Multi-valent Cation Conductors and their Application for Electrochemical Use

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The results of this study are summarized in the followings, (1) YPO_4 shows a zircon-type crystal structure, which is a stereochemically rough one. Although this compound includes no divalent cation, if calcium is doped as a phosphate, the crystal can contain the interstitial calcium ion, which plays an important role for the calcium ion conduction. The conductivity is 5x10^<-3>Scm^<-1> at 800ﾟC. In the case of magnesium, the similar result is obtained. But the magnesium ion conductivity is not so high as the calcium ion conductivity. In the solid solutions based on vanadate and arsenate, di-valeut ion conduction is not observed, although they have almost the same crystal structure.(2) Calcium sulfate, having a strained NaCl-type structure, shows calcium ion conduction, if another compound is doped intending formation of interstitial calcium ion. The Conductivity of the sample including 5 m/o excess calcium is 3x10^<-3>Scm^<-1> at 1000ﾟC. We can also introduce calcium ion vacancy to the host crystal by doping of Al_2(SO_4)_2. In that case, the similar conduction behavior is observed, but the conductivity itself is relatively lower.(3) If we substitute divalent cations for alkali ions of the conventional alkali ion conductors we can obtain cation conductor only in the special case such as ramsdellite-based system. However, these are unstable and apt to decompose into two phases at lower temperature ranges.(4) The ionic conductors found on this study are possible to employ electrochemically as electrolytes, considering emf response on construction of cell and formation of calcium compound on electrolysis.