IFLP   13074
INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Mössbauer Line tracking study of α--transition in FeS
Autor/es:
P.MENDOZA ZÉLIS; G.A. PASQUEVICH; A. VEIGA; M.B. FERNÁNDEZ VAN RAAP; F.H. SÁNCHEZ
Lugar:
La Plata, Argentina
Reunión:
Conferencia; 75- XI Latin American Conference on the Applications of the Mössbauer Effec; 2008
Resumen:
<!-- /* Font Definitions */ @font-face {font-family:Advt93-r; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-charset:0; mso-generic-font-family:auto; mso-font-format:other; mso-font-pitch:auto; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0pt; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB;} @page Section1 {size:595.3pt 841.9pt; margin:70.85pt 85.05pt 70.85pt 85.05pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The α-structural transition on slightly non stoichiometric FeS is studied by Mössbauer Spectroscopy and Mössbauer Line Tracking methodology [1]. Recent results from different authors lead to uncertainties about FeS transitions that appear in phase diagram handbooks [2]. According to the most recent reports the superstructure derived form the NiAs-type structure transforms into the MnP orthorhombic one near 400K [3,4]. Both phases coexist within a temperature interval which, depending on sulphur concentration, goes from a few degrees to around 200 K. They are antiferromagnetic with iron atoms located at unique crystallographic sites. The environment of the probes are different enough as to allow hyperfine fields from both phases to be distinguished. For a Mössbauer Line Tracking experiment a conventional pulse height selection branch, and a Mössbauer driving system in which a novel programmable constant-velocity scaler [5] replaces the usual multiscaler, are used. This set up allows the independent measurement of any channel of a Mössbauer spectrum during an arbitrary period of time. Then, the acquisition of a spectrum region does not necessarily include its central part.  Here, this methodology is used to perform a quasi-continuous temperature study of the a-transition. One or more absorption lines, from both phases, can be followed simultaneously while temperature is varied within the coexistence region. This work is also used as an appropriate test for this novel technique. Therefore, not only the physics of the a-transition is treated in this contribution, but a description of the technique and a discussion of the applied line tracking algorithm are also presented.   [1] A. Veiga, et. al., Experimental Design and Methodology for a new Mössbauer scan experiment: Absorption line tracking, Proceedings ICAME 2007. In press at Hyperfine  Interact. [2] Massalski, T. B. (1996). Editor. Binary Alloys Phase Diagrams, 2nd ed. plus updates. Materials Park, Ohio: ASM International. [3] Kyung Seon Baek, et. al. Effects of sulfur vacancies on the crystallographic and spin rotation transition of iron sulfide, Phys. Rev. B, 41, 9024,1990 [4] Fan Li, Phase tranistion in near stoichiometric iron sulfide, Jour. Alloys and Comp., 238, 73 [5] A. Veiga et al., Advances in constant velocity Mössbauer instrumentación”, Hyperfine Interact., 167, (2006) pp 905-909.  
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