Disorder−Order Ferroelectric Transition in the Metal Formate Framework of [NH<sub>4</sub>][Zn(HCOO)<sub>3</sub>] XuGuan-Cheng MaXiao-Ming ZhangLi WangZhe-Ming GaoSong 2010 A three-dimensional chiral metal formate framework compound, [NH<sub>4</sub>][Zn(HCOO)<sub>3</sub>], undergoes a paraelectric−ferroelectric phase transition at 191 K triggered by the disorder−order transition of NH<sub>4</sub><sup>+</sup> cations within the structure.