Superionicity and Polymorphism in Calcium Fluoride at High Pressure

Abstract

We present a combined experimental and computational first-principles study of the superionic and structural properties of CaF2 at high P-T conditions. We observe an anomalous superionic behavior in the low-P fluorite phase that consists in a decrease of the normal-> superionic critical temperature with compression. This unexpected effect can be explained in terms of a P-induced softening of a zone-boundary $X$ phonon which involves exclusively fluorine displacements. Also we find that superionic conductivity is absent in the high-P cotunnite phase. Instead, superionicity develops in a new low-symmetry high-T phase that we identify as monoclinic (space group P2_1/c). We discuss the possibility of observing these intriguing phenomena in related isomorphic materials.

arXiv comment5 pages, 5 figures

References in corpus (7)

• Phonons and related properties of extended systems from density-functional perturbation theory
• Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations
• Ab initio melting curve of molybdenum by the phase coexistence method
• The kinetics of homogeneous melting beyond the limit of superheating
• Constraints on the phase diagram of molybdenum from first-principles free-energy calculations
• Insights into the Phase Diagram of Bismuth Ferrite from Quasi-Harmonic Free Energy Calculations
• Melting properties of a simple tight-binding model of transition metals: I.The region of half-filled d-band

Cited by in corpus (16)

• Simulation and understanding of quantum crystals
• Influence of lattice dynamics on lithium-ion conductivity: A first-principles study
• Prediction of giant mechanocaloric effects in fluorite-structured superionic materials
• Prediction of large barocaloric effects in thermoelectric superionic materials
• High-pressure high-temperature phase diagram of zinc
• High-pressure phases of group II difluorides: polymorphism and superionicity
• Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF 3 , CsCaF 3 and BaLiF 3
• Lithium Diffusion in Li2X(X=O, S and Se): Ab-initio Simulations and Neutron Inelastic Scattering Measurements
• Thermal conductivity of CaF${}_2$ at high pressure
• Lattice induced crystallization of nanodroplets: the role of finite-size effects and substrate properties in controlling polymorphism
• Novel phase of beryllium fluoride at high pressure
• High-pressure CaF2 revisited: a new high-temperature phase and the role of phonons in the search for superionic conductivity
• Comment on "High-pressure phases of group-II difluorides: Polymorphism and superionicity"
• Predicting the lattice thermal conductivity of solids by solving the Boltzmann transport equation: AFLOW - AAPL an automated, accurate and effcient framework
• Is the normal to superionic transformation occurring in type-II fast-ion conductors a real thermodynamic phase transition?
• Theory-Guided Discovery of Pressure-Induced Transitions in Fast-Ion Conductor BaSnF4