Novel sol-gel processing techniques of ceramic based electrodes as well as solid-electrolytes were developed for designing new functional electrochemical sensor devices for environmental gases and/or ions. A polymer precursor method using acetylacetone - poly(vinyl alcohol) (PVA) was developed for preparing perovskite-type oxide fine powders and thin-films. Wet-chemical preparation routes for pyrochlore-type oxides and metal-sulfides could be developed by some precipitation techniques.
　　　Solid-state electrochemical sensor devices combined with a sodium ionic conductor disc and pyrochlore-type oxide, perovskite-type oxide, and metal-sulfides as sensing electrodes have been investigated for the detection of NO_x, CO₂, and SO₂, respectively. Among the various sensor devices tested, the Pb₂Ru_1.5Pb_0.5O_7-z, the La_0.8Ba_0.2CoO₃, and the CdS-based electrode materials gave good sensitivities to NO_x, CO₂, and SO₂, respectively, at 300-500℃.
　　　New amperometric-, electrochromic-, and impedance metric- sensing techniques to hydrogen phosphate ion (environmental ion) with high sensitivity and selectivity were developed by the use of ceramic-based electrodes. Anodic current of the La_0.8Sr_0.2CoO₃ thin-film-based electrode showed good properties of amperometric sensing to hydrogen-phosphate ion. It has been trying to develop high-performance opto-electrochemical phosphate-ion sensors based on electrochromism (EC) of metal-oxide thin-film electrodes such as NiO, Co₃O₄, etc. A new solid-electrolyte ion sensor device using an Na-ion conductor as an impedance metric transducer and a perovskite-type oxide thin-film as a receptor, respectively, could be also demonstrated. The AC impedance of the device with the LaCoO₃ receptor was found to vary logarithmically with increasing K₂HPO₄ concentration with the 90% response time of ca. 2 min at room temperature.