Giant electromechanical strain response in lead‐free SrTiO3‐doped (Bi0.5Na0.5TiO3–BaTiO3)–LiNbO3 piezoelectric ceramics

Lead‐free 0.985[(0.94?x)Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xSrTiO₃]–0.015LiNbO₃ [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (P_r), coercive field (E_c), negative strain (S_neg) and piezoelectric coefficient (d₃₃). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, S_max/E_max of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the S_max/E_max was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.     

Large electric‐field‐induced strain and enhanced piezoelectric constant in CuO‐modified BiFeO3‐BaTiO3 ceramics

In this work, we fabricated the (1‐x)BiFeO₃‐xBaTiO₃+y‰ mol CuO ceramics by the modified thermal quenching technique. The pure perovskite phase was formed and a morphotropic phase boundary (MPB) was observed in the ceramics with x = 0.30‐0.33. The addition of CuO can significantly enhance the density of the BiFeO₃‐BaTiO₃ material. Importantly, an enhanced piezoelectric constant (d₃₃=165 pC/N), a large electric‐field‐induced strain (?S = 0.54%: peak to peak strain) and a large piezoelectric actuator constant (d₃₃*=449 pm/V) together with a high Curie temperature (T_C) of 503°C were observed in the ceramics with x = 0.30 and y = 5. As a result, the enhanced piezoelectricity and large electric‐field‐induced strain could significantly stimulate further researches in BFO‐based ceramics.     

Low‐Temperature Sintering of Bi0.5(Na,K)0.5TiO3 for Multilayer Ceramic Actuators

We investigated the influence of CuO amount (0.5–3.0 mol%), sintering temperature (900°C–1000°C), and sintering time (2–6 h) on the low‐temperature sintering behavior of CuO‐added Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (BNKT22) ceramics. Normalized strain (S_max/E_max), piezoelectric coefficient (d₃₃), and remanent polarization (P_r) of 1.0 mol% CuO‐added BNKT22 ceramics sintered at 950°C for 4 h was 280 pm/V, 180 pC/N, and 28 μC/cm², respectively. These values are similar to those of pure BNKT22 ceramics sintered at 1150°C. In addition, we investigated the performance of multilayer ceramic actuators made from CuO‐added BNKT22 in acoustic sound speaker devices. A prototype sound speaker device showed similar output sound pressure levels as a Pb(Zr,Ti)O₃‐based device in the frequency range 0.66–20 kHz. This result highlights the feasibility of using low‐cost multilayer ceramic devices made of lead‐free BNKT‐based piezoelectric materials in sound speaker devices.     

Large Electromechanical Response in Lead‐Free La‐Doped BNKT–BST Piezoelectric Ceramics

Piezoceramics 0.99[(Bi_0.5Na_0.4K_0.1)_1?xLa_xTiO₃]?0.01[Ba_0.7Sr_0.3TiO₃] (BNKT–BST–La_x, x = 0–0.030) were synthesized using a conventional solid‐state reaction method. X‐ray diffraction revealed a phase transition from a tetragonal to cubic phase at x ≥ 0.005. The maximum dielectric constant as well as the depolarization temperature (T_d) decreased with increasing La content. La addition interrupted the polarization and strain hysteresis loops and demonstrates that the ferroelectric order of the BNKT–BST ceramics lead to a reduction in the remnant polarization and coercive field. However, the destabilization of the ferroelectric order is accompanied by a significant increase in the unipolar strain which is highest at x = 0.020 with a value of ~0.39% and corresponding normalized strain, d^*₃₃ (= S_max/E_max) of 650 pm/V. It was observed that the unipolar strain of x = 0.020 is very temperature insensitive up to 125°C, even at 125°C the d^*₃₃ is as high as ~431 pm/V. Moreover, an electric‐field‐dependent XRD was conducted to identify the main source of the high strain and a recoverable transformation from cubic to a rhombohedral–tetragonal mixed phase was observed. The recoverable field‐induced phase transformation is suggested to be the main cause for the obtained large strain at x = 0.020 in the BNKT–BST–La_x ceramics.     

Temperature‐insensitive strain behavior in 0.99[(1−x)Bi0.5(Na0.80K0.20)0.5TiO3−xBiFeO3]–0.01Ta lead‐free piezoelectric ceramics

Lead‐free 0.99[(1?x)Bi_0.5(Na_0.80K_0.20)_0.5TiO₃?xBiFeO₃]–0.01Ta (BNKT20–100xBF–1Ta) lead‐free piezoelectric ceramics were fabricated through conventional solid state sintering method. Results showed that change of BF content in the BNKT20–100xBF–1Ta induced a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long‐range ferroelectric order. A large electric‐field‐induced strain of 0.36% (at 80 kV/cm driving field, corresponding to a large signal of ~450 pm/V) which is derived from a reversible field‐induced ergodic relaxor to ferroelectric phase transformation, was obtained in the composition with x=0.01 near the ferroelectric‐ergodic relaxor phase boundary. Moreover, an attractive property for application in nonlinear actuators demanding enhanced thermal stability was obtained in this material, which showed a temperature‐insensitive strain characteristic in the temperature range from room temperature to 100°C.     

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.     

Composition‐ and Temperature‐Dependent Large Strain in (1−x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 Ceramics

Ternary solid solutions of (1 ? x)(0.8Bi_0.5Na_0.5TiO₃–0.2Bi_0.5K_0.5TiO₃)– xNaNbO₃ (BNKT–xNN) lead‐free piezoceramics were fabricated using a conventional solid‐state reaction method. Pure BNKT composition exhibited an electric‐field‐induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric‐to‐relaxor temperature T_F‐R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic‐to‐ergodic relaxor transition was presented, which featured the pinched‐shape polarization and sprout‐shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT–0.04NN, and the large strain was attributed to the reversible electric‐field‐induced transition between ergodic relaxor and ferroelectric phase.     

Dielectric,ferroelectric and field-induced strain behavior of K0.5Na0.5NbO3-modified Bi0.5(Na0.78K0.22)0.5TiO3 lead-free ceramics

Lead-free piezoelectric (1 ? x)Bi_0.5(Na_0.78K_0.22)_0.5TiO₃–xK_0.5Na_0.5NbO₃ (BNKT–xKNN, x = 0–0.10) ceramics were synthesized using a conventional, solid-state reaction method. The effect of KNN addition on BNKT ceramics was investigated through X-ray diffraction (XRD), dielectric, ferroelectric and electric field-induced strain characterizations. XRD revealed a pure perovskite phase with tetragonal symmetry in the studied composition range. As the KNN content increased, the depolarization temperature (T_d) as well as maximum dielectric constant (?_m) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 μC/cm²) and small piezoelectric constant (27 pC/N) at 3 mol% KNN. As a result, at x = 0.03 a significant enhancement of 0.22% was observed in the electric field-induced strain, which corresponds to a normalized strain (S_max/E_max) of ～434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature.     

Piezoelectric Property and Strain Behavior of Pb(Yb0.5Nb0.5)O3–PbHfO3–PbTiO3 Polycrystalline Ceramics

(1?x)Pb(Hf_1?yTi_y)O₃–xPb(Yb_0.5Nb_0.5)O₃ (x = 0.10–0.44, y = 0.55–0.80) ceramics were fabricated. The morphotropic phase boundary (MPB) of the ternary system was determined by X‐ray powder diffraction. The optimum dielectric and piezoelectric properties were achieved in 0.8Pb(Hf_0.4Ti_0.6)O₃–0.2Pb(Yb_0.5Nb_0.5)O₃ ceramics with MPB composition, where the dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p, and Curie temperature T_c were found to be on the order of 1930,480 pC/N, 62%, and 360°C, respectively. The unipolar strain behavior was evaluated as a function of applied electric field up to 50 kV/cm to investigate the strain nonlinearity and domain wall motion under large drive field, where the high field piezoelectric d₃₃* was found to be 620 pm/V for 0.82Pb(Hf_0.4Ti_0.6)O₃–0.18Pb(Yb_0.5Nb_0.5)O₃. In addition, Rayleigh analysis was carried out to study the extrinsic contribution, where the value was found to be in the range 2%–18%.     

Electrocaloric behavior and piezoelectric effect in relaxor NaNbO3-based ceramics

We firstly reported the electrocaloric properties in relaxor (1−x−y)NaNbO₃–yBaTiO₃–xCaZrO₃ ceramics, and high electrocaloric effect (∆T ~0.451 K and∣∆T/∆E∣~0.282 Km/MV) can be realized in the ceramics (x = 0.04 and y = 0.10) under low temperature and low electric field. Relaxor behavior of NaNbO₃ ceramics can be found by doping both BaTiO₃ and CaZrO₃. In addition, optimized piezoelectric effects (d₃₃ ~235 pC/N and d₃₃* ~230 pm/V) can be observed in the ceramics (x = 0.04 and y = 0.10) due to the involved morphotropic phase boundary (MPB). Excellent piezoelectric effect (ie, d₃₃~330 pm/V at 41°C, and d₃₃*~332 pm/V at 60°C) can be found because of the characteristics of MPB. Good temperature reliability of piezoelectric effect can be shown because of both MPB and relaxor behavior. We believe that the ceramics with high electrocaloric effect and good piezoelectric effect can be considered as one of the most promising lead-free materials for piezoelectric devices.     

Large Strain Response and Fatigue‐Resistant Behavior in Ternary Bi0.5Na0.5TiO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 Solid Solutions

A ternary solid solution (1 ? x)(0.88Bi_0.5Na_0.5TiO₃–0.12BaTiO₃)‐xBi(Zn_0.5Ti_0.5)O₃ (BNBZT, BNBZTx) was designed and fabricated using the traditional solid‐state reaction method. The temperature and composition dependence of dielectric, ferroelectric, piezoelectric, and fatigue properties were systematically investigated and a schematic phase diagram was proposed. The substitution with Bi(Zn_0.5Ti_0.5)O₃ was found to shift the phase transition (ferroelectric tetragonal to relaxor pseudocubic phase) to lower temperatures. At a critical composition x of 0.05, large electric‐field‐induced strain response with normalized strain S_max/E_max as high as 526 pm/V was obtained under a moderate field of 4 kV/mm around room temperature. The strain exhibited good temperature stability within the temperature range of 25°C–120°C. In addition, excellent fatigue‐resistant behavior was observed in the proposed BNBZT solid solution after 10⁶ bipolar cycles. These give the BNBZT system great potential as environmental friendly solid‐state actuator.     

The Composition and Temperature‐Dependent Structure Evolution and Large Strain Response in (1−x)(Bi0.5Na0.5)TiO3−xBa(Al0.5Ta0.5)O3 Ceramics

The (1?x) (Bi_0.5Na_0.5)TiO₃?xBa(Al_0.5Ta_0.5)O₃((1?x)BNT‐xBAT) lead‐free piezoceramics was fabricated using a conventional solid‐state reaction method. The temperature and composition‐dependent strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties have been systematically investigated to develop lead‐free piezoelectric materials with large strain response for actuator application. As the BAT content increased, the FE order is disrupted resulting in a degradation of the remanent polarization, coercive field, and the depolarization temperature (T_d). A large strain of 0.36% with normalized strain d₃₃* = 448pm/V was obtained for the optimum composition x = 0.045 at room temperature. The bipolar and unipolar strains for the compositions x = 0.035 and x = 0.04 reach almost identical maximum values when the temperature is in the vicinity of their respective depolarization temperature (T_d). The Raman‐spectra analysis, macroscopic properties, thermal depolarization results, and temperature‐dependent relationships of both polarization and strain demonstrated that the origin of the large strain response for this investigated system is attributed to a field‐induced relaxor to FE phase transformation.     

Phase Diagram and Enhanced Piezoelectric Response of Lead‐Free BaTiO3–CaTiO3–BaHfO3 System

Three composition groups in the BaTiO₃–CaTiO₃–BaHfO₃ ternary system, (1 ? x)Ba(Hf_yTi_1?y)O₃–x(Ba_1?zCa_z)TiO₃ (abbreviated as BH_yT–xBC_zT with x = 0–1.0, y = 0.16, z = 0.20; x = 0–1.0, y = 0.16, z = 0.30; x = 0–1.0, y = 0.20, z = 0.30, respectively), have been designed for investigating the variation of the intermediate O‐phase region and its effect on the electrical properties. The temperature‐composition phase diagram of each group has been proposed based on the X‐ray diffraction patterns and the temperature‐dependent dielectric behaviors. The enhanced piezoelectric properties are achieved in the O–T phase boundary compositions of the three groups, which are BH_0.16T–0.58BC_0.20T, BH_0.16T–0.48BC_0.30T and BH_0.20T–0.53BC_0.30T, respectively. Piezoelectric coefficient d₃₃ of 448 pC/N is obtained in BH_0.20T–0.53BC_0.30T, which is higher than those of the other two phase boundary compositions. The O‐phase zone in BH_0.20T–xBC_0.30T is narrower than those in the BH_0.16T–xBC_0.20T and BH_0.16T–xBC_0.30T. In spite of its small O‐phase volume occupancy, the O‐phase plays a key role in the properties of the system. Our work confirms that the enhancement in piezoelectric properties is not only related to the O–T phase boundary near room temperature (RT), but also related to the shift of T_R‐O toward RT. In addition, a quantitative relation between the phase boundary composition and atomic mole ratio of Hf to Ca (R_m) is proposed, which the R_m value corresponding to the phase boundary is about 0.58. The results clearly demonstrate that in this system high piezoelectric properties are achieved by tuning the specific R_m value. Such a work may provide new clues for designing lead‐free piezoelectric materials with enhanced piezoelectric property.     

Microstructure,Ferroelectric, Piezoelectric,and Ferromagnetic Properties of Sc‐Modified BiFeO3–BaTiO3 Multiferroic Ceramics with MnO2 Addition

0.725BiFe_1?xSc_xO₃–0.275BaTiO₃ + y mol% MnO₂ multiferroic ceramics were fabricated by a conventional ceramic technique and the effects of Sc doping and sintering temperature on microstructure, multiferroic, and piezoelectric properties of the ceramics were studied. The ceramics can be well sintered at the wide low sintering temperature range 930°C–990°C and possess a pure perovskite structure. The ceramics with x/y = 0.01–0.02/1.0 sintered at 960°C possess high resistivity (~2 × 10⁹ Ω·cm), strong ferroelectricity (P_r = 19.1–20.4 μm/cm²), good piezoelectric properties (d₃₃ = 127–128 pC/N, k_p = 36.6%–36.9%), and very high Curie temperature (618°C–636°C). The increase in sintering temperature improves the densification, electric insulation, ferroelectric, and piezoelectric properties of the ceramics. A small amount of Sc doping (x ≤ 0.04) and the increase in the sintering temperature significantly enhance the ferromagnetic properties of the ceramics. Improved ferromagnetism with remnant magnetization M_r of 0.059 and 0.10 emu/g and coercive field H_c of 2.51 and 2.76 kOe are obtained in the ceramics with x/y = 0.04/1.0 (sintered at 960°C) and 0.02/1.0 (sintered at 1050°C), respectively. Because of the high T_C (636°C), the ceramic with x/y = 0.02/1.0 shows good temperature stability of piezoelectric properties. Our results also show that the addition of MnO₂ is essential to obtain the ceramics with good electrical properties and electric insulation.     

Dielectric Relaxor Evolution and Frequency‐Insensitive Giant Strains in (Bi0.5Na0.5)TiO3‐Modified Bi(Mg0.5Ti0.5)O3–PbTiO3 Ferroelectric Ceramics

The 0.45Bi(Mg_0.5Ti_0.5)O₃–(0.55 ? x)PbTiO₃–x(Bi_0.5Na_0.5)TiO₃ (BMT–PT–xBNT) ternary solid solution ceramics were prepared via a conventional solid‐state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse‐to‐relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d₃₃* of ~590 pm/V) was obtained at room temperature for the composition with x = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field‐induced large strain was found to own a frequency‐insensitive characteristic.     

Large Electromechanical Strain in Lead‐Free Binary System K0.5Bi0.5TiO3‐Bi(Mg0.5Ti0.5)O3

Solid solution formation in the lead‐free binary system (1?x)K_0.5Bi_0.5TiO₃?xBi(Mg_0.5Ti_0.5)O₃ has been studied for compositions x ≤ 0.12. X‐ray powder diffraction shows single‐phase perovskite for x < 0.1, and a mixed phase region between tetragonal and pseudocubic phases for compositions 0.04 ≤ x ≤ 0.06. Large electromechanical strains of ~0.3% at fields of 50 kV/cm are recorded in the mixed phase region, with d₃₃* (S_max/E_max) values of ~600 pm/V. The materials sustain polarization at low electric fields with remnant polarization ~18 μC/cm² and coercive field ~20 kV/cm for x = 0.06. Relative permittivity‐temperature plots display relaxor characteristics, with peak temperature ~340°C.     

Effect of Texture on Temperature‐Dependent Properties of K0.5Na0.5NbO3 Modified Bi1/2Na1/2TiO3–xBaTiO3

Textured (1?x?y)Bi_1/2Na_1/2TiO₃–xBaTiO₃–yK_0.5Na_0.5NbO₃ (BNT–100xBT–100yKNN) ceramics with a {001} pseudocubic (pc) orientation were fabricated by templated grain growth using Bi_1/2Na_1/2TiO₃ templates. Temperature‐dependent electromechanical results demonstrate that the strain response of templated BNT–xBT–yKNN ceramics is stable from room temperature (RT) to 125°C. The temperature‐dependent strain and polarization response are compared to randomly oriented ceramics, for BNT–100xBT–2KNN (0.05 ≤ x ≤ 0.07). Textured BNT–7BT–2KNN reached a maximum 0.47% strain response at 5 kV/mm, an almost 50% increase compared to randomly oriented BNT–7BT–2KNN. Over the temperature range RT–125°C, the strain response of templated BNT–6BT–2KNN degraded from 0.38% to 0.22% (?42.1%) compared to 0.37% to 0.18% (?51.4%) for randomly oriented ceramics. The temperature‐dependent strain response suggests that templated BNT–100xBT–100yKNN ceramics are well suited for elevated temperature applications.     

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.     

Remarkably High‐Temperature Stability of Bi(Fe1−xAlx)O3–BaTiO3 Solid Solution with Near‐Zero Temperature Coefficient of Piezoelectric Properties

The 0.72Bi(Fe_1?xAl_x)O₃–0.28BaTiO₃ (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead‐free high‐temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high‐temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x < 0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x ≈ 0.01, finally to pseudocubic phases when x > 0.03. Remarkably high‐temperature stability with near‐zero temperature coefficient of piezoelectric properties (TCk_p), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d₃₃ = 151 pC/N, k_p = 0.31 and super‐high‐temperature stability of T_d = 420°C, TCk_p = 1 × 10^?4. It is considered that the observed strong piezoelectricity and remarkably high‐temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk_p value and the pseudocubic phases possess a negative TCk_p value. Thus, the TCk_p value of BFAx–BT ceramics can be tuned by composition of x.     

Photoluminescence and Temperature Dependent Electrical Properties of Er‐Doped 0.94Bi0.5Na0.5TiO3‐0.06BaTiO3 Ceramics

Er‐doped 0.94Bi_0.5Na_0.5TiO₃‐0.06BaTiO₃ (BNT‐6BT: xEr, x is the molar ratio of Er³⁺ doping) lead‐free piezoceramics with x = 0–0.02 were prepared and their multifunctional properties have been comprehensively investigated. Our results show that Er‐doping has significant effects on morphology of grain, photoluminescence, dielectric, and ferroelectric properties of the ceramics. At room temperature, the green (550 nm) and red (670 nm) emissions are enhanced by Er‐doping, reaching the strongest emission intensity when x = 0.0075. The complex and composition‐dependent effects of electric poling on photoluminescence also have been measured. As for electrical properties, on the one hand, Er‐doping tends to flatten the dielectric constant‐temperature (ε_r‐T) curves, leading to temperature‐insensitive dielectric constant in a wide temperature range (50°C–300°C). On the other hand, Er‐doping significantly decreases the ferroelectric‐relaxor transition temperature (T_F–R) and depolarization temperature (T_d), with the T_F–R decreasing from 76°C to 42°C for x = 0–0.02. As a result, significant composition‐dependent electrical features were found in ferroelectric and piezoelectric properties at room temperature. In general, piezoelectric and ferroelectric properties tend to become weaker, as confirmed by the composition‐dependent piezoelectric coefficient (d₃₃), planar coupling factor (k_p), and the shape of polarization‐electric field (P–E), current‐electric field (J–E), bipolar/unipolar strain‐electric field (S–E) curves. Furthermore, to understand the relationship between the T_F–R/T_d and the electrical properties, the composition of x = 0.0075 has been intensively studied. Our results indicate that the BNT‐6BT: xEr with appropriate Er‐doping may be a promising multifunctional material with integrated photoluminescence and electrical properties for practical applications.