Absence of metastable states in strained monatomic cubic crystals

Mehl, Michael J.; Aguayo, A.; Boyer, L. L.; Coss, Romeo de

doi:10.1103/physrevb.70.014105

Cited by 30 publications

(25 citation statements)

References 30 publications

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“…A negative c 66 corresponds to an unstable long-wavelength part of the transverse phonon mode T [100] [0ξ0]. Apart from Ta, this elastic instability was reported before [24,60]. To complete the picture of the bcc transition metals, we note that Fe was predicted to order antiferromagnetically and to be unstable due to c 66 < 0 at the bct local minimum of its EBP [61].…”

Section: B Elements With Stable Cubic Structurementioning

confidence: 92%

Metastable cubic and tetragonal phases of transition metals predicted by density-functional theory

Schönecker

Koepernik

et al. 2015

RSC Adv.

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By means of density-functional calculations, we systematically investigated 24 transition metals for possible metastable phases in body-centered tetragonal structure (bct), including face-centered cubic (fcc) and body-centered cubic (bcc) geometries. A total of 36 structures not coinciding with equilibrium phases were found to minimize the total energy for the bct degrees of freedom. Among these, the fcc structures of Sc, Ti, Co, Y, Zr, Tc, Ru, Hf, Re, and Os, and bct Zr with c/a = 0.82 were found to be metastable according to their computed phonon spectra. Eight of these predicted phases are not known from the respective pressure-temperature phase diagrams. Possible ways to stabilize the predicted metastable phases are illustrated.

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Section: B Elements With Stable Cubic Structurementioning

confidence: 92%

Metastable cubic and tetragonal phases of transition metals predicted by density-functional theory

Schönecker

Koepernik

et al. 2015

RSC Adv.

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“…Mehl et al (2004) investigated this extended tetragonal Bain path in some detail for elements that are thermodynamically stable in fcc or bcc structures. For Sr the secondary minimum coincides with the bcc lattice, and for Ba with the fcc lattice.…”

Section: Effect Of Anharmonicitymentioning

confidence: 99%

Lattice instabilities in metallic elements

et al. 2012

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Most metallic elements have a crystal structure that is either body-centered cubic (bcc), facecentered close packed, or hexagonal close packed. If the bcc lattice is the thermodynamically most stable structure, the close-packed structures usually are dynamically unstable, i.e., have elastic constants violating the Born stability conditions or, more generally, have phonons with imaginary frequencies. Conversely, the bcc lattice tends to be dynamically unstable if the equilibrium structure is close packed. This striking regularity essentially went unnoticed until ab initio total-energy calculations in the 1990s became accurate enough to model dynamical properties of solids in hypothetical lattice structures. After a review of stability criteria, thermodynamic functions in the vicinity of an instability, Bain paths, and how instabilities may arise or disappear when pressure, temperature, and/or chemical composition is varied are discussed. The role of dynamical instabilities in the ideal strength of solids and in metallurgical phase diagrams is then considered, and comments are made on amorphization, melting, and low-dimensional systems. The review concludes with extensive references to theoretical work on the stability properties of metallic elements.

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“…In all the cases, we find imaginary phonon frequencies that clearly indicate the dynamic instability of bulk Ru and Os, in the bct structure. It should be noted that the imaginary phonon branch in the Γ → X direction reveals an elastic instability related to a negative value of the elastic constant C ′ = (c 11 − c 12 )/2 [1,7,18]. Additionally, the effect of the epitaxial and uniaxial strains on the phonon dispersion was evaluated.…”

Section: Resultsmentioning

confidence: 99%

“…Regardless of the prediction of a ferromagnetic order in the local minimum of the Bain path for Ru and Os in the bct structure with c/a < 1, a study on the dynamical stability in these materials has not yet been reported to the best of our knowledge. From a theoretical point of view, the stability analysis of a given crystal structure is necessary to evaluate if under small deformations of the lattice, the atoms return to their assumed equilibrium position, which identify a truly metastable phase [1,7,8,9].…”

Section: Introductionmentioning

confidence: 99%

On the dynamical stability of ferromagnetic Ru and Os in the bct structure: a first-principles study

Cifuentes-Quintal

Coss

2015

Philosophical Magazine Letters

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Recent theoretical studies have predicted magnetic states for Ru and Os in the body centered tetragonal structure (bct) with c/a < 1. In this study, we present first principles calculations of the phonon dispersion for ferromagnetic Ru-and Os-bct along the epitaxial and uniaxial Bain paths, to evaluate their dynamical stability. The phonon dispersions were computed using the density functional perturbation theory, including the gradient corrections to the exchange-correlation functional within the plane-waves ultrasoftpseudopotential approximation. The phonon dispersion for the local minimum in the Bain path with c/a < 1 as well as the uniaxial and epitaxial strained structures are analyzed. We find imaginary frequencies along different directions of the Brillouin zone, which indicates that both systems are dynamically unstable. Consequently, ferromagnetic Ru and Os in the body centered tetragonal structure with c/a < 1 are not truly metastable phases.

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Absence of metastable states in strained monatomic cubic crystals

Cited by 30 publications

References 30 publications

Metastable cubic and tetragonal phases of transition metals predicted by density-functional theory

Metastable cubic and tetragonal phases of transition metals predicted by density-functional theory

Lattice instabilities in metallic elements

On the dynamical stability of ferromagnetic Ru and Os in the bct structure: a first-principles study

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