First-principles study of alloying effect of transition metals on He in titanium ditritide

Due to its inert reactivity with almost elements, 3He produced from tritium decay has extremely detrimental effects on the tritide. To refrain from this 3He-induced damage, an efficient way is to increase the stability of 3He in metal tritide by alloying. Using a first-principles discrete variational method in two cluster models, one for a low 3He concentration and the other for a high 3He concentration, the authors study the alloying effect of 3d and 4d transition metals on the stability of 3He in TiT2 system. It is found that the preferring and metastable sites of 3He are affected by 3He concentration: 3He prefers to stay at original tetrahedral interstitial site when 3He concentration is low but moves to octahedral site when 3He concentration is high enough. A criterion of alloying effect is proposed, according to which Nb, Y, Zr, Pd, Ru, Tc, Rh, Cr, Mo and Ag are suggested to be the beneficial alloying elements for increasing the stability of 3He in the alloyed TiT2 with a low 3He concentration and Y, Nb, Mo, Zr, Cr, Tc, Ru, Rh and Cu for that with a high 3He concentration. Our results of alloying effect are supported by the positron annihilation spectroscopy (PAS) measurements for He-implanted Ti, TiMoYAl and TiZrYAl films.