Invar behaviour and in situ observation of the nitriding process in R2Fe17Nx intermetallics

Thermal expansion measurements in the high range of temperature (300-1000 K) have been performed from starting R2Fe17 intermetallics (R=Nd and Er). Large anomalies in the thermal expansion were observed during the nitriding process for increasing temperatures, which have allowed us to study the dynamics of the nitrogen absorption. From our results it is clear that this process takes place in the range of temperature 500-700 K. Large invar anomalies starting at high temperature ((733±5) K for Nd and (688±5) K for Er) have been also observed in the thermal expansion for decreasing temperatures, being an indication of the strong magnetovolume effect which apparently is responsible for the large increase of the Curie temperature in the R2Fe17Nx compounds. (orig.)