Piezoelectric and Ferroelectric Properties of Lead-free 0 . 9 ( Na 0 . 97 K 0 . 03 NbO 3 )-0 . 1 BaTiO 3 Solid Solution

Lead-free piezoelectric 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 ceramic has been synthesized using conventional solid-state reaction method. The results of X-ray diffraction analysis (XRD) show that the prepared sample displays typical perovskite structure with tetragonal space group P4mm. The crystal structure of 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 powder was determined by Rietveld refinement analysis. The charge density distribution of the prepared sample has been investigated by using maximum entropy method. The optical band gap of the solid solution has been investigated using UV-visible spectroscopy (UV-Vis). Scanning electron microscopic (SEM) measurements were performed to study the surface morphology. The elemental composition of the 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 sample was analyzed by energydispersive X-ray (EDS) spectrometer. The ferroelectric nature of the sample has been determined through polarization and electric field hysteresis measurements. Introduction. Lead-based piezoelectric materials like PZT (lead zirconate titanate) are the most widely used piezoelectric materials for its superior piezoelectric properties, but these Pb-based systems are highly toxic and volatile causing serious environmental hazards [1,2]. Recently, considerable research has been intensified on lead-free based piezoelectric materials [3]. In this context, (Na, K) NbO3 based ceramic systems are emerging as promising candidates for replacement of lead-based ceramics due to their excellent piezoelectric properties, high Curie temperature and environmental friendliness. Pure NKN ceramics are difficult to synthesize using the solid state reaction method due to the evaporation of K2O and Na2O at high temperatures and degradation of resistivity and the piezoelectric properties. It is also very difficult to control the evaporation of Na2O and K2O by muffling. So, to synthesize the pure NKN samples and optimizations have been adapted by adjusting the Na/K ratio in A site of perovskite structure [4]. Several research works have been carried out by doping the extrinsic materials to increase the piezoelectric properties of NKN-based ceramic materials. Dopants such as LiTaO3 [5], CuO [6], ZnO, LiSbO3 [7], LiNbO3 [8], BaTiO3 [9], SrTiO3 [10], CaTiO3 [11], AgTaO3 [12], Fe2O3 [13], and Sb2O5 [14] have been added to NKN-based ceramics to form new NKN-based ceramic systems. In the present work, we report 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 ceramic was synthesized by solid-state reaction method. The ferroelectric and piezoelectric properties of 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 ceramic were analyzed through charge density studies. Experimental. Solid solution sample of 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 was prepared by conventional solid-state reaction method. Na2CO3 (99.99%), K2CO3 (99.99%), Nb2O5 (99.99%), BaCO3 (9.99%) and TiO2 (99.99%) were used as starting materials. The raw powders were weighed in the stoichiometric ratio of 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 and mixed through ball milling using agate balls for 2 h. Then, the powder was calcined at 950 oC for 4 h. The powder was then pressed © 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/ Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954 MMSE Journal. Open Access www.mmse. xyz 144 into discs (pellets) using a hydraulic press with 12 mm diameter and 1 mm thickness. These pellets were then finally sintered at 1250 °C for 2 h. The prepared solid solution was characterized using various techniques. The crystal structure and phase formation were confirmed by analyzing X-ray diffraction pattern of the sample obtained by X-ray diffractometer (Bruker AXS D8 Advance) in a wide range of angles (10° to 120°) with a scanning step size 0.02° at room temperature using CuKα radiation (λ = 1.54056 Å). Surface morphological and the compositional study was carried out using a scanning electron microscope (SEM) (JEOL JSM-6390LV) equipped with energy dispersive X-ray spectrometer (EDS) (JEOL JED-2300). Optical band gap analysis was carried out using Varian, Cary 5000 spectrophotometer in the wavelength range of 200-2000 nm. Piezoelectric constant (d33) of the sample was measured using a Piezo-d33 meter (SINOCERA, YE2730A d33 meter), after poling the pellet of the prepared ceramic sample in silicone oil at temperature 80 °C under 3-4 kV/mm for 30 min with no leakage current. P-E hysteresis loop was obtained by Radiant Precision Workstation ferroelectric testing system at room temperature. Results and discussion. Structural analysis Fig. 1(a) shows the powder X-ray diffraction pattern of the 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 solid solution. No peak corresponding to any secondary phase was observed in the X-ray diffraction pattern. It can be concluded that the Na0.97K0. 03NbO3 and BaTiO3 ceramics form a homogeneous perovskite ABO3 structure. The crystal structure of 0.9(Na0.97K0.03NbO3)-0.1BaTiO3 ceramic possess tetragonal with P4mm symmetry. The inset of fig. 1(a) shows the splitting of the 46° diffraction peak (200) into (200) and (002) indicates tetragonal symmetry. In our work, the Rietveld refinement [15] was performed through the JANA 2006 program [16]. The fitted profile is shown in fig. 1(b). The lattice parameters and unit cell volume were calculated through of Rietveld refinement and are as presented in table 1. Table 1. Structural parameters.