Geometric Variations and Electron Localizations in Intermetallics: The Case of La2Sb Type Compounds

Structural diversity among multinary pnictide oxides: a minireview focused on semiconducting and superconducting heteroanionic materials

Incorporating different anions with varied ionic sizes and charges is a rapidly growing approach to bring out unusual physical properties among various classes of solid-state materials, pnictides and chalcogenides in particular. This minireview is focused on hetero-anionic materials based on the pnictogens, which have been demonstrated to offer an impressive diversity of crystal chemistry and electronic structures. In addition, many pnictide oxides or oxypnictides, over the course of the last decade, have been shown to exhibit a broad spectrum of superconducting, magnetic, and semiconducting properties. However, the structural diversity of the mixed-anion materials is far greater than the several known structure types, or their variants, of the well-known layered superconductive materials. Therefore, with this treatise, we aim to provide a comprehensive overview of the crystal chemistry of pnictide oxides by recounting almost 40 different structures of such ternary and multinary compounds. In addition to the structural aspects, we also highlight some of the challenges associated with the synthesis, and briefly summarize reported, to date, physical properties of this remarkable class of solids.

Ferroelectricity and multiferroicity in anti-Ruddlesden-Popper structures

Combining ferroelectricity with other properties such as visible light absorption or long-range magnetic order requires the discovery of new families of ferroelectric materials. Here, through the analysis of a high-throughput database of phonon band structures, we identify a structural family of anti-Ruddlesden-Popper phases [Formula: see text]O (A=Ca, Sr, Ba, Eu, X=Sb, P, As, Bi) showing ferroelectric and antiferroelectric behaviors. The discovered ferroelectrics belong to the new class of hyperferroelectrics that polarize even under open-circuit boundary conditions. The polar distortion involves the movement of O anions against apical A cations and is driven by geometric effects resulting from internal chemical strains. Within this structural family, we show that [Formula: see text]O combines coupled ferromagnetic and ferroelectric order at the same atomic site, a very rare occurrence in materials physics.

Superconductivity at 4.8 K and Violation of Pauli Limit in La2IRu2 Comprising Ru Honeycomb Layer

We discovered superconductivity at 4.8 K in the hexagonal layered compound La₂IRu₂ comprising a triangular lattice of the La and a honeycomb lattice of the Ru atoms. First-principles calculations reveal a two-dimensional band structure made up of La 5d and Ru 4d electrons and formal oxidation states +1.5 for the La and the uncommon oxidation state -1 for the Ru atoms. The temperature dependence of the specific heat indicates fully gapped superconductivity. Nevertheless, the upper critical field of this compound violates the Pauli limit. We argue that the high upper critical field is ascribed to an antisymmetric spin-orbit coupling in the unique multilayer structure.

Hydrogen Insertion in the Intermetallic GdScGe: A Drastic Reduction of the Dimensionality of the Magnetic and Transport Properties

Intermetallic phases have been investigated with respect to their ability to accept small atoms in interstitial sites without changing the host structure. Among those, the intermetallic compounds crystallizing in the tetragonal CeScSi-type structure are able to absorb hydrogen atoms. These compounds are of particular interest because they can show electride-like character and, therefore, can be exploited as new catalysts. Here we report the case of GdScGe which uptakes hydrogen at 623 K and under a H₂ gas pressure between 0.5 and 4 MPa. The formation of the hydride GdScGeH, with H atoms entering into the [Gd₄] tetrahedra, preserves the host structure but induces an anisotropic volume expansion with a strong increase of the c-parameter and a slight decrease of the a-parameter. Interestingly, we show for the first time for this family of materials that hydrogen insertion reduces the dimensionality of the magnetic and transport properties from 3D to quasi-2D which results in a vanishing of the ferromagnetic order ( T_C = 350 K for GdScGe) and a change of the metallic conduction behavior to a nonmetallic one. As evidenced by density functional theory calculations, such drastic effects are accounted for through the Gd-H chemical bonding effect and the oxidizing effect of H whereas the volume expansion plays only a minor role.

Facile synthesis of heterotrimetallic metal-string complex [NiCoRh(dpa)4Cl2] through direct metal replacement

This communication provides a practical strategy for the synthesis of heterotrimetallic extended metal atom chains with supported dpa(-) ligands. The transformation of the CoCoRh to a NiCoRh trinuclear complex can be achieved by direct metallic replacement. Furthermore, the first (CoRh)(4+) metal-metal bond is described here.