Grain-size dependence of Snoek peaks in niobium

The effect of grain size on the oxygen and nitrogen Snoek peaks in niobium has been studied. It has been observed that the conversion factor K given by C = K_max, where C is the concentration of oxygen or nitrogen and _max the height of the corresponding Snoek peak, is concentration independent up to about 0.06 and 0.04 wt % oxygen and nitrogen respectively.The variation of K with grain size (d) obeys the relationship K = K₀ + k_Kd^–1/2, where K₀ represents the value of K for an aggregate of crystals without boundaries and k_K the grain size dependence of K.