Ferroelastic phase transition with large spontaneous strain caused by freezing the conformational dynamics of ammonium†
Abstract
By adjusting the substituent group of the organic ammonium in three molecular ionic complexes, [A][Fe3O(O2CH)8(H2O)]2 (A = NH3(CH2)3NH3 for 1, CH3NH2(CH2)3NH3 for 2 and CH3CH2NH2(CH2)3NH2CH2CH3 for 3), crystallized in the 2/m point group at room temperature with similar structure, conformational transformation-caused dynamic disorder and pseudosymmetry is realized in 3. When the conformational interchange of the ammonium is frozen, the disorder–order 2/mF ferroelastic phase transition is presented, which leads to dielectric relaxation and a large spontaneous strain of 0.207.