Technical Articles

Crystal structures of carbonates Cs₂Sr₂(CO₃)₃ and Rb₂Sr₂(CO₃)₃ from powder data

S. F. Jin^a1, M. Li^a1, J. G. Guo^a1, W. Y. Wang^a1, Y. P. Xu^a1 and X. L. Chen^a1 c1

^a1 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China

Abstract

Two carbonates Cs₂Sr₂(CO₃)₃ and Rb₂Sr₂(CO₃)₃ were synthesized by solid-state reaction at high temperatures, and their crystal structures were determined from X-ray powder diffraction data. Because of the presence of heavy atoms and heavy peak overlapping, proper restrains on light-atom groups were found essential to obtain satisfactory results. The title compounds are isostructural to an early reported compound Cs₂Ba₂(CO₃)₃ and crystallize in cubic space group I2₁3, with unit-cell dimensions a=10.072 64(2) Å for the cesium phase and a=9.855 56(7) Å for the rubidium phase. Unlike most carbonates, the title compounds feature in mutually perpendicular CO₃ atomic groups. Our results also indicate that the global instability index is a more sensitive parameter in evaluating the structure rationality over the agreement factors. Moreover, differential thermal analysis and thermogravimetric analysis measurements reveal that Cs₂Sr₂(CO₃)₃ and Rb₂Sr₂(CO₃)₃ are stable in air up to 796 and 880 °C, respectively.

(Received February 08 2010)

(Accepted April 17 2010)

Key Words:

• carbonate;
• X-ray diffraction;
• Rietveld refinement;
• thermal behavior

Correspondence:

^c1 Author to whom correspondence should be addressed. Electronic mail: chenx29@iphy.ac.cn