Refinement of the (NH4)3H(SO4)2 crystal structure: II. X-ray and neutron single-crystal diffraction from phase II at room temperature

Abstract

The crystal of (NH4)3H(SO4)2 is of special interest due to the possible influence of ammonium ion on the series of phase transitions: I↔II↔ III↔IV↔V↔VII. Earlier, the x-ray single-crystal diffraction study of phase II of the (NH4)3H(SO4)2 crystal showed that the crystal structure of this compound had two crystallographically independent groups of the ammonium ions NH4(1) and NH4(2) but orientational positions of these ammonium ions were not determined exactly. The refinement of the NH4(1) and NH4(2) orientational positions in phase II was carried out by the x-ray and neutron single-crystal diffraction study. The analysis of difference Fourier maps of electron charge density and nuclear density suggested the possibility of disordering of NH4(2) ammonium ions.