbation theory

Abstract

The elastic properties and mechanical stability of zirconium alloys and zirconium hydrides have been investigated within the framework of density functional perturbation theory. Results show that the lowest-energy cubic Pn3[combining macron]m polymorph of δ-ZrH1.5 does not satisfy all the Born requirements for mechanical stability, unlike its nearly degenerate tetragonal P42/mcm polymorph. Elastic moduli predicted with the Voigt-Reuss-Hill approximations suggest that mechanical stability of α-Zr, Zr-alloy and Zr-hydride polycrystalline aggregates is limited by the shear modulus. According to both Pugh's and Poisson's ratios, α-Zr, Zr-alloy and Zr-hydride polycrystalline aggregates can be considered ductile. The Debye temperatures predicted for γ-ZrH, δ-ZrH1.5 and ε-ZrH2 are θD = 299.7, 415.6 and 356.9 K, respectively, while θD = 273.6, 284.2, 264.1 and 257.1 K for the α-Zr, Zry-4, ZIRLO and M5 matrices, i.e. suggesting that Zry-4 possesses the highest micro-hardness among Zr matrices.

Structure and thermodynamic properties of zirconium hydrides by structure search method and first principles calculations

“…Weck et al also reported two P222 structures [46] which are different from the P222 structure found in our calculations. As a comparison, we optimized the Weck's structures and found that their symmetries are actually P4 2 As is shown in Figure 2b, phonon density of states of P4 2 /mmc, Ccce and P222 structures have no imaginary frequencies.…”

“…For ZrH, the γ-ZrH with tetragonal cell has been experimentally observed, but its stability is still in a dispute. Though γ-ZrH was previously reported to be of P4 2 /n symmetry with a = b = 4.586 Å, c = 4.948 Å (space group # 86) [45] with four Zr atoms and four H atoms in a unit cell, its actual symmetry is P4 2 /mmc (space group # 131) [46] with a Zr 2 H 2 unit cell. A Cccm structure was also reported by Kolesnikov et al in 1994 [47], with lattice constants being a = 4.549 Å, b = 4.618 Å and c = 4.965 Å.…”

Infrared and Raman spectroscopy of α‐ZrW2O8: A comprehensive density functional perturbation theory and experimental study

“…Both functionals were found in previous studies to correctly describe the geometric parameters and properties of a variety of Zr compounds and oxides. [38][39][40][46][47][48] Properties such as the thermodynamic ones previously calculated with PBEsol for non-NTE materials and oxides showed overall improvement compared with PBE results. [47,49,50] PBEsol elasticity and thermodynamics calculations for α-ZrW 2 O 8 also exhibit better agreement with experiments than other functionals.…”

“…This DFPT approach was utilized in previous computational studies to successfully predict the properties of various Zr-containing compounds and crystalline materials. [38][39][40][41]46,48,49,[55][56][57] 3 | RESULTS AND DISCUSSION…”

“…[37] The accuracy of DFPT methods was extensively tested in previous lattice dynamics studies. [38][39][40][41][42][43] Details of our computational and experimental approaches are presented in the next section, followed by a detailed analysis and discussion of our results, and a summary of our findings and conclusions.…”