Electrical conductivity, thermal expansion, and oxygen loss and oxygen transport rates have been determined for the electrochemically vapor deposited thin films of magnesium-doped lanthanum chromite which is currently used as the interconnection material in the high temperature solid oxide fuel cell. Electrical conductivity of these interconnection films has been found to decrease with a decrease in oxygen pressure; these conductivities at different oxygen partial pressures have been related theoretically to the oxygen loss data. The conductivity of the presently used interconnection material is adequate for the solid oxide fuel cell operation, but can be increased by increasing the magnesium concentration in the lanthanum chromite. The thermal expansion of the interconnection films has been found to be about 12 to 14% lower than of the calcia-stabilized zirconia support tube of the solid oxide fuel cell. It is considered desirable to increase this thermal expansion by chemical modification of the interconnection material. The permeation rates of oxygen through electrochemically vapor deposited thin films of magnesium-doped lanthanum chromite under fuel cell operating conditions have been found to be extremely low. Such oxygen permeation, therefore, should not cause any significant loss in the open circuit voltage or the efficiency of the solid oxide fuel cell under normal operating conditions. 10 refs., 17 figs.