大きな熱電能をもつミスフィット層状化合物 (Ca₂CoO_3pCoO₂) の変調構造

抄録

Crystal structure of the thermoelectric compound known as “Ca₃Co₄O₉” has been determined using a 3+1 dimensional superspace group approach. The cobaltite has been revealed to be a misfit layer compound which consists of two monoclinic subsystems of [CoO₂] and [Ca₂CoO₃] . The [CoO₂] subsystem has a CdI_2- type triangular lattice of cobalt, while the [Ca₂CoO₃] subsystem compises a three-layered ordered rock salt-type slab. Since the both subsystems have incommensurate b-axis lengths, the structure formula is expressed as [Ca₂CoO₃] _pCoO₂, wherep=b_CoO2/b_Ca2CoO3. Due to the potential interaction between the subsystems, atomic displacive modulation is observed for each atom. The most significant modulation has been found in the Co-O layer of the [Ca₂CoO₃] subsystem.