Crystal Growth and Piezoelectric Properties of Lead-free Based K_0.5Na_0.5NbO₃ by the Floating Zone Method

Abstract

International audienceThe floating zone method (FZM) is used to grow large crystal ingots of lead-free (K0.5Na0.5)NbO3 (KNN), (K0.5Na0.5)(Nb0.95Mn0.05)O3 (KNN-Mn), and (K0.5Na0.5)(Nb0.95Ta0.05)O3 (KNN-Ta). FZM allows high quality crystal to be obtained without using a crucible. However, the KNN molten zone is instable at high temperature (∼1200 °C) due to its incongruent melting and alkali segregation. The challenge of this work is to control the stability and the viscosity of the molten zone which allows long growth in order to achieve large volume single crystals. Our work reveals that the use of a slight overpressure of gas (O2 or N2) and doping KNN with Mn and Ta allows the molten zone to be maintained over 50 h. In such conditions, the as-grown crystals are preferentially oriented along the [011] direction and display piezoelectric properties such as kt of 0.48, d33 of 65–70 pC/N, ε33,rS of 123–148, δe of 0.03–0.07, and δm of 0.11–0.21. The ferroelectric measurements show saturated hysteresis loops with a decrease in EC and Pr when attaining single crystal after several hours of growth. High resolution transmission electron microscopy (HRTEM) investigations show complex domain structures that are mainly attributed to the accommodation of the stresses occurring during the crystal growth in the high thermal gradient and in the phase transition from tetragonal to orthorhombic phases during cooling

Advanced Synthesis on Lead‐Free KxNa(1−x)NbO3 Piezoceramics for Medical Imaging Applications

“…In a recent paper, a new technique similar to the top‐seeded solution growth (TSSG–Figure a) allowed to obtain complex stoichiometry without contamination. This procedure, called floating zone method (FZM–Figure b), was used to prepare large KNN crystals (Figure a) doped with Mn and Ta …”

“…a) Large crystal of KNN‐Ta grown by FZM. Reproduced with permission . Copyright 2016, American Chemical Society.…”

(K,Na)NbO3-based piezoelectric single crystals: Growth methods, properties, and applications

“…5. These can be considered as a first [45], (b) self-flux growth using Pt spatula as nucleation site [46], (c) TSSG [47,48], (d) solid-state crystal growth with KTaO 3 seed [49], (e) seed-free solid-state crystal growth [50], (f) modified Bridgman method [51], and (g) floating zone method [52]. Note the different scales on the pictures.…”

“…)][52,93,94,95]. Pure KNN and Mn-doped KNN crystal growth, performed by Inagaki et al at 3 mm/h and 25 rpm, was difficult due the poor viscosity of the liquid and the molten zone instability.…”

Composite microstructures and piezoelectric properties in tantalum substituted lead-free K0.5Na0.5Nb1-xTaxO3 ceramics

“…The effects of tantalum as single doping element on niobium site was studied on thin films [25,26], single crystal [27][28][29] and bulk ceramics [30][31][32]. Concerning bulk ceramics, Chen et al prepared Ta doped KNN ceramics from a powder obtained with a two-stage microwave hydrothermal process.…”