Growth and characterization of high quality single crystals of NaxCoO2

A systematic study of growing NaxCoO2 (x = 0.32-1.00) single crystals has been performed to determine phase stability and the effect of structure and magnetic property on the sodium content in this system. We give experimental evidence that high quality alpha-phase Na-x center dot CoO2 crystals with x = 0.90-1.00 could be obtained using optical floating zone method, while other phases with lower sodium content of x < 0.90 are observed to contain Na2O, CO3O4 and Na-poor compound. Furthermore, we demonstrate that the magnetic transition temperature depends strongly on the Na content in the single crystals. Implications of the Na effect for understanding of the structure and magnetization are discussed. (C) 2007 Elsevier B.V. All rights reserved.