References
- Ivanov , S. , Mihalcenko , V. and Venevtsev , Yu. 1979 . Dokl. Akad. Nauk. SSSR , 248 : 865
- Tanaka , M. , Shiozaki , Y. and Sawaguchi , E. 1979 . J. Phys. Soc. Jap. , 47 : 1588
- Zvirgzds , J. and Zvirgzde , J. 1980 . phys. stat. sol. , b101 : K21
- Ehses , K. , Bock , H. and Fisher , K. 1981 . Ferroelectrics , 37 : 507
- Willis , B. and Pryor , A. 1975 . Thermal Vibrations in Crystallography , p. 147 Cambridge Univ. Press .