Fig. 3: Regulation of OOCs by tuning Nb and O content.

Temperature dependence of internal friction (at 1.0 Hz) and the fitting results in the (a–d) Ti–30Zr–xNb-3O (x = 18, 22, 26 and 30 at.%) and (g, h) Ti–30Zr–14Nb–yO (y = 1 and 3 at.%) MEAs. The solid black circles and the blue curves are the experimental results and the sum of the cumulative fitting peaks, respectively. The yellow and green curves correspond to the relaxation processes of the randomly distributed oxygen atoms (RDOAs). The red curves indicate the reorientation of OOCs. The calculated percentages of the oxygen atoms involved in the formation of OOCs are indicated by red arrows. Fewer oxygen atoms participate in the formation of OOCs with increasing Nb content. More oxygen atoms in Ti–30Zr–14Nb–3O participate in the formation of OOCs than that in Ti–30Zr–14Nb–1O MEA. e, i, j The 3D reconstruction of OOCs obtained via cluster analysis in Ti–30Zr–26Nb–3O, Ti–30Zr–14Nb–1O, and Ti–30Zr–14Nb–3O MEAs. Green, purple, orange, and blue colors correspond to Ti, Zr, Nb, and O atoms, respectively. f1, k1 3D APT tip reconstruction of the Ti–30Zr–30Nb–3O and Ti–30Zr–14Nb–4O MEAs, respectively. The thresholds for the isocomposition surface are 5.1 at.% and 6.8 at.%, respectively. Oxygen segregates at grain boundaries (GB). Other elements were hidden for a simplified illustration. f2, k2 The corresponding 1D concentration profiles across the grain boundaries (black arrows in f1 and k1).