Electron spin resonance and magnetic susceptibility suggest superconductivity in Na doped WO3 samples A. Shengelaya, S. Reich, Y. Tsabba and K. A. Müller Eur. Phys. J. B, 12 1 (1999) 13-15 Published online: 15 November 1999 DOI: 10.1007/s100510050969