Humidity sensors using KH2PO4-doped porous (Pb,La)(Zr,Ti)O3

Humidity sensing devices were prepared by using fine porous (Pb, La)(Zr, Ti)O₃ (PLZT) particles with ferroelectricity instead of insulating metal oxides such as alumina and zircon. The impedance of PLZT with 1 wt %. KH₂PO₄ was 10⁶ and lower than that of zircon with 3.8 wt % KH₂PO₄ by a factor of 10² in a dry atmosphere. In addition, the impedance in a humid atmosphere was controlled by the adding of potassium dihydrogen phosphate and changed by about four orders of magnitude in the humidity region 0 to 90% relative humidity at 1 kHz for samples burnt at 700° C. The humidity dependence of impedance is mainly governed by the change of coverage of adsorbed water. The hydrophilicity is affected by the burning temperature and lanthanum content of PLZT used as starting particle for porous PLZT ceramics burnt with KH₂PO₄. From complex impedance analysis it is confirmed that the resistive component inserted in parallel with the capacitive component decreases steeply with an increase in humidity, while the capacitive component is poorly dependent on the humidity.