K0.5Na0.5NbO3 Research Articles

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 kij, Qm, dij, and a small εT33 to generate a large power output. Texturing was used to enhance the piezoelectricity of KNN-related piezoceramics. In particular, the kij and dij values of the KNN-based piezoceramics were considerably improved after texturing along the [001] direction, with a small change in the εT33/ε0 value, indicating that the [001]-textured KNN-based thick films are good candidates for use in PEHs. The 0.97(K0.5Na0.5)(Nb0.93Sb0.07)O3-0.03CaZrO3 [KN(N0.93S0.07)-CZ] thick film was textured along the [001] direction, and this thick film exhibited a large kp (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(N0.93S0.07)-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(N0.93S0.07)–CZ thick film is a good candidate for use in PEHs.

Real-Time Capturing of Microscale Events Controlling the Sintering of Lead-Free Piezoelectric Potassium-Sodium Niobate.

Sintering is a very important process in materials science and technological applications. Despite breakthroughs in achieving optimized piezoelectric properties, fundamentals of K0.5 Na0.5 NbO3 (KNN) sintering are not yet fully understood, facing densification versus grain growth competition. At present, microscale events during KNN sintering under reducing atmospheres are real-time monitored using a High Temperature-Environmental Scanning Electron Microscope. A two contacting KNN particles model satisfying the Kingery and Berg's bulk diffusion model is reported. Dynamic events like individual grain growth and grain elimination process are explored through a postanalysis of recorded image series. The diffusion coefficient for oxygen vacancies of 10-8 cm2 s-1 and average boundary mobility of 10-9 cm4 J-1 s-1 are reported for the KNN ceramics. Moreover, the local pore shrinkage is consistent with the Kingery and François's concept of pore stability except that pore curvatures are not all concave, convex or flat due to anisotropic grain-boundary energies. The global grain growth kinetics are described using parabolic and/or cubic laws. The effect of atmospheres and microstructure evolution on the intrinsic and extrinsic contributions to the dielectric response using Rayleigh's law is also explored. These results bring a new breath for KNN sintering studies in order to adapt the sintering process.

Destabilization of the ferroelectric order in Na0.5Bi0.5TiO3–6 wt% BaTiO3 ceramics through doping

One of the most promising candidates to replace lead-based compounds in actuator applications are Na0.5Bi0.5TiO3 (NBT)-based materials. K0.5Na0.5NbO3 (KNN)-modified NBT-BaTiO3 (NBT-BT) solid solutions exhibit giant large-signal strain–electric-field coefficients (Smax/Emax) exceeding 500 pm V−1. However, despite the promising properties of the ceramics reported in the literature, the synthesis of these materials remains challenging, leaving gaps in the understanding of the synthesis-property relationship. In this contribution, we investigate the microstructure and the electrical properties while changing the composition to destabilize the ferroelectric order in the material, which is the key to achieve large strain response. Measurements of dielectric and ferroelectric properties reveal that Na- or Ti-deficiency or excess of Bi decrease the ferroelectric-to-relaxor transition temperature and remnant polarization, indicating a destabilization of the ferroelectric order. Additionally, the use of KNO3 instead of K2CO3 as the potassium source in KNN results in an additional destabilizing effect on the ferroelectric order, which can be attributed to better incorporation of K+ into the perovskite structure. The results identify the key aspects of the synthesis of NBT-BT-KNN ceramics to obtain high Smax/Emax values.

Improving the energy storage performances of Bi(Ni0.5Ti0.5)O3-added K0.5Na0.5NbO3-based ceramics

K0.5Na0.5NbO3 (KNN)-based ceramics are ideal alternatives to lead-containing ceramics because of their high maximum polarization and relatively large breakdown strength, however the low energy efficiency (η) remains a constraint on application. In this work, a novel (1-x)K0.5Na0.5NbO3-xBi(Ni0.5Ti0.5)O3 [(1-x)KNN-xBNiT] ceramics were designed and prepared using traditional solid state reaction method. An optimal recoverable energy storage density (Wrec) of 2.61 J/cm3 accompanied by an ultrahigh η of 82.6% was simultaneously achieved in 0.85KNN-0.15BNiT ceramic under 280 kV/cm. Furthermore, a favorable temperature and frequency stability (the variation of Wrec and < 3% over the range of 25–150 °C and 1–100 Hz) of energy storage performances (ESP) can be obtained. Meanwhile, 0.85KNN-0.15BNiT ceramic exhibits an outstanding power density (47.8 WM/cm3) and a fast discharge speed (t0.9 = 46.9 ns) under 120 kV/cm. These results reflect that 0.85KNN-0.15BNiT ceramic is a deserved candidate for the application of high energy storage devices.

Effect of incorporation of piezoelectric phases on antibacterial and cellular response of borate bioactive glass

The present study investigates the consequences of incorporation (30 vol %) of piezoelectric Na0.5K0.5NbO3 (NKN) and BaTiO3 (BT) phases and surface polarization (20 kV at 500 °C) on in-vitro antibacterial and cellular response of borate bioactive glass (1393B3, BBG). XPS analyses elucidated that the surface chemistry of optimally processed composites remains unaffected after surface polarization treatment. The piezoelectric BT and NKN enhance the antibacterial activity of BBG by ∼ (53, 57%) and (51, 54%) for E. coli and S. aureus bacteria stains, respectively. The SEM images of bacteria, adhered on unpolarized and polarized surfaces demonstrate bacteria specific response. The combined action of piezoelectric phase and surface polarization increases the growth rate of osteoblast like MG-63 cells on negatively polarized BBG- BT (30 vol %) and BBG- NKN (30 vol%) composites by ∼ 76 and 82% respectively. Overall, the piezoelectric secondary phase incorporated in BBG as well as surface polarization increases the cellular and antibacterial response significantly.

Dielectric Properties of Low Concentration Barium Doped K&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt; Lead Free Ceramics Prepared via Solid State Reaction Method

In this work, the effect of low concentration of Barium (Ba) on the density, crystal structure, microstructure and dielectric properties of K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramic samples have been systematically studied. The samples were calcined at 850 °C for 6 hours and pressed using a hydraulic hand press to produce a green body disc. In this way, the green body disc of KNN was doped with 0.00 to 0.10 mol % of Ba concentration and was placed in an alumina crucible before conventional sintering at 1120 °C for 2h in air atmosphere. The increasing amount of Ba shifting all the diffraction peaks to a higher angle was measured using X-Ray Diffraction. Doping the Ba also improved the density of the KNN body. The most densified body was identified for x= 0.05 mol% of Ba which is 4.21355 g/cm3. The microstructure of the surface becomes finer and smaller after Ba doping. This shifting diffraction peaks and densified body is responsible for the enhancement of dielectric properties with the optimum value obtained from the sample doped with x= 0.05 mol%. The results show that relative permittivity (ɛr) was improved by the increment of Ba2+ concentration for 0.05 mol% which is 183.9856 for 1 kHz.

Single-Beam Acoustic Tweezer Prepared by Lead-Free KNN-Based Textured Ceramics.

Acoustic tweezers for microparticle non-contact manipulation have attracted attention in the biomedical engineering field. The key components of acoustic tweezers are piezoelectric materials, which convert electrical energy to mechanical energy. The most widely used piezoelectric materials are lead-based materials. Because of the requirement of environmental protection, lead-free piezoelectric materials have been widely researched in past years. In our previous work, textured lead-free (K, Na)NbO3 (KNN)-based piezoelectric ceramics with high piezoelectric performance were prepared. In addition, the acoustic impedance of the KNN-based ceramics is lower than that of lead-based materials. The low acoustic impedance could improve the transmission efficiency of the mechanical energy between acoustic tweezers and water. In this work, acoustic tweezers were prepared to fill the gap between lead-free piezoelectric materials research and applications. The tweezers achieved 13 MHz center frequency and 89% −6 dB bandwidth. The −6 dB lateral and axial resolution of the tweezers were 195 μm and 114 μm, respectively. Furthermore, the map of acoustic pressure measurement and acoustic radiation calculation for the tweezers supported the trapping behavior for 100 μm diameter polystyrene microspheres. Moreover, the trapping and manipulation of the microspheres was achieved. These results suggest that the KNN-based acoustic tweezers have a great potential for further applications.

Significant increase in comprehensive energy storage performance of potassium sodium niobate-based ceramics via synergistic optimization strategy

K0.5Na0.5NbO3 (KNN)-based ceramics are considered as one of the most promising lead-free dielectric ceramics owing to relatively high dielectric breakdown strength (DBS) resulted from their unique submicron grains. Unfortunately, it has been difficult to increase recoverable energy-storage density (Wrec) and energy-storage efficiency (η) simultaneously at present. Herein, we propose a synergistic optimization strategy, namely, simultaneously enhancing DBS by tailoring grain size to submicron scale and inducing the temperature range between the maximum dielectric permittivity temperature (Tmax) and the Burns temperature (TB) to room temperature, for solving the bottleneck. (1-x)K0.5Na0.5NbO3-xBi(Ni0.5Zr0.5)O3 (KNN-BNZ) ceramics were chosen as an example to illustrate the validity of this strategy. An ultrahigh Wrec of 8.09 J·cm−3 was obtained at the optimum composition of x = 0.15 under the electric field of 870 kV·cm−1, which is much higher than those of other reported KNN-based ceramics. Most importantly, this high Wrec was accompanied by a high η of 88.46%, which is superior to those of other KNN-based ceramics and very important for practical applications. The excellent comprehensive energy storage performance was resulted from the polar nanoregions, which is confirmed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), piezo-force microscopy (PFM) and first-order reversal curve (FORC) distributions. The work not only finds out novel KNN-based ceramics with excellent comprehensive energy storage properties, but also provides a remarkable designing strategy for exploring a series of novel lead-free dielectric ceramics with high energy storage properties for practical applications in the future.

Tetragonal tungsten bronze phase potential in increasing the piezoelectricity of sol-gel synthesized (K0.5Na0.5)1-xLixNbO3 ceramics

(K,Na)NbO3 (KNN)-based ceramics have been proven to be formidable candidates among lead-free piezoelectric materials, yet poor reproducibility always hinders their progress. In the present study, the effects of low lithium substitution on the electrical properties and microstructure of (K0.5Na0.5)1-xLixNbO3 (KNLN) ceramics were investigated. All samples were synthesized by the sol-gel method. The Curie temperature (TC) of the ceramics shifted to higher temperature and gradually decreased the monoclinic-tetragonal (TM-T) phase transition. Li+ substitution had a prominent effect on the ferroelectric properties and improved the piezoelectric coefficient (d33) up to 181 pC/N. X-Ray Diffraction (XRD) studies and Field Emission Scanning Electron Microscopy (FESEM) images revealed an inevitable tetragonal tungsten bronze (TTB) secondary phase, which was formed during the preparation process. It was demonstrated that the volatilization of Li+ cations facilitated TTB growth. The coexistence of two different phase structures proved to enhance the KNN piezoelectric performance.

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering.

It is challenging to achieve highly tunable multifunctional properties in one piezoelectric ceramic system through a simple method due to the complicated relationship between the microscopic structure and macroscopic property. Here, multifunctional potassium sodium niobate [(K, Na)NbO3 (KNN)]-based lead-free piezoceramics with tunable piezoelectric and electrostrictive properties are achieved by controlling the long-range ferroelectric ordering (LRFO) through antimony (Sb) doping. At a low Sb doping, the slightly distorted NbO6 octahedron and the softened B-O repulsion well maintain the LRFO and induce plenty of nanoscale domains coexisting with a few polar nanoregions (PNRs). Thereby, the diffused rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence with distinct dielectric jumping is constructed near room temperature, by which the nearly 2-fold increase in the piezoelectric coefficient (d33 ∼ 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27-120 °C) are obtained. At a high Sb doping, the LRFO is significantly destroyed, leading to predominant PNRs. Thus, a typical relaxor is obtained at the ferroelectric-paraelectric phase transition near room temperature, in which a large electrostrictive coefficient (Q33 = 0.035 m4/C2), independent of the electric field and temperature, is obtained and comparable to that of lead-based materials. Therefore, our results prove that controlling the LRFO is a feasible way to achieve high-performance multifunctional KNN-based ceramics and is beneficial to the future composition design for KNN-based ceramics.

Effect of BaZrO3 amounts on the domain structure and electrical properties of lead-free piezoelectric KNN-based films

K0.5Na0.5NbO3 (KNN)-based bulk ceramics show superior piezoelectric coefficient by constructing the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases. However, it is a challenge for KNN films to obtain the superior electrical properties with the same MPB composition, because of the serious volatilization of alkali ions and substrate-induced stress. Therefore, the MPB composition in films could be different from bulk ceramics. The lead-free piezoelectric 0.92KNN-0.07BaZrO3 (BZ)-0.01Bi0.5Na0.5TiO3 (BNT) and 0.91KNN-0.08BZ-0.01BNT films were prepared, referring to the MPB composition of bulk ceramics. For comparison, the 0.95KNN-0.04BZ-0.01BNT and 0.88KNN-0.11BZ-0.01BNT films far away from the MPB composition of bulk ceramics were prepared together. Their crystallographic phase, domain morphologies and ferroelectric switching show a dependence of BZ amount. With increase of the BZ content, the (100)-preferential orientation and out-of-plane self-polarization of films enhanced. Because the 0.08 BZ film shows the higher self-polarization and lower KNN content, compared with 0.04 BZ film, it shows the stronger piezoelectric response but not a higher dielectric constant.

Screen Printed Copper and Tantalum Modified Potassium Sodium Niobate Thick Films on Platinized Alumina Substrates.

We show how sintering in different atmospheres affects the structural, microstructural, and functional properties of ~30 μm thick films of K0.5Na0.5NbO3 (KNN) modified with 0.38 mol% K5.4Cu1.3Ta10O29 and 1 mol% CuO. The films were screen printed on platinized alumina substrates and sintered at 1100 °C in oxygen or in air with or without the packing powder (PP). The films have a preferential crystallographic orientation of the monoclinic perovskite phase in the [100] and [−101] directions. Sintering in the presence of PP contributes to obtaining phase-pure films, which is not the case for the films sintered without any PP notwithstanding the sintering atmosphere. The latter group is characterized by a slightly finer grain size, from 0.1 μm to ~2 μm, and lower porosity, ~6% compared with ~13%. Using piezoresponse force microscopy (PFM) and electron backscatter diffraction (EBSD) analysis of oxygen-sintered films, we found that the perovskite grains are composed of multiple domains which are preferentially oriented. Thick films sintered in oxygen exhibit a piezoelectric d33 coefficient of 64 pm/V and an effective thickness coupling coefficient kt of 43%, as well as very low mechanical losses of less than 0.5%, making them promising candidates for lead-free piezoelectric energy harvesting applications.

Synthesis of (K, Na)NbO3 piezoelectric crystals with tunable K/Na ratios

(K, Na)NbO3 (KNN) lead-free piezoelectric crystals with different K/Na molar ratios were synthesized through a hydrothermal method using isopropanol/deionized water as the reaction medium. It is shown that cube-like KNN crystals were synthesized at a relatively low [OH–] concentration. The structure of the as-synthesized KNN crystals transfers from a NaNbO3-type orthorhombic phase to a KNbO3-type tetragonal phase with the increase of the K/Na ratio. This principle is also instructive in a finer range of K/Na ratio (0.71:0.29–0.73:0.27), indicating a facile synthesis route and recommended conditions for the synthesis of KNN materials with a morphotropic phase boundary (MPB) between NaNbO3 and KNbO3.

Giant Grain Growth in (K,Na)NbO3 Ceramics

In this manuscript, an interesting phenomenon is reported. It has been reported that the growth of single crystals is observed in donor-doped (K,Na)NbO3 (KNN)-based ceramics. It is very interesting that the growth happens without the addition of a seed. The growth of huge grains (single crystal, approximately 30 mm,) occurs due to the abnormal grain growth (AGG) in KNN-based ceramics. In the AGG compositions, moreover, the seed plates can be synthesized by not topochemical reaction but simple molten salt synthesis (SMSS) which is a simple-and-cheap process. They can be a good candidate for the seeds at reactive templated grain growth (RTGG) or templated grain growth (TGG) process.

All-Inorganic Flexible (K, Na)NbO3-Based Lead-Free Piezoelectric Thin Films Spin-Coated on Metallic Foils.

Flexible piezoelectric thin films are raising interest in energy harvesting and wearable electronics, although their direct fabrication is challenging in the selection of substrates and thermal processing. In this work, we developed direct fabrication of flexible lead-free (K, Na)NbO3 (KNN)-based piezoelectric films on commercially available metallic foils by sol-gel processing. Stainless steel and platinum foils are selected as flexible substrates because of their good thermal stability, robust flexibility, and cost-efficiency. The sol-gel-processed KNN-based thin films on both of the metallic foils show good flexibility, with the bending radii reaching ±3 mm. The flexible thin films grown on stainless steel and platinum foils present high breakdown electric fields that reach 1760 and 2530 kV/cm, respectively, resulting from the fine-grained dense structure, limited leakage current density, and suppressed mobility of charged carriers. Improved effective piezoelectric coefficient d33,eff* (75.4 pm/V) with a slight decrease after bending was obtained in the flexible thin films on Pt when compared to their rigid counterparts. The flexible lead-free piezoelectric thin films with combined high breakdown electric fields and piezoelectric and energy storage properties may pave the way for integrating KNN-based multifunctional thin films into flexible electronics.

Microwave-absorbing performance of a radar-absorbing structure composed of K0.5Na0.5NbO3/ZrO2/Al2O3 heterojunction

We fabricated a ZrO2/Al2O3 ceramic using the 3D plasma spraying technology, and the surface morphology and electrical properties of the prepared ceramic were investigated. The microwave-absorbing performance of the ceramic was studied based on the measured electrical properties. Furthermore, a radar-absorbing structure (RAS) was designed based on the fabricated ZrO2/Al2O3 ceramic with a K0.5Na0.5NbO3 (KNN) film heterojunction. The relationship between the structural parameters of the RAS and the microwave performance was explored. The changes in the absorption performance and band structure of the RAS with the resistance of the KNN film were investigated. The analytical results showed that the structural parameters of the KNN film can facilitate the absorption intensity as well as the bandwidth of the RAS while inducing electromagnetic coupling in the RAS system. The improvement in the absorption performance could be attributed to the resonance coupling between the ZrO2/Al2O3 ceramic and the KNN film.

Energy storage performance of K0.5Na0.5NbO3-based ceramics modified by Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3

The damage of lead-based ceramics to our environment and health completely hindered their industrial applications. K0.5Na0.5NbO3 (KNN) ceramic material is considered as a good substitute for lead-free ceramics because of its high dielectric constant, excellent piezoelectric properties, high Curie temperature and sustainability. However, it is challenging to achieve their high energy-storage performances because of their large energy loss density (Wloss) under an applied electric field. Thus, this work proposes a combinatorial optimization strategy of inducing polar nano-regions and improving breakdown strength (BDS) to enhance the energy-storage performances of the KNN-based ceramics. As a result, we obtained a record high recoverable energy-storage density (Wrec) value of 7.4 J·cm−3 for the Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3 (BZNT)-modified KNN ceramic mainly due to its enhanced BDS. Furthermore, remarkable temperature stability was obtained for the 0.90KNN-0.10BZNT ceramic over a wide temperature range (20–180 °C). Remarkably, the first-order reversal curve (FORC) confirmed the excellent energy-storage performances of the 0.90KNN-0.10BZNT ceramic, which we ascribed to its enhanced relaxation behavior. Additionally, 0.90KNN-0.10BZNT material exhibited excellent pulsed charge/discharge properties of the high power density (184.84 MW·cm−3) and fast discharge time (46.3 ns). Our results demonstrated a novel strategy for improving the energy-storage performances of dielectric ceramics. This strategy could be used to design other or similar materials for various applications.

Frequency-Tunable Slot-Loop Antenna Based on KNN Ferroelectric Interdigitated Varactors

A miniature frequency-tunable slot-loop antenna (0.128 λ 0 × 0.077 λ 0) based on ferroelectric K0.5Na0.5NbO3 (KNN) interdigitated varactors is investigated at Ku-band. KNN material has been selected among the ferroelectric oxide family because of its competitive properties for microwave applications. Its high permittivity value ( ϵr a 360 at 10 GHz) and its wide frequency tunability under an external static electric field E bias make it a promising candidate for frequency-agile antennas and circuits at microwaves. The antenna prototype has been designed and elaborated on MgO substrate ( ϵr = 9.8 and tan δ a 10−4 at 10 GHz). Fabrication details including laser microetching process of the ferroelectric layer are also described. The center frequency of the slot-loop antenna can therefore be tuned monotonously from 15.22 to 15.97 GHz under E bias = 88 kV/cm, leading to a frequency tunability rate equal to 4.6%. These results demonstrate for the first time the ability of the KNN material to be used for miniature tunable antennas, in comparison with BaxSr1−xTiO3, currently considered as the most relevant material for such applications.

Thickness-Dependent Domain Relaxation Dynamics Study in Epitaxial K0.5Na0.5NbO3 Ferroelectric Thin Films.

We explored the time dependence of the nanoscale domain relaxation mechanism in epitaxial K0.5Na0.5NbO3 (KNN) thin films grown on La0.67Sr0.33MnO3/SrTiO3 (001) substrates over the thickness range 20-80 nm using scanning probe microscopy. Kelvin probe force microscopy (KFM) and piezoresponse force microscopy were performed on pulsed-laser-deposition-deposited KNN thin films for studying the time evolution of trapped charges and polarized domains, respectively. The KFM data show that the magnitude and retention time of the surface potential are the maxima for 80 nm-thick film and reduce with the reduction in the film thickness. The charging and discharging of the samples reveal the easier and stronger electron trapping compared to hole trapping. This result further indicates the asymmetry between retention of the pulse-voltage-induced upward and downward domains. Furthermore, the time evolution of these ferroelectric nanodomains are found to obey stretched exponential behavior. The relaxation time (T) has been found to increase with increase in thickness; however, the corresponding stretched exponent (β) is reduced. Moreover, the written domain can retain for more than 2300 min in KNN thin films. An in-depth understanding of domain relaxation dynamics in Pb-free KNN thin films can bridge a path for future high-density memory applications.

Simultaneously improving piezoelectric properties and temperature stability of Na0.5K0.5NbO3 (KNN)-based ceramics sintered in reducing atmosphere

It is a very difficult work to sinter K0.5Na0.5NbO3 (KNN)-based materials with good reduction resistance in strong reducing atmosphere. 0.945K0.48Na0.52Nb0.96Ta0.04O3−0.055BaZrO3 + 0.03ZrO2 + y mol%MnO (KNNT−0.055BZ + 0.03Zr + yMn) ceramics sintered in reducing atmosphere were prepared successfully by conventional solid-state reaction methods. MnO dopant increases grain size at y = 5–8 due to strong lattice distortion and then decreases grain size at y = 9 due to much Mn4Nb2O9 accumulated at the grain boundary. MnO dopant as an excellent sintering aid can effectively reduce volatilization of alkali metal by decreasing the sintering temperature (Tsinter). Reducing alkali metal volatilization can greatly reduce oxygen vacancies and improve piezoelectric properties. MnO dopant can improve the anti-reduction properties. The KNNT−0.055BZ + 0.03Zr + yMn ceramics at y = 6–9 show outstanding anti-fatigue of unipolar piezoelectric strain under the synergistic effect of reduced oxygen vacancies due to reduced volatilization and increased grain size. Piezoelectric properties and temperature stability of KNNT−0.055BZ + 0.03Zr ceramics sintered in reducing atmosphere are improved simultaneously by MnO dopant. Optimum inverse piezoelectric coefficient (d33*) of ceramics at y = 8 reaches up to 480 pm/V under low driving electric field E = 20 kV/cm at room temperature, and its temperature stability of d33* reaches 158 °C. It will be an excellent lead-free material candidate for the preparation of multilayer piezoelectric actuators co-fired with nickel electrode.