67 research outputs found
Phase boundary between Na-Si clathrates of structures I and II at high pressures and high temperatures
Understanding the covalent clathrate formation is a crucial point for the
design of new superhard materials with intrinsic coupling of superhardness and
metallic conductivity. Silicon clathrates have the archetype structures that
can serve an existant model compounds for superhard clathrate frameworks
"Si-B", "Si-C", "B-C" and "C" with intercalated atoms (e.g. alkali metals or
even halogenes) that can assure the metalic properties. Here we report the in
situ and ex situ studies of high-pressure formation and stability of clathrates
Na8Si46 (structure I) and Na24+xSi136 (structure II). Experiments have been
performed using standard Paris-Edinburgh cells (opposite anvils) up to 6 GPa
and 1500 K. We have established that chemical interactions in Na-Si system and
transition between two structures of clathrates occur at temperatures below
silicon melting. The strong sensitivity of crystallization products to the
sodium concentration have been observed. A tentative diagram of clathrate
transformations has been proposed. At least up to ~6 GPa, Na24+xSi136
(structure II) is stable at lower temperatures as compared to Na8Si46
(structure I)
Equation of state of single-crystal cubic boron phosphide
The 300 K equation of state of cubic (zinc-blende) boron phosphide BP has
been studied by in situ single-crystal X-ray diffraction with synchrotron
radiation up to 55 GPa. The measurements have been performed under
quasi-hydrostatic conditions using a Ne pressure medium in a diamond anvil
cell. A fit of the experimental p-V data to the Vinet equation of state yields
the bulk modulus B0 of 179(1) GPa with its pressure derivative of 3.3(1). These
values are in a good agreement with previous elastic measurements, as well as
with semiempirical estimations
Boron phosphide under pressure: in situ study by Raman scattering and X-ray diffraction
Cubic boron phosphide BP has been studied in situ by X-ray diffraction and
Raman scattering up to 55 GPa at 300 K in a diamond anvil cell. The bulk
modulus of B0 = 174(2) GPa has been established, which is in excellent
agreement with our ab initio calculations. The data on Raman shift as a
function of pressure, combined with equation-of-state data, allowed us to
estimate the Gr\"uneisen parameters of the TO and LO modes of zinc-blende
structure, {\gamma}GTO = 1.16 and {\gamma}GLO = 1.04, just like in the case of
other AIIIBV diamond-like phases, for which {\gamma}GTO > {\gamma}GLO = 1. We
also established that the pressure dependence of the effective electro-optical
constant {\alpha} is responsible for a strong change in relative intensities of
the TO and LO modes from ITO/ILO ~0.25 at 0.1 MPa to ITO/ILO ~2.5 at 45 GPa,
for which we also find excellent agreement between experiment and theory
Phonon study of rhombohedral BS under high pressure
Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under
pressures up to 34 GPa at room temperature. No pressure-induced structural
phase transition was observed, while strong pressure shift of Raman bands
towards higher wavenumbers has been revealed. IR spectroscopy as a
complementary technique has been used in order to completely describe the
phonon modes of r-BS. All experimentally observed bands have been compared with
theoretically calculated ones and modes assignment has been performed. r-BS
enriched by 10B isotope was synthesized, and the effect of boron isotopic
substitution on Raman spectra was observed and analyzed
Recent Developments of High-Pressure Spark Plasma Sintering: An Overview of Current Applications, Challenges and Future Directions
International audienceSpark plasma sintering (SPS), also called pulsed electric current sintering (PECS) or field-assisted sintering technique (FAST) is a technique for sintering powder under moderate uniaxial pressure (max. 0.15 GPa) and high temperature (up to 2500 °C). It has been widely used over the last few years as it can achieve full densification of ceramic or metal powders with lower sintering temperature and shorter processing time compared to conventional processes, opening up new possibilities for nanomaterials densification. More recently, new frontiers of opportunities are emerging by coupling SPS with high pressure (up to ~10 GPa). A vast exciting field of academic research is now using high-pressure SPS (HP-SPS) in order to play with various parameters of sintering, like grain growth, structural stability and chemical reactivity, allowing the full densification of metastable or hard-to-sinter materials. This review summarizes the various benefits of HP-SPS for the sintering of many classes of advanced functional materials. It presents the latest research findings on various HP-SPS technologies with particular emphasis on their associated metrologies and their main outstanding results obtained. Finally, in the last section, this review lists some perspectives regarding the current challenges and future directions in which the HP-SPS field may have great breakthroughs in the coming years
Recent Developments of High-Pressure Spark Plasma Sintering: An Overview of Current Applications, Challenges and Future Directions
Spark plasma sintering (SPS), also called pulsed electric current sintering (PECS) or field-assisted sintering technique (FAST) is a technique for sintering powder under moderate uniaxial pressure (max. 0.15 GPa) and high temperature (up to 2500 °C). It has been widely used over the last few years as it can achieve full densification of ceramic or metal powders with lower sintering temperature and shorter processing time compared to conventional processes, opening up new possibilities for nanomaterials densification. More recently, new frontiers of opportunities are emerging by coupling SPS with high pressure (up to ~10 GPa). A vast exciting field of academic research is now using high-pressure SPS (HP-SPS) in order to play with various parameters of sintering, like grain growth, structural stability and chemical reactivity, allowing the full densification of metastable or hard-to-sinter materials. This review summarizes the various benefits of HP-SPS for the sintering of many classes of advanced functional materials. It presents the latest research findings on various HP-SPS technologies with particular emphasis on their associated metrologies and their main outstanding results obtained. Finally, in the last section, this review lists some perspectives regarding the current challenges and future directions in which the HP-SPS field may have great breakthroughs in the coming years
In Situ High-Pressure Synthesis of New Outstanding Light-Element Materials under Industrial P-T Range
International audienceHigh-pressure synthesis (which refers to pressure synthesis in the range of 1 to several GPa) adds a promising additional dimension for exploration of compounds that are inaccessible to traditional chemical methods and can lead to new industrially outstanding materials. It is nowadays a vast exciting field of industrial and academic research opening up new frontiers. In this context, an emerging and important methodology for the rapid exploration of composition-pressure-temperature-time space is the in situ method by synchrotron X-ray diffraction. This review introduces the latest advances of high-pressure devices that are adapted to X-ray diffraction in synchrotrons. It focuses particularly on the “large volume” presses (able to compress the volume above several mm3 to pressure higher than several GPa) designed for in situ exploration and that are suitable for discovering and scaling the stable or metastable compounds under “traditional” industrial pressure range (3–8 GPa). We illustrated the power of such methodology by (i) two classical examples of “reference” superhard high-pressure materials, diamond and cubic boron nitride c-BN; and (ii) recent successful in situ high-pressure syntheses of light-element compounds that allowed expanding the domain of possible application high-pressure materials toward solar optoelectronic and infra-red photonics. Finally, in the last section, we summarize some perspectives regarding the current challenges and future directions in which the field of in situ high-pressure synthesis in industrial pressure scale may have great breakthroughs in the next years
Equations of state of new boron-rich selenides B6Se and B12Se
International audienceTwo novel of boron-rich selenides, orthorhombic B6Se and rhombohedral B12Se, have been recently synthesized at high pressure-high temperature conditions. Room-temperature compressibilities of these phases were studied in a diamond anvil cell using synchrotron powder X-ray diffraction. A fit of experimental p-V data by third-order Birch-Murnaghan equation of state yielded the bulk moduli of 155(2) GPa for B12Se and 144(3) GPa for B6Se. No pressure-induced phase transitions have been observed in the studied pressure range, i.e. up to 35 GPa
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