Effects of Sb on structure, micro structure and electrical characteristics of Sb-modified (K 0

. Lead-free (Na 0.59 K 0.41 )(Nb 1-x Sb x )O 3 ceramic ( x = 0 ÷ 0.12) were prepared by the solid phase reaction method. The influence of Sb concentration on the structure, microstructure and electrical properties of the ceramic was studied. Results indicate that the presence of pure perovskite phase was revealed by XRD patterns recorded for the ceramics, which also showed a shift in structure from orthorhombic to mixed rhombohedral and tetragonal with an increase in x value. At x = 0.06, the ceramics express the best microstructure, the particles were tightly packed with an average particle size of 1.76 µm. The (Na 0,59 K 0,41 )(Nb 0,94 Sb 0,06 )O 3 ceramics have the best dielectric and ferroelectric properties: the ceramic density (  ) is 4.48 g/cm 3 (relative density: 98.7% of the theoretical value); highest dielectric constant at T C (  max ) of 12031; dielectric constant at RT ( ε ) of 945; low dielectric loss (tanδ) of 0.15; and high remanent polarization ( P r ) of 11,2  C/cm 2 ; and the reactance field ( E c ) of 8.7 kV/cm, and the phase transition temperatures ( T C ) of 372  C, and ( T O-T ) of 157  C.


Introduction
One of the most innovative new materials is ferroelectric ceramics, which is highly significant in a variety of technical fields.Due to lead oxide's toxicity and high vapor pressure during processing, which can pollute the environment, piezoceramic systems have been manufactured and primarily used for lead (PZT) based piezoelectric ceramics for many years [1][2][3][4].
Consequently, a great deal of basic and applied research has been carried out on lead-free piezoelectric ceramics [5][6][7].Among them, (K, Na)NbO3 (KNN) based piezoelectric ceramics was the most interested because of its strong ferroelectricity and high Curie temperature (about 420 ℃) [8,9], thereby it has become one of the most promising candidates for replacing Pb-based ceramics.By using a template grain growth method, Li et al. [10]
The sample was then calcined for two hours at 850 °C after being dried, pressed, and heated through two cycles of calcination.The calcined powders were then ball-milled for 20 h and compressed into disks (diameter: 12 mm; thickness: 1.5 mm) at a pressure of 1.5 T/cm 2 and sintered at 1090 °C for 2 h to produce KNNST ceramics.
The XRD (D8 ADVANCE) technique was used to determine the crystal structure of ceramics, and an SEM system (Hitachi S 4800) was used to assess the morphology and microstructure of the samples.The Archimedes method was used to calculate ceramic density, while the Sawyer-Tower method was used to examine ferroelectric hysteresis loops.The capacitance and dielectric loss of the ceramic samples (RLC HIOKI 3532) were measured using an impedance analyzer.

Results and discussion
The (1.32 Å) that are present in the A-site, as shown in the ABO3 model [5,20,[22][23][24].The results agreed well with previously reported results Jiang et al.

Conclusions
The traditional mixed-oxide process was used to produce lead-free (K0. created textured KNN-based lead-free ceramics in 2018, which showed improved electrical properties like piezoelectric constant (d33 ≈ 700 pC/N) and electromechanical coupling factor (kp ≈ 0.76).Recently, a novel strategy is developed to construct the R-T phase boundary by adding an ABO3-type component, which can tailor TR-O and TO-T to room temperature simultaneously, and is beneficial to establish the R-T phase boundary, leading to the improvement of piezoelectric properties in the KNN-based materials [4, 11].Therefore, the (K0.41Na0.59)(Nb1-xSbx)O3combined with Sb element were introduced to stabilize the perovskite structure and form the R-T phase boundary in the KNN based ceramics.Our recent study's [12] findings indicate that lead-free (K0.41Na0.59)NbO3ceramics had the best electrical characteristics (ε = 470, kp = 0.32, kt = 0.5, d33 = 120 pC/N, Pr = 11.6 µC/cm 2 ) were obtained.This study aimed to address the need for practical applications by examining the impact of (K0.41Na0.59)NbO3lead-free.
changes in the structure of the Sb-doped KNN ceramics containing different amounts of Sb are shown in Fig. 1.As shown in Fig. 1(a), a pure perovskite phase is observed.To study in more detail the phase structure of KNNS ceramics, the XRD patterns investigated at 2θ = 21-24° (Fig. 1(b)) and 2θ = 44-47° (Fig. 1(c)), respectively.The ceramic's structure appears to change from an orthorhombic phase (O-phase) with two split peaks at (202)O, lower angle: (020)O; higher angle; a  c > b) to the tetragonal phase (T-phase) with (200)T/(002)T peaks, as shown in Fig. 1(c).The change in phase structure of the (K0.41Na0.59)(Nb1-xSbx)O3ceramics could be attributed to the fact that the ionic radius of the Sb 3+ (0.76 Å) or Sb 5+ (0.62 Å) ions were comparable to the radius of the Nb 5+ atoms (0.78 Å) in the B-site and smaller than the radii of atoms such as K + (1.64 Å) and Na +

Fig. 2
Fig. 2 shows the microstructure of (K0.41Na0.59)(Nb1-xSbx)O3ceramics sintered at 1090°C for 2 h.As can be seen in Fig. 2, the average grain size of the ceramics ranged from 0.67 to 2.39 m, and all ceramics possessed prominent grain boundaries.Generally speaking, with the addition of Sb modifies the microstructure of KNNS ceramics.As illustrated in Fig. 2(f), the grain size increased as the Sb concentration rose and peaked at 2.39 µm at x = 0.03.In the undoped KNN ceramic sample, the grain boundary is very clear, with many voids (Figure 2(a)), demonstrating low ceramic density (Fig. 3(a).The microstructure of the ceramic becomes denser, the grains are uniform, and the voids decrease with a ceramic pore size in the vessel of 1.76 µm (Figure 2(c).This is consistent with the increase in ceramic density with increasing Sb concentration.In other words, at x = 0.06, the best microstructure, the sample with the most tightly packed particles and the fewest

Table 1 .
Compilation of physical properties for the KNN-based ceramics with the other reported data