1. D. F. Kalinovich, L. I. Kuznetsova, and E. T. Denisenko, Poroshk. Metall., No. 11, 98 (1987).
2. I. A. Bondar’ and A. E. Mal’shikov, Phosphates of the Group IV Elements (Nauka, St. Petersburg, 1992) [in Russian].
3. Yu. I. Gnatyuk, V. I. Yatsniev, N. P. Smirnova, et al., Teor. Eksp. Khim. 41(6), 354 (2005).
4. I. C. Marcu, J. M. M. Millet, and J. M. Hermann, Catal. Lett. 78(1–4), 273 (2002).
5. C. Srilakshhmi, K. Ramesh, P. Nagaraju, et al., Catal. Lett. 106(3–4), 115 (2006).