Electrocaloric effect and pyroelectric performance in (K,Na)NbO3-based lead-free ceramics

The issue of how to achieve an electrocaloric effect (ECE) and pyroelectric effect in a material simultaneously remains to be a challenge for developing practical solid-state cooling devices and RF-detectors. Here, we structure a polymorphic phase transition (PPT) region by doping modification in KNN-based ceramics, which are developed to achieve the ECE. The direct measured ECE and pyroelectric properties are investigated in lead-free (1-x)K_0.5Na_0.5NbO₃-xBi_0.5Na_0.5ZrO₃ (KNN-xBNZ) ceramics. The adiabatic temperature change (∆T) of 0.22 K at 100°C, 0.14 K at 70°C and 0.16 K at 30°C can be obtained under an electric field of 35 kV cm^–1 for x = 0.03, 0.04 and 0.05, respectively. In addition, the temperature dependence of pyroelectric coefficient (p) is established for all compositions via the Byer-Roundy method. A large p of 454.46 × 10^–4 C m^–2 K^–1 is detected at Curie temperature (T_C) in the ceramics with x = 0.03. Achieving electrocaloric effect and pyroelectric performance simultaneously may shed light and provide a feasible design scheme for developing practically useful electrocaloric and pyroelectric materials.     

Large electrocaloric responses in [Bi1/2(Na,K)1/2]TiO3‐based ceramics with giant electro‐strains

The electrocaloric effect (ECE) is investigated through indirect measurement in two lead‐free [Bi_1/2(Na,K)_1/2]TiO₃‐based ceramics that were previously reported to display giant electro‐strains. In the Nb‐doped ceramic, denoted as BNKT‐2.5Nb, a decent temperature change of ΔT=1.85 K and an electrocaloric responsivity of ΔT/ΔE=0.37 (10^?6Km V^?1) are found around room temperature (32°C). While in the Ta‐doped ceramic, BNKT‐1.5Ta, a wide operation temperature range (T_span ~55 K) is observed near room temperature. Additional electrical measurements, as well as transmission electron microscopy experiments, are performed to identify the mechanisms of the ECE in both ceramics.     

Effect of sintering temperature on the ferroelectric property and electrocaloric effect of Pb0.8Ba0.2ZrO3 ceramics

This work presents the effects of sintering temperature ranging from 1200 °C to 1300 °C at intervals of 20 °C on the crystal structure, ferroelectric properties, and electrocaloric effect (ECE) of Pb_0.8Ba_0.2ZrO₃. Samples sintered at 1240 °C, 1260 °C, and 1280 °C have large remanent polarization and small coercive field. Meanwhile, samples sintered at 1260 °C, 1280 °C, and 1300 °C possess large breakdown field strength. Samples sintered at 1260 °C for 4 h exhibit the optimal ferroelectric properties. Antiferroelectricity-ferroelectricity (AFE-FE) phase transition occurs at room temperature T₁ (279 K). Directly examining ECE at this temperature is meaningful, and the temperature change is 0.068 K at approximately 60 °C and 30 kV/cm. Results laid the foundation for studying the performance of ferroelectric and ECE within this phase-transition temperature range and provide a reference for new solid-state refrigeration technology.     

Improvement of microwave dielectric properties of the LiNb0.6Ti0.5O3 M-phase by doping with (Co1/3Nb2/3)4+

Structural evolution and microwave dielectric properties of LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ (.05≤x≤.2) ceramics have been studied in this paper. Although the doped compositions maintain the M-phase solid solutions, compositional fluctuation due to nonuniform dispersion of minor dopants could be observed as x < .05, and trace amount of Li₂TiO₃-based solid solution (Li₂TiO₃ss) secondary phase presents in the x > .05 compositions. The microwave dielectric properties could be remarkably improved by the doping of (Co_1/2Nb_1/2)⁴⁺ in comparison to the undoped counterpart. Optimized microwave dielectric properties with Q × f = ∼6500 GHz, ε_r = ∼74 and τ_f = +8.2 ppm/°C could be obtained at x = .10 after sintering at 1050°C/2 h. The sintering temperature could be further reduced to 900°C/2 h by adding .2 wt% B₂O₃ without affecting significantly its microwave dielectric properties: ε_r = 73, Q × f = 6000 GHz, τ_f = +8.5 ppm/°C. The LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ ceramics obtained in this case exhibit large dielectric permittivity coupled with much improved Q × f values, near zero τ_f, and low sintering temperature simultaneously, which makes it a promising high-k microwave dielectric material for low temperature cofired ceramic applications.     

The influence of phase transition on electrocaloric effect in lead‐free (Ba0.9Ca0.1)(Ti1−xZrx)O3 ceramics

In this paper, the influence of phase evolution on polarization change and electrocaloric response in lead‐free (Ba_0.9Ca_0.1)(Ti_1?xZr_x)O₃ ceramics (BCTZ) was systematically investigated. With increasing Zr/Ti ratio, the phase structure and phase transition behavior were greatly changed, resulting in various temperature and electric field dependence of electrocaloric responses. For x=0.05, a peak electrocaloric temperature change 1.64 K (at 130°C) and corresponding entropy change 1.78 J·kg^?1·K^?1 were obtained for 0‐7 kV·mm^?1 electric field. Negative electrocaloric temperature change in ?0.1 K was obtained below Curie temperature (T_c), which may be induced by the orthorhombic‐tetragonal ferroelectric phase transition. With the increase in x, the peak value of the electrocaloric response decreased but much better temperature stability was observed. Simultaneously the negative electrocaloric response gradually disappeared with the disappearance of the low temperature ferroelectric‐ferroelectric phase transition. For x=0.2, electrocaloric response showed good temperature stability ranging from room temperature to 130°C, attributing to the relaxor ferroelectric feature.     

Non-ergodic – ergodic transition and corresponding electrocaloric effect in lead-free bismuth sodium titanate-based relaxor ferroelectrics

The ferroelectric refrigeration technology based on electrocaloric effect (ECE) is a promising environmental way to replace the gas compression refrigeration. Lead-free bismuth sodium titanate (NBT)-based relaxor ferroelectric ceramics have advantages of a large ECE within a wide temperature range around the depolarization temperature (T_d), but the T_d of pure NBT is too high to meet the application requirements. Here, we systematically studied the electrocaloric effect in (0.95-x)(Na_0.5Bi_0.5)TiO₃-0.05SrTiO₃-x(K_0.5Na_0.5)NbO₃ ((0.95-x)NBT-0.05ST-xKNN) ceramics and its relation with the relaxor behavior. The addition of KNN enhances the relaxor character, and shifts the T_d from 120 °C to a low temperature even below 0 °C. The directly measured ECE shows a peak of high ?T_max = 0.88 K (@ 60 °C) for x = 0.05 under an electric field of 40 kV/cm and a wide temperature span of 79 °C (≥ 80% of ?T_max). The x = 0.07 sample exhibits the optimal room-temperature ECE performance with a high ?T_30 °C = 0.71 K because the non-ergodic – ergodic phase transition occurs near room temperature. The electric field–temperature phase diagram reveals the origin of the enhanced ECE as the electric-field-induced transition between polar nanoregions (PNRs) and long-range ferroelectric domain.     

Anisotropic field induced phase transitions and negative electrocaloric effect in rhombohedral Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The electrocaloric effect (ECE) of Mn doped Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT:Mn) single crystals with particular emphasis on the impact of crystallographic orientations and phase transitions were investigated systematically. Orientation-dependent phase transitions have been demonstrated by the dielectric and strain behaviors. Intriguingly, the negative ECE of –0.02?°C and –0.002?°C were obtained firstly in [001]-oriented PIN-PMN-PT:Mn crystals near the rhombohedral→tetragonal phase transformation and in [011]-oriented crystals near the rhombohedral→orthorhombic phase transformation, respectively. However, only the positive ECE was found in [111]-oriented crystals near the tetragonal→rhombohedral phase transition. Additionally, the maximum ECE temperature changes calculated in [001]-, [011]- and [111]-oriented crystals were 0.33?°C, 0.46?°C and 0.38?°C, respectively. Our results suggest that the negative ECE is attributed to electric field-induced phase transitions, whose critical field decreases with the increase of temperature. The phase transition-mediated coexistence of positive and negative effects in the relaxor-ferroelectric single crystals is beneficial to enhance the efficiency of the solid-state cooling devices.     

Electrical properties and temperature stability of SrTiO3-modified (Bi1/2Na1/2)TiO3-BaTiO3-(K1/2Na1/2)NbO3 piezoceramics

SrTiO₃-modified lead-free piezoelectric ceramics, (0.93-x)Bi_0.5Na_0.5TiO₃-xSrTiO₃-0.06BaTiO₃-0.01 K_0.5Na_0.5NbO₃ [(BNT-xST)-BT-KNN, x = 0-0.06], were prepared using a conventional solid-state reaction method. The XRD structure analysis and electric properties characteristics revealed the ST-induced phase transformation from the ferroelectric phase to the relaxor phase and their coexistence state. Benefiting from the ST-destructed ferroelectric long-range orders, the high normalized strain value of 600 pm/V was obtained in the (BNT-0.02ST)-BT-KNN ceramic at 5 kV/mm. The ST-generated relaxor phase was found to have a constructive effect on improving the temperature stability and restraining the hysteresis of the electric-field-induced strain. The normalized strain of (BNT-0.06ST)-BT-KNN ceramics could be kept at a high value ~337 pm/V at elevated temperature up to 120°C.     

Large direct and inverse electrocaloric effects in lead-free Dy doped 0.975KNN-0.025NBT ceramics

Undoped and Dy³⁺ doped 0.975 K_1/2Na_1/2NbO₃-0.025Na_1/2Bi_1/2TiO₃ (0.975KNN-0.025NBT) ceramics were synthesized using the solid-state synthesis method. X-ray diffraction analysis revealed pure perovskite structure without any secondary phases. The dielectric investigations of both ceramics revealed low dielectric losses in the dysprosium doped ceramic, particularly for temperatures higher than 100 °C. The dielectric loss anomaly around room temperature corroborates the polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases detected by XRD investigations. The electrocaloric effect (ECE) was investigated using the indirect method based on the Maxwell equation and thermal P–E hysteresis loops. The maximum ECE value was found equal to 0.63 K at 83 °C for KNNBT0.025. However, in Dy doped KNNBT0.025 ceramics, both direct and inverse ECE responses were found with values of 1.01 K at 118 °C and −1.79 K at 80 °C, respectively. Besides, yellow light emission was detected under an excitation wavelength of 350 nm. The simultaneous existence of high ECEs, good dielectric performance, and photoluminescence properties makes KNNBT-Dy a promising candidate for solid-state refrigeration and optoelectronic devices.     

Effects of Postdensification Annealing upon Microstructures and Microwave Dielectric Characteristics in Ba((Co0.6−x/2Zn0.4−x/2Mgx)1/3Nb2/3)O3 Ceramics

Effects of postdensification annealing upon microstructures and microwave dielectric characteristics in Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ (x = 0, 0.1, 0.2, and 0.3) complex perovskite ceramics have been investigated. Long‐time annealing at temperatures below the order–disorder transition temperature enhances the cation ordering degree and promotes the ordering domain growth. The most significant improvement of Qf value is obtained together with the suppressed temperature coefficient of resonant frequency in the samples annealed at 1400°C for 12 h, while the dielectric constant decreases slightly. The Qf value of ceramics annealed at 1400°C mainly attributes to the enhanced cation ordering degree, because their low‐energy domain boundaries are not detrimental to the Qf value. As the annealing temperature increases close to the transition temperature, coarse ordering domains with high‐energy boundaries are formed, and then the Qf value steadily decreases because of the inferior domain structure, even the cation ordering degree increases. The microwave dielectric characteristics of Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ ceramics are affected by the common function of ordering degree and domain structure. The best combination of microwave dielectric characteristics is obtained in the composition of x = 0.3 after annealing at 1400°C for 12 h: ε_r = 33.2, Qf = 117 200 GHz, and τ_f = 8.6 ppm/°C.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

High electrocaloric effect in hot‐pressed Pb0.85La0.1(Zr0.65Ti0.35)O3 ceramics with a wide operating temperature range

The temperature stability of the electrocaloric effect (ECE) in relaxor ferroelectric Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ (PLZT) prepared by the hot‐press sintering method has been investigated. Compared to the PLZTs prepared via the conventional sintering process, the hot‐pressed PLZTs exhibit larger ECE and superior temperature stability. The hot‐pressed sample with an appropriate content of excess PbO presents a high ΔT of 2.4°C and ΔS of 2.3 J kg^?1·K^?1, both of which are 30% greater than those of the conventionally sintered samples measured at 100 kV·cm^?1. More importantly, the hot‐pressed specimens display great stable electrical properties, including the dielectric breakdown strength and electrical resistivity in the temperature range from 0°C to 100°C, whose ECE instability, especially, is only one‐half that of the samples prepared by the conventional solid‐state method. In addition, the ECE and its stability of the hot‐pressed sample can be further enhanced by increasing the operating electric field to a relatively high level of 200 kV·cm^?1. This work demonstrates hot‐press sintering is an effective method to fabricate ferroelectric ceramics with high ECE as well as desirable temperature stability.     

Temperature-stable Na0.5Bi0.5TiO3-based ceramics with favorable low-temperature dielectric and energy storage property

In this work, (1 − x)(0.94Na_0.5Bi_0.5TiO₃–0.06BaTiO₃)–xKTaO₃ (x = 0–0.30) ceramics are developed for dielectric capacitor applications. The introduction of KTaO₃ from x = 0 to 0.30 increases the tolerance factor t from 0.984 to 1.005 and causes the decrease of ferroelectric rhombohedral phase in the ceramics. Besides, a gradual structural change toward a higher symmetry can be detected, accompanied by the obvious domain refinement. In the aspect of electrical property, the strengthened dielectric relaxation leads to the greatly enhanced thermal stability of dielectric response. The decline in T_s from 98 to −96°C causes a significant widening of the low-temperature region with temperature-stable dielectric constant ε_r and low dielectric loss tan δ. The x = 0.30 ceramic shows a high ε_r (25°C) of 1094 with the temperature coefficient of capacitance ≤±15% over −70 to 200°C, which exceeds the X9R standard. Meanwhile, tan δ is less than 0.02 in a wide temperature range of −35 to 300°C. In addition, the ultrafine grain size of 290 nm, large bandgap of 3.22 eV, and high resistance of the x = 0.30 ceramic contribute to its electrical breakdown strength. A linear-like P–E loop with the large discharged energy density W_D ∼ 3.50 J/cm³ and high energy efficiency η ∼ 90.1% is obtained under 28 kV/mm at room temperature. The thermal stability of the energy storage performance is also satisfactory with the variation of W_D less than 15% over −40 to 200°C, and the η is higher than 85%.     

Enhanced electrocaloric response and energy storage performance of Li-substituted BaTiO3 ceramics

Recently, ferroelectric and antiferroelectric ceramic materials have gained a lot of interest for the development of environment-friendly highly-efficient electrocaloric refrigeration and energy-storage devices. In this work, lead-free Ba_1−xLi_xTiO₃ ceramics with x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05 were synthesized by the conventional solid-state reaction method, and the effect of Li doping on dielectric, leakage current, ferroelectric, electrocaloric, and energy storage properties of BaTiO₃ ceramics was systematically investigated. The XRD and Raman studies confirmed that the structure of Ba_1−xLi_xTiO₃ remains tetragonal as for BaTiO₃. The Li substitution shifted the phase transition (T_C) of BaTiO₃ slightly towards the lower temperature side. Significant drop in leakage current was observed with an addition of Li content. The maximum values of the electrocaloric effect (ΔT), electrocaloric responsivity, and coefficient of performance were found to be 1.44 K, 0.24 × 10⁻⁶ K m/V, and 5.75, respectively, for x = 0.04 at an applied field of 60 kV/cm near the Curie temperature. The maximal value of energy storage density was found to be 0.42 J/cm³ with an energy storage efficiency of 60% for x = 0.05. Our results suggested that lead-free Ba_1−xLi_xTiO₃ ceramic material is a promising candidate for potential applications in solid-state refrigeration technology and high-efficiency energy storage devices.     

High-energy storage density in NaNbO3-modified (Bi0.5Na0.5)TiO3-BiAlO3-based lead-free ceramics under low electric field

Ceramic-based dielectric capacitor are highly suitable for pulsed power applications due to their high power density and excellent reliability. However, the ultrahigh applied electric field limit their applications in integrated electronic devices. In this work, (1−x){0.96(Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃-0.04BiAlO₃}-xNaNbO₃ (BNT-BA-xNN, x = 0, 0.04, 0.08, 0.12, and 0.16) ternary ceramics were designed to achieve excellent energy storage properties. It was found that the introduction of NaNbO₃ (NN) effectively increase the difference (ΔP) between P_max and P_r, resulting in an obvious enhancement of the energy storage properties. High recoverable energy storage density, responsivity, and power density, that is, W_rec = 2.01 J/cm³, ξ = W_rec/E = 130.69 J/(kV⋅m²), and P_D = 25.59 MW/cm³, accompanied with superior temperature stability were realized at x = 0.14 composition. In addition, the thermal stable dielectric properties of the sample can be prominently improved with increasing NN content. The temperature coefficient of capacitance (TCC) of x = 0.16 composition is lower than 15% over the temperature range from 49°C to 340°C, with a high dielectric permittivity of 1647 and a low dielectric loss (0.0107) at 150°C. All these features show that the BNT-BA-xNN ceramics are promising materials for energy storage application.     

High permittivity (1−x)Bi1/2Na1/2TiO3‐xPbMg1/3Nb2/3O3 ceramics for high‐temperature‐stable capacitors

(1?x)Bi_1/2Na_1/2TiO₃‐xPbMg_1/3Nb_2/3O₃[(1?x)BNT‐xPMN] ceramics have been fabricated via a conventional solid‐state method for compositions x ≤ 0.3. The microstructure, phase structure, ferroelectric, and dielectric properties of ceramics were systematically studied as high‐temperature capacitor materials. XRD pattern certified perovskite phase with no secondary phase in all compositions. As PMN concentration increased, the phase of (1?x)BNT‐xPMN ceramics transformed from ferroelectric to relaxor gradually at room temperature, with prominent enhancement of dielectric temperature stability. For the composition x = 0.2, the temperature coefficient of capacitance (TCC) was <15% in a wide temperature range from 56 to 350°C with high relative permittivity (>3300) and low dielectric loss (<0.02) at 150°C, which indicated promising future for (1?x)BNT‐xPMN system as high‐temperature stable capacitor materials.     

Dielectric properties and electrocaloric effect of yttrium-modified BaTiO3 ceramics

The electrocaloric effect (ECE) is a promising candidate to replace the vapor-compression cooling technology, which has reached its end of improving the energy utilization efficiency. In the present work, the Y-modified BaTiO₃ ceramics with nominal compositions of Ba(Ti_1-xY_x)O₃ (abbreviated as BT-100xY, where x = 0.0125, 0.025, 0.0375, 0.050 and 0.0625) have been prepared through the conventional solid-state reaction sintering method. The dielectric properties and electrocaloric effect of BT-100xY ceramics have been investigated in detail. The XRD patterns indicate that all the BT-100xY ceramics possess pure perovskite structure without secondary phases. The temperature dependence of dielectric permittivity reveals that the BT-1.25Y, 2.5Y, 3.75Y and 5.0Y are normal ferroelectrics, and the BT-6.25Y is a relaxor ferroelectric. The ECE is calculated through the indirect equation based on Maxwell relation. The BT-2.5Y exhibits the largest ΔT = 1.26 K and the largest ΔS = 1.68 J/kg · K among all the BT-100xY ceramics, and the BT-2.5Y also exhibits the largest ΔT/ΔE = 0.296 × 10^?6 K · m/V and the largest ΔS/ΔE = 0.394 × 10^?6 J · m/kg · K?V. The ECE in our work is comparable with or even larger than that of BaTiO₃-based ceramics previously reported, which indicates that the BT-100xY ceramics are promising ECE materials.     

Tuning the electrocaloric effect by tailoring phase fraction in BaTiO3-based ferroelectrics

The giant electrocaloric effect (ECE) in ferroelectrics arouses enthusiasm on the electrocaloric refrigeration for its zero global-warming-potential. Previous studies have observed that large ECE response occurs around ferroelectric-paraelectric phase transition in BaTiO₃-based ferroelectrics. However, few attention is paid to the effect of phase fraction on ECE performance. In this work, Ba_1-xSr_xTi_0.95Sn_0.05O₃ ceramics which display varied phase fraction of orthorhombic and tetragonal (O and T) phase at room temperature, are developed to reveal the influence of phase fraction on the electric properties, especially ECE performance. The electrocaloric temperature change (ΔT) is enhanced in composition with equal phase fraction of O and T, which also shows excellent piezoelectric property. Intrinsically, a number of nanodomains are formed due to the incorporation of Sr²⁺, greatly benefiting the invertibility of domains under the electric field. It is believed that this study opens a new way for designing and understanding of ECE in BT-based ceramics.     

High quality factor microwave dielectric ceramics in the (Mg1/3Nb2/3)O2–ZrO2–TiO2 ternary system

Novel high quality factor microwave dielectric ceramics (1?x)ZrTiO₄?x(Mg_1/3Nb_2/3)TiO₄ (0.325≤x≤0.4) and (ZrTi)_1?y(Mg_1/3Nb_2/3)_yO₄ (0.2≤y≤0.5) with the addition of 0.5 wt% MnCO₃ in the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system were prepared, using solid‐state reaction method. The relationship between the structure and microwave dielectric properties of the ceramics was studied. The XRD patterns of the sintered samples reveal the main phase belonged to α‐PbO₂‐type structure. Raman spectroscopy and infrared reflectivity (IR) spectra were employed to evaluate phonon modes of ceramics. The 0.65ZrTiO₄?0.35(Mg_1/3Nb_2/3)TiO₄?0.5 wt% MnCO₃ ceramic can be well densified at 1240°C for 2 hours and exhibits good microwave dielectric properties with a relative permittivity (ε_r) of 42.5, a quality factor (Q×f) value of 43 520 GHz (at 5.9 Ghz) and temperature coefficient of resonant frequency (τ_f) value of ?5ppm/°C. Furthermore, the (ZrTi)_0.7(Mg_1/3Nb_2/3)_0.3O₄?0.5 wt% MnCO₃ ceramic sintered at 1260°C for 2 hours possesses a ε_r of 31.8, a Q×f value of 35 640 GHz (at 6.3 GHz) and a near zero τ_f value of ?5.9 ppm/°C. The results demonstrated that the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system with excellent properties was a promising material for microwave electronic device applications.     

Structural and Dielectric Properties in (1−x)BaTiO3–xBi(Mg1/2Ti1/2)O3 Ceramics (0.1 ≤ x ≤ 0.5) and Potential for High‐Voltage Multilayer Capacitors

Structural and dielectric properties of (1?x)BaTiO₃–xBi(Mg_1/2Ti_1/2)O₃ (x = 0.1–0.5) were investigated to understand the binary system and utilize it for high‐voltage, high energy density capacitors. The solubility limit for Bi(Mg_1/2Ti_1/2)O₃ in a BaTiO₃ perovskite was between x = 0.4 and x = 0.5. A phase with pseudocubic symmetry was formed for x = 0.1–0.4; a secondary phase developed at x = 0.5. Dielectric measurements showed highly diffusive and dispersive relaxor‐like characteristics from 10 to 40 mol% of Bi(Mg_1/2Ti_1/2)O₃. These compositions also showed high relative permittivity with low‐temperature coefficients of permittivity over a wide range of temperatures ?100°C–600°C. Relaxation behavior was quantitatively investigated using the Vogel–Fulcher model, which revealed the activation energy of 0.17–0.22 eV. Prototyped multilayer capacitors of 18 mm × 17 mm × 4 mm dimensions with a capacitance of 12.5 nF at 1 kHz were successfully constructed and demonstrated multiple charge–discharge characteristics up to 10 kV.