Microtwinning hypothesis for a more ordered vaterite model

摘要

An orthorhombic fully ordered structural model is proposed for vaterite [space group Amal, a = 8.4721(5) A, 6=7.1575(7) A, c=4.1265(4) A, Z=4, and V=250.23(4) Å~3]. It is based on a microtwinning hypothesis, with three domains rotated by 120° along the orthorhombic a axis, regenerating a pseudohexagonal habit. The solution came from direct space ab initio calculations applied to the powder diffraction data. However, five weak superstructure reflections seen in single-crystal and powder diffraction experiments, leading to a six times larger unit cell, are still unexplained.