INFLUENCE OF NEIGHBOURING CHROMIUM ATOMS ON HYPERFINE FIELDS AT⁵⁷Fe NUCLEI AND ISOMER SHIFTS IN Fe-Cr ALLOYS

Abstract

RksurnB. -En utilisant plusieurs modkles diffkrents on a montrk que parmi les modeles en deux couches employks pour lisser les spectres Mossbauer des alliages Fe-Cr, le mieux appropriC est celui qui inclut uniquement les contributions des atomes de Cr situks dans les deux premikres sphkres de coordination. Utilisant ce modde pour lisser les spectres Mossbauer d'alliages Fe-Cr avec diffkrentes concentrations de chrome (1-15 at % Cr) on a montrk que la variation du champ magnktique hyperfin au site de 57Fe(AHl) produite par une impuretk dans la premikre sphkre de coordination est supkrieure a celle (AH2) produite par une impuretk qui est un second proche voisin.Le rapport R = AHllANz depend de la concentration et les lissages par moindre carrk de nos donnees montrent qu'on peut le mettre sous la forme R = 1,24 + 0,03 c pour le modkle M 12 ou R = 1,24 + 0,02 c pour le modkle M 12 BW.On a aussi ktudik le problkme de l'additivitk des effets dus aux atomes de Cr aussi bien sur les champs magnktiques hyperfins au site des noyaux 57Fe que sur les dkplacements isomkriques. On observe une additivitk partielle et totale pour le champ magnktique hyperfin, alors que pour le dkplacement isomerique il n'y a qu'une additivitk totale avec d'assez grandes erreurs expkrimentales.Abstract. -Using several different models it has been shown, that among the two-shell models employed for fitting the Mossbauer spectra of Fe-Cr alloys the most adequate is the one, which includes only contributions from those Cr atoms which occupy the first two coordination spheres. Employing then this model for fitting the Mossbauer spectra of Fe-Cr alloys having different chromium concentration (1-15 at % Cr) it has been revealed, that the change of the hyperfine magnetic field at 57Fe nuclei, AH,, due to an impurity atom in the first coordination sphere is higher than the change, AH2, due to a second-nearest neighbour impurity.The ratio R = AH IIAHz turns out to be concentration dependent and least-squeres fits to our data show that it may be expressed as R = 1.24 + 0.03 c for the M 12-model or R = 1.24 + 0.02 c for the M 12 BW-model. The problem of the additivity of the observed effects of Cr atoms both on the hyperfine magnetic fields at 57Fe nuclei and on the isomer shifts was also investigated. For the hrnf partial and total additivity is observed, whilst for the IS only total additivity occurs within rather high experimental errors.

Change of Cr atoms distribution in Fe85Cr15 alloy caused by 250keV He+ ion irradiation to different doses

“…Very good fits (in terms of  2 ) were obtained and the best-fit values of the spectral parameters are presented in Table 1. Noteworthy, these values are in a very good agreement with the corresponding ones obtained previously for Fe-Cr alloys [14][15][16][17][18][19].…”

“…It is worth noting that contrary to other microscopic methods like ATP and TEM, MS gives information on the whole sample with a resolution of a unit cell. More details can be found elsewhere [14][15][16][17][18][19].…”

Short-range order in iron-rich Fe-Cr alloys as revealed by Mössbauer spectroscopy

“…This condition significantly reduces N from 63 to e. g. N = 4 (x = 1), N = 10 (x = 10), N = 14 (x = 15). Using the above described procedure, we have successfully fitted all the measured spectra with the following values of the spectral parameters: ∆B 1 = 31.0 ± 0.5 kOe, ∆B 2 = 21.3 ± 0.6 kOe, ∆IS 1 = −0.022 ± 0.001 mm/s and ∆IS 2 = −0.009 ± 0.001 mm/s which agree well with those previously reported 11,12 . The values of P (m, n) determined from the analysis for the most significant 6 configurations are presented in Fig.…”

“…Additionally, theoretical calculations predicted the existence of such an inversion, but for different values of x 9,10 . The aim of the present investigation was to study the issue in more detail using MS, since this method applied to the Fe-Cr alloys can provide precise and relevant information on SRO for each statistically meaningful atomic configuration, (m, n), where m is the number of Cr atoms in the first-nearest neighbor shell, 1N N , and n is the number in the second-nearest neighbor shell, 2N N 11,12 . Such information would be much more detailed than the one recently found with ND 7 , where the inversion of the SRO parameter was found as the average over the 1N N −2N N volume.…”

Characterization of ODS Steels after Gamma Irradiation for Application in ALLEGRO Reactor

“…Dilute iron alloys Fe-X, where X is a 3d transition element, are intensively studied for last 40 years using the Mössbauer spectrometry [2]. Hyperfine magnetic fields (B hf ) and isomer shifts (IS) at 57 Fe nuclei, are used for investigation of the changes in phase composition caused by X element in alloy structure by various authors [3][4][5][6].…”