Moessbauer study of 57Fe in the hydrides and deuterides of tantalum

The Moessbauer absorption of dilute substitutional 57Fe probes in hydrides and deuterides of tantalum was studied at hydrogen-to-metal ratios near 0.5 and 0.75 and at temperatures between 78 K and 400 K. The transition from slow to fast hydrogen diffusion is observed in the Moessbauer spectra between about 200 and 350 K. It is most clearly reflected by the intensity of the Moessbauer resonance, which decreases by a factor fstr when the quasielastic Moessbauer line becomes too broad to contribute noticeably to the observed intensity. The values of fstr range between 0.60 in TaD0.53 and 0.46 in TaH0.78. The displacements u1 of substitutional iron probes caused by a single nearest interstitial derived from these data are substantially larger than those of Ta atoms. (orig.)