3 research outputs found
Low-Temperature Synthesis and Magnetostructural Transition in Antiferromagnetic, Refractory Nanoparticles: Chromium Nitride, CrN
Nanostructured chromium
nitride (CrN), both a hard material and
a high-melting compound that is used in the medical industry and for
new energy-harvesting applications, was synthesized phase-pure for
the first time via low-temperature solution synthesis in liquid ammonia.
TEM analysis confirms the nanoscale character of CrN. The antiferromagnetic
properties of the agglomerates of nanoparticles are discussed in comparison
to literature data on the bulk materials. SQUID and DSC measurements
show the transition from paramagnetic to antiferromagnetic at 258.5
K. In situ low-temperature X-ray diffraction patterns confirm the
magnetostructural phase transition at this temperature, not seen before
for nanoscale CrN. This structural distortion was calculated earlier
to be driven by magnetic stress. The bottom-up synthesis of CrN allows
for the production of nearly oxygen- and carbon-free and highly dispersed
fine particles
Rapid Microwave Preparation and Composition Tuning of the High-Performance Magnetocalorics (Mn,Fe)<sub>2</sub>(P,Si)
Rapid preparation utilizing assisted
microwave heating permits significantly shorter preparation times
for magnetocaloric compounds in the (Mn,Fe)<sub>2</sub>(P,Si) family,
specifically samples of (Mn,Fe)<sub>2−δ</sub>P<sub>0.5</sub>Si<sub>0.5</sub> with starting compositions of δ = 0, 0.06,
and 0.12. To fully understand the effects of processing and composition
changes on structure and properties, these materials are characterized
using synchrotron powder diffraction, neutron powder diffraction,
electron microprobe analysis (EMPA), X-ray fluorescence (XRF), and
magnetic measurements. The diffraction analysis reveals that increasing
δ results in decreasing amounts of the common Heusler (Mn,Fe)<sub>3</sub>Si secondary phase. EMPA shows (Mn,Fe)<sub>2</sub>(P,Si) in
all three samples to be Mn and P rich, whereas XRF demonstrates that
the bulk material is Mn rich yet P deficient. Increasing δ brings
the Mn/Fe and P/Si ratios closer to their starting values. Measurements
of magnetic properties show an increase in saturation magnetization
and ordering temperature with increasing δ, consistent with
the increase in Fe and Si contents. Increasing δ also results
in a decrease in thermal hysteresis and an increase in magnetic entropy
change, the latter reaching values close to what have been previously
reported on samples that take much longer to prepare
Forced Disorder in the Solid Solution Li<sub>3</sub>P–Li<sub>2</sub>S: A New Class of Fully Reduced Solid Electrolytes for Lithium Metal Anodes
All-solid-state batteries based on non-combustible solid
electrolytes
are promising candidates for safe energy storage systems. In addition,
they offer the opportunity to utilize metallic lithium as an anode.
However, it has proven to be a challenge to design an electrolyte
that combines high ionic conductivity and processability with thermodynamic
stability toward lithium. Herein, we report a new highly conducting
solid solution that offers a route to overcome these challenges. The
Li–P–S ternary was first explored via a combination
of high-throughput crystal structure predictions and solid-state synthesis
(via ball milling) of the most promising compositions, specifically,
phases within the Li3P–Li2S tie line.
We systematically characterized the structural properties and Li-ion
mobility of the resulting materials by X-ray and neutron diffraction,
solid-state nuclear magnetic resonance spectroscopy (relaxometry),
and electrochemical impedance spectroscopy. A Li3P–Li2S metastable solid solution was identified, with the phases
adopting the fluorite (Li2S) structure with P substituting
for S and the extra Li+ ions occupying the octahedral voids
and contributing to the ionic transport. The analysis of the experimental
data is supported by extensive quantum-chemical calculations of both
structural stability, diffusivity, and activation barriers for Li+ transport. The new solid electrolytes show Li-ion conductivities
in the range of established materials, while their composition guarantees
thermodynamic stability toward lithium metal anodes