Possible role of hydroxyl group on local structure and phase transition of KNbO3 and KTaO3 nanocrystals

We investigate the structural and phase transition characteristics of hydrothermally grown KNbO3 and KTaO3 nanocrystals. Field emission scanning electron microscope and transmission electron microscope measurements clearly show that the KNbO3 crystal has a nanorod shape while the KTaO3 crystal has a nanocube shape. Fourier transform infrared spectroscopy measurement reveals the existence of a hydroxyl group in both nanocrystals. The hydroxyl group seems to be related to the enlarged lattice constants, the lowered structural phase transition temperatures, the broad phonon width and the increased number of Raman-active phonon modes in KNbO3 and KTaO3 nanocrystals.