Phonon Anomaly in High-Pressure Zn

Li, Zhiqiang; Tse, John S.

doi:10.1103/physrevlett.85.5130

Cited by 45 publications

(35 citation statements)

References 32 publications

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“…A computational study on bcc Nb under pressure showed that topological transitions occur at 5 and 60 GPa [367], consistent with measurements of pressure-induced changes in the superconducting transition temperature [368]. A computational study on hcp Zn showed an electronic topological transition at high compression that was responsible for a change in compressibility and the axial ratio of the structure [369]. Experimental evidence for a change in phonon frequencies in Zn was found by inelastic neutron scattering at a pressure of approximately 6.8 GPa [362], but the effect on elastic constants has been questioned [370].…”

Section: Kohn Anomalies and Electronic Topological Transitionsmentioning

confidence: 57%

Vibrational thermodynamics of materials

Fultz¹

2010

Progress in Materials Science

570

428

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Abstract. The literature on vibrational thermodynamics of materials is reviewed. The emphasis is on metals and alloys, especially on the progress over the last decade in understanding differences in the vibrational entropy of different alloy phases and phase transformations. Some results on carbides, nitrides, oxides, hydrides and lithium-storage materials are also covered.Principles of harmonic phonons in alloys are organized into thermodynamic models for unmixing and ordering transformations on an Ising lattice, and extended for non-harmonic potentials. Owing to the high accuracy required for the phonon frequencies, quantitative predictions of vibrational entropy with analytical models prove elusive. Accurate tools for such calculations or measurements were challenging for many years, but are more accessible today. Ab-initio methods for calculating phonons in solids are summarized. The experimental techniques of calorimetry, inelastic neutron scattering, and inelastic x-ray scattering are explained with enough detail to show the issues of using these methods for investigations of vibrational thermodynamics. The explanations extend to methods of data analysis that affect the accuracy of thermodynamic information.It is sometimes possible to identify the structural and chemical origins of the differences in vibrational entropy of materials, and the number of these assessments is growing. There has been considerable progress in our understanding of the vibrational entropy of mixing in solid solutions, compound formation from pure elements, chemical unmixing of alloys, order-disorder transformations, and martensitic transformations. Systematic trends are available for some of these phase transformations, although more examples are needed, and many results are less reliable at high temperatures. Nanostructures in materials can alter sufficiently the vibrational dynamics to affect thermodynamic stability. Internal stresses in polycrystals of anisotropic materials also contribute to the heat capacity. Lanthanides and actinides show a complex interplay of vibrational, electronic, and magnetic entropy, even at low temperatures.A "quasiharmonic model" is often used to extend the systematics of harmonic phonons to high temperatures by accounting for the effects of thermal expansion against a bulk modulus. Non-harmonic effects beyond the quasiharmonic approximation originate from the interactions of thermally-excited phonons with other phonons, or with the interactions of phonons with electronic excitations. In the classical high temperature limit, the adiabatic electron-phonon coupling can have a surprisingly large effect in metals when temperature causes significant changes in the electron density near the Fermi level. There are useful similarities in how temperature, pressure, and composition alter the conduction electron screening and the interatomic force constants. Phononphonon "anharmonic" interactions arise from those non-harmonic parts of the interatomic potential that cannot be accounted for by the quasiharmonic ...

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Section: Kohn Anomalies and Electronic Topological Transitionsmentioning

confidence: 57%

Vibrational thermodynamics of materials

Fultz¹

2010

Progress in Materials Science

570

428

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“…Li and Tse confirmed the c/a anomaly, although the magnitude of their anomaly is much smaller than other calculations. 12 Steinle-Neumann et al pointed out that the c/a anomaly is very sensitive to the Brillouin-zone sampling, and should disappear if a sufficient number of k points is used for the calculation. 13 Kechin studied details of the ETTs at the K and L symmetry points of the Brillouin zone.…”

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confidence: 99%

Axial ratio of Zn at high pressure and low temperature

et al. 2002

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High-pressure powder x-ray-diffraction experiments have been carried out on Zn with a He-pressure medium up to 18 GPa at 40 K. No anomaly in the volume dependence of the c/a axial ratio has been found within experimental errors. The c/a anomaly, which has been predicted to appear associated with the electronic topological transitions, should be extremely small. Thermal expansion of Zn rapidly decreases under high pressure, yielding nearly identical axial ratios at room and low temperatures.

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“…With increasing pressure, the low-frequency optical phonon branch gradually softens at the at H point. This phonon softening may be because of the ETT transition described above [29]. In contrast, the acoustic phonon branches harden with increasing pressure.…”

Section: The Lattice Dynamical Properties Of Malsimentioning

confidence: 92%