High pressure and elastic properties of a guanidinium-formate hybrid perovskite

The high pressure and elastic properties of a hybrid ABX₃-type perovskite, [C(NH₂)₃][Cd(HCOO)₃] (CdGF), based on the A-site guest molecules are revealed via combining the high-pressure synchrotron X-ray diffraction experiments with density functional theory (DFT) calculations. The experimental results indicate that the anisotropic axial compressibilities are K_a = 2.8(4) and K_c = 20.9(10) TPa^-1 within the pressure scope of 4.12 GPa, and calculations reveal the microscopic evolution of structure under pressure and demonstrate that this structural anisotropy is a consequence of the directional guest molecule and the cooperative effect of hydrogen bonding and octahedral tilting. In addition, full elastic constants of the perovskite were calculated to describe Young's moduli, shear moduli and Poisson's ratios. Notably, these discrete moduli are governed by the orientational guest molecule suggesting that the perovskite may display positive (negative) linear compression if it is flexible (rigid) along one principal axis.