ChemInform Abstract: CHARAKTERISTISCHE ROENTGENTEMPERATUR UND WAERMEAUSDEHNUNGSKOEFFIZIENT VON MG2SI

Abstract

Mit Hilfe einer Präzisionsröntgenmethode wird die Temperaturabhängigkeit der Gitterperiode von Mg2Si im Bereich von 20‐300°C gemessen.

Anharmonic effects in Mg2X (X = Si, Ge, Sn) compounds studied by Raman spectroscopy

“…Since y T > 0, this means that" v > 0 and therefore (aw / aT) v 0, i. e. , the explicit contribution tends to decrease the frequency with increasing T. According to a general scheme suggested in reference [5], the fact that q 0.5 is indicative of predominantly covalent bonding. This is consistent with the results of references [12][13][14] and [21,22] where analogous conclusions are reached. On the other hand, the above results are contrary to those of references [23,24] where it was concluded that the bonding is largely ionic.…”

“…-Corrected phonon linewidths (fullwidth at half maximum) as a function of temperature. The solid lines represent best least square fits to equation (14).…”

“…Temperature dependent data for the volume thermal expansion coefficient f3 can be found in references [14] and [15] for Mg2Si and Mg2Ge respectively, in the temperature range 300-530 K. For M92Sn only the room temperature value of fl could be found in the literature [16], while for higher temperatures provision has been taken so that the f3 ( T) curve has the same behaviour as those of Mg2Si and Mg2Ge. The values of f3 for lower temperatures were calculated using existing Debye temperatures [17] and the expression [6,18] where D ( n ) is the Debye integral…”

“…A different way of looking at the relative importance of the two contributions is to calculate the so-called implicit fraction [5], that is the ratio where y p, y v are the Grüneisen parameters at constant pressure and constant volume, respectively, given by Table II. -Values for the various coefficients appearing in equations (9,14).…”