1. J.D. Mackenzie, in: Modern Aspects in the Vitreous State, vol. 3, Butterworth, London, 1964
2. Conduction in glasses containing transition metal ions
3. D. Adler, in: Amorphous Semiconductors, CRC, Cleveland, OH, 1971
4. I.G. Austin, E.J. Garbett, in: Electronic and Structural Properties of Amorphous Semiconductors, P.G. LeComber, J. Mart (Eds.), Academic Press, London, 1973
5. D.L. Griscom, in: Material Science Research, L.D. Pye, V.D. Frechett, N.J. Kreidl (Eds.), Vol.12, Borate Glasses, Plenum, New York, 1978, p. 36