The research team led by Prof. Anna Gągor, conducting studies on a new class of environmentally friendly hybrid bismuth(III)-based double perovskites—considered as alternative to widely used lead-based materials—synthesized and comprehensively characterized a new compound, (Pip)₂[KBiBr₆]. The results demonstrate that this material uniquely combines structural, ferroelastic, and optical properties.

The crystal structure consists of one-dimensional inorganic columns built from BiBr₆ octahedra and KBr₆ polyhedra, separated by organic piperidinium cations. Near room temperature, the compound undergoes a reversible order–disorder phase transition, leading to a reduction of crystal symmetry and the formation of switchable ferroelastic domains. The mechanism of this transition is governed by the progressive ordering of Pip molecules and formation of hydrogen bonds at the organic–inorganic interface, as confirmed by structural, dielectric, and calorimetric studies.

The material also exhibits unusual luminescent properties, including high-energy excitonic emission and characteristic Bi³⁺- related luminescence. DFT calculations confirmed that electron and hole transport in this system is largely of a local character. This achievement opens new perspectives for the design of low-dimensional functional materials combining ferroic and optoelectronic properties.