Controlled Growth of a Highly Energetic, Less Electron-Dense Tetrahedral Fe³⁺ Phase on the Surface of -Fe₂O₃ Nanoparticles toward Enhanced Optical, Magnetic, and Supercapacitive Performance

Nanoplate to pseudocubic-shaped hematite (& alpha;-Fe2O3) nanoparticles along with the gradual engravementoftetrahedral Fe3+ has been synthesized by controlling theprecursor (FeCl3 & BULL;6H(2)O) concentration from0.005 M (A(1)) to 0.2 M (A(4)). The role of thesurfactant polyvinylpyrrolidone on the preferential plane ([110] to[012]) growth and highly energetic tetrahedral Fe3+ phase(increases 2.7 times for A(4) than A(1)) nucleationover the hematite surface has been elucidated from the HRTEM images,XPS, and Raman spectroscopy. This tetrahedral phase and the morphologyvariation facilitate the Fe-Fe interaction significantly, whichimproves the saturation magnetization from 0.13 emu/g (A(1)) to 0.37 emu/g (A(4)). Stronger magnetic d-d couplingin the A(4) sample promotes dominant photoluminance (PL)spectra. It also exhibits linear dependence with the excitation wavelength(300-380 nm) that can be exploited in the design of a UV detector.The supercapacitive performance of ethylene glycol supported PEDOT-PSS-& alpha;-Fe2O3 composite films as negative electrode materials,in the voltage window of -1.3 to -0.5 V, suggests thismaterial to be a promising candidate for the next-generation chargestorage devices. The sample engraved with the richest Fe3+ ions shows the highest specific capacitance of 705.7 F/g in 2 MSO3 (2-) electrolytes, and its cyclic stabilityincreases to 111% over 1500 cycles.