This proposal aims at better understanding the role of the disordered NH4+ ions in driving the ferroelectric transition in [NH4][Zn(HCOO)3] and that of hydrogen bonding in stabilizing the ferroelectric phase.In order to perform a full characterization, we propose to study the structure of the ammonium-zinc formate as a function of temperature. The ferroelectric transition occurs at 192K, therefore a measurement at 300K will elucidate the paraelectric phase. Additional data at 175, 100 and 20K will provide information on the development of the ferroelectric distortion mode and on the order parameter. In addition, the analysis of the temperature dependence of the atomic displacement parameters between 20 and 175K will give information about the low frequency normal modes contributing to the structural phase transition.