Microwave synthesis of LaCrO₃

Abstract

The synthesis of LaCrO₃ from a stoichiometric mixture of Cr₂O₃ and La₂O₃ powder by microwave irradiation was examined using a multi-mode 28 GHz microwave heating system. In the La₂O₃-Cr₂O₃ system, Cr₂O₃ strongly absorbs microwaves while La₂O₃ is transparent to microwaves. The reaction proceeded rapidly and LaCrO₃ could be synthesised within 15 min of irradiation. Surprisingly, the temperature required for the microwave synthesis (440°C) is much lower than that for conventional synthesis (>1200°C) using an electric furnace. The effect of the partial pressure of oxygen in the microwave chamber on the formation of LnCrO₃ was investigated. The formation of LnCrO₃ is enhanced with increase in the partial pressure of oxygen for Ln=La and Nd, while opposite behavior is seen for Ln=Gd, Tb, Dy and Ho.

References

1. A. Furusaki, H. Konno and R. Furuichi, J. Mater. Sci., 1995, 30, 2829.
2. M. Yoshimura, S. T. Song and S. Somiya, J. Ceram. Soc. Jpn., 1982, 90, 91.
3. S. Nakayama and M. Sakamoto, J. Ceram. Soc. Jpn., 1992, 100, 342.
4. K. G. K. Warrier, H. K. Varma, T. V. Mani and A. D. Damodaran, J. Am. Ceram. Soc., 1992, 75, 1990.
5. D. R. Baghurst, A. M. Chippindale and D. M. P. Mingos, Nature, 1988, 332, 311.
6. P. D. Ramesh, B. Vaidhyanathan, M. Ganguli and K. J. Rao, J. Mater. Res., 1994, 9, 3025.
7. D. R. Baghurst and D. M. P. Mingos, J. Chem. Soc., Chem. Commun., 1988, 829.
8. B. Vaidhyanathan, M. Ganguli and K. J. Rao, Mater. Res. Bull., 1995, 30, 1173.
9. D. M. P. Mingos and D. R. Baghurst, Chem. Soc. Rev., 1991, 20, 1.
10. W. H. Sutton, Ceram. Bull., 1989, 68, 376.
11. T. Saji, New Ceramics, 1995, 5, 21 (in Japanese).
12. L. M. Sheppard, Ceram. Bull., 1988, 67, 1656.
13. A. T. Rowley, R. Wroe, D. Vazquez-Navarro, W. Lo and D. A. Cardwell, J. Mater. Sci., 1997, 32, 4541.
14. N. Sakai and S. Stølen, J. Chem. Thermodyn., 1995, 27, 493.
15. D. B. Meadowcroft and J. M. Wimmer, Am. Ceram. Soc. Bull., 1979, 58, 610.