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Register a new userMelting and crystallization of Sn, Bi and Pb nanoparticles in contact with Al
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The results of studies of supercooling upon crystallization value of Bi, Sn and Pb nanosized particles on the Al substrate and between the Al layers have been presented. It has been shown the efficiency of usage of layered film systems for investigation of the limiting supercooling in particle-matrix systems with an eutectic type of interaction between components. The obtained results have been discussed and compared with literature data. ----- Predstavleny rezultaty issledovanij pereohlazhdenij pri kristallizacii nanorazmernyh chastic Bi, Sn i Pb na Al podlozhke i mezhdu sloyami alyuminiya. Pokazana effektivnost ispolzovaniya sloistyh plenochnyh sistem dlya issledovaniya predelnogo pereohlazhdeniya v sistemah chastica-matrica s evtekticheskim tipom vzaimodejstviya mezhdu komponentami. Poluchennye rezultaty obsuzhdeny i sopostavleny s literaturnymi dannymi.
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The results of studies of melting and crystallization processes in Bi-Ge layered film system are presented. These systems were prepared by subsequent condensation of components in vacuum. It has been shown that the melting temperature in system under study decreases with the decrease of Bi film thickness. The differential technique used for melting temperature registration enables us to measure the value of eutectic temperature $T_epsilon$ = 542 K in the system. The values of supercooling upon crystallization ($Delta T$ = 93 K) and wetting angle ($theta = 68^circ$) have been determined for Bi islands on amorphous Ge substrate.
The decomposition and the reformation of the (Bi,Pb)2Sr2Ca2Cu3O10+d (?Bi,Pb(2223)?) phase have been investigated in-situ by means of High-Temperature Neutron Diffraction, both in sintered bulk samples and in Ag-sheathed monofilamentary tapes. Several decomposition experiments were performed at various temperatures and under various annealing atmospheres, under flowing gas as well as in sealed tubes, in order to study the appropriate conditions for Bi,Pb(2223) formation from the melt. The Bi,Pb(2223) phase was found to melt incongruently into (Ca,Sr)2CuO3, (Sr,Ca)14Cu24O41 and a Pb,Bi-rich liquid phase. Phase reformation after melting was successfully obtained both in bulk samples and Ag-sheathed tapes. The possibility of crystallising the Bi,Pb(2223) phase from the melt was found to be extremely sensitive to the temperature and strongly dependent on the Pb losses. The study of the mass losses due to Pb evaporation was complemented by thermogravimetric analysis which proved that Pb losses are responsible for moving away from equilibrium and therefore hinder the reformation of the Bi,Pb(2223) phase from the melt. Thanks to the full pattern profile refinement, a quantitative phase analysis was carried out as a function of time and temperature and the role of the secondary phases was investigated. Lattice distortions and/or transitions were found to occur at high temperature in Bi,Pb(2223), Bi,Pb(2212), (Ca,Sr)2CuO3 and (Sr,Ca)14Cu24O41, due to cation diffusion and stoichiometry changes. The results indicate that it is possible to form the Bi,Pb(2223) phase from a liquid close to equilibrium conditions, like Bi(2212) and Bi(2201), and open new unexplored perspectives for high-quality Ag-sheathed Bi,Pb(2223) tape processing.
Two nanosized PrF3 samples were synthesized using two different procedures. The X-ray and HRTEM experiments showed high crystallinity of synthesized sample. Comparison of enhanced 141Pr NMR spectra of microsized (45 $mu$m) and nanosized PrF3 powder is presented. Experimental data on spin kinetics of 3He in contact with PrF3 nanoparticles at T = 1.5 K are reported.
Higher order topological insulators (HOTIs) are a new class of topological materials which host protected states at the corners or hinges of a crystal. HOTIs provide an intriguing alternative platform for helical and chiral edge states and Majorana modes, but there are very few known materials in this class. Recent studies have proposed Bi as a potential HOTI, however, its topological classification is not yet well accepted. In this work, we show that the (110) facets of Bi and BiSb alloys can be used to unequivocally establish the topology of these systems. Bi and Bi$_{0.92}$Sb$_{0.08}$ (110) films were grown on silicon substrates using molecular beam epitaxy and studied by scanning tunneling spectroscopy. The surfaces manifest rectangular islands which show localized hinge states on three out of the four edges, consistent with the theory for the HOTI phase. This establishes Bi and Bi$_{0.92}$Sb$_{0.08}$ as HOTIs, and raises questions about the topological classification of the full family of Bi$_{x}$Sb$_{1-x}$ alloys.
The magnetic behavior of $Fe_{3-x}O_4$ nanoparticles synthesized either by high-temperature decomposition of an organic iron precursor or low-temperature co-precipitation in aqueous conditions, is compared. Transmission electron microscopy, X-ray absorption spectroscopy, X-ray magnetic circular dichroism and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulk-like magnetic and electronic properties, while nanoparticles synthesized by co-precipitation show much poorer crystallinity and particle-like phenomenology, including reduced magnetization, high closure fields and shifted hysteresis loops. The key role of the crystal quality is thus suggested since particle-like behavior for particles larger than about 5 nm is only observed when they are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or bio-distribution studies.
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