Refinement of the crystal structure of [Rb x (NH4)1−x ]3H(SO4)2(x = 0.11) by single-crystal X-ray and neutron diffraction: I. Phase II at 300 K

Abstract

The crystal structure of a mixed [Rb0.11(NH4)0.89]3H(SO4)2 crystal was refined using single-crystal X-ray and neutron diffraction at 300 K. The refinement confirmed that the phase II of the crystal belongs to the monoclinic crystal system (space group C2/c). It was shown that, according to the single-crystal neutron diffraction data, ammonium ions can be represented as regular tetrahedra. The analysis of the constructed difference Fourier maps of the electron and nuclear densities of ammonium ions revealed the presence of additional peaks, which can indicate the dynamic disorder of ammonium ions in the phase II. The results obtained con-firmed that the phase transition to the orientational-glass state can occur in the mixed [Rb0.11(NH4)0.89]3H(SO4)2 crystal with a decrease in the temperature.