Local deuterium order in apparently disordered Laves phase deuteride YFe2D4.2

Deuterium short-range order in cubic Laves phase deuteride YFe2D4.2 was studied by neutron (ToF) powder diffraction experiments and Pair Distribution Function (PDF) analysis between 290 and 400 K. The minimal allowed D–D distance of 2.1 Å in a metal deuteride (Switendick rule) has been experimentally proved in the HT-disordered phase YFe2D4.2. It has been found that the distribution of deuterium atoms around the iron is not random, and cannot be explained only by applying the Switendick rule. The first coordination sphere of iron atoms in the high temperature (HT)-disordered phase resembles between 350 and 400 K the coordination observed in the low temperature (LT)-ordered phase. Reversed Monte Carlo modeling of the Pair Distribution Function of the HT-disordered phase prefers the coordination FeD5 and FeD4 in agreement with the LT-ordered phase.