Thermal dependence of birefringence

The dependence of birefringence on the temperature seems to be correlated to the temperature dependence of the lattice parameters ratio c/a shown in Fig. 102. 

Reproduced from [440], A. I. Agulyansky, J. Ravez, Eur. J. Solid State Inorg. Chem. 30 (1993) 673, Copyright 1993, with permission of Elsevier. 

Ferroelectric properties - piezoelectric, pyroelectric and related properties 

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