Engineering Elastic Properties of Isostructural Molecular Perovskite Ferroelectrics via B-Site Substitution

Managing elastic properties of ABX₃ type molecular perovskite ferroelectrics is critical to their future applications since these parameters determine their service durability and reliability in devices. The abundant structural and chemical viability of these compounds offer a convenient way to manipulate their elastic properties through a facile chemical approach. Here, the elastic properties and high-pressure behaviors of two isostructural perovskite ferroelectrics, MDABCO-NH₄ I₃ and MDABCO-KI₃ (MDABCO = N-methyl-N'-diazabicyclo[2.2.2]octonium) is systematically investigated, via the first principles calculations and high-pressure synchrotron X-ray diffraction experiments. It is show that the simple replacement of NH₄ ⁺ by K⁺ on the B-site respectively results in up to 48.1%, 52.4%, and 56.3% higher Young's moduli, shear moduli and bulk moduli, which is attributed to the much stronger KI coordination bonding than NH₄ …I hydrogen bonding. These findings demonstrate that it is possible to tune elastic properties of molecular perovskite ferroelectrics via simply varying the framework assembling interactions.