Intergrowth and thermoelectric properties in the Bi–Ca–Co–O system

Single crystals of the Bi–Ca–Co–O system have been grown using the flux method with cooling from 900 and 950∘C, respectively. The single crystals are characterized by transmission electron microscopy and X-ray diffraction. The misfit cobaltite [Ca2Bi1.4Co0.6O4]RS[CoO2]1.69[Ca2Bi1.4Co0.6O4]RS[CoO2]1.69 single crystals with quadruple (n=4n=4) rocksalt (RS) layer are achieved with cooling from 900∘C. Such a crystal exhibits room-temperature thermoelectric power (TEP) of 180μV/K, much larger than that in Sr-based misfit cobaltites with quadruple RS layer. However, intergrowth of single crystals of quadruple (n=4)(n=4) and triple (n=3)(n=3) RS-type layer-based misfit cobaltites is observed with cooling from 950∘C. Both of TEP and resistivity were obviously enhanced by the intergrowth compared to [Ca2Bi1.4Co0.6O4]RS[CoO2]1.69[Ca2Bi1.4Co0.6O4]RS[CoO2]1.69 single crystal, while the power factor at room temperature remains unchanged.