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 degrees 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) single crystals with quadruple (n = 4) rocksalt (RS) layer are achieved with cooling from 900 degrees C. Such a crystal exhibits room-temperature thermoelectric power (TEP) of 180 mu V/K, much larger than that in Sr-based misfit cobaltites with quadruple RS layer. However, intergrowth of single crystals of quadruple (n = 4) and triple (n = 3) RS-type layer-based misfit cobaltites is observed with cooling from 950 degrees C. Both of TEP and resistivity were obviously enhanced by the intergrowth compared to [Ca2Bi1.4CO0.6O4](RS)[CoO2](1.69) single crystal, while the power factor at room temperature remains unchanged. (C) 2007 Published by Elsevier B.V.