Figure 1 Literature birefringence data: (a) measurements made in Oxford (600  nm); (b) measurements made in Katowice (546  nm); (c) Kleemann et al. (1986); (d) Fesenko & Kolesova (1959); (e) Shirane et al. (1956) (589  nm); (f) Kobayashi & Yamada (1959) (550  nm); (g) Kobayashi & Yamada (1959) (600  nm); (h) Mabud & Glazer (1979).

© International Union of Crystallography 2004