Ferroelastic n-butylammonium dihydrogenphosphate

Crystals of n-butylammonium dihydrogenphosphate, C4H9NH3+. H2PO4-, reveal f erroelasticity at room temperature and a number of phase transitions when h eated up to approximately 373 K. Some of these phase transitions show hyste resis effects. All atoms except two H atoms exist in pairs linked by the lo st symmetry operations derived from the prototypic space group P2/b2(1)/n2( 1)/a. Each of these two different H atoms is involved in an asymmetric hydr ogen bond between an oxygen pair. Ferroelastic switching is concomitant wit h jumps of these hydrogen species from donor to acceptor O atoms. The studi ed structure belongs to the structural family of n-hexyl- to n-decylammoniu m dihydrogenphosphates and differs by localization of alternating layers fr om n-propyl- and n-pentylammonium dihydrogenphosphates. The studied crystal was slightly twinned; the minor domain constituted approximately 2 degrees .