Structure and Piezoelectricity Due to B Site Cation Variation in ABⁿ⁺Cl_n+2Hybrid Histammonium Chlorometallate Materials

To provide new insights for understanding the influence of B site cations on the structure in chlorometallate materials of the form ABⁿ⁺Cl_n+2, we report novel organic-inorganic hybrid metallates (OIHMs) incorporating histammonium (HistNH₃) dications and various transition-metal and main group B site cations. Single crystals of OIHMs with the basic formula (HistNH₃Mⁿ⁺Cl_n+2, M = Fe, Co, Ni, Cu, Zn, Cd, Hg, Sb, Sn, Pb, Bi) were grown and their structures characterized by single-crystal X-ray crystallography. HistNH₃CoCl₄, HistNH₃ZnCl₄, and HistNH₃SbCl₅were crystallized in a non-centrosymmetric space group and were subsequently studied with piezoresponse force microscopy (PFM). While bulk measurements of crystals and poly(vinylidene difluoride) (PVDF)/metallate composite films exhibited low bulk response values, the surface-measured local response values using PFM were 5.17 pm/V for HistNH₃CoCl₄, 22.6 pm/V for HistNH₃ZnCl₄, and 2.9 pm/V for HistNH₃SbCl₅compared with 2.50 pm/V for PVDF reference samples. The magnitudes of the d₃₃coefficient, net dipole, and cation-Cl bond dipole obtained from the density functional theory calculations confirm the higher response in HistNH₃ZnCl₄compared to HistNH₃CoCl₄. Density of states and crystal orbital Hamilton population analysis indicate that the higher net dipole in HistNH₃ZnCl₄compared to HistNH₃CoCl₄is due to the lower hybridization of the M-Cl bond.