X-ray investigation of the α-α' phase transition of hydrogen in Pd1-xAgxalloys

Abstract

The alpha - alpha ' phase transition of hydrogen in Pd0.9Ag0.1 and Pd0.8Ag0.2 has been investigated by X-ray scattering. The sample contained a constant, average hydrogen concentration, close to the critical concentration. However, a critical point could not be observed, and the alpha and alpha ' phases coexisted up to T>Tc, where Tc is taken from solubility measurements. This effect is discussed in terms of internal stress fields, originating from hydrogen exchange between the two phases, which are embedded in an elastically responding host lattice. The internal stresses prevent the phases from merging into one homogeneous phase above Tc; they have been determined to be of the order of 108 N m-2. In an accompanying study the lattice parameter change of Pd0.9Ag0.1 per% hydrogen concentration has been determined to be (6.6+or-0.2)*10-4.