Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions.

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La Sr MnO epitaxial thin films, both at the surface and throughout the bulk.

Ordering of Oxygen Vacancies and Related Ferroelectric Properties in HfO_{2-δ}.

Using density functional theory combined with an evolutionary algorithm, we investigate ferroelectricity in substoichiometric HfO_{2-δ} with fixed composition δ=0.25. We find that oxygen vacancies tend to cluster in the form of two-dimensional extended defects, revealing several patterns of local relative arrangements within an energy range of 100 meV per Hf atom.

Ab initio phase diagrams of Hf-O, Zr-O and Y-O: a comparative study.

We present phase diagrams of binary oxides, Hf-O, Zr-O and Y-O, obtained by ab initio evolutionary simulations, in order to explore possible metastable crystalline suboxide structures which could be quenched during the electroforming processes within the conductive filaments in stoichiometric HfO2, ZrO2 and Y2O3 host materials, in resistive switching devices. We find that, in the range MO-MO2 (where M = Hf, Zr, Y), the most energetically favourable atomic configurations have properties which facilitate the ionic conduction of oxygen. Namely, the calculations reveal that oxygen vacancies tend to order in arrays of one-dimensional channels, along which the migration barrier of anions is much lower than for the stoichiometric hosts.

Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO3 as the Origin of Volume Collapse.

A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. We report that the charge glass state is realized in a perovskite compound PbCrO3, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system.

Ferroelectricity, nonlinear dynamics, and relaxation effects in monoclinic Sn2P2S6.

An ab initio-based model of the temperature-induced ferroelectric phase transition in Sn2P2S6 (SPS) as a prototype of an unconventional ferroelectric is developed. The order parameter in SPS is found as the valley line on a total-energy surface of the zone-center fully symmetrical Ag and polar Bu distortions. Significant nonlinear coupling between order parameter and strain is observed.