| Research Abstract |
At first, we have investigated on the samples in the systems CaSO_4-CaCl_2 and SrSO_4-SrCl_2, and CaCO_3-CaCl_2 and SrCO_3-SrCl_2. In each system, if the additives content was between 10-30 mol%, the solid solutions were found to be formed, which means that SO_4^<2-> or CO_3^<2-> can be substituted by the chloride ions. And, although the based materials showed very low conductivity in all cases, the conductivity in the substituted samples grew higher with increasing additive components. The charge carrieres in these samples were found to be only ions, not electrons. Here, we paid attention to the materials composed of carbonate in order to make a CO_2 sensor stable in the environment containing fairly high concentration of CO_2 gas. Judging from the EMF response of the cell, these materials were found to be a candidate for it.
Next, in order to study the oxide ion conduction in the solid solutions based on Scheelite- and Spinel-type compounds, which have not been investigated at all as to their ionic conduction, we synthesized the solid solutions of Pb_<1-x>Ln_xWO_<4+X/2>, Pb_<1-X>Ln_<2x/3>WO_4 and Zn_<2-x/2>Ti_<1-x>Ta_xO_4, and measured their conductivities. As a result, in the former two systems, the high oxide ion conduction was observed, the value of which exceeded 10^<-2> Scm^<-1> at 800ﾟC.In the latter case, such a high conductivity was not observed but the oxide ion conduction was found to be possible in the closest packing structure of oxide ions. Even in the case of the Scheelite-type structure, the cation (lithium ion) conduction was found to be observed, if we designed the substitution as Ca_<1-x>Li_<2x>WO_4. In this case, the lithium ion conduction was considered to be ascribed by the interstitial lithium ions by the result of the observation of NRG.
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