LaFe11.8Si1.2 INS study

Origin Project containing final figures and raw/processed inelastic neutron scattering data for x=1.2 as well as linescans extracted for background subtraction (Figure 4 & 5).</p

Exploring the Potential of Nitride and Carbonitride MAX Phases: Synthesis, Magnetic and Electrical Transport Properties of V₂GeC, V₂GeC_0.5N_0.5, and V₂GeN

The chemical composition variety of MAX phases is rapidly evolving in many different directions, especially with the synthesis of carbides that contain two or more metals on the M-site of these layered solids. However, nitride and carbonitride MAX phases are still underrepresented, and only a few members have been reported that are for the most part barely characterized, particularly in terms of magnetic and electronic properties. Here, we demonstrate a simple and effective synthesis route, as well as a comprehensive characterization of three MAX phases, (i) V2GeC, (ii) the hitherto unknown carbonitride V2GeC0.5N0.5, and (iii) the almost unexplored nitride V2GeN. By combining a microwave-assisted precursor synthesis with conventional heat treatment and densification by spark plasma sintering, almost phase-pure (carbo)nitride products are obtained. Magnetic measurements reveal an antiferromagnetic-paramagnetic-like phase transition for all samples in the temperature range of 160–200 K. In addition, increasing the amount of nitrogen on the X-site of the MAX phase structure leads to a constant increase in the magnetic susceptibilities while the electrical resistivity is constantly decreasing. Overall, these findings provide crucial insights into how to tune the electronic and magnetic properties of MAX phases by only varying the chemical composition of the X-site. This further substantiates the demand for (carbo)nitride research with the potential to be extended to the remaining elemental sites within the MAX phase structure to push toward controlled material design and to achieve desired functional properties, such as ferromagnetism

Chemical State, Distribution, and Role of Ti- and Nb-Based Additives on the Ca(BH₄)₂ System

Light metal tetrahydroborates are regarded as promising materials for solid state hydrogen storage. Due to both a high gravimetric hydrogen capacity of 11.5 wt % and an ideal dehydrogenation enthalpy of 32 kJ mol^–1 H₂, Ca­(BH₄)₂ is considered to be one of the most interesting compounds in this class of materials. In this work, a comprehensive investigation of the effect of different selected additives (TiF₄, NbF₅, Ti-isopropoxide, and CaF₂) on the reversible hydrogenation reaction of calcium borohydride is presented combining different investigation techniques. The chemical state of the Nb- and Ti-based additives is studied by X-ray absorption spectroscopy (e.g., XANES). Transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDX) was used to show the local structure, size, and distribution of the additive/catalyst. ¹¹B­{¹H} solid state magic angle spinning-nuclear magnetic resonance (MAS NMR) was carried out to detect possible amorphous phases. The formation of TiB₂ and NbB₂ nanoparticles was observed after milling or upon sorption reactions of the Nb- and Ti-based Ca­(BH₄)₂ doped systems. The formation of transition-metal boride nanoparticles is proposed to support the heterogeneous nucleation of CaB₆. The {111}­CaB₆/{1011}­NbB₂, {111}­CaB₆/{1010}­NbB₂, as well as {111}­CaB₆/{1011}­TiB₂ plane pairs have the potential to be the matching planes because the <i>d</i>-value mismatch is well below the <i>d</i>-critical mismatch value (6%). Transition-metal boride nanoparticles act as heterogeneous nucleation sites for CaB₆, refine the microstructure thus improving the sorption kinetics, and, as a consequence, lead to the reversible formation of Ca­(BH₄)₂