Evolution of Pressure-induced Shear Amorphization in Rare-earth Hexaboride

Research on rare-earth hexaborides mainly focuses on tuning the electronic structure from insulating-to-metallic state and vice versa (referred as exotic phenomena) by high pressure experiments via displacive phase transformations, however, the structural evolution that contributing to this underlying failure mechanism remains not well understood. Herein, we examined the pressure induced structural evolution through a model system of europium hexaboride (EuB6). Transmission electron microscopy reveal that the nanoscale amorphous shear bands mediated by dislocations play a decisive role in deformation failure of EuB6 subjected to high pressure nanoidentation at room temperature. Density functional theory simulations confirm that these amorphous bands evolve by breaking B-B bonds within B6 octahedron of EuB6 during shear deformation. Our results underscore an important damage mechanism in hard and fragile hexaborides at high shear pressures.

Магнитные свойства Eu-=SUB=-0.9-=/SUB=-Yb-=SUB=-0.1-=/SUB=-B-=SUB=-6-=/SUB=-

The magnetic properties of substitutional solid solutions Eu_0.9Yb_0.1B_6 have been investigated in the temperature range of 2–300 K in fields up to 5 T. The data obtained confirm that the state with the electronic and magnetic phase separation (typical of europium hexaboride) is implemented in Eu_0.9Yb_0.1B_6 when the system metallization ( T _M ≈ 15 K) precedes the ferromagnetic ordering ( T _C ≈ 11.4 K). An analysis of the curves M ( H ) in the Belov–Arrott coordinates makes it possible to evaluate spontaneous magnetization M _sp and zero field susceptibility χ_0 and determine the character of their critical behavior near the Curie point. The calculated critical indices (γ ≈ 1.28 and β ≈ 0.34) are in agreement with the predictions of the three-dimensional Heisenberg model.

Synthesis and characterization of EuB6 by borothermic reduction of Eu2O3

Carbon free high pure europium hexaboride is an urgent need for the fast breeder nuclear reactor program. The properties of EuB6 are highly influenced by the presence of one or more substitutional impurities, particularly, carbon, oxygen and nitrogen. In the present investigation carbon and nitrogen free high pure europium hexaboride was synthesized by borothermic reduction of europium oxide Eu2O3 (using boron as a reducing agent) at relatively low temperature (< 900?C). Glassy B2O3, the by-product of the synthesis process, was leached out completely in slightly acidic warm water from which boron could be recovered by usual electrolysis process. The product obtained was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis. Oxidation behaviour of pressureless sintered EuB6 pellets (> 90 % of theoretical density) was studied at 850?C and revealed that an adherent thin surface of Eu2O3 was formed which prevent the further oxidation.