Chloride ion (Cl-) conducting characteristics were investigated in calcium
doped lanthanum oxychlorides which show a high stability even in a high hum
id atmosphere and at an elevated temperature. The Cl- ion conductivity of t
he oxychloride is approximately 10(-4.5) S.cm(-1) at 700 degreesC and the C
l- ion transference number is almost unity. The development of new types of
Cl- ion conducting solid electrolytes with a high durability opens a door
to realize a new application for functional materials.