We report how mechanical and dynamical properties in formate-based perovskites can be manipulated by the preparation of an A-site solid-solution. In the series [NH3NH2]1-x[NH3OH]xZn(HCOO)3 with xmax = 0.48, the substitution of [NH3NH2]+ by [NH3OH]+ is accompanied by a series of complex changes in crystal chemistry which are analysed using PXRD, SCXRD, 1H solid state NMR, DSC and nanoindentation. NMR shows increased motion of [NH3NH2]+ in [NH3NH2]0.52[NH3OH]0.48Zn(HCOO)3, which results in a shift of the ferroelectric-to-paraelectric phase transition temperature from Tc = 352 K (x = 0) to Tc = 324 K (x = 0.48). Additionally, the loss of hydrogen bonds directly influences the mechanical response of the framework; the elastic moduli and hardnesses decrease by around 25% from E110 = 24.6 GPa and H110 = 1.25 GPa for x = 0, to E110 = 19.0 GPa and H110 = 0.97 GPa for x = 0.48. Our results give an in-depth insight into the crystal chemistry of ABX3 formate perovskites and highlight the important role of hydrogen bonding and dynamics.
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