High-pressure structure of Li 2 CO 3

The high-pressure behavior of Li2CO3 is studied up to 25 GPa with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil cells and synthesis using a multi-anvil apparatus. A new non-quenchable hexagonal polymorph (P63=mcm; Z ¼ 2) occurs above 10 GPa with carbonate groups in a staggered configuration along the c-axis—a ¼ 4:4568ð2Þ Aand c ¼ 5:1254ð6Þ Aat 10 GPa. Two columns of face-shared distorted octahedra around the Li atoms are linked through octahedral edges. The oxygen atoms are coordinated to one carbon atom and four lithium atoms to form a distorted square pyramid. Splittings of X-ray reflections for the new polymorph observed above about 22 GPa under non-hydrostatic conditions arise from orthorhombic or monoclinic distortions of the hexagonal lattice. The results of this study are discussed in relation to the structural features found in other Me2CO3 carbonates (Me: Na, K, Rb, Cs) at atmosphericc onditions. r 2003 Elsevier Science (USA). All rights reserved.