Simultaneous realization of high d33 and large strain in (K,Na,Li) (Nb,Sb)O3-(Ca,Sr)ZrO3 materials and their application in piezoelectric actuators

A pseudocubic-tetragonal-orthorhombic (PC-T-O) multi-structure was developed in the 0.96(K_0.5Na_0.47Li_0.03) (Nb_0.92Sb_0.08)O₃-0.04(Ca_0.5Sr_0.5)ZrO₃ [(KN_0.47L_0.03)NS-CSZ] lead-free piezoceramic. The PC structure observed in this sample was deemed to have an R3m rhombohedral structure. This sample demonstrated a large d₃₃ (560 pC/N) owing to the existence of the PC-T-O multi-structure. The (KN_0.47L_0.03)NS-CSZ thick film also exhibited a large d₃₃ (560 pC/N) and strain (0.19% at 4.0 kV/mm). The large strain was sustained even after the application of 10⁶ electric-field cycles. Therefore, the (KN_0.47L_0.03)NS-CSZ thick film exhibited excellent fatigue characteristics and was utilized to fabricate a planar-type actuator, which achieved a large displacement (300 μm) and acceleration (872 G) at 125 V/mm. A cantilever-type multilayer actuator was also prepared using five layers of the (KN_0.47L_0.03)NS-CSZ thick film and demonstrated a large displacement (3500 μm) and acceleration (42.96 G) at 250 V/mm. Therefore, the (KN_0.47L_0.03)NS-CSZ thick film is a good candidate for fabricating various piezoelectric actuators.     

High-power piezoelectric energy harvester produced using [0 0 1]-textured (Na,K)NbO3-based lead-free piezoceramics

High-power piezoelectric energy harvesters (PEHs) require piezoceramics with a large k_p and d₃₃ but small ε^T₃₃/ε₀ values. The [0 0 1]-textured 0.96(Na, K)(Nb_1−xSb_x)–0.04SrZrO₃ piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (k_p) and piezoelectric charge constant (d₃₃); however, the increase of dielectric constant (ε^T₃₃/ε₀) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d₃₃ × g₃₃ value of 21.5 pm²/N, where g₃₃ is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type-1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.     

Application of [001]-textured (K,Na)(Nb,Sb)O3-CaZrO3 thick films to piezoelectric energy harvesters

A (K, Na)NbO₃ (KNN)-based lead-free piezoceramic for a piezoelectric energy harvester (PEH) should exhibit a large k_ij, Q_m, d_ij, and a small ε^T₃₃ to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the k_ij and d_ij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the ε^T₃₃/ε₀ value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K_0.5Na_0.5)(Nb_0.93Sb_0.07)O₃-0.03CaZrO₃ [KN(N_0.93S_0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large k_p (0.57) and d₃₃ × g₃₃ (25.7 pm²/N), which is the largest d₃₃ × g₃₃ of the KNN-based piezoceramics reported to date. A cantilever PEH fabricated using the textured KN(N_0.93S_0.07)-CZ thick film exhibited a power density of 21.4 μW/mm³ at the resonance frequency. This is the highest power density observed for PEHs fabricated using lead-free piezoceramics. The PEH also exhibited a power density of 0.023 μW/mm³ at the off-resonance frequency. Therefore, the textured KN(N_0.93S_0.07)–CZ thick film is a good candidate for use in PEHs.     

Preparation and Electric Properties of Bi0.5Na0.5TiO3–Bi(Al0.5Ga0.5)O3 Lead‐Free Piezoceramics

A new lead‐free BNT‐based piezoelectric ceramics of (1 ? x)Bi_0.5Na_0.5TiO₃–xBi(Al_0.5Ga_0.5)O₃ (x = 0, 0.02, 0.03, 0.04, and 0.05) were synthesized using a conventional ceramic fabrication method. Their structures and electrical properties were investigated. All the samples show a typical ferroelectric P(E) loops and S(E) curves at room temperature. The optimal properties are obtained at the composition of the x = 0.03. The substitution of Bi(Al_0.5Ga_0.5)O₃ enhances piezoelectric constant and increases Curie temperature from 58 pC/N and 310°C of pure BNT to 93 pC/N and 325°C of the x = 0.03. The temperature‐dependent P(E) loops and S(E) curves of 0.97BNT–0.03BAG indicate that phase transition from ferroelectric to antiferroelectric takes place over a very wide temperature region from 80°C to 180°C. The results show that the introduction of BAG improves the electrical properties of BNT.     

Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure

CuO‐added 0.96(Na_0.5K_0.5)(Nb_1‐xSb_x)O₃‐0.04SrTiO₃ ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb⁵⁺ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d₃₃ values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d₃₃ of 358 pC/N, k_p of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm.     

First-principles study of the stability,electronic and mechanical properties of Cr2N and CrN with the variation of Ni doping concentration

First-principles approach was applied to investigate the stability, electronic and mechanical properties of Cr_2-xNi_xN (x = 0, 0.083, 0.167,0.250, 0.333) and Cr_1-xNi_xN (x = 0,0.125,0.25,0.375, 0.5). The calculated formation enthalpy and mechanical stability results show that Cr_2-xNi_xN and Cr_1-xNi_xN are all stable. The bulk, shear and Young's modulus results indicate that different variation trend is observed in Cr_2-xNi_xN and Cr_1-xNi_xN with the increase of x. Base on Pugh and Pettifor criteria, Cr₂N belongs to the brittle area and the ductility of Cr_2-xNi_xN increases with the increment of x, obtain the maximum results when x = 0.333. However, CrN, which belongs to the ductile area, alloying with Ni decreases its ductility and increases its brittleness, reach the maximum brittleness when x = 0.5. The charge density difference study reveals that the doped Ni atom affects the interaction between Cr and N in Cr_2-xNi_xN and Cr_1-xNi_xN differently. Furthermore, the stress-strain curve of Cr₂N, Cr_1.833Ni_0.167N, and Cr_1.667Ni_0.333N under shear and tensile deformation shows that the ultimate stress of Cr₂N is decreased and its ductility increased. Nevertheless, the stress-strain curve of CrN, Cr_0.75Ni_0.25N, and Cr_0.5Ni_0.5N under shear and tensile deformation indicates that the strength of CrN can be enhanced and its deformation process is significantly changed when x = 0.25.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

Properties and structures of nonstoichiometric (K,Na)NbO3‐based lead‐free ceramics

The 0.968[(K_0.48Na_0.52)]Nb_0.95+xSb_0.05O₃–0.032(Bi_0.5Na_0.5)ZrO₃ [KNN_xS–BNZ] lead‐free ceramics with nonstoichiometric niobium ion were fabricated via conventional solid‐state sintering technique and their piezoelectric, dielectric and ferroelectric properties were investigated. When x = 0.010, enhanced piezoelectric properties (d₃₃ ≈ 421 pC/N and k_p ≈ 0.47) were obtained due to the construction of rhombohendral—tetragonal phase boundary near room temperature. The KNN_xS–BNZ ceramics possesses enhanced Curie temperature (T_c) with improved piezoelectric constant. A large d₃₃ of ~421 pC/N and a high T_c ~256°C can be simultaneously induced in the ceramics with x = 0.010. Especially, good thermal stability was observed in a broad temperature range. The results indicated that our work could benefit development of KNN‐based ceramics and widen their application range.     

Synthesis,characterization and magnetic properties of polythiophene/SrFe12-x(ZrZn)0.5xO19 nanocomposite as a microwave absorber

Ferrites are an important group of magnetic materials which are used as absorbers. The incorporation of ferrite and conducting polymer achieves great enhancement in microwave absorption properties. The nanocomposites of hexagonal ferrites embedded by conducting polymers such as polypyrrole, polyaniline and polythiophene (PTH) have been paid much attention. In the present study, strontium hexagonal ferrite doped by Zr and Zn with the final formula of SrFe_12-x(ZrZn)_0.5xO19 considering x = 0.9 and embedded by PTH was produced to achieve a nanocomposite with the highest microwave absorbing ability. In this study, after synthesis of SrFe₁₂O₁₉(ZrZn)_0.5xO19 and PTH, the nanocomposite was prepared by in situ polymerization. Wrapping the ferrite particles and PTH chains could form nanocomposite properly, and therefore acceptable interactions were observable between SrFe_12-x(ZrZn)_0.5xO19ferrite particles and PTH polymer chains in the composites. Assessing the X-ray diffraction (XRD) patterns of SrFe_12-x(ZrZn)_0.5xO19, PTH, and PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite indicated that the PTH characteristic peak shifts slightly and its peak intensity reduces, which may be attribute to the coating of PTH polymer chains onto SrFe_12-x(ZrZn)_0.5xO19 particles. We revealed also lower magnetic properties in the obtained nanocomposite. The morphological assessment also suggested that PTH could effectively coat the SrFe_12-x(ZrZn)_0.5xO19 particles. The synergistic effect of SrFe_12-x(ZrZn)_0.5xO19 particle plus PTH leads to microwave absorption percentage higher than 95% by PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite. Overall, nanocomposite creating by coupling interaction between SrFe_12-x(ZrZn)_0.5xO19 particles (x = 0.9) and PTH can effectively lead to achieve the highest rate of absorption of electromagnetic waves.     

Thermally stable high strain and piezoelectric characteristics of (Li,Na, K)(Nb,Sb)O3-CaZrO3 ceramics for piezo actuators

The 0.97(Na_0.5K_0.5)(Nb_1−xSb_x)O₃-0.03CaZrO₃ ceramic with x = 0.09 exhibits a high d₃₃ of 518 pC/N and a strain of 0.13% at 4.0 kV/mm owing to its orthorhombic-pseudocubic polymorphic phase boundary (PPB) structure. However, these values decreased considerably above 90°C owing to its low Curie temperature (T_C), indicating that its thermal stability is not sufficient for practical applications. Li₂O was added to the specimen with x = 0.11 to improve its thermal stability of the strain and d₃₃ by increasing the T_C without degrading the actual d₃₃ and strain values. The 0.97(Li_0.04Na_0.46K_0.5)(Nb_0.89Sb_0.11)O₃-0.03CaZrO₃ ceramic, having an orthorhombic-tetragonal PPB structure, exhibits a d₃₃ of 502 pC/N and a strain of 0.16%. This large strain was maintained up to 150°C and the d₃₃ slightly decreased to 475 pC/N at 130°C. Therefore, this lead-free ceramic displays excellent piezoelectric characteristics with improved thermal stability, indicating that it can be applied to piezoelectric actuators.     

Hydrothermal synthesis and piezoelectric property of Ta-doping K0.5Na0.5NbO3 lead-free piezoelectric ceramic

Ta-doping K_0.5Na_0.5Nb_1−xTa_xO₃ (x = 0.1, 0.2, 0.3, 0.4) powder was synthesized by hydrothermal approach and its ceramics were prepared after sintering and polarizing treatment in this work. The K_0.5Na_0.5Nb_0.7Ta_0.3O₃ ceramics near morphotropic phase boundary (MPB), which exhibited optimum piezoelectric properties of d₃₃ = 210 pC/N and good electromechanical coupling factors of K_p = 0.3. The domain structure has been observed from TEM images which indicates that the K_0.5Na_0.5Nb_0.7Ta_0.3O₃ ceramics have good piezoelectric and ferroelectric properties for it is near the MPB.     

Crystallographic texture and phase structure induced excellent piezoelectric performance in KNN-based ceramics

It is difficult to maintain strong piezoelectric properties over a wide temperature range in (K,Na)NbO₃ (KNN)-based ceramics owing to the polymorphic phase boundary (PPB). Here, we propose advantageously utilizing the synergistic effect of crystal orientation and phase structure to address this issue. The 〈0 0 1〉_pc textured (1 − x)(K_0.48Na_0.52)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Ag_0.5)ZrO₃ (KNNS–xBAZ) ceramics with different phase structures were synthesized via the templated grain growth method. A high piezoelectric coefficient (d₃₃) of 505 ± 25 pC/N, an electric field-induced strain of 0.21%, and a superior temperature stability (d₃₃ exhibited a high retention of ≥78% at the temperature up to 200°C; strain maintained within 5.7% change over a temperature range of 30–150°C) were simultaneously achieved in textured KNNS–0.03BAZ ceramics. The flattened Gibbs free energy induced by the R–O–T multiphase coexistence, the strong anisotropy of crystals, and the abundant nanodomains contributed to the enhanced piezoelectric properties. The contribution of the strong anisotropy of crystals in 〈0 0 1〉_pc textured ceramics compensates for the deterioration of the piezoelectric properties caused by the phase structure deviation from the PPB with increasing temperature, which benefits the superior temperature stability of the textured KNNS–0.03BAZ ceramics. The previous merits prove that utilizing the synergistic effect of crystal orientation and phase structure is an effective strategy to boost the piezoelectricity and their temperature stability of KNN-based ceramics.     

Piezoelectric performance of 0.5BaZr0.2Ti0.8O3-0.5Ba1-xCaxTiO3 at triple phase point

0.5BaZr_0.2Ti_0.8O₃-0.5Ba_1-xCa_xTiO₃ ceramic samples with x = 15–35% have been fabricated to investigate the composition-driven phase evolution, ferroelectric, and piezoelectric properties. X-ray diffraction and temperature-dependent permittivity studies reveal the structural phase transition from the rhombohedral (R) to R + orthorhombic (O) and then O + tetragonal (T) having a tricritical triple phase points consisting of the R + O + T at x = 29.6%. The average grain size tends to increase with x but there is an exception of reducing grain size for x = 29.6%. The triple phase point displays the outstanding properties, such as minimum relaxation time (τ = 6.4 ms), large piezoelectric response (d₃₃ = 543 pC/N), high saturation polarization (P_S = 16.5 μC/cm²), small coercive field (E_c = 0.6 kV/cm), and high dielectric permittivity, over 8700 peaking at 21,765. These parameters reduce drastically at the O/R and O/T phase boundaries. Our studies indicate the important role of multiphase coexistence for enhancing the piezoelectric properties.     

Dielectric,Ferroelectric, and Piezoelectric Properties of BiFeO3–BaTiO3 Ceramics

Perovskite solid solution ceramics of (1 ? x)BiFeO₃–xBaTiO₃ (1 ? x)BF–xBT, 0.2 ≤ x ≤ 0.45) with high electrical resistivity were prepared by solid‐state reaction method. Actual ferroelectric hysteresis loops and temperature dependence of dielectric constant of the ceramics were obtained. Ceramics of 0.7BF–0.3BT with small rhombohedral distortion show highest remnant polarization (P_r = 26.0 μC/cm²) and piezoelectric coefficient (d₃₃ = 134 pC/N). Compositions with pseudo‐cubic symmetry (intermediate phases) show relaxor‐like dielectric anomaly. The values of P_r and d₃₃ decrease with increasing BT content, from 24.8 μC/cm² and 104 pC/N for 0.65BF–0.35BT to 8.2 μC/cm² and 5 pC/N for 0.55BF–0.45BT.     

The Relationship Between Phase Structure and Electrical Properties in (1 − x)(Bi0.5Na0.5TiO3–Ba0.5K0.5TiO3–BaTiO3)‐ xK0.5Na0.5NbO3 Quaternary Lead‐Free Piezoelectric Ceramics

(1 ? x)(0.85Bi_0.5Na_0.5TiO₃–0.11Ba_0.5K_0.5TiO₃–0.04BaTiO₃)‐ xK_0.5Na_0.5NbO₃ lead‐free piezoelectric ceramics with x = 0.00, 0.02, 0.03, 0.04, 0.05, and 0.10 were prepared by a conventional solid state method. A coexistence of rhombohedral (R) and tetragonal (T) phases was found in the system, which tended to evolve into pseudocubic symmetry when x increases. The x = 0.04 sample exhibited improved electrical properties: the dielectric constant ε_r = 1900 with the low loss tangents 0.06, the S_max/E_max of ~400 and ~460 pm/V under unipolar and bipolar electric field, respectively. Meanwhile, piezoelectric constant d₃₃ still maintained ~160 pC/N. These could be owed to the formation of polar nanoregions for relaxor phase.     

Influence of Stoichiometric Ratio and Mn-Doping on the Surface Morphology and Dielectric Properties of Perovskite (La,Sr)FeO3 Films

Lanthanum strontium ferrite (La_1−x Sr _x FeO₃, x = 0.1, 0.3, 0.5, 0.7) (LSF) films were prepared on platinized/silica/silicon (Pt/SiO₂/Si) substrates by a sol–gel method. The crystallization, surface morphology and dielectric properties of the LSF films have been studied. Among the samples, La_0.5Sr_0.5FeO₃ thin film have the most homogeneous, smooth surface and the best dielectric properties (ε _r  = 2881.58, tanδ = 1.20) at the frequency of 1 kHz. Mn-doping (y) in La_0.5Sr_0.5FeO₃ further improves the dielectric properties (ε _r  = 2922.91, tanδ = 1.11) of the film. Both ε _r and tanδ values of the Mn-doped (y = 0.02) La_0.5Sr_0.5FeO₃ films decreases with increasing the frequency. The biggest ε _r value is 3238.18 at the frequence of 0.02 kHz.     

Giant dielectric constant and tunable phase-transition characteristics of ZnF2/BaF2-modified BaTiO3 thick films

High performance capacitors have been investigated to meet higher integration density with optimized charge-storing capability. Here, we introduce nonconventional thick film dielectric compositions based on 95BaTiO₃–xZnF₂–(2−x)BaF₂–3glass (x = 0.5, 1.0, and 1.5) where the relative content of ZnF₂/BaF₂ is critical in controlling dielectric behavior. The thick films were prepared on Cu foils by regular screen-printing and then firing at 950°C in inert atmosphere. As an optimal example, thick film composition modified with 1.0ZnF₂/1.0BaF₂ exhibited a dielectric constant of ~1903 and a dielectric loss of ~0.04 at 1 MHz with dispersive dielectric relaxation behavior, which are far better than any reported corresponding values so far. Particularly, it was very interesting to observe that Curie temperature was tunable from −19 to +34°C, depending on the relative content of fluoride additives only within the 2 mol% range. Dependency of the relative contents of the fluorides is primarily investigated with regard to microstructure and dielectric properties.     

Piezoelectric properties of [001]-textured high-power PMnN-PZT piezoceramics sintered at a low temperature

The 1.0 mol% CuO-added 0.14Pb(Mn1/3Nb2/3)O₃-0.86Pb(Zr_0.55Ti_0.45)O₃ (CPMnN-PZT) piezoceramics were synthesized at low temperatures (≤ 950 °C) by the columbite method to remove the pyrochlore phase. It exhibited a high Q_m of 3016 and a high T_C of 309 °C. However, it showed small d₃₃ and k_p values of 143 pC/N and 0.43, respectively. The CPMnN-PZT piezoceramic was textured along the [001] direction using BaTiO₃ (BT) templates to enhance its soft piezoelectric properties. The [001]-textured CPMnN-PZT + y vol% BT piezoceramics (1.0 ≤ y ≤ 5.0) were densified at a low temperature of 950 °C with a high Lotgering factor (≥ 92%). The textured sample (y = 1.0) showed a high Q_m of 1400 with increased d₃₃ and k_p values of 278 pC/N and 0.58, respectively, and its piezoelectricity showed excellent temperature stability up to 225 °C. Therefore, the textured CPMnN-PZT sample can be used for developing high-power piezoelectric devices.     

Improvement of piezoelectricity of (Na,K)Nb-based lead-free piezoceramics using [001]-texturing for piezoelectric energy harvesters and actuators

0.96(Na_0.5K_0.5)(Nb_0.93Sb_0.07)O₃?(0.04?x)BaZrO₃?x(Bi_0.5Ag_0.5)ZrO₃[NKNS?(0.04?x)BZ?xBAZ] ceramics are well textured along the [001] direction using 3.0 mol% NaNbO₃ seeds. The textured-NKNS?0.02BZ?0.02BAZ thick film has a rhombohedral-orthorhombic-tetragonal (R-O-T) structure with a large proportion of the O-R structure (> 80%). This specimen exhibits the largest values for d₃₃ (805 pC/N) and d₃₃ ×g₃₃ (29.5 ×10^?12 m²/N), which are the largest d₃₃ and d₃₃ ×g₃₃ values of NKN-based piezoceramics to date. It exhibits a large strain (0.17% at 4.0 kV/mm). Therefore, it is an outstanding piezoceramic material for piezoelectric energy harvesters (PEHs) and actuators. A PEH and actuator are fabricated using this specimen. The PEH shows a large power density (4.3 mW/cm³), which is the largest value among the PEHs produced by lead-free piezoceramics. The actuator exhibits a large acceleration (50.8 G) and displacement (3.9 mm), which are the best actuating properties among the actuators produced by lead-free piezoceramics. Therefore, texturing is an excellent technique for improving the piezoelectricity of NKN-based piezoceramics.     

Phase transition,microstructure, and dielectric properties of Li/Ta/Sb co-doped (K,Na)NbO3 lead-free ceramics

Li/Ta/Sb co-doped lead-free (K_0.4425Na_0.52Li_0.0375)(Nb_0.93−xTa_xSb_0.07)O₃ (abbreviated KNLNST_x) piezoelectric ceramics, with Ta-doping ratio of x ranging from 0.0275 to 0.0675, were synthesized using the conventional solid-state reaction method at the sintering temperature of 1130 °C. The effects of Ta content on the microstructure, dielectric properties, and phase transition behavior of the prepared ceramics were systematically investigated. The X-ray diffraction results show that all KNLNST_x ceramics formed a secondary phase, which is assigned to the tetragonal tungsten-bronze type (TTB) structure phase, and showed a phase transition from an orthorhombic symmetry to a tetragonal symmetry across a composition region of 0.0375<x<0.0475. The grain shape and size that correspond to the phase structure transformations can be clearly observed in the scanning electron microscopy images. As x increased to 0.0475, the KNLNST_0.0475 ceramics changed from orthorhombic to tetragonal structure and showed excellent piezoelectric properties of d₃₃=313 pC/N, k_p=47%, and ε_r=1825. By contrast, samples of x=0.0375 with orthorhombic symmetry exhibited poor piezoelectric properties, with d₃₃=200 pC/N and ε_r=1015. These results indicate that phase structure is vital in the piezoelectric properties of KNN lead-free ceramics.