Low-Temperature Synthesis and Characterization of Phase-Pure Nanocrystalline BaAl2Ti6O16 Hollandite

Abstract

Nanocrystalline BaAl2Ti6O16 (BAT) with a hollandite-type structure was synthesized using a barium aluminum titanyl tartrate (BATT) precursor via a controlled thermal decomposition method. The thermal behaviour of the precursor was studied using simultaneous thermogravimetric and differential thermal analyses (TG–DTA), which revealed a three-step mass loss process associated with dehydration and subsequent decomposition of the tartrate complex. Complete decomposition was achieved at approximately 500°C. X-ray diffraction (XRD) analysis indicated that the product remained amorphous below 700°C, with crystallization into a pure hollandite phase beginning at 800°C. The degree of crystallinity increased progressively up to 1250°C without the formation of any secondary phases. Fourier-transform infrared (FTIR) spectroscopy confirmed the gradual removal of organic moieties and formation of metal–oxygen bonds (Al–O, Ti–O, and Ba–O) during thermal treatment. Particle size distribution and field emission scanning electron microscopy (FE-SEM) studies revealed nanosized crystallites in the range of 27–60 nm, which was further corroborated by transmission electron microscopy (TEM). The SAED patterns confirmed the polycrystalline nature of the synthesized nanoparticles. Dilatometric analysis demonstrated that the shrinkage of the compacted powder commenced above 800°C, while the sintered pellet exhibited a thermal expansion coefficient of 8.80 × 10⁻⁶ K⁻¹, consistent with literature values. The density of the sintered pellets exceeded 97% of the theoretical value, highlighting the excellent sinterability of the powder derived from the tartrate route. This study establishes a facile, low-temperature chemical route for producing phase-pure, nanocrystalline BaAl₂Ti₆O₁₆ hollandite with desirable thermal and structural stability, suitable for advanced ceramic and nuclear waste immobilization applications.