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External irradiation with heavy ions of neodymium silicate apatite ceramics and glass-ceramics
摘要： This work aims at comparing the damage induced in the Nd silicate apatite ceramic (Ca2Nd8(SiO4)6O2) by medium energy (ME) and swift heavy ion (SHI) irradiations to evaluate the effects of nuclear collisions and intense electronic excitations for ME ions and SHI ions respectively. The macroscopic induced changes were studied as a function of the fluence by swelling and hardness measurements, whereas structural modifications were followed by X-ray diffraction, Raman spectroscopy and grazing incidence EXAFS (Nd L3-edge). At ME (1.9e6.75 MeV Au ions), radiation-induced amorphization occurred above 6.22 (cid:1) 1013 Au/cm2 associated with a volume expansion of about 8% and a drop of 37% in hardness. At SHI (90 MeV Xe ions or 35 MeV Ar ions), similar macroscopic and structural changes were observed. The electronic stopping power threshold of Nd silicate apatite for amorphization was assessed at about Se ? 5 keV/nm. As apatite crystals containing actinides could be present in rare-earths rich nuclear glasses, SHI irradiation with Xe (995 MeV) ions was also used to damage the Nd silicate apatite crystals dispersed in a soda-lime aluminoborosilicate simplified nuclear glass over a depth of about 60 mm, to evaluate the possible formation of cracks in the residual glass due to crystals swelling. In spite of apatite crystals amorphization under SHI irradiation in the glass-ceramics, no cracking was observed in the glassy phase even close to the biggest crystals which could be explained by strain relaxation in the glass due to plastic deformation (creep) induced by SHI ion beam.
关键词： Amorphization,Glass-ceramic,Neodymium silicate apatite,Heavy ions irradiation
更新于2025-09-23 15:23:52
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The amorphization of metal nanoparticles in graphitic shells under laser pulses
摘要： It is shown that graphitic shells encapsulating metal nanoparticles facilitate the amorphization of metals and stabilize the amorphous phase against recrystallization. In an in-situ electron microscopy experiment, where the objects are exposed to laser pulses during their observation, the amorphization of iron and cobalt nanocrystals in graphitic shells is demonstrated. The infrared nanosecond pulses lead to fast melting of the metal which then dissolves carbon atoms from the shell. Fast cooling of the liquid solution after the pulse results in the solidification of an amorphous metal-carbon phase. The amorphous phase is metastable and can be recrystallized by repeated laser pulses or slow thermal annealing. The recrystallization needs heterogeneous nucleation but is unfavorable at the metal-graphite interface and so stabilizes the amorphous phase against recrystallization. The analysis of the experiments explains the formation mechanisms of an amorphous metal-carbon phase as a metastable solution of carbon in a transition metal and shows how that the encapsulation by a graphitic shell can be a route towards the stabilization of otherwise unfavorable amorphous metal or metal-carbon phases.
关键词： amorphization,electron microscopy,metal nanoparticles,graphitic shells,laser pulses
更新于2025-09-16 10:30:52
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Pressure-Induced Broadband Emission of 2D Organic-Inorganic Hybrid Perovskite (C <sub/>6</sub> H <sub/>5</sub> C <sub/>2</sub> H <sub/>4</sub> NH <sub/>3</sub> ) <sub/>2</sub> PbBr <sub/>4</sub>
摘要： 2D Ruddlesden–Popper halide perovskites, which incorporate hydrophobic organic interlayers to considerably improve environmental stability and optical properties diversity, have attracted substantial research attention for optoelectronic applications. The burgeoning broad emission arising from exciton self-trapping of 2D perovskites shows a strong dependence on a deformable structure. Here, the pressure-induced broadband emission of layered (001) Pb-Br perovskite with a large Stokes shift in the visible region is observed by finely improving lattice distortion to increase exciton–phonon coupling under hydrostatic pressure. Band gap narrows ≈0.5 eV under modest pressure, mainly due to the large compressibility of the orientational organic layer, confirming that the bulky organic cations notably influence the structure and, in turn, the various properties of materials. Sequential amorphization of the organic and inorganic layer is confirmed by high pressure Raman and X-ray diffraction measurements, suggesting the particularity of layered crystal structures. The mechanism constructed here offers a new route for tuning the optical properties of 2D perovskites.
关键词： broadband emission,band-gap narrowing,pressure,perovskites,amorphization
更新于2025-09-10 09:29:36
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Re-amorphization of GeSbTe alloys not through a melt-quenching process
摘要： Ge–Sb–Te (GST) alloys are one of the most successful chalcogenides used in rewritable optical discs and electric non-volatile memories. In these materials the structural phase transition between amorphous and crystalline states is used for recording. Here, we report that a melt-quenching method is not necessarily the only way to form a high-resistance phase. We found that amorphous-like grains with high resistance are formed in the GST crystal film by holding it at above the crystallization temperature under an external magnetic field, followed by cooling accompanied with pulse current injection. The treatment may open new route for ultra-low current switching phase change memory.
关键词： pulse current injection,Ge–Sb–Te alloys,phase change memory,re-amorphization,magnetic field
更新于2025-09-09 09:28:46
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Stored energy release in neutron irradiated silicon carbide
摘要： The purpose of this investigation is to experimentally quantify the stored energy release upon thermal annealing of previously irradiated high-purity silicon carbide (SiC.) Samples of highly-faulted poly-crystalline CVD b-SiC and single crystal 6HeSiC were irradiated in a mixed spectrum ?ssion reactor near 60 (cid:1)C in a ?uence range from 5 (cid:3) 1023 to 2 (cid:3) 1026 n/m2 (E > 0.1 MeV), or about 0.05e20 dpa, in order to quantify the stored energy release and correlate the release to the observed microscopic swelling, lattice dilation, and microstructure as observed through TEM. Within the ?uence of this study the crystalline material was observed to swell to a remarkable extent, achieving 8.13% dilation, and then cross a threshold dose for amorphization at approximately 1 (cid:3) 1025 n/m2 (E > 0.1 MeV) Once amorphized the material attains an as-amorphized swelling of 11.7% at this irradiation condition. Coincident with the extraordinary swelling obtained for the crystalline SiC, an equally impressive stored energy release of greater than 2500 J/g at the critical threshold for amorphization is inferred. As expected, following amorphization the stored energy in the structure diminishes, measured to be approximately 590 J/g. Generally, the ?ndings of stored energy are consistent with existing theory, though the amount of stored energy given the large observed crystalline strain is remarkable. The overall conclusion of this work ?nds comparable stored energy in SiC to that of nuclear graphite, and similar to graphite, a stored energy release in excess of its speci?c heat in some irradiation conditions.
关键词： Neutron irradiation,Amorphization,Silicon carbide,Swelling,Stored energy
更新于2025-09-04 15:30:14