3 research outputs found
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 V<sub>2</sub>GeC, V<sub>2</sub>GeC<sub>0.5</sub>N<sub>0.5</sub>, and V<sub>2</sub>GeN
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(BH<sub>4</sub>)<sub>2</sub> 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<sup>–1</sup> H<sub>2</sub>, Ca(BH<sub>4</sub>)<sub>2</sub> 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 (TiF<sub>4</sub>, NbF<sub>5</sub>, Ti-isopropoxide, and CaF<sub>2</sub>) 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. <sup>11</sup>B{<sup>1</sup>H} solid state magic angle spinning-nuclear magnetic resonance (MAS
NMR) was carried out to detect possible amorphous phases. The formation
of TiB<sub>2</sub> and NbB<sub>2</sub> nanoparticles was observed
after milling or upon sorption reactions of the Nb- and Ti-based Ca(BH<sub>4</sub>)<sub>2</sub> doped systems. The formation of transition-metal
boride nanoparticles is proposed to support the heterogeneous nucleation
of CaB<sub>6</sub>. The {111}CaB<sub>6</sub>/{1011}NbB<sub>2</sub>, {111}CaB<sub>6</sub>/{1010}NbB<sub>2</sub>, as well as {111}CaB<sub>6</sub>/{1011}TiB<sub>2</sub> 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 CaB<sub>6</sub>, refine the microstructure thus improving
the sorption kinetics, and, as a consequence, lead to the reversible
formation of Ca(BH<sub>4</sub>)<sub>2</sub>