Structural changes in PdDx in the temperature region of the 50 K anomaly

Diffuse neutron scattering in β-PdDx (for x = 0.710, 0.742, 0.754 and 0.780) was observed around the 1 {{1}\over{2}}, 0)* point in reciprocal space in the temperature range between 50 and 150 K. The detailed shape of the diffuse pattern is dependent on the deuterium concentration for x between 0.71 and 0.742 and nearly independent for higher concentrations. An increase of the diffuse intensities was found when cooling down the samples to 50 K and was associated with the anomaly of the resistivity. During an annealing treatment in PdD0.780 at 70 and 75 K, superlattice reflections appeared at ({{4}\over{5}}, {{2}\over{5}}, 0)* and equivalent positions whose intensity after 53 h was 2% of the intensity of the 200 Bragg reflection of the sublattice.