Possible nucleation of a 2D superconducting phase on WO3 single crystals surface doped with Na+

WO3 crystals with a surface composition of Na0.05WO3 were grown. These crys tals exhibit a sharp diamagnetic step in magnetization at 91 K, and a magne tic hysteresis below this temperature. As the temperature is lowered below 100 K in transport measurements, a sharp metal to insulator transition is o bserved, this is followed by a sharp decrease in the resistivity when the t emperature is lowered to about 90 K. When the surface of the crystals was c overed by gold the depth of the diamagnetic step had decreased considerably . These results indicate a possible nucleation of a superconducting phase o n the surface of these crystals. This is a non cuprate system exhibiting: a critical temperature in the HTS range.