Study of the conduction mechanism of MgAl₂O₄ at different environmental humidities

In this paper, the electrical properties of MgAl₂O₄, which has been proposed as a sensitive material for humidity detection devices, are discussed in relation to its microstructure. MgAl₂O₄ was studied both in bulk and in thin-film forms. Different pellets of MgAl₂O₄ were obtained by sintering powders prepared by different processes, in order to produce a different microstructure 80 nm thick thin-films were prepared by radio-frequency sputtering on a Si/SiO₂ substrate. Surface area, density and pore-size distribution were measured for the pellets. The microstructure of all the specimens was observed using SEM. The electrical behaviour of the specimens was studied using electrochemical impedance spectroscopy in the frequency range from 10^-2 to 10⁵ Hz at relative humidity (RH) values ranging from 5 to 85%. The variation of dielectric parameters, calculated at different frequencies as a function of RH, was investigated to study the conduction mechanism. The humidity-sensitive electrical properties of MgAl₂O₄ were correllated with its microstructure. In order to determine the conduction carriers, the samples were polarized at 1 V dc and the charging and discharging currents were measured.