Atomic and domain structure of the low-temperature phase of barium metagermanate (BaGeO3)

The crystal structure of the low-temperature form of barium metagermanate (BaGeO3) has been determined from laboratory X-ray powder diffraction data collected at 298.5 (5) K. The structure was found to consist of alternating layers of Ba cations and [GeO3](3) rings, and is closely related to pseudowollastonite. The rings show a twofold positional disorder owing to stacking faults. The stacking is not random, but can be rationalized by a twinning mechanism mapping the two non-congruent enantiomorphic polytypes of the structure onto each other. This model also explains the diffuse scattering and twinning observed in SAED and HRTEM, as well as the size and strain-like broadening effects found in the XRPD pattern.