Effect of temperature on the intensity of the relaxation due to interstitial oxygen in niobium

A niobium sample with oxygen content close to 0.15 at. % was tested under torsion on an apparatus for measurement of the internal friction on which the frequencies could be varied from 10-5 to 10 Hz. The internal friction peaks were obtained isothermally at temperatures from 75 to 1790C. The inverse of the relaxation intensity was graphed as a function of the absolute temperature of measurement. The variation law Δ = 1/T which corresponds to a zero critical temperature is followed up to 1320C and then a saturation appears. This saturation can arise from the appearance of a niobium-rich phase of the Nb/sub x/O type