Nanoscale characterization of beryllide materials

The most recent version of the Helium Cooled Pebble Bed (HCPB) foreseen for the European DEMO blanket considers solid blocks of titanium beryllide as neutron multiplicator material. The advantage of beryllide materials over pure beryllium is their higher operating temperature, higher corrosion resistance, lower swelling, and retention of tritium under neutron irradiation. Understanding the micro- and nanostructure especially after neutron irradiation is of crucial importance for the qualification process of the material. The focus of this work will lie on the transmission electron microscopy (TEM) characterization of a titanium beryllide/beryllium composite material irradiated at two different temperatures during the HIDOBE neutron irradiation campaign. In particular, the structure and chemistry of the nanosized cavities in the pure beryllium region and the beryllide region was analyzed and is compared to each other. Apart from the cavities, structural defects were observed in the beryllide region that are not known from irradiated pure beryllium. The presented results can be used for understanding and quantifying for example tritium retention in beryllide materials and to further optimize the material synthesis and the breeding blanked design in general

Atomic structure and domain wall pinning in samarium-cobalt-based permanent magnets

A higher saturation magnetization obtained by an increased iron content is essential for yielding larger energy products in rare-earth Sm₂Co₁₇-type pinning-controlled permanent magnets. These are of importance for high-temperature industrial applications due to their intrinsic corrosion resistance and temperature stability. Here we present model magnets with an increased iron content based on a unique nanostructure and -chemical modification route using Fe, Cu, and Zr as dopants. The iron content controls the formation of a diamond-shaped cellular structure that dominates the density and strength of the domain wall pinning sites and thus the coercivity. Using ultra-high-resolution experimental and theoretical methods, we revealed the atomic structure of the single phases present and established a direct correlation to the macroscopic magnetic properties. With further development, this knowledge can be applied to produce samarium cobalt permanent magnets with improved magnetic performance

Synthesis, morphology, thermal stability and magnetic properties of α″-Fe16N2 nanoparticles obtained by hydrogen reduction of γ-Fe2O3 and subsequent nitrogenation

International audienc

High-Pressure Synthesis of Novel Boron Oxynitride B6N4O3 with Sphalerite Type Structure

A novel crystalline boron oxynitride (BON) phase has been synthesized under static pressures exceeding 15 GPa and temperatures above 1900 degrees C, from molar mixtures of B2O3 and h-BN. The structure and composition of the synthesized product were studied using high-resolution transmission electron microscopy, electron diffraction, automated diffraction tomography, energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS). BON shows a hexagonal cell (R3m, Z = 3) with lattice parameters a = 2.55(5) A and c = 6.37(13) angstrom, and a crystal structure closely related to the cubic sphalerite type. The EELS quantification yielded 42 at % B, 35 at % N, and 23 at % 0 (B:N:O approximate to 6:4:3). Electronic structure calculations in the framework of Density Functional Theory have been performed to assess the stabilities and properties of selected models with the composition B6N4O3. These models contain ordered structural vacancies and are superstructures of the sphalerite structure. The calculated bulk moduli of the structure models with the lowest formation enthalpies are around 300 GPa, higher than for any other known oxynitride