Highly Responsive H ₂ S Gas Sensor Based on Hydrothermally Synthesized Cubic Spinel MgFe ₂ O ₄

ABSTRACT Phase‐pure cubic spinel MgFe 2 O 4 nanoparticles were synthesized via a hydrothermal route, followed by calcination at different temperatures (600 –1000°C) to investigate their structural evolution and gas‐sensing performance. X‐ray diffraction analysis confirmed that calcination at 1000°C yields a single‐phase MgFe 2 O 4 structure with improved crystallinity, preferential (311) orientation, and an average crystallite size of 57 nm. Increasing calcination temperature resulted in reduced microstrain and dislocation density, indicating enhanced structural stability. Optical studies revealed a slight narrowing of the band gap from 2.05 to 2.03 eV due to improved crystallinity and cation redistribution. Thick films fabricated using the optimized MgFe 2 O 4 sample exhibited pronounced selectivity toward H 2 S gas. The sensor demonstrated a maximum response of 89.5% for 500 ppm H 2 S at an operating temperature of 250°C, along with a rapid response time and a shorter recovery time. These results indicate that hydrothermally synthesized MgFe 2 O 4 is a promising material for reliable and selective H 2 S gas sensing applications.