Effect of hydroxyl group on global and local structures of hydrothermally grown KNbO3 nanorods

We report the annealing temperature dependence of global and local structures of hydrothermally grown KNbO3 nanorods. With increasing annealing temperature, the amount of hydroxyl groups in the KNbO3 nanorods decreased and finally disappeared at about 800 °C. Morphology of the nanorods seemed not to change significantly, however, X-ray intensity ratio between (0 2 2) and (2 0 0) planes, i.e., I0 2 2/I2 0 0, increased with decreasing lattice hydroxyl group contents. This result could be attributed to the fact that the hydroxyl groups were desorbed more effectively along the [0 1 1] direction than in other directions due to the elongated nanorod along the [0 1 1] direction. The frequencies of external and bending modes, besides stretching mode, showed red-shift with decreasing lattice hydroxyl group contents. This result implied that the lattice hydroxyl groups existed as interstitial defects near K ions.