Nanocrystalline triple perovskite compounds A₃Fe₂BO₉ (A = Sr, Ba; B = W, Te) with ferromagnetic and dielectric properties for triboelectric energy harvesting

Four iron-based triple tungstate and tellurate perovskites have been synthesized in the nanocrystalline form using a simple sol-gel citrate route: Sr₃Fe₂WO₉ (SFWO), Ba₃Fe₂WO₉ (BFWO), Sr₃Fe₂TeO₉ (SFTO), and Ba₃Fe₂TeO₉ (BFTO). Strontium-based compounds crystallize in the tetragonal space group I4/m, while barium-based compounds crystallize in the hexagonal space group P6₃/mmc. All compounds possess a ferromagnetic order with high values for room-temperature magnetization. The magnetic state as traced by Mössbauer spectroscopy is heterogeneously related to disorder. The compounds also possess relatively high dielectric constants (20-199.16) measured at 1 MHz and a moderate loss factor. The synthesized triple perovskite compounds were utilized in the fabrication of vertical contact mode triboelectric nanogenerators (TENGs). The working mechanism and the electrical response of the TENGs were extensively studied. The TENG device based on BFTO/Kapton triboelectric layers produces the highest output of 88 V/2.69 μA. For the first time, the surface polarity of the triple perovskite was shown using a Kelvin probe force microscopy technique (KPFM), which elucidates the positive polarity of the triboelectric layer. Furthermore, the TENG device was used to charge several capacitors and to carry out the powering of electronics that make it an excellent choice for various self-powered applications.