Enhanced dielectric and piezoelectric properties in Na0.5Bi4.5Ti4O15 ceramics with Pr-doping

The bismuth layer-structured Na_0.5Bi_4.5-xPr_xTi₄O₁₅ (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr³⁺) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr³⁺ contents on dielectric, ferroelectric and piezoelectric properties of Na_0.5Bi_4.5Ti₄O₁₅ ceramics were investigated. The grain size of Pr³⁺-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature T_c gradually decreased with increasing Pr³⁺ contents, and the dielectric loss decreased at high temperature by Pr³⁺-doping. Moreover, the activation energy (E_a), resistivity (Z’), remanent polarization (2P_r) and piezoelectric constant (d₃₃) increased by Pr³⁺-doping. The NBT-xPr³⁺ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), E_a of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d₃₃ of 18 pC/N, 2P_r of 12.04 μC/cm². The enhancement was due to the addition of Pr³⁺ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr³⁺ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na_0.5Bi_4.5Ti₄O₁₅ ceramics in electrical properties.     

Compensation for volatile elements to modify the microstructure and energy storage performance of (W,Ni)-codoped Na0.5Bi0.5TiO3 ceramic films

This work reports the characteristics of nonstoichiometric Na_0.5+xBi_0.5+yTi_0.96W_0.01Ni_0.03O₃ (x?=?0.0%, y?=?1.0%; x?=?0.5%, y?=?2.0%; x?=?1.0%, y?=?4.0%) ceramic films derived from chemical solution deposition and the role played by excess Na/Bi in modifying microstructure and electrical properties. Single perovskite phase structure can be maintained in all compositions. Decreased grain size can be obtained with the increasing compensation for volatile Na/Bi elements. Particularly, extra amounts of 0.5?mol% Na and 2.0?mol% Bi leads to reduced leakage and enhanced ferroelectric polarization. Meanwhile, due to the high breakdown electrical field strength and large difference between maximum and remanent polarization, an excellent energy storage performance can be achieved in Na_0.505Bi_0.52Ti_0.96W_0.01Ni_0.03O₃ sample, which is distinguished by a recoverable energy storage density of 40.5?J/cm³ and an energy storage efficiency of 43.6% at 2515?kV/cm as well as a good frequency stability. Hence, the regulation for the content of volatile elements is effective to modify the electrical response of Na_0.5Bi_0.5TiO₃-based materials.     

Structural investigation of Li1−xNi0.5Co0.25Mn0.25O2 by in situ XAS and XRD measurements

A combination technique of in situ synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) was employed to study the Li_1−xNi_0.5Co_0.25Mn_0.25O₂ cathode material for Li-ion battery. The Li/Li_1−xNi_0.5Co_0.25Mn_0.25O₂ cell with x = 0.82 charged to 4.5 V showed the first charge capacity of 225 mAh/g. The X-ray absorption near edge structure (XANES) indicated that the initial valences were +2/+3, +3 and +4 for Ni, Co and Mn, respectively. The main redox reaction during delithiation was achieved by Ni via the reaction Ni²⁺ → Ni³⁺ followed by Ni³⁺ → Ni⁴⁺. The oxidation states of Co and Mn remained Co³⁺ and Mn⁴⁺. The bond length of Ni-O decreased drastically, while the Co-O and Mn-O distances exhibited a slight change with the decrease of Li content in the electrode. It was further revealed that all the second shell metal-metal (Ni-M, Co-M and Mn-O) distances decreased due to the oxidation of metal ions. In situ XRD data showed that both a- and c-axes varied with different Li contents in this material system. At the beginning of charge, there was a contraction along the c-axis and a slight expansion along the a-axis. As x reached 0.57, the trend of the variation in c-axis was opposite. The changes of lattice parameters could be explained by the balance between ionic radius and the repulsive force of the layer-structured material.     

Electrical and photoluminescence properties of Sm3+ doped Na0.5La0.5Bi8-xSmxTi7O27 ceramics

In this study, Sm³⁺ doped Na_0.5La_0.5Bi_8-xSm_xTi₇O₂₇ (NBT-BITL-xSm, x = 0, 0.01, 0.015, 0.02, and 0.03) ceramics were synthesized via a conventional solid-state reaction process. The structural, electrical, and photoluminescence properties of NBT-BITL-xSm ceramics were systematically investigated. The crystal structure of NBT-BITL-xSm was refined using XRD Rietveld refinement and found to possess a single orthorhombic structure at room temperature. Raman spectroscopy revealed that Sm³⁺ ions preferred to substitute for Bi³⁺ located in the A-sites of pseudo-perovskite layers, inducing a slight decrease in orthorhombic distortion. Strong characteristic emission peaks of Sm³⁺ ions were observed in orange-red regions under a 407 nm laser source, and the sample with x = 0.015 achieved the optimal photoluminescent property. Dielectric measurements showed double anomaly permittivity peaks at the temperature of 589 and 600^°C (T_m and T_c, respectively). The complex impedance spectrum indicated that the electrical conductivities mainly originated from crystal grains at high temperature. The activation energy was calculated to be 1.37–1.44 eV from Arrhenius fitting results. After Sm³⁺ substitution, the activation energy for conductivity was increased as a result of reduced oxygen vacancies.     

Effects of (Cr0.5Ta0.5)4+ on structure and microwave dielectric properties of Ca0.61Nd0.26TiO3 ceramics

The Ca_0.61Nd_0.26Ti_1-x(Cr_0.5Ta_0.5)_xO₃ (CNT-CTx) ceramics with orthorhombic perovskite structure were prepared using the conventional solid-state method. The X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectra (XPS) were employed to investigate the correlations between crystal structure and microwave dielectric properties of CNT-CTx ceramics. The XRD results showed that all CNT-CTx samples were crystallized into the orthorhombic perovskite structure. The SEM micrographs indicated that the average grain size of samples depended on the sintering temperature. As (Cr_0.5Ta_0.5)⁴⁺ concentration increased, there was a significant decrease in the average grain size of samples. The short range order (SRO) structure and structural distortion of oxygen octahedra proved to exist in CNT-CTx crystals according to the analysis of Raman spectra results. The microwave dielectric properties highly depended on the full width at half maximum (FWHM) of Raman spectra, oxygen octahedra distortion, reduction of Ti⁴⁺ to Ti³⁺ and bond valence. At last, the CNT-CT0.05 ceramic sintered at 1420?°C for 4?h exhibited the good and stable comprehensive microwave dielectric properties: relative permittivity of 96.5, quality factor of 14,360?GHz, and temperature coefficient of resonant frequency of +153.3?ppm/°C.     

Thermally-stable large strain in Bi(Mn0.5Ti0.5)O3 modified 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics

(1-x)[0.8Bi_0.5Na_0.5TiO₃-0.2Bi_0.5K_0.5TiO₃]-xBi(Mn_0.5Ti_0.5)O₃ (x = 0–0.06, BNKMT100x) lead-free ferroelectric ceramics were prepared via solid state reaction method. Bi(Mn_0.5Ti_0.5)O₃ induces a structure transition from rhombohedral-tetragonal morphotropic phases to pseudo-cubic phase. Moreover, the wide range of compositions within x = 0.03–0.055 exhibit large strain of 0.31%–0.41% and electrostrictive coefficient of 0.027–0.041 m⁴/C². Especially, at x = 0.04, the large strain and electrostrictive coefficient are nearly temperature-independent in the range of 25–100 °C. The impedance analysis shows the large strain and electrostrictive coefficient originate from polar nanoregions response due to the addition of Bi(Mn_0.5Ti_0.5)O₃.     

Physical properties of new,lead free (Na0.5Bi0.5)(1−x)BaxTi(1−x)(Fe0.5Nb0.5)xO3 ceramics

This study reports on the synthesis of polycrystalline samples of (Na_0.5Bi_0.5)_(1−x)Ba_xTi_(1−x)(Fe_0.5Nb_0.5)_xO₃ with x=0, 0.025, 0.05, 0.075, and 0.1, using the solid-state reaction technique. It investigates the effects of the substitution of sodium and bismuth by barium in the A site and of titanium by iron and niobium in the B site with regard to the free NBT symmetry and dielectric properties were investigated. The crystallographic and dielectric properties were also investigated. The diffractograms showed that all the samples had a single phase character. The increase of ceramic lattice parameters induced an increase in the size of the perovskite lattice. This increase was caused by the increase of the radii of the A and B sites. Room temperature X-ray data revealed that the ceramic structures underwent a gradual distortion with the increase in the composition fraction. Dielectric permittivity was measured in the temperature range of 120–780 K with frequencies ranging from 1 to 10³ KHz. Three anomalies, namely T_d, T₁ and T_m, were detected and noted to coexist at lower T_d and T_m as the rate of substitutions increased. All the samples exhibited a diffuse phase transition and implied better dielectric permittivity maxima values at temperatures approaching room temperature, since the substitution rate values increased more than that of pure NBT. A relaxor behavior with ΔT_m=14 K and ε'_rmax=3876 at 1 kHz was observed for (Na_0.5Bi_0.5)_0.9Ba_0.1Ti_0.9(Fe_0.5Nb_0.5)_0.1O₃ ceramic.     

Ferroelectric properties and core shell domain structures of Fe-modified 0.77Bi0.5Na0.5TiO3-0.23SrTiO3 ceramics

The crystal structure, domain patterns, and ferroelectric properties of Fe-modified BNT-ST [0.77(Bi_0.5Na_0.5)TiO₃-0.23Sr(Ti_1-xFe_x)O₃] ceramics, fabricated by a conventional solid-state reaction, were investigated. Core-shell structures were observed and the volume fractions of the core-domain and shell (relaxor-matrix) were found to be dependent on Fe-modification content. The crystal structures of the core-domain and the relaxor-matrix were rhombohedral with the space group R3c, and the tetragonal with the space group P4bm, respectively. Compositional inhomogeneity, specifically, the enrichment of Bi³⁺ and Na⁺ and the considerable depletion of Sr²⁺, were observed in the core-domain region, and was reduced by substituting Ti⁴⁺ with Fe³⁺. The Fe-modification of the BNT-23ST ceramics promoted the diffusion of Sr²⁺ ions into the core region and shifted ferroelectric behaviour towards ergodic-relaxor behaviour. This improved the effective d₃₃* of BNT-23ST ceramics to over 500 pm/V at 2 kV/mm.     

Influence of the tetravalent cation on the high-voltage electrochemical activity of LiNi0.5M1.5O4 spinel cathode materials

The electrochemical properties of substituted LiNi_0.5Mn_1.5−xM_xO₄ spinels at high potential (>4 V vs Li⁺/Li) have been investigated for M = Ti and Ru, in order to determine the role of the tetravalent cation in such systems where nickel is a priori the only electroactive species. These systems are found to form extended solid solutions (up to x = 1.3 and x = 1.0 for Ti and Ru, respectively) that were characterized by X-ray diffraction and Raman spectroscopy. Titanium substitution induces a drastic decrease in high potential electrochemical capacity, whereas the capacity is maintained and the kinetics are even improved in the presence of ruthenium. These results are completed by new results on the Li_4−2xNi_3xTi_5−xO₁₂ spinel system, which shows not any high potential activity in spite of the presence of up to 0.5 Ni²⁺ per spinel formula unit on the octahedral site. Taking into account previous data on LiNi_0.5Ge_1.5O₄, we clearly show that even if the tetravalent cation does not participate in the overall redox reaction, electrochemical activity is only possible when nickel is surrounded by tetravalent cations able to accept a local variation of valence (Mn, Ru), whereas full-shell cations such as Ti⁴⁺ and Ge⁴⁺ block the necessary electron transfer pathways in the spinel oxide electrode.     

High temperature stable dielectric properties and enhanced energy-storage performance of (1− x)(0.85Na0.5Bi0.5TiO3 − 0.15Ba0.8Ca0.2Ti0.8Zr0.2O3)− xK0.5Na0.5NbO3 lead-free ceramics

Novel high temperature ceramic capacitors (1??x)(Na_0.5Bi_0.5TiO₃ ??0.15Ba_0.8Ca_0.2Ti_0.8Zr_0.2O₃)??xK_0.5Na_0.5NbO₃ were synthesized in the solid-state reaction route. The influence of K_0.5Na_0.5NbO₃ modification on dielectric behavior, energy-storage properties, ac impedance and temperature stable dielectric performance were systematically investigated. The reduced grain size and enhanced relaxor properties are obtained with the addition of KNN. The content of x?=?0.1 exhibits a stable permittivity (~ 1630) and dielectric loss (<?0.05) over a relatively broad temperature range (66–230?°C). A variation in permittivity within ±?15% can be observed over a pretty wide temperature range of 66–450?°C. Beyond that, this ceramic shows enhanced energy-storage properties with the density (W_rec) of 0.52?J/cm³ and efficiency (η) of 80.3% at 110?kV/cm. The possible contributions of the grain and the grain boundary to the ceramic capacitance are discussed by the ac impedance spectroscopy.     

Dielectric temperature stability of Nb-modified Bi0.5(Na0.78K0.22)0.5TiO3 lead-free ceramics

In this study, the phase structure, microstructure and dielectric properties of Bi_0.5(Na_0.78K_0.22)_0.5(Ti_1-xNb_x)O₃ lead-free ceramics prepared by traditional solid phase sintering method were studied. The second phase pyrochlore bismuth titanate (Bi₂Ti₂O₇) was produced in the system after introduction of Nb⁵⁺. The dielectric constant of the sample (x = 0.03) sintered at 1130 °C at room temperature reached a maximum of 1841, and the dielectric loss was 0.045 minimum. It had been found that the K⁺ and Nb⁵⁺ co-doped Bi_0.5Na_0.5TiO₃ (BNT) lead-free ceramics exhibited outstanding dielectric-temperature stability within 100–400 °C with T_cc ≤±15%. Result of this research provides a valuable reference for application of BNT based capacitors in high temperature field.     

High energy storage performance of [(Bi0.5Na0.5)0.94Ba0.06]0.97La0.03Ti1-x(Al0.5Nb0.5)xO3 ceramics with enhanced dielectric breakdown strength

Novel lead-free [(Bi_0.5Na_0.5)_0.94Ba_0.06]_0.97La_0.03Ti_1-x(Al_0.5Nb_0.5)_xO₃ ceramics (BNBLT-xAN) were prepared by the conventional solid state sintering method. The dielectric, ferroelectric, ac impedance and energy-storage performance were systematically investigated. Temperature dependent permittivity curves showed that relaxation properties of sintered ceramics gradually diminished with the increase of AN. The introduction of AN gave rise to a slimmer polarization hysteresis loop (P-E) and an enhanced dielectric breakdown strength (DBS). Therefore, the optimum energy-storage performance were realized at x?=?0.05 with the energy-storage density (W_rec) of 1.72?J/cm³ and energy-storage efficiency (η) of 85.6% at 105?kV/cm, accompanied with the excellent temperature stability and fatigue performance. The results demonstrated that BNBLT-xAN system was a promising lead-free candidate for energy-storage applications.     

Influences of phase transition and microstructure on dielectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Zr<Subscript>1-x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>3</Subscript> ceramics

Bismuth sodium zirconate titanate ceramics with the formula Bi_0.5Na_0.5Zr_1-xTi_xO₃ [BNZT], where x = 0.3, 0.4, 0.5, and 0.6, were prepared by a conventional solid-state sintering method. Phase identification was investigated using an X-ray diffraction technique. All compositions exhibited complete solubility of Ti⁴⁺ at the Zr⁴⁺ site. Both a decrease of unit cell size and phase transition from an orthorhombic Zr-rich composition to a rhombohedral crystal structure in a Ti-rich composition were observed as a result of Ti⁴⁺ substitution. These changes caused dielectric properties of BNZT ceramics to enhance. Microstructural observation carried out employing SEM showed that average grain size decreased when addition of Ti increased. Grain size difference of BNZT above 0.4 mole fraction of Ti⁴⁺ displayed a significant increase of dielectric constant at room temperature.     

Piezoelectric properties and microstructures of ZnO-doped Bi0.5Na0.5TiO3 ceramics

This article studies the microstructure and piezoelectric properties of a ceramic lead-free NBT under different amount of ZnO doping. X-ray diffraction shows that Zn²⁺ diffuses into the lattice of (Bi_0.5Na_0.5)TiO₃ to form a solid solution with a pure perovskite structure. By modifying the zinc oxide content, the sintering behavior of (Bi_0.5Na_0.5)TiO₃ ceramics was significantly improved and the grain size was increased. The piezoelectric coefficient d₃₃ for the 1.0 wt.% ZnO-doped (Bi_0.5Na_0.5)TiO₃ ceramics sintered at 1050 °C was found to be 95 pC/N, and the electromechanical coupling factor k_p = 0.13. However, the piezoelectric coefficient d₃₃ for the 0.5 wt.% ZnO-doped (Bi_0.5Na_0.5)TiO₃ ceramics sintered at 1140 °C was found to be 110 pC/N, and the electromechanical coupling factor k_p = 0.17.     

High energy storage density and discharging efficiency in La3+/Nb5+-co-substituted (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

In this work, [(Bi_1-xLa_x)_0.5Na_0.5]_0.94Ba_0.06(Ti_1-5y/4Nb_y)O₃ ceramics have been developed by the dual-substitution of La³⁺ for Bi³⁺ and Nb⁵⁺ for Ti⁴⁺ and prepared by an ordinary sintering technique. All ceramics can be well-sintered at 1200 °C. The addition of La³⁺ and Nb⁵⁺ reduces the grain size and improve the dielectric breakdown strength of the ceramics; moreover, after the introduction of La³⁺ and Nb⁵⁺, the remanent polarization of the ceramics is significantly reduced, while the maximum polarization remains the same large value as that of the ceramic without the doping of La³⁺ and Nb⁵⁺. As a result, high energy storage density and discharge efficiency are achieved at x/y = 0.07/0.02, giving the large storage density of 1.83 J/cm³ and high discharging efficiency of 70%. The present work presents a feasible strategy to develop energy storage materials based on perovskite ferroelectrics by the partial substitutions in the A and B sites.     

Phase transition induced morphotropic phase boundary behavior and the electric properties in strontium modulated Bi4.5Na0.5Ti4O15 lead-free ceramics

Lead-free (Bi_0.5Na_0.5)_1-xSr_xBi₄Ti₄O₁₅ ceramics (x = 0–0.9) are fabricated by solid state reaction process. XRD analysis shows the symmetry divergence from tetragonal to orthorhombic phase accompanied by morphotropic phase boundary with increasing strontium content. Raman spectra confirm the incorporation of strontium into (Bi_2.5Na_0.5Ti₄O₁₃)^2- layers. SEM graphs exhibit the typical plate-like morphology with regular variation of grain size and crystallization as strontium increases. Multistage ferroelectric transition is observed with x = 0.2–0.4. Piezoelectric performance measurements present the well thermal stability at x = 0.4. The dielectric properties display a shifting of Curie temperature towards low temperature with increasing strontium ions. It can be due to the crystal lattice distortion by larger radius of strontium and the increasing tolerance factor. ac conductivity and impedance measurements suggest that electron hopping mainly contributes to the low temperature region. Ionization conductivity by oxygen vacancy migration including first-ionization and double-ionization plays the dominating role in the middle and high temperature region. The controllable properties indicate the potential applications for electric devices of (Bi_0.5Na_0.5)_1-xSr_xBi₄Ti₄O₁₅ ceramic.     

Structure–property relationships of perovskite-structured Ca0.61Nd0.26Ti1-x(Cr0.5Nb0.5)xO3 ceramics

A series of Ca_0.61Nd_0.26Ti_1-x(Cr_0.5Nb_0.5)_xO₃ (CNTCNx) (0 ≤ x ≤ 0.1) ceramics were prepared via a solid state reaction method. All CNTCNx samples were crystallized into the orthorhombic perovskite structure. The SEM micrographs indicated that the average grain sizes of samples depended on (Cr_0.5Nb_0.5)⁴⁺ concentration. And as (Cr_0.5Nb_0.5)⁴⁺ concentration increased, the average grain size of samples decreased significantly. The short range order (SRO) structure and structural distortion of oxygen octahedra proved to exist in CNTCNx crystals from Raman spectra analysis results. The microwave dielectric properties highly depended on the B-site bond strength, oxygen octahedra distortion, reduction of Ti⁴⁺ to Ti³⁺ and internal strain η. At last, the CNTCN0.06 ceramic sintered at 1400 °C for 4 h exhibited good and stable comprehensive microwave dielectric properties of ε_r = 92.3, Q × f = 13,889 GHz, τ_f = + 152.8 ppm/°C.     

Large electro-strain with excellent fatigue resistance of lead-free (Bi0.5Na0.5)0.94Ba0.06Ti1-x(Y0.5Nb0.5)xO3 perovskite ceramics

A series of lead-free (Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1-x(Y_0.5Nb_0.5)_xO₃ (for 0 ≤ x ≤ 0.03) perovskite ceramics were fabricated using a solid-state reaction technique. The effects of (Y_0.5Nb_0.5)⁴⁺ ions doping on phase structure, piezoelectric properties, AC impedance, and fatigue resistance were systematically studied. Crystal structure as a function of the composition revealed a single perovskite lattice structure with dense micromorphology. The transition temperature of the non-ergodic and ergodic relaxor ferroelectric phase shifted to near ambient temperature with increasing composition, which was related to the destruction of the long-range ordered ferroelectric domains. Hence, the transformation of ferroelectric-to-relaxor phase was easier under applied electric field at room temperature. The ceramic for x = 0.01 composition attained a large unipolar strain of ~ 0.452% with a corresponding normalized strain (d₃₃*) of ~ 603 pm/V under applied 75 kV/cm field. Besides, the excellent fatigue resistance of the sample was obtained after 10⁵ switching cycles under 70 kV/cm. These phenomena demonstrated that (Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1-x(Y_0.5Nb_0.5)_xO₃ ceramics might be suitable for a wide range of electronic equipment applications such as actuators and sensors.     

Impedance spectroscopy of Na0.5Bi4.50+xTi4Oy (x = -0.02, 0, 0.02) ceramics with excellent dielectric properties

The electric and dielectric properties of Na_0.5Bi_4.50+xTi₄O_y (x = −0.02, 0, 0.02) prepared by conventional mixed oxide route have been investigated by impedance spectroscopy (IS) over a wide temperature range. Single-phase bismuth layer-structured perovskite patterns were observed through X-ray diffraction of the three samples Na_0.5Bi_4.5Ti₄O₁₅, Na_0.5Bi_4.48Ti₄O_y, and Na_0.5Bi_4.52Ti₄O_y. The results show that the relative permittivity (εr) increases with the increase in temperature and reaches its maximum at about 675℃. With the continuous increase in temperature, the permittivity decreases gradually. Both relative permittivity and dielectric loss show great stability at the low-temperature zone. The ceramic of x = 0.02 with Ea of 1.09 eV has the maximum oxygen ionic transport number between 600 and 800℃ for all samples. And at this time, it has the maximum electrical conductivity. All the results indicated that Na_0.5Bi_4.50+xTi₄O_y (x = −0.02, 0, 0.02) ceramics were promising base materials for high-temperature capacitor because of their high dielectric properties.     

Enhanced piezoelectric performance in Na0.5Bi4.5Ti4O15-based bismuth-layered ceramics by Nb/Mn doping modification

In this work, Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y bismuth-layered ferroelectric ceramics were prepared by a solid-state reaction method. The effect of Nb⁵⁺ content on crystal morphology, electrical properties, and piezoelectric performance were systematically investigated. The results show that the introduction of Nb⁵⁺ into Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics to replace Ti⁴⁺ increases the ratio of b/a lattice parameter, leading to the TiO₆ octahedral distortion and the structural transformation tendency from the orthorhombic to tetragonal phase, which facilitates dipole movements of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics. Therefore, the ferroelectric properties of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics are improved, and an enhanced piezoelectric coefficient of 30 pC/N combining great temperature stability with d₃₃ value higher than 25 pC/N in the temperature range of 25°C–450°C has been realized in Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics with x = 0.08 mol. Our work provides a good model for designing lead-free ultrahigh Curie temperature piezoelectric devices that can be practically applied in extremely harsh environments.