The effects of precursors on the morphology and microstructure of potassium sodium niobate nanorods synthesized by molten salt synthesis

Abstract

(K, Na)NbO₃ (KNN) nanorods were fabricated by molten salt synthesis (MSS) from Nb₂O₅ and K₂Nb₄O₁₁ precursors, respectively. The phase and composition of the KNN nanorods were characterized by X-ray diffraction and inductively coupled plasma spectrometry. The microstructure and crystal growth orientation of the KNN nanorods were investigated by scanning electron microscopy and transmission electron microscopy. All the products were proved to be single-crystalline. The KNN nanorods produced from Nb₂O₅ precursors were short and agglomerate with an aspect ratio of 6 : 1, while those produced from K₂Nb₄O₁₁ precursors showed an aspect ratio of nearly 15 : 1, which could be utilized for bio-sensing and energy-harvesting microdevices. It was proposed that the shortness and agglomeration of the KNN nanorods produced from Nb₂O₅ precursors originated from the layered structures of the pristine precursors used in fabricating Nb₂O₅. The KNN nanorods produced from K₂Nb₄O₁₁ showed a preferable stoichiometry with a K/Na ratio closer to 50 : 50 than those produced from Nb₂O₅, which was attributed to the ability of the K₂Nb₄O₁₁ nanorods to maintain the K content during the reaction process. In addition, the piezoelectric properties of individual KNN nanorods produced from Nb₂O₅ and K₂Nb₄O₁₁ precursors were confirmed by piezoresponse force microscopy, with the converse piezoelectric coefficient d^*₃₃ calculated to be 95 pm V⁻¹ and 201 pm V⁻¹, respectively. The results obtained in this work would provide a valuable guide for further improvement of the MSS process to synthesize KNN nanorods with a large aspect ratio and high performance.