1. O L Anderson and K Zou, Phys. Chem. Minerals 16, 642 (1989)
2. K Devlal and B R K Gupta, DAE Solid State Physics Symposium, December 26–30 (Gurunanak Dev University, Amritsar, India, 2004)
3. K Y Singh and B R K Gupta, Physica B334, 266 (2003)
4. L M Thomas and J Shanker, Phys. Status. Solidi B189, 363 (1995)
5. J Freund and R Ingalls, J. Phys. Chem. Solids 50, 263 (1989)