Anomalies in the thermal expansion of niobium hybrides NbH0.87 and NbH0.9

The temperature dependences of the linear expansion coefficients of NbH 0.87 and NbH 0.9 were determined at 77-430 K. The volume jumps at the phase transitions β → α', λ → β, and γ → βwere determined. dT c /dP was determined for these transitions as well as γ Gr and their temperature dependences. The anomalous behavior of α(T) of the β phase of NbH 0.9 and the lattice compression as a result of the β → α' transition were analyzed using a model proposed by Vaks and Zimenko [J. Phys. Condens. Matter 1, 9085 (1989)] for the composition dependence of the degree of order in the hydrogen sublattice of the β phase of NbH x