Defect study of yttrium-hydrogen solid solutions

The resistivity anomaly near 170 K in α-YD(D)sub(x) solid solutions due to the ordering of hydrogen into a paired configuration is analysed in detail. Defects are introduced into the ordered structure by a quench from room temperature and by electron irradiation at 20 K (Esub(e-)= 0.35 to 0.8 MeV) resulting in residual resistivity increases, Δrhoq and Δrhosub(irr), which are functions of H concentration, x, with a strong isotope effect on Δrho sub(irr). The electron energy dependence of Δrhosub(irr) is fitted with theoretical electron-hydrogen collisions cross sections reproducing the correct behaviour when using a displacement threshold of Tsub(d)(H) approx. 0.1 eV, which corresponds to the binding energy, Esub(b), of the ordered structure. The latter has been determined to Esub(b)(H) 61 + - 2 meV and Esub(b)(D) = 70 + - 2 meV. An annealing study of the introduced Δrhoq and Δrhosub(irr) shows that they are due to defects in the ordered H structure; they recover in the anomaly region, with an activation energy for migration of Esub(m)(H) = 200 to 220 meV and Esub(m)(D) = 250 to 300 meV. The recovery temperature for Δrhosub(irr) decreases slightly with increasing x but is independent of the incident electron dose, giving an indication about the defect cascade structure. The results are discussed in the framework of the lattice gas picture and compared with those obtained earlier on the similar systems α-ScH(D)sub(x) and α-LuH(D)sub(x). (author) (author)