MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF SI-DOPED ALPHA-FE2O3 HUMIDITY SENSOR

The humidity sensitivity of Si-doped alpha-hematite sintered compacts was investigated by precision volt-amperometric and impedance spectros copy techniques in the 0-95% relative humidity (r.h.) range. 130 m2/g specific area alpha-hematite powders were dispersed in 3-amino-propyl- trihydroxy-silane solution and dried at 120-degrees-C to yield 2 wt.% Si. Sintering was performed at 50-degrees-C steps in the temperature r ange 850-1100-degrees-C. Compacts were characterized by SEM, mercury i ntrusion and nitrogen adsorption techniques. The electrical response o f Si-doped alpha-Fe2O3 was affected by the microstructure and sinterin g temperature. The 850-950-degrees-C sintered compacts showed a linear response of impedance, in the logarithmic scale, in the whole investi gated r.h. range. The variation of impedance was measured from 10(8) ( 0% r.h.) to 10(4) ohm (95% r.h.). The response times of the sensors we re evaluated by 0-60 r.h. variations. The results were compared with u ndoped sintered compacts.