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