Synthesis and Piezoelectricity of Single‐Crystalline ( K,Na ) NbO 3 Nanobars

Piezoelectric nanostructures have many important applications in nanodevices and micro‐electro‐mechanical systems. This work developed a topochemical method based on Molten‐Salt Synthesis for synthesizing one‐dimensional nanoscale single crystals of lead‐free ( K,Na ) NbO 3 ( KNN ) piezoelectric oxides. The synthesis process started from molten‐salt reaction between Nb 2 O 5 powders and KCl to produce high‐aspect‐ratio K 2 Nb 8 O 21 bar‐shaped particles which were transformed to Nb 2 O 5 nanobars via ion‐exchange and thermal decomposition steps, and finally, KNN nanobars were formed also by molten‐salt reaction among Nb 2 O 5 nanobars as templates, and K 2 CO 3 and Na 2 CO 3 in KCl salts. The as‐synthesized KNN nanobars were proved to be single crystals by transmission electron microscopy. The piezoelectricity of an individual KNN nanobar was confirmed by scanning probe microscopy, as the effective piezoelectric coefficient d 33 * was measured to be 113 pm/V.