1. H. D. Megaw, ?Crystal structures, a working approach?. (W.B. Saunders, Philadelphia, 1973).
2. R. A. Young, ?Mechanism of the phase transition in quartz?. Georgia Institute of Technology, AFOSR-2569 (1962).
3. H. G. Winkler,Acta Crystallogr. 1 (1948) 27.
4. H. Schulz, W. Hoffmann andG. M. Muchow,Z. Kristallogr. 134 (1971) 1.
5. C. T. Li,ibid. 127 (1968) 327.