1. P. W. McMillan, in “Glass-Ceramics” edited by J. P. Roberts and P. Popper (Academic Press, New York, 1979) p. 9.
2. F. M. Ernsberger, in “Advance in Glass Technology” edited by J. D. Mackenzie (Plenum Press, New York, 1962) p. 551.
3. R. H. Doremus, in “Glass Science” edited by D. R. Ulhmann (Wiley, New York, 1973) p. 24.
4. T. Komatsu, R. Sato, K. Imai, K. Matusita and T. Yamashita, Jpn J. Appl. Phys.
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5. R. Sato, T. Komatsu, K. Matushita and T. Yamashita, ibid.
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