Enhanced ammonia sensing performance of barium hexaferrite enabled through Zn doping: Mechanistic study considering modulation of Fe2+/Fe3+ ratio and oxygen vacancy

Barium hexaferrite (BaFe12O19) is an unexplored metal-oxide semiconductor with regard to ammonia (NH3) gas sensing. Herein, we have achieved substantial enhancement in response towards NH3 by virtue of Zn doping in BaFe12O19, synthesized via facile solid-state route. The improved response (Rgas/Rair) of Zn-doped BaFe12O19 towards 1 ppm NH3 was 7.36 at 250 °C which was ~300% higher than pure BaFe12O19. Moreover, fast response/recovery time (2.66 s/35.25 s), good selectivity and long-term stability (100 days) towards NH3 has been achieved when Zn was incorporated. The lower limit of detection of Zn doped BaFe12O19 was estimated ~150 ppb, that exceedingly favours lower concentration range of NH3 detection. Excellent sensing behaviour of Zn-doped BaFe12O19 samples was attributed to modulation of Fe2+/Fe3+ ratio, oxygen vacancies and improved oxygen adsorbing ability as confirmed from X-ray photoelectron spectroscopy (XPS) study. Also, the improvement in sensing activity was validated through quenching of photoluminescence (PL) spectra in favour of electron-hole separation. The usefulness of developed Zn-doped BaFe12O19-based sensor for environmental air-quality surveillance and individualized health monitoring can be concluded through the sensor's notable resolution in detection of wide range (150 ppb - 100 ppm) of ammonia concentration.