Do the RPdIn (R = rare earth) deuterides break the Switendick rule?

Abstract In this paper we focus our attention on the structural and magnetic properties of the RPdIn (R = La, Ce, Pr, Nd, Ho, Er) deuterides. The RTIn compounds having the ZrNiAl-type of crystal structure were suspected of breaking the Switendick 2 A limit on the nearest H–H distances. As the search for new materials with extraordinarily short H–H distances is of the utmost importance in the context of hydrogen storage (gaseous or electrochemical), we address this intriguing issue very carefully with X-ray and neutron scattering studies, including in situ experiments under D 2 pressure and high-resolution time-of-flight neutron scattering. Additionally, symmetrical analysis (SA) of the possible hydrogen occupancies and related distortions of the coordination polyhedra are discussed and placed in the context of the experimental data. In particular, we show that occupancy of a certain position by hydrogen leads to the well-defined structural and magnetic behavior of the hydride. According to our results, the scenario of ultra-low H–H distances must be dismissed for the RPdIn deuterides. As well as interesting structural features, we investigate the magnetic properties of the obtained deuterides, hinting at an unusual phenomenon at low temperatures. According to the results of the magnetic susceptibility, neutron diffraction and inelastic neutron scattering experiments, there are grounds to claim that the CePdInD1.1 compound is a candidate for heavy-fermion behavior.