Synthesis and Piezoelectricity of Single‐Crystalline (K,Na)NbO₃ Nanobars

Abstract

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)NbO3 (KNN) piezoelectric oxides. The synthesis process started from molten‐salt reaction between Nb2O5 powders and KCl to produce high‐aspect‐ratio K2Nb8O21 bar‐shaped particles which were transformed to Nb2O5 nanobars via ion‐exchange and thermal decomposition steps, and finally, KNN nanobars were formed also by molten‐salt reaction among Nb2O5 nanobars as templates, and K2CO3 and Na2CO3 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 d33* was measured to be 113 pm/V.

Integrated hybrid life cycle assessment and supply chain environmental profile evaluations of lead-based (lead zirconate titanate) versus lead-free (potassium sodium niobate) piezoelectric ceramics

“…Moreover, KNN is compatible with low cost Ni internal electrodes for MLAs unlike its competitor BNT which requires complex non-standard metallisation solutions or the use of inert noble metals such as Pt and AgPd. [24][25][26] Hence, KNN is gradually becoming regarded as the leading candidate to replace PZT for piezoelectric applications 4,10,12,27 should WEEE and RoHS exemptions be lifted. 4,12 Given these attributes, KNN is thus the focus of comparison with PZT in the current work.…”

“…control actuation in aero-engines to enhance fuel efficiency) 7,9,10 as well as a general demand for piezoelectrics to function at higher performance levels in a number of emerging market sectors.…”

Preparation of rod-like Nb2O5 particles by molten-salt process and the mechanism for the anisotropic grain growth

“…In those studies, specific template particles have to be used for the texturing of certain materials, which requires the achievement of various template particles for different materials in advance. However, it is probable that all niobate-based ceramics can be textured by a TGG method using Nb 2 precursor by molten-salt method and ion-exchange process [10], however, the process was quite complicated and time consuming, so it is not suitable for industrial applications.…”

Are lead-free piezoelectrics more environmentally friendly?

“…Although not as performant as PZT, KNN is amenable to doping to improve its piezoelectric performance, compatible with low cost nickel internal electrodes for multilayering [21] and endowed with a high Curie temperature (T C > 400°C), making ceramics difficult to depole [1,3,22,23] during operation. These factors have led to many academic research groups touting KNN-based ceramics as the most likely to succeed in substituting PZT in applications, should exemptions to WEEE and RoHS for piezoelectric ceramics be revoked.…”

“…These factors have led to many academic research groups touting KNN-based ceramics as the most likely to succeed in substituting PZT in applications, should exemptions to WEEE and RoHS for piezoelectric ceramics be revoked. [4,15,22,24] However, before exploitation can be contemplated, a critical assessment of all aspects of KNN-based technology must be undertaken. New Pb-free materials must offer not only technical parity to their traditional counterparts, but also a superior environmental and social footprint.…”