An Estimation of Force Constant Change of Mössbauer ¹¹⁹Sn Impurity Nuclei in Palladium Host

Abstract

Precision measurements are made of the second order Doppler shift and absorption areas of the Mossbauer line of ll9Sn, present as a dilute impurity in palladium lattice, over a range from liquid helium temperature to about 750 O K . The weighted mean temperatures have been determined from the moments w ( -2 ) , w ( -l), w ( + l), and w( + 2 ) of the phonon frequency distribution in the palladium lattice as seen by the Mossbauer l19Sn impurity atoms. Assuming a Debye spectrum, ratios of the impurity-host t o host-host spring force constants have been estimated from the characteristic temperatures on the basis of Mannheim's model of nearest neighbour central forces. The Sn-Pd force constant has been found weaker than the equivalent Pd-Pd force constant indicating the presence of resonance band modes without any evidence of localised impurity modes.Es werden Prlzisionsmessungen der Doppler-Verschiebung zweiter Ordnung und der Absorptionsflachen der MoDbauerlinie von ll9Sn, das als verdunnte Storstelle im Palladiumgitter vorliegt, im weiten Temperaturbereich vom flussigen Helium bis etwa 750 O K durchgefuhrt. Die gewichteten mittleren Temperaturen werden aus den Momenten w ( -2 ) , w ( -l), w ( + l ) und w ( + 2 ) der Verteilung der Phononenfrequenzen im Palladiumgitter bestimmt, die auf die 119Sn-Mol3bauerstorstellen einwirken. Unter der Annahme eines DebyeSpektrums werden die Verhaltnisse der Storstellen-Wirtsgitter-zu den Wirtsgitter-Wirtsgitter-Federkonstanten aus den charakteristischen Temperaturen auf der Basis des Modells yon Mannheim fur die Zentralkrafte der iiachsten Nachbarn berechnet. Es wird gefunden, daD die Sn-Pd-Kraftkonstante schwacher als die aquivalente Pd-Pd-Kraftkonstante ist, was die Anwesenheit von Resonanzmoden anzeigt, ohne irgendeinen Hinweis auf lokalisierte Storstellenmoden.

Force Constant Change in Sn–Impurity Systems: 107Pd:119 Sn, 197Au:119Sn, and 63.5Cu:119Sn

“…Our results are further supported by the analysis of Grow et al [(i], who found the value of A'/A = 0.44 with no evidence of a localized mode in the IO' Pd: IlsSn system. I n addition, Puri and Gupta [19], analysing their measurements of f in the framework of the Debye model got X'/A = 0.47, which obviously is comparable to our resuit. Van Landuyt et al reported nieasurcmcnts of f-values up to 300 K and assumed, quite explicabIy, that there is no need for any correction for anharmonicity, since the Debye temperature of Pd is 275 K. However, in view of the available measurcments of the system lo7Pd:11%n up to 729 K by Pnri and Gupta [19] an attempt to calculate the recoilless fraction over the entire temperature rangc, neccssitatcd the incorporation of anharmonicity.…”