Atomic reconstruction induced by uniaxial stress in MnP.

In condensed matter physics, pressure is frequently used to modify the stability of both electronic states and atomic arrangements. Under isotropic pressure, the intermetallic compound MnP has recently attracted attention for the interplay between pressure-induced superconductivity and complicated magnetic order in the vicinity . By contrast, we use uniaxial stress, a directional type of pressure, to investigate the effect on the magnetism and crystal structure of this compound. An irreversible magnetisation response induced by uniaxial stress is discovered in MnP at uniaxial stress as low as [Formula: see text]. Neutron diffraction experiments reveal that uniaxial stress forms crystal domains that satisfy pseudo-rotational symmetry unique to the MnP-type structure. The structure of the coexisting domains accounts for the stress-induced magnetism. We term this first discovered phenomenon atomic reconstruction (AR) induced by uniaxial stress. Furthermore, our calculation results provide guidelines on the search for AR candidates. AR allows crystal domain engineering to control anisotropic properties of materials, including dielectricity, elasticity, electrical conduction, magnetism and superconductivity. A wide-ranging exploration of potential AR candidates would ensure that crystal domain engineering yields unconventional methods to design functional multi-domain materials for a wide variety of purposes.

Characteristic fast H- ion conduction in oxygen-substituted lanthanum hydride.

Fast ionic conductors have considerable potential to enable technological development for energy storage and conversion. Hydride (H-) ions are a unique species because of their natural abundance, light mass, and large polarizability. Herein, we investigate characteristic H- conduction, i.e., fast ionic conduction controlled by a pre-exponential factor. Oxygen-doped LaH3 (LaH3-2xOx) has an optimum ionic conductivity of 2.6 × 10-2 S cm-1, which to the best of our knowledge is the highest H- conductivity reported to date at intermediate temperatures. With increasing oxygen content, the relatively high activation energy remains unchanged, whereas the pre-exponential factor decreases dramatically. This extraordinarily large pre-exponential factor is explained by introducing temperature-dependent enthalpy, derived from H- trapped by lanthanum ions bonded to oxygen ions. Consequently, light mass and large polarizability of H-, and the framework comprising densely packed H- in LaH3-2xOx are crucial factors that impose significant temperature dependence on the potential energy and implement characteristic fast H- conduction.

Nephelauxetic effect of the hydride ligand in Sr2LiSiO4H as a host material for rare-earth-activated phosphors.

Strontium lithium orthosilicate hydride Sr2LiSiO4H was synthesized by the reaction of Sr2SiO4 with LiH at 700 °C in a H2 rich atmosphere. Rietveld refinement of the neutron powder diffraction pattern revealed that Sr2LiSiO4H is isostructural to Sr2LiSiO4F (space group P21/m) and its channel-like structure preferentially accommodates H- ions over F- ions. In addition, Sr2LiSiO4H is stable in air and its Eu2+-doped analog exhibits yellow photoluminescence with an emission band at 544 nm and a broad excitation band ranging from 250 to 450 nm. These bands were observed in the longer wavelength region when compared with those displayed by Sr2LiSiO4F:Eu2+. The red shift, which is induced by H- substitution, is consistent with the constrained density functional theory calculations, predicting the photo-excitation and emission energies of 4f-5d transitions. The present study reports the synthesis of stable oxyhydrides acting as phosphor hosts for rare earth ions. The phosphor hosts exhibit large nephelauxetic effects owing to the presence of H- ligands.