The perovskites and perovskite-related structures exhibit several features of technical as well as fundamental interest. Technically useful properties include oxide-ion conduction with/without electronic conduction, oxidation catalysis, ferroic displacements in classic and relaxor ferroelectrics, half-metallic ferromagnetism and high-temperature superconductivity. Of more fundamental interest is the ability to tune, by chemical substitution on the large-cation subarray, transition-metal oxides through the crossover on the transition-metal array from localized dn configurations to itinerant d-electron behaviour without/with changing the valence state of that array. The localized-electron configurations may exhibit cooperative Jahn–Teller distortions that introduce anisotropic exchange interactions. At crossover, bond-length fluctuations may segregate into an ordered array of alternating covalent and ionic bonding in a single-valent perovskite; multicentre polarons or correlation bags may replace small polarons in a mixed-valent system. Bond-length fluctuations at crossover give vibronic conduction and suppression of the phonon contribution to the thermal conductivity; the fluctuations may order, to give high-temperature superconductivity, or transform to quantum–critical-point behaviour at lowest temperatures. Crossover of σ-bonding electrons in the presence of localized spins associated with π-bonding electrons gives rise to the colossal magnetoresistance phenomenon above a ferromagnetic Curie temperature.

https://iopscience.iop.org/article/10.1088/0034-4885/67/11/R01/pdf

Electronic and ionic transport properties and other physical aspects of perovskites

A versatile method for combining density functional theory in the local density approximation with dynamical mean-field theory (DMFT) is presented. Starting from a general basis-independent formulation, we use Wannier functions as an interface between the two theories. These functions are used for the physical purpose of identifying the correlated orbitals in a specific material, and also for the more technical purpose of interfacing DMFT with different kinds of band-structure methods (with three different techniques being used in the present work). We explore and compare two distinct Wannier schemes, namely the maximally localized Wannier function and the $N\text{th}$ order muffin-tin-orbital methods. Two correlated materials with different degrees of structural and electronic complexity, $\mathrm{Sr}\mathrm{V}{\mathrm{O}}_{3}$ and $\mathrm{Ba}\mathrm{V}{\mathrm{S}}_{3}$, are investigated as case studies. $\mathrm{Sr}\mathrm{V}{\mathrm{O}}_{3}$ belongs to the canonical class of correlated transition-metal oxides, and is chosen here as a test case in view of its simple structure and physical properties. In contrast, the sulfide $\mathrm{Ba}\mathrm{V}{\mathrm{S}}_{3}$ is known for its rich and complex physics, associated with strong correlation effects and low-dimensional characteristics. Insights into the physics associated with the metal-insulator transition of this compound are provided, particularly regarding correlation-induced modifications of its Fermi surface. Additionally, the necessary formalism for implementing self-consistency over the electronic charge density in a Wannier basis is discussed.

/pdf/dynamical-mean-field-theory-using-wannier-functions-a-418eqlyldq.pdf

Dynamical mean-field theory using Wannier functions: A flexible route to electronic structure calculations of strongly correlated materials

The new perovskite PbVO3 was synthesized under high-temperature and high-pressure conditions. Its crystal structure (a = 3.80005(6) A, c = 4.6703(1) A, Z = 1, S.G. P4mm) contains isolated layers of corner-shared VO5 pyramids, which are formed instead of octahedra due to a strong tetragonal distortion (c/a = 1.23). The lead atom is shifted out of the center of the unit cell toward one of two [VO2]-layers due to the influence of the lone pair. This new perovskite exhibits a semiconductor-like ρ(T) dependence down to 2 K. This behavior can be qualitatively explained by taking into account strong electron correlations in electronic structure calculations.

/pdf/synthesis-structure-and-properties-of-new-perovskite-pbvo3-k56t8ex8sl.pdf

Synthesis, Structure, and Properties of New Perovskite PbVO3

Recent findings on intriguing physical properties of new A-site-ordered perovskite structure oxides are reviewed. High-pressure and high-temperature conditions stabilize the square-coordinated Jahn−Teller Cu2+ ions in the original 12-fold-coordinated positions of the perovskite structure. The special-ordered arrangement of the square-coordinated A′O4 units that align perpendicularly to each other sets a characteristic structural framework, and the presence of Cu2+ ions at the A′ site and A′−B interactions play crucial roles for the diverse and intriguing physical properties.

A-site-ordered perovskites with intriguing physical properties.

With their broad range of properties, ABO3 transition metal perovskite oxides have long served as a platform for device applications and as a testing bed for different condensed matter theories. Their insulating character and structural distortions are often ascribed to dynamical electronic correlations within a universal, symmetry-conserving paradigm. This view restricts predictive theory to complex computational schemes, going beyond density functional theory (DFT). Here, we show that, if one allows symmetry-breaking energy-lowering crystal symmetry reductions and electronic instabilities within DFT, one successfully and systematically recovers the trends in the observed band gaps, magnetic moments, type of magnetic and crystallographic ground state, bond disproportionation and ligand hole effects, Mott vs. charge transfer insulator behaviors, and the amplitude of structural deformation modes including Jahn-Teller in low temperature spin-ordered and high temperature disordered paramagnetic phases. We then provide a classification of the four mechanisms of gap formation and establish DFT as a reliable base platform to study the ground state properties in complex oxides. It is often stated that first principles studies of transition metal oxides require dynamically correlated methods to correctly produce gap formation, magnetism and structural distortions. Varignon et al. show instead that static correlations are sufficient to capture these features in the ABO3 oxide series.

/pdf/origin-of-band-gaps-in-3d-perovskite-oxides-30cum4ojmi.pdf

P.S. Danielson

Papers

Alkaline-earth vanadium (IV) oxides having the AVO3 composition

A high-pressure modification of MgVO3

The preparation and characterization of CdVO3 prepared at ambient and high pressure