Phonons and anomalous thermal expansion behaviour in crystalline solids

Abstract

Anomalous thermal expansion behaviour of several open frame-work compounds has been extensively investigated using the techniques of inelastic neutron scattering and lattice dynamics. These compounds involve increasing level of structural complexity and flexibility, which leads to increased values of thermal expansion coefficients approaching colossal values. In several compounds, neutron inelastic scattering experiments have produced quantitative estimates of the anharmonicity of phonons over a range of low energies, and thereby explained the observed thermal expansion quantitatively. The anharmonicity is found to be an order of magnitude larger than that in usual materials. Lattice dynamical calculations have correctly predicted the observed anharmonicity in the neutron experiments and revealed the overall nature of phonons involved. In compounds showing negative thermal expansion, the phonons responsible have rather low energies up to 10 meV. In most compounds, the anharmonic phonons span all over the Brillouin zone, while in some cases the specific phonons are limited to certain wave-vectors. The nature of specific phonons responsible for anomalous behavior is found to be different in all these compounds.These phonons generally involve transverse vibrations, librations and internal distortions of the polyhedral units. The paper reviews recent advances in the understanding of anomalous thermal expansion behaviour.

Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites

“…Remarkably, there exists a growing class of materials with strong, isotropic, robust, and thermally persistent NTE that arises from structural motifs (Martinek and Hummel, 1968; Mary et al, 1996; Evans et al, 1997a,b; Pryde et al, 1997; Ernst et al, 1998; Perottoni and Jornada, 1998; Ramirez and Kowach, 1998; Ramirez et al, 2000; Mittal et al, 2001, 2004, 2018; Cao et al, 2002, 2003; Ouyang et al, 2002; Drymiotis et al, 2004; Hancock et al, 2004b; Kennedy and White, 2005; Lee et al, 2005; Tucker et al, 2005, 2007; Pantea et al, 2006; Figueirêdo and Perottoni, 2007; Han and Goddard, 2007; Keen et al, 2007, 2011; Schlesinger et al, 2008; Zhou et al, 2008; Greve et al, 2010; Gallington et al, 2013, 2014; Gupta et al, 2013; Morelock et al, 2013b; Bridges et al, 2014; Sanson, 2014). NTE in these systems is often discussed in connection with transverse fluctuations of a linkage between volume-defining vertices, which may accompany the librational, or hindered rotational motion of polyhedral subunits.…”

Lithium diffusion in Li2X ( X=O , S, and Se): Ab initio simulations and inelastic neutron scattering measurements

“…The thermal expansion behaviour has been computed under the quasiharmonic approximation [60]. Each phonon mode of energy E qj (j th phonon mode at point q in the Brillouin zone)…”

Effect of hydration and ammonization on the thermal expansion behavior of ZrW2O8 : Ab initio lattice dynamical perspective

“…The low energy spectrum of W2 atom does not show significant changes, while the higher energy spectrum alters significantly. Spectral weight of other atoms is also redistributed significantly.The spectral weight redistribution is very prominent in case of insertion of H2 O in ZrW 2 O 8 . One can observe new peaks in the density of states of various oxygen atoms, which may be due to bonding of various terminal oxygen atoms with the neighbouring H 2 O molecule.…”

“…In this paper we extensively investigate and compare the phonon dynamics and its relevance to the thermal expansion behaviour in ZrW 2 The present study deals with microscopic understanding of how the thermal expansion coefficient may be tailored by engineering the low-energy phonon dynamics of a material. It is important to achieve controlled thermal expansion behaviour in a single homogenous phase mediated by phonons.…”