Synthesis of Norbergite Fe₃BO₆ of Single Crystallites from a Borate Glass

Abstract

Iron oxyborate Fe₃BO₆ is one of the important ceramics of the norbergites useful for electrodes in lithium ion batteries, gas sensors and biological probes. A facile biofriendly method of rapid cooling of a borate glass-melt (starting composition 40Fe₂O₃-60 B₂O₃), after an isothermal heating for 30 min at ∼1220°C in air, is explored in view of producing Fe₃BO₆ single crystallites. The method is feasible to scale-up for high yield. Scanning electron microscopic images of as-cooled rectangular bars or laminates of Fe₃BO₆ crystallites measure 1–2 μm length, 0.51 μm width and ∼45 nm thickness. A single phase compound, Fe₃BO₆, as analyzed from the X-ray diffractogram, shows an orthorhombic crystal structure (Pnma space group), with lattice parameters a = 1.0048 nm, b = 0.8531 nm, c = 0.4466 nm, and density 44.76 g.cm₋₃. It is highly stable in air unless heating above 700°C. At room temperature these Fe₃BO₆ crystallites behave as the surface modified antiferromagnet, showing a nearly linearly increasing magnetization (i.e. a very small value of the order of a few 10⁻⁴ emu.g⁻¹) against applied magnetic field and a peculiar open hysteresis loop with a huge coercivity ∼2105 Oe.

Keywords:

• Fe₃BO₆
• Facile synthesis
• Microstructure
• Magnetic studies
• Thermal stability