Synthesis and characterization of two-dimensional lead-free (K, Na)NbO3 micro/nano piezoelectric structures

Li-Qian Cheng,Yiwen Sun,Mei Feng,Ze Xu,Zhen Zhou

doi:10.1007/s40145-019-0344-2

Li-Qian Cheng, Yiwen Sun + Show 3 more

Open Access

https://doi.org/10.1007/s40145-019-0344-2

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Abstract

Two-dimensional (2D) lead-free (K, Na)NbO3 (KNN) micro/nano structures with controllable K/Na ratio were successfully fabricated via a two-step molten salt synthesis (MSS). In this work, the reaction factors, including the proportion of molten salts, the types of carbonates, the sintering temperature, and the sintering time, were discussed in detail and the optimized condition was identified. The microstructure of KNN was confirmed by confocal Raman spectroscopy, while piezoresponse force microscopy (PFM) was applied to measure three-dimensional (3D) morphology and piezoelectric properties of KNN particles. The as-synthesized KNN platelets apparently possess anisotropic morphology and uniform structure, the size of which reaches 5–20 µm in length/width and 0.5–1 µm in thickness. It should be noted that the K/Na ratios of the KNN crystals are basically consistent while the proportion of salts changes within a certain range. The enrichment of Na element in the products is also observed, which owes to the smaller ionic radius of Na+ comparing to that of K+. This result provides a reference for the further preparation of textured ceramics and flexible piezoelectric generators.

Highlights

Piezoelectric materials are functional materials which can interconvert mechanical and electrical energies
There are a few of BNN2 and BNN4 phases as marked in Fig. 1(a), it has no significant effect on the topochemical micro-crystal conversion (TMC) due to their similar structures to that of the BNN5 crystals
2D plate-like lead-free KNN structures were successfully synthesized via a two-step molten salt synthesis (MSS)

Summary

Introduction

Piezoelectric materials are functional materials which can interconvert mechanical and electrical energies. The textured lead-free ceramics with high piezoelectric performance are expected according to the work reposted by Saito et al [9]. In order to obtain the textured KNN materials with high piezoelectric response, one of the challenges is the fabrication of plate-like particles as templates [21]. The plate-like KNN particles are expected to inherit the morphology and structure of the precursor [28,29,30]. There are many studies on the preparation of single-crystal NaNbO3 structures through the plate-like precursors [9,31,32,33], while the reports on KNN structures are relatively few. Compared to NaNbO3 two-dimensional (2D) templates, KNN plate-like crystals are expected to possess high piezoelectric properties, and might be much similar to the ceramic matrix [35,36]. The microstructure and piezoresponses of the KNN micro/nano-structures were addressed by Raman and piezoresponse force microscopy (PFM), respectively

Experimental

Results and discussion

Conclusions