  Effects of x-ray irradiation on the crystal structure and the electrical
resistance were examined at low temperatures for the insulating phase of spinel
compound CuIr2S4. We found that the resistance decreases by more than five
decades by irradiation at 8.5 K. The structural change from triclinic to
tetragonal was observed at the same time. The x-ray-induced conductance is
deduced to result from the destruction of Ir4+ dimers formed in the insulating
phase. Slow relaxation of the resistance in the x-ray-induced state is also
reported.
