Energy landscapes of perfect and defective solids: from structure prediction to ion conduction

Abstract

The energy landscape concept is increasingly valuable in understanding and unifying the structural, thermodynamic and dynamic properties of inorganic solids. We present a range of examples which include (i) structure prediction of new bulk phases including carbon nitrides, phosphorus carbides, LiMgF3 and low-density, ultra-flexible polymorphs of B2O3, (ii) prediction of graphene and related forms of ZnO, ZnS and other compounds which crystallise in the bulk with the wurtzite structure, (iii) solid solutions, (iv) understanding grossly non-stoichiometric oxides including the superionic phases of δ-Bi2O3 and BIMEVOX and the consequences for the mechanisms of ion transport in these fast ion conductors. In general, examination of the energy landscapes of disordered materials highlights the importance of local structural environments, rather than sole consideration of the average structure.

A mechanism for aragonite to post-aragonite transition in MCO3 (M = Ca, Sr and Ba) carbonates: evidence of a hidden metastable polymorph

“…When kinetic aspects are at play, the study of paths connecting minima on the potential energy surface (PES) of compounds becomes necessary. 26,27 These paths traverse through saddle points that correspond to unstable structures. The status of a structure as stable, metastable, or unstable is not fixed but depends on temperature and pressure conditions.…”

Manifestation of site energy landscapes for ion transport in borate glasses

“…There seems to be consensus that in a perfect crystal, all atoms of the same chemical type at equivalent crystal sites have identical site energy and feel identical barriers, corresponding to delta-distributions of energy minima and maxima. 4,38 In an amorphous structure of a glass, broad distributions of site energies (potential minima) and barriers (saddle point energies) characterize the energy landscape for the mobile ions. 39,40 As of now, there doesn’t seem to exist a consensual protocol for construction of site energy landscapes, i.e.…”

“…The potential energy landscape of mobile ions in solid-state materials and the atomic scale structure are intimately interrelated. [1][2][3][4] This interrelation and the resultant properties, e.g. the mobility of the ions, [5][6][7][8][9][10][11] is of paramount interest in contemporary material science with direct applications in energy storage and conversion.…”

Free energy predictions for crystal stability and synthesisability

“…For example, the oxygen sublattice melting in Bi 2 O 3 , La 2 Mo 2 O 9 and Bi 4 V 2 O 11 . 70 The entropy of the disordered system can be estimated from simple considerations based on available interstitial sites, 71 or more elaborate methods based on thermodynamic integration can be applied. 54 As ionic conductors are important for applications in batteries and fuel cells, it will be advantageous if simple but accurate models for prediction of their stability can be established.…”