Total energy and electronic structure calculations of C15 Laves-phase compounds MV<sub>2</sub> (M=Zr, Hf or Ta): Elastic properties

Chu, F.; Šob, Mojmı́r; Siegl, R.; Mitchell, T. E.; Pope, D. P.; Chen, S. P.

doi:10.1080/01418639408240258

Cited by 34 publications

(7 citation statements)

References 27 publications

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“…HfV 2 C15 Laves phase has been studied as an attractive superconducting material for technical applications [1,2] which can be influenced by its structural transformation [3][4][5]. Electronic structure, elastic properties and total energies of C15 Laves phases of MV 2 type (M = Zr, Hf, or Ta) were studied with the help of ab initio calculations in [6][7][8] and the relations between electronic structure, elastic moduli and stability were analysed. It was found that the HfV 2 C15 Laves phase compound, which is cubic at room temperature, undergoes a structural transformation to a non-Laves orthorhombic phase at low temperatures [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Modelling of phase equilibria in the Hf-V system below room temperature

Vřešťál

Pavlů

Wdowik

et al. 2017

J min metall B Metall

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Phase transformation from orthorhombic HfV 2 structure to cubic C15 Laves phase structure, which occurs during heating at about 114 K, is well known. In this contribution, a thermodynamic description of this phenomenon is provided supported by ab initio calculations. We utilize the third generation of thermodynamic database extending the Scientific Group Thermodata Europe (SGTE) unary data to zero Kelvin and demonstrate that it may be also applied to intermetallic phases. The data from a recent thermodynamic assessment of the Hf-V system (valid for temperatures above 298.15 K) were used and extended to zero Kelvin by the same method as it was used for unary data. Under the assumption of validity of harmonic approximation and electronic contribution to the heat capacity, the thermodynamics of C15 and orthorhombic phase were described. With the help of ab initio approach, we demonstrate that the HfV 2 orthorhombic phase and C15 Laves phase are mechanically stable at 0 K and thanks to entropy stabilization they are in equilibrium with pure element phases in the temperature region of structural change.

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Section: Introductionmentioning

confidence: 99%

Modelling of phase equilibria in the Hf-V system below room temperature

Vřešťál

Pavlů

Wdowik

et al. 2017

J min metall B Metall

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“…However, the thermal expansion coefficient of C15 TaV 2 was found to be positive [2]; thus, the unusual temperature behaviour is likely due to the second term of equation (1). A mechanism based on electronic structure was proposed to explain the unusual behaviour found in a number of C15 materials [1,[3][4][5][6][7]. The C15 crystal structure gives doubly-degenerate electronic levels at the X point of the Brillouin zone.…”

Section: Introductionmentioning

confidence: 99%

Elastic properties of the Ta–V system: bcc Ta_0.33V_0.67and C15 TaV₂

Agosta

Leisure

Skripov

2007

Philosophical Magazine

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Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta 0.33 V 0.67 over the temperature range 3.5-300 K; the results were compared to earlier measurements on C15 TaV 2 . The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295 K for the C15 phase and 315 K for the bcc phase.

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“…The exchange and correlation potential used in the calculations was the von Barth-Hedin local density formalism. The details of the calculation were presented in Ref, [23].…”

Section: Experimental Procedures and Calculation Methodsmentioning

confidence: 99%

“…The A& values for C15 M V 2 (M=Zr, Hf, or Ta) are listed in Table 2 TABLE 2 The energy gap, A&, of C15 MV2 (M=Zr, Hf, or Ta). In this case, it can be shown that the electronic contribution to the shear modulus, c;, follows the equation [23]:…”

Section: Elastic Propertiesmentioning

confidence: 99%

“…It can be seen from Table 1 that the theoretical lattice parameter (a) is just 1-2 % off of the experimental value (a,), which shows good agreement between the theoretical and the experimental results. The energy-band structures of the C15 MV2 (M=Zr, Hf, or Ta) along the high--symmetry directions in the Brillouin zone were obtained at the equilibrium configurations [23].…”

Section: Elastic Propertiesmentioning

confidence: 99%

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Phase stability and elasticity of C15 transition-metal intermetallic compounds

Chu

Mitchell

Chen

et al. 1997

JPE

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First-principle quantum mechanical calculations based on the local-density-functional theory have been performed to study the electronic, physical and metallurgical properties of C15 intermetallics MV2 (M=Zr, Hf, or Ta). The elastic constants of C15 HfV2+Nb were measured by the resonant ultrasound spectroscopy technique. The phase stability of C15 HfV2+Nb was studied by specific heat measurements and by transmission electron microscopy in a low temperature specimen holder. The total energies and their lattice volume dependence were used to obtain the equilibrium lattice constants and bulk modulus. The band structures at the X-point near the Fermi level were employed to understand the anomalous temperature dependence of shear modulus of the C15 intermetallics. It was found that the double degeneracy with a linear dispersion relation of electronic levels at the X-point near the Fermi surface is mainly responsible for the C15 anomalous elasticity. The density of states at the Fermi level, N(EF), and the Fermi surface geometry were obtained to understand the low temperature phase instability of C15 H N 2 and ZrV2 and the stability of C15 TaV2. It was proposed that the large N(EF) and Fermi surface nesting are the physical reasons for the structural instability of the C15 HfV2 and ZrV2 at low temperatures. The relationship between the anomalous elasticity and structural instability of C15 HfV2 and ZrV2 were also discussed.

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Total energy and electronic structure calculations of C15 Laves-phase compounds MV₂ (M=Zr, Hf or Ta): Elastic properties

Cited by 34 publications

References 27 publications

Modelling of phase equilibria in the Hf-V system below room temperature

Modelling of phase equilibria in the Hf-V system below room temperature

Elastic properties of the Ta–V system: bcc Ta_0.33V_0.67and C15 TaV₂

Phase stability and elasticity of C15 transition-metal intermetallic compounds

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Total energy and electronic structure calculations of C15 Laves-phase compounds MV2 (M=Zr, Hf or Ta): Elastic properties

Cited by 34 publications

References 27 publications

Modelling of phase equilibria in the Hf-V system below room temperature

Modelling of phase equilibria in the Hf-V system below room temperature

Elastic properties of the Ta–V system: bcc Ta0.33V0.67and C15 TaV2

Phase stability and elasticity of C15 transition-metal intermetallic compounds

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Product

Resources

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Total energy and electronic structure calculations of C15 Laves-phase compounds MV₂ (M=Zr, Hf or Ta): Elastic properties

Elastic properties of the Ta–V system: bcc Ta_0.33V_0.67and C15 TaV₂