In order to increase the humidity sensitivity of PbTiO_3 , using Ti (0-n-Bu)_4(or (n-BuO)4Ti), Pb(OAc)_2 and Ca(OAc)_2 as the starting materials, K+-modified and Ca~(2+)-doped PbTiO_3 nano-film ( K+-Cat Pbi_x TiO_3, abbreviated as K-CPT) was prepared by sol-gel method, namely, spin-coating sol on a-Al_2O_3 substrate plated with Ag-Pd alloy interdigital electrode and then sintered at 850 TV1 h for crystallization. Its property of resistance-relative humidity was tested at the constant temperature of (20 ±0.1) °C , and compared with pure PbTiO_3(PT), Ca~(2+)-doped PbTiO_3(CPT) and Li+-modified Ca~ (2+)-doped PbTiO_3 nano-film (Li+-CaA:Pbi_;[TiO3) Li-CPT for short). Process parameters were investigated by orthogonal design. The results indicated that the film prepared with formula of x -0.35 and K+ content= 1.0% (K/Ti, mol/mol), and sintered at 850 t/l h, displayed the sensitivity S = 3.3 X 103in the range of RH = 8.0% -93.6%, response time r = 15 s and humidity hysteresis sg ±2%; the total sensitivity S^IO4 in the extrapolation range of RH = 0.0% - 100.0% . The film was characterized by XRD, SEM and TEM, which showed the tetragonal nano-polycrystalline with 10 nm of grain size and electric domain structure reticulated pores and obvious grain boundary like island with 4 pan X 5 f*m area.

Key words: POTASSIUM, MODIFICATION, CALCIUM, DOPE, LEAD TITANATE, NANOPHASE MATERIALS, THIN FILMS, STRUCTURE CHARACTERISTICS, ORTHOGONAL TEST, XRD