High piezoelectric, dielectric relaxation and semiconductor properties in a one-dimensional organic-inorganic hybrid complex: [2-methyl-1,5-pentanediamine][BiCl₅]

Molecular-based phase change materials are a kind of special multi-functional molecular material, which can possess ferroelectric, pyroelectric, dielectric, piezoelectric, nonlinear and semiconductor properties; in particular, organic-inorganic hybrid complexes, containing both organic and inorganic materials, have received much attention. In the past ten years, although a lot of breakthroughs have been made, the key parameters still need to be further explored. In this work, we have synthesized a group of organic-inorganic hybrid multifunctional materials with dielectric relaxation, [2-MPDA][BiX5] (2-MPDA = 2-methyl-1,5-pentanediamine, X = Cl, Br, I), and the variable temperature structure, DSC (differential scanning calorimetry), variable temperature dielectric, SHG (second harmonic generation), ultraviolet absorption and piezoelectric properties were measured and analyzed. The results show that [2-MPDA][BiCl5] (1) has a reversible structural phase transition near 166 K, and the space groups of [2-MPDA][BiBr5] (2) and [2-MPDA][BiI5] (3) are Pnma. The band gap is 3.02 eV, 2.63 eV and 1.93 eV at 460 nm, 490 nm and 660 nm, respectively. The piezoelectric coefficient d33 = 6 pC N-1 along the c-axis of compound 1 is the same as that of KTP (b-aixs), and is better than that of ZnO (c-aixs), croconic acid (c-aixs) and Nylon-11 (thin film). This work provides a new idea and method for the exploration of molecular-based lead-free structure phase change multifunctional materials.