Inelastic Neutron Scattering and Lattice Dynamics: Perspectives and Challenges in Mineral Physics

Abstract

An understanding of the fundamental physics of the Earth's interiorrequires information about the phase transitions and thermodynamicproperties of key mantle-forming mineral phases. Inelastic neutronscattering (INS) is an indispensable tool for determining key latticedynamics properties like the phonon dispersion relation (PDR) anddensity of states, which govern a wide range of material behaviorsincluding structural phase transitions, thermodynamic properties,elasticity, and melting. In this chapter we review recent reportedstudies involving INS and lattice dynamics calculations of geophysicallyimportant minerals. We also review recent applications of INS involvingexperimental and theoretical ab initio and atomistic studies of thephonon spectra and thermodynamic properties of minerals and of othernovel phenomena like high-pressure phonon softening, structural phasetransitions, pressure-induced amorphization, magnetic excitations,melting, etc. We discuss the current understanding of the dynamicalbehavior, thermodynamic properties, and phase transitions of key mantlecomponents like the olivine and pyroxene end members forsterite andenstatite, the mineral zircon, important silica polymorphs, andmagnesium oxide; recent results on water and ice; other complexsilicates; hydrogen storage materials; etc. Inelastic neutron scatteringand complementary techniques like inelastic X-ray scattering have beenused to explore the high-pressure PDR and density of states of iron,diamond, and magnesium oxide; to study magnetic excitations; to estimatethe magnetic contributions to thermodynamic properties; etc. Thetheoretical calculations enable fruitful microscopic interpretations ofcomplex experimental data and provide an atomic-level understanding ofvibrational and thermodynamic properties.