Mechanisms of Combustion Synthesis and Magnetic Response of High-Surface-Area Hexaboride Compounds

Abstract

We present an analysis of the combustion synthesis mechanisms for the preparation of hexaboride materials using three compounds as model systems: EuB(6), YbB(6), and YB(6). These three hexaborides were chosen because of the differences in ionic radii between Eu(3+), Yb(3+), and Y(3+), which is a factor in their stability. The powders were prepared using metal nitrates, carbohydrazide, and two different boron precursor powders. The resulting materials were analyzed by X-ray diffraction, which showed that combustion synthesis is effective for the synthesis of EuB(6), since the Eu(3+) ion has an ionic radius greater than ∼1 Å. The synthesis of YbB(6) and YB(6) is not as effective because of the small size of the Yb(3+) and Y(3+) ions, making the hexaborides of these metals less stable and resulting in the synthesis of borates due to the presence of oxygen during the combustion process. Scanning electron microscopy and dynamic light scattering of the EuB(6) powders shows that the particle size of the hexaboride product is dependent on the particle size of the boron precursor. The magnetic susceptibility of our EuB(6) powders manifests irreversible behavior at low applied fields, which disappears at higher fields. This behavior can be attributed to the increase in size and number of magnetic polarons with increasing magnetic field.

Mechanisms of pore formation in high-temperature carbides: Case study of TaC prepared by spark plasma sintering

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New Methods for Preparing Submicrometer Powders of The Tungstate‐Ion Conductor Sc2(WO4)3 and its Al and In Analogs

“…In this work, the combustion synthesis of M 2 (WO 4 ) 3 powders prepared using urea and carbohydrazide as fuels is reported for the first time. The sintering behavior of the two different powders is compared as are the electrical properties of the resulting polycrystalline ceramics.…”

Nanodomains and local structure in ternary alkaline-earth hexaborides

“…Both are annealed under argon at NIST to reduce intrinsic defect concentrations. The three ternary alkaline-earth hexaborides (MB 6 , M = Ca 0.5 Sr 0.5 , Ca 0.5 Ba 0.5 and Sr 0.5 Ba 0.5 ) were identical to those previously reported by Cahill and co-workers (Cahill, Alberga et al, 2017), prepared using combustion synthesis techniques (Kanakala et al, 2010(Kanakala et al, , 2011Kelly et al, 2010). Precursors were heated to 773 K with carbohydrazide as a fuel source.…”