Hydrogen absorption effects on the physical properties of ball-milled LaNiSn intermetallic compounds
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2016
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INTERNATIONAL CONFERENCE ON HYPERFINE INTERACTIONS AND THEIR APPLICATIONS
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A polycrystalline samples were prepared by arc melting high-purity elements under argon
atmosphere. The samples were re-melted several times to ensure homogeneity. After
arc-melting, the samples were annealed in vacuum at 800°C for 28h. After that, some
samples were milled using a Ball milling technique. The hydrogenation was carried out by
the Sievert’s method using a high purity hydrogen gas. X-ray diffraction (XRD)
measurements indicate the formation of the TiNiSi-type orthorhombic structure with space
group Pnma for the unmilled sample and its hydride. The milled samples show broad peaks
and poor crystallinity hindering the analysis of the structural properties. One sample was
milled with 10wt% of graphite. The analysis of the graphite-milled sample reveals that
graphite preserves the structural properties (the sample shows better crystalline quality)
and acts as a catalyst for the absorption of hydrogen. The analyses of the XRD patterns
show that the structural parameters are modified after the hydrogenation. The
transmission electron microscope images corroborate the XRD data. Mössbauer spectra
(297K) of the unmilled LaNiSn show the presence of only one doublet inconsistency with
the one symmetry site of Sn atoms in the TiNiSn-type structure. Moreover, spectra of the
milled samples are better reproduced by considering three doublets. Those components
were associated with Sn atoms occupying regular sites (D1), Sn atoms substituting Ni atoms
(D2) and Sn atoms of some spurious phase or Sn atoms localized in the interface region of
the grains (D3). The spectral area of the D1 component decreases at expenses of the other
two components. However, the isomeric shift (IS) of D1 and D2 shows a constant value as
the milling time is increased. The IS of the third doublet shows some fluctuating behavior
likely related to its small spectral area. The quadrupole splitting (QS) of D2 component
shows larger value than that of the D1 component and both show clear increasing tendency
as the milling time is increased. After the hydrogenation, the IS shows an increase related
to the samples before hydrogenation. However, the IS of the D1 and D2 components do not
undergo a drastic change in value with the milling time. The value of the QS of D1 and D2
components show an increase with the milling time. This result has been assigned to the
indirect interaction between Sn and H atoms which causes an asymmetric electron
distribution around the Sn atoms.
Como referenciar
ANDRE-FILHO, J.; COAQUIRA, J.A.H.; MESTNIK-FILHO, J.; CARBONARI, A.W.; NAGAMINE, L.C.C.M. Hydrogen absorption effects on the physical properties of ball-milled LaNiSn intermetallic compounds. In: TEMST, KRISTIAAN (ed.); VANTOMME, ANDRE (ed.); COTTENIER, STEFAAN (ed.); PEREIRA, LINO (ed.). In: INTERNATIONAL CONFERENCE ON HYPERFINE INTERACTIONS AND THEIR APPLICATIONS, July 3-8, 2016, Leuven, Belgium. Abstract... Leuven, Belgium: Instituut voor Kern- en Stralingsfysica, 2016. Disponível em: http://repositorio.ipen.br/handle/123456789/28011. Acesso em: 30 Dec 2025.
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