Enhanced Thermoelectric Properties of Misfit Bi 2 Sr 2-x Ca x Co 2 O y : Isovalent Substitutions and Selective Phonon Scattering.

Layered Bi-misfit cobaltates, such as Bi 2 Sr 2 Co 2 O y , are the natural superlattice of an electrically insulating rocksalt (RS) type Bi 2 Sr 2 O 4 layer and electrically conducting CoO 2 layer, stacked along the crystallographic c-axis. RS and CoO 2 layers are related through charge compensation reactions (or charge transfer). Therefore, thermoelectric transport properties are affected when doping or substitution is carried out in the RS layer. In this work, we have shown improved thermoelectric properties of spark plasma sintered Bi 2 Sr 2-x Ca x Co 2 O y alloys (x = 0, 0.3 and 0.5). The substitution of Ca atoms affects the thermal properties by introducing point-defect phonon scattering, while the electronic conductivity and thermopower remain unaltered.