Structural Study of Langbeinite-Type (NH₄)₂Cd₂(SO₄)₃ Crystal in the High-Temperature Phase

We determined the crystal structure of the high-temperature cubic phase of the langbeinite-type (NH ₄ ) ₂ Cd ₂ (SO ₄ )t ₃ . The observed Cd-O atomic distances are considerably shorter than the standard Cd-O. The structure refinement revealed that the SO ₄ ion has several disordered arrangements indicating the existence of the steric hindrance between Cd and SO ₄ . These results are quite similar to the previously reported characteristics of several K ₂ B ₂ (SO ₄ ) ₃ -type langbeinites. We conclude that the steric hindrance between Cd and SO ₄ dominates the phase transition, while the NH ₄ ion plays no direct role on the phase transition.

Keywords:

• Langbeinite
• phase transitions
• x-ray diffraction

Acknowledgment

The authors thank Foundation for Promotion of Material Science and Technology of Japan (MST Foundation) for the financial support.

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005; received for publication January 26, 2006.