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Environmentally friendly lead-free dielectric ceramics have attracted wide attention because of their outstanding power density, rapid charge/dischargerate, and superior stability. Nevertheless, as a hot material in dielectric ceramic capacitors, the energy storage performance of Na0.5Bi0.5TiO3-based ceramics has been not satisfactory because of their higher remnant polarization value and low dielectric breakdown strength, which is a problem that must be urgently overcome. In this work, the (1 - x) (0.6Na0.5Bi0.5TiO3 - 0.4Sr0.7Bi0.2TiO3) - xBa(Mg1/3Ta2/3)O3 (BNST-xBMT) systems were designed based on a dual optimization strategy of domain and bandgap to solve the above problems. As a result, a record-breaking ultrahigh energy density and excellent efficiency (Wrec = 8.58 J/cm3, η = 93.5%) were obtained simultaneously under 565 kV/cm for the BNST-0.08BMT ceramic. The introduction of Sr0.7Bi0.2TiO3 induces the formation of nanodomains in BNT-based ceramics, leading to slim P-E curves, and the further modification of Mg/Ta reduces the grain sizes and increases the bandgap width, resulting in significant enhancement of the dielectric breakdown strength. Moreover, excellent stability and superior discharge performance (Wd = 4.7 J/cm3, E = 320 kV/cm) in the BNST-0.08BMT ceramic were also achieved. The results suggest that the BNST-0.08BMT ceramic shows potential applicability for dielectric energy storage ceramics. Simultaneously, the composition-design concept in the system provides a good reference for the further development of ceramic dielectric capacitors.

The influence of B-site complex ions substitution on the dielectric and piezoelectric properties of (Bi0.5Na0.5)0.93Ba0.07Ti1–x(W0.5Mg0.5)xO3 (BNBT–xWM) ceramics was studied in detail. X-ray diffraction patterns revealed that B-site substitution resulted in a phase transition from the tetragonal phase to pseudocubic phase. Ferroelectric to relaxor (FE-RE) phase transition temperature TF-R decreased with increasing (W0.5M0.5)4+ dopants, finally below room temperature. The destabilization temperature of piezoelectric constant d33, together with ferroelectric response was decreased with increasing x. However, the strains could be significantly enhanced with the addictive of (W0.5M0.5)4+, and a large strain of 0.325% with a normalized strain, d33* of 541.7 pm/V could be achieved for x = 0.04 ceramics [ergodic relaxor (ER) dominant]. The enhanced strains might attribute to the composition-induced NR–ER transition and high dynamic polar-nanoregions (PNRs), which strongly affecting piezoelectric and dielectric properties.

(1-x)H3BO3-xPE (x = 0.0–0.5) microwave dielectric polymer-ceramics (composite ceramics) with ultra-low sintering temperatures (60–110 °C) were prepared via the traditional solid-state method to improve the moisture-proof ability of H3BO3 matrix ceramics. X-ray diffraction (XRD), back-scattered scanning electron microscopy (EDS-SEM), and Raman spectroscopy confirmed that H3BO3 and PE could coexist without intermediate phases. As the x value increased, the dielectric Q value and resonant frequency (Q × ƒ) decreased from 116,000 GHz (at 15.0 GHz) to 37,000 GHz (at 16.3 GHz), the relative permittivity (er) varied between 2.83 and 2.14, and the temperature coefficient of the resonant frequency (τƒ) shifted from −147 ppm/°C to +27 ppm/°C in the (1-x)H3BO3-xPE (0.0 ≤ x ≤ 0.5) microwave ceramics at their optimal sintering temperatures. A near-zero τƒ value (+9 ppm/°C) was obtained in the 0.7H3BO3-0.3 PE composite, which simultaneously exhibited an er value of ~2.38 and a Q × ƒ value of ~46,000 GHz (at 15.7 GHz) after sintering at 100 °C for 1 h. Interestingly, through the hydrolysis experiment (24–384 h), the Q × ƒ values of the 0.7H3BO3-0.3 PE and/or 0.6H3BO3-0.4 PE polymer-ceramics were basically maintained at approximately 35,000–40,000 GHz. These results showed that the novel (1-x)H3BO3-xPE polymer-ceramics should be the potential candidates for ultra-low temperature co-fired ceramic (ULTCC) technology.

Lead-free (1-x)BaTiO3-xSr(Zn1/3Nb2/3)O3 (abbreviated as BT-xSZN, x = 0–0.08) relaxor ferroelectric ceramics were prepared using the traditional solid phase technology, and the effects of SZN modification on their phase structures, microstructures, dielectric performance, ferroelectricity and energy storage performance were studied in detail. A pure perovskite phase was observed in the BT-xSZN ceramics. The BT-based ceramics modified by SZN exhibited refined grain size. As the SZN content was increased, the breakdown strength initially increased and then decreased, and the ferroelectric loops gradually became ‘slim’. The BT-xSZN (x = 0.07) ceramics demonstrated a favourable energy storage performance with high recoverable energy density (Wrec = ~1.45 J/cm3) and energy storage efficiency (η = ~83.12%) at 260 kV/cm. Results indicate that the energy storage performance of BaTiO3 ceramics modified by SZN can be remarkably improved, widening their applications in energy storage at low temperatures.

A depolarized electric field (Edp) of ferroelectrics to boost the carrier separation and migration rate is critical to promote the field of visible light photocatalytic hydrogen evolution (PHE). Here, the PHE performance of high-field poled semiconducting (1 − x)KNbO3–xBa(Ni1/2Nb1/2)O3−δ (abbreviated as (1 − x)KN-xBNN, x = 0, 0.02, 0.05, 0.10, and 0.20) ferroelectric ceramics were systematically studied under full spectrum (λ > 320 nm) and visible light (λ > 420 nm), respectively. Benefiting from their narrow bandgap and sub-bandgap, all the Ba, Ni-modified KN ceramic powders exhibited a PHE response under visible light irradiation. Notably, the visible light PHE rate of the high-field poled 0.95KN–0.05BNN ceramic powder can be promoted to 415.16 μmol g−1 h−1, which is 17.8-fold higher than that of the unpoled sample (23.26 μmol g−1 h−1). The boosting PHE rate in poled samples can be attributed to the high-field polarization of the material, which can significantly affect the lattice structure and cause an ordered ferroelectric-domain structure to form a depolarized electric field (Edp). EPR spectroscopy indicated that the poled 0.95KN–0.05BNN sample exhibited a superior catalytic activity of ˙OH evolution compared with its unpoled counterpart, suggesting the dependence of high photocatalytic performance on the unique field-induced polarization structure by an outer electric field. Moreover, a higher photo-excited transient photocurrent in the poled 0.95KN–0.05BNN specimen further proved the positive effect of Edp on the photovoltaic response. The formation of Edp in the semiconducting (1 − x)KN–xBNN ferroelectric favors the separation and transportation of photogenerated carriers. Thus, the synergistic effect of narrow bandgap and high-field polarization ability is the key to enhance the visible light photocatalysis of semiconducting ferroelectrics. Boosting the visible light photoelectrochemical catalytic activity of semiconducting (1 − x)KN–xBNN ferroelectrics through high-field polarization may provide a useful strategy to design new ferroelectric-based semiconductor materials.

Perovskite-oxide (1 − x)KNbO3-xBaCo1/2Nb1/2O3−δ (KN-BCN; x = 0.00–0.20) ferroelectric semiconductor ceramics with oxygen defects are successfully prepared via a conventional solid-state sintering method. X-ray diffraction data indicate that the crystal symmetry evolves from orthogonal to tetragonal at increasing x values. Raman spectroscopic analysis confirms the long-range polarization of all compositions. X-ray photoelectron spectroscopy shows that the detailed chemical formula of 0.90KN-0.10BCN ceramics is 0.90KNbO3-0.10BaCo1/2Nb1/2O2.90. Room-temperature ferroelectricity weakens when the x value increases. The optical band gap narrows from 3.25 eV for x = 0.00 to 1.57 eV for x = 0.20, and the minimum value of ∼ 1.28 eV occurs in the 0.90KN-0.10BCN ceramic. Impedance analysis illustrates that the conduction mechanism of grains is mainly internal electron conduction, and that of the grain boundary is intrinsic conduction. The conducting mechanism of the ceramic system follows ohmic behavior by log I–log U curves. The maximum short-circuit photocurrent density and open-circuit photovoltage are 6.68 nA cm−2 and 0.80 V, and stable output is maintained. The KN-BCN ceramic system can be used in photovoltaic materials.

The development of ferroelectric (FE) ceramics with high recoverable energy-storage density (Wrec) critically affects the miniaturization and integration of advanced pulse-power capacitors. However, most lead-free FE materials have the shortcomings of large remanent polarization and low dielectric breakdown strength. In this work, a strategy of composition control was implemented to improve the Wrec of lead-free ceramics. The effects of Li and Nb ion incorporation on the structure, dielectric, and ferroelectric properties of the highly insulating (Na0.5Bi0.5)TiO3–BaTiO3 (NBT–BT) ceramic was investigated. X-ray diffraction analysis of the samples revealed that the pure phase was isostructural to (Na0.5Bi0.5)TiO3. Dielectric measurements exhibited two pronounced anomalies which shift a certain angle within the depolarization-temperature range. The effects of LiNbO3 content on the breakdown characteristics and discharge energy storage of NBT–BT ceramics were investigated. An enhanced discharged energy density of 1.05 J/cm3, calculated from a hysteresis loop, was observed at x = 4 mol%. The improved structure also resulted in an increase of up to 61% in breakdown strength.

Perovskite oxide (1-x) KNbO3–xBaFeO3-δ (KN–BF; x = 0.00–0.10) ferroelectric semiconductor ceramics are prepared via traditional solid-state synthesis and air sintering. All ceramics show a single perovskite structure and a long-range polarity order by X-ray diffraction (XRD) and Raman spectra, respectively. A minimum optical band gap of approximately 1.82 eV, which is approximately 43% lower than that of pure KN (approximately 3.22 eV), is obtained for the x = 0.10 sample. The ferroelectric behavior of the samples weakens with the increase in BF doping content. The activation energies of the ferroelectric domain and domain wall of 0.93KN–0.07BF ceramics are approximately 0.26 eV and approximately 0.52 eV, respectively, which are ascribed to the conduction mechanism of the first and second ionizations of oxygen, respectively. For the 0.93KN–0.07BF sample, along the positive polarization direction, the short-circuit photocurrent density and open-circuit photovoltage are 11.39 nA cm−2 and 0.217 V under AM1.5 standard sunlight. The results guarantee the feasibility of applying KN–BF ceramics to ferroelectric photovoltaic devices.

(1–x)NdGaO3-xBi0.5Na0.5TiO3 [(1–x)NdGaO3-xBNT, 0.05 ≤ x ≤ 0.7)] ceramic systems were fabricated using a conventional solid-state reaction, and their phase structures, microstructures, and microwave dielectric characteristics were systematically investigated. The XRD patterns results showed an orthorhombic perovskite structure as the main phase with a Pbnm space group at x = 0.05. In a range of x = 0.1–0.3, the main Nd3Ga5O12 cubic structure phases (Ia-3d space group) had been formed due to the increase in the cation vacancies resulting from the Na and Bi ion volatilization at the higher densification sintering temperatures (1400–1450 °C). As (Na0.5Bi0.5)2+ ions increased and the sintering temperatures decreased, the orthorhombic perovskite-type Pnma space group solid solutions (the main phases) were detected at x = 0.4 and 0.5, accompanied with a certain amount of second phase Bi2O3 in the samples at x = 0.6 and 0.7. The results of Raman spectroscopy analysis, EDS data analysis, and surface morphologies observations were basically in keeping well with the XRD analysis results, wherein the Raman-active modes also implied that the crystal structure of the main phase actually had a tendency to change the perovskite structure when x = 0.3. The er value increased gradually as the x value increased from 0.05 to 0.5 because of the increase in the ionic polarizability, and increased slowly at x = 0.6, then decreased slightly as the x value further increased to 0.7 due to the formation of the second phase. The Q × f values of the (1-x)NdGaO3-xBNT (x = 0.05–0.7) ceramic systems were strongly influenced by the densification, lattice defects, and phase composition and content. The τf values could be well predicted by replacing Na, Bi and Ti ions with suitable substitutions for these ceramic systems. As a result, the new temperature-stable ceramics with optimal dielectric properties of er ~43.1, Q × f ~6700 GHz (at 5.85 GHz), and τf ~ −24.5 ppm/°C and er ~ 44.5, Q × f ~ 5600 GHz (6.12 GHz), and τf ~ +2.4 ppm/°C were obtained in the (1-x)NdGaO3-xBNT composite series at x = 0.5 and x = 0.6 sintered at 1320 °C and 1250 °C for 4 h, respectively.

BNT-based ceramics are very attractive for the electrical energy storage and electric field-induced strain. However, the reported BNT-based ceramics are usually the perovskite solid solution. In this work, the super adjustability of Cs2Nb4O11 antiferroelectric phase for lead-free (1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xCs2Nb4O11 ceramics with complex-phase are carefully studied. The Bi0.5(Na0.82K0.18)0.5TiO3 ceramics modified by a trace of Cs2Nb4O11 component suddenly transform to antiferroelectric phase from typical ferroelectric. A giant strain of 0.48% and a d33* of 600 pm/V are obtained originating from a reversible transition between antiferroelectric and ferroelectric states. And a high energy density of 1.0 J/cm3 is also achieved by reversible phase transitions. Therefore, the composite ceramics by designing tungsten bronze and perovskite complex phase illustrate great potential for actuator or energy storage applications.

In this study, (1–x)Bi0.5Na0.5TiO3– xBiScO3 (BNT–xBS) ceramics were synthesized via conventional solidstate reaction sintering. The effects of the BiScO3 content on the surface microstructure, energy storage, strain, and dielectric properties of BNT–xBS ceramics were systemically investigated. Results indicated that the phase structure of BNT–xBS ceramics transformed from the rhombohedral phase into the pseudo-cubic phase. As the increasing BiScO3 content, the average grain size decreased. BiScO3 destroyed the long-range ordered ferroelectric phase, enhancing relaxor behavior. Energy storage density initially increased and then decreased, reaching a maximum of 0.17 J/cm3 at x = 0.1. In addition, the maximum energy storage efficiency was 59% at x = 0.2. The BiScO3 content significantly affected the electrical properties of BNT– xBS ceramics.

(1 − x)[0.9(Bi0.5Na0.5)TiO3–0.1BiScO3]–xBaTiO3 (BNT–BS–xBT) ceramics are prepared by the traditional solid-state sintering. The structure, morphology, ferroelectricity, strain, energy storage, dielectricity, and impedance of the BNT–BS–xBT ceramics are investigated. XRD shows that all ceramics have pseudo-cubic structures. The results also show that BT can refine the grain size of the ceramics and reduce the corresponding density. At x = 0.20, the energy storage performance of the ceramics is optimum (Wrec = 0.563 J/cm3, η = 63%). At x = 0.10, the electrostriction coefficient (Q33) of the ceramics reaches 2.72325 × 10−2 m4/C2. Dielectric and impedance spectroscopies show that the ceramics are relaxor ferroelectrics and have good insulation properties.

In view of lead-free low-softening CuO–ZnO–B2O3–Li2O glass, novel glass/Al2O3 ceramic composites were prepared by solid-state reaction route for ultra-low temperature co-fired ceramic (ULTCC) applications. The phase evolution and compositions, microstructure and microwave dielectric properties of the composites were studied by XRD, SEM and dielectric property measurement. Four phases including Cu2Al6B4O17, Li2CuB4O8, CuB2O4 and Al2O3 coexist in the glass/Al2O3 ceramic composites sintered in the range of 640–660 °C. However, the contents and types of the phases depend on the composition of the composites and firing temperature. The optimum properties with a permittivity er = 3.79, a quality factor Q × f = 38557 GHz (at 16.64 GHz) and a temperature coefficient of resonance frequency τf≈0 ppm/oC as well as a heat conductivity λ = 1.46W(mK)−1can be achieved for the glass/ceramic composite containing 10 wt% Al2O3 sintered at 640 °C. Moreover, the composite can be co-fired compatible with Ag and Al electrodes.The as-prepared glass/Al2O3ceramic composites are promising candidate for ULTCC application.

We prepared 15.16SrO–(16.84 − x)BaO–xK2O–32Nb2O5–28B2O3–8P2O5 glass ceramic composites with different K:Ba ratios through melt-casting followed by controlled crystallization. Although the dielectric constant of these samples decreased with an increase in x, a maximum theoretical energy density of 12.83 J/cm3 was obtained at x = 10.104. High breakdown strength (1844 kV/cm) and low dielectric loss (

The (1-x)CaTiO3-xBi0.5Na0.5TiO3 [(1-x)CT-xBNT), x = 0.1–0.6] microwave ceramics were studied by traditional solid-state method. Crystal structures, microstructures, microwave dielectric properties and impedance analysis of the as-prepared ceramics were investigated systematically. Refinement of X-ray diffraction patterns from all of the samples were pure orthorhombic structure with Pbnm space group. The Raman spectra of (1-x)CT-xBNT were in accord with the previous reports except that some abnormal modes appeared in high-wavenumber of 1200 cm−1-3400 cm−1. The microstructures were dominated by even grains and the average sizes increased gradually with an increase in Bi0.5Na0.5TiO3 (BNT) content. The microwave dielectric constant, er, improved from 184 to 487, and the quality factor, Q×f, decreased constantly from 6973 GHz to 157 GHz as the amount of BNT in (1-x)CT-xBNT increased. However, the temperature coefficient of resonant frequency, τf, was restricted to fluctuating from 680 ppm/°C to 820 ppm/°C due to that the oxygen octahedral was twisted. For analysis and modeling of impedance data of 0.7CT-0.3BNT ceramics, the most appropriate equivalent circuits were found to consist of a parallel resistor-capacitor-constant phase element (R-CPE-C). And the activation energy for grains, 1.8 eV, was different to that in the grain boundaries, 1.0 eV.

Microwave dielectric ceramics with xSr0.1Ca0.9TiO3–(1−x)Bi0.1Na0.1Li0.4Sm0.4TiO3 (xSCT–BNLST) compositions were prepared through the conventional oxide-state reaction. X-ray diffraction results showed that the symmetry in xSCT–BNLST system were improved with the increase of x. Based on the calculation results, the deviation of observed dielectric polarizabilities from theoretical values could be ascribed to the increase of A-site ionic polarizability and B-site bond valence. The decreased temperature coefficient of resonant frequency, τf, was dependent on the B-site bond valence in the tilted region. With the increase of temperature, the samples changed their main conductive carrier, from first ionization of oxygen vacancies to second ionization of oxygen vacancies. Optimum microwave dielectric properties were achieved, for 0.09SCT–BNLST ceramic with relative permittivity, er = 111, quality factor, Q × f = 3819 GHz and τf ~ 0 ppm/°C. The system has the potential for use in dielectrically loaded antennas and C0G high-frequency filter applications.

Doping in bismuth sodium titanate (BNT)-based ceramic is often intended to realize excellent direct piezoelectric responses mainly through A-site substitution and generate ultrahigh strain behaviors mainly by B-site doping, which indicate the different effects of the doping on direct and converse piezoelectricity. Here, we reported simultaneous occurrences of anomalies in electric field and temperature dependence of direct/converse piezoelectric responses of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3(BNT-BT6) ceramics by detailed analyses of the weak-field piezoelectric coefficient d33, high-field piezoelectric coefficient d 33 ∗ , and small signal bias-field piezoelectric coefficient d 33 ∗ (E = 0). The multiple piezoelectric responses presented similar anomalies at critical field Ep = 20 kV/cm and critical temperature Tf = 120 °C. The analogous changes in direct/converse piezoelectric behaviors are highly related to the electric-field/temperature-driven phase transformation, which could boost polarization reorientation and domain switching to a lager extent. Particularly, the phase transition resulted in an obvious increase in high-field piezoelectric coefficient d 33 ∗ , and so offer a potential strategy for further development of high-performance lead-free piezoelectric materials.

Ultrahigh dielectric constant (er) (1-x-y)Bi0.5Na0.5TiO3-xLi0.5Sm0.5TiO3-yNa0.5La0.5TiO3 (BNT-LST-NLT, 0.3 ≤ x ≤ 0.7, 0.0 ≤ y ≤ 0.4) microwave ceramic systems were fabricated using a conventional solid-state reaction method, and their phase structures, microstructures, and microwave dielectric characteristics were systematically investigated. From XRD pattern analyses and refinement results, (1-x-y)BNT-xLST-yNLT (x = 0.3–0.6 and y = 0.4–0.1) samples were crystallized into a cubic perovskite structure, and XRD peaks corresponding to the (031), (131), and (230) planes were identified as super-reflections belonging to the tilt system of orthorhombic a−a−b+ with the Pnma space group. In particular, on the basis of the Raman spectra and microwave dielectric properties analysis results, the crystal structure of the sample (x = 0.6 and y = 0.1) sintered at 1200 °C for 4 h was considered to be closer to orthorhombic symmetry. In addition, solid orthorhombic perovskite-type solutions were formed together with a small amount of secondary phase Sm2Ti2O7 as x = 0.6 and y = 0.2, 0.3. However, an increase in the Sm2Ti2O7 phase content was also detected for x = 0.7 and y = 0.0, accompanied by the perovskite phase. For the microwave dielectric properties, the er and Q×f values strongly depended on the apparent density, ionic polarizability, phase structure, and phase composition, and also, the τf value was predicted by adjusting the tolerance factor (t). The er and τf values basically agreed with the existing models, such as the mixing rule. As a result, the (1-x-y)BNT-xLST-yNLT (x = 0.6 and y = 0.1) ceramic sample sintered at 1200 °C for 4 h exhibited superior microwave dielectric properties of er ~ 149.1, Q×f ~ 3270 GHz, and τf ~ 39.1 ppm/°C.

Lead-free Bi0.5(Na0.82K0.18)0.5Ti1-x(Sr1/3Nb2/3)xO3 (abbreviated as BNKT-xSN, x = 0.02–0.045) ceramics were fabricated via the conventional ceramic process, and the (Sr1/3Nb2/3)4+ complex-ions were used to modify the phase transition and multifarious electrical responses of BNKT-xSN ceramics. The SN complex-ions absolutely incorporate into the lattice of BNKT matrix to form perovskite structure. The grain morphologies and size are almost unaffected by SN complex-ions. The phase transition concerning ferroelectric type transforming into ergodic relaxor happens with increasing SN content, and the corresponding critical point is x = 0.035. The phase transformation process results in the improvement of energy storage density (W = 0.754 J/cm3) at 80 kV/cm and a high bipolar strain (S = 0.25%) with small hysteresis. The dielectric constant at Tm peaks gradually decreases with increasing SN content, and the ferroelectric-relaxor transition temperature (TF-R) is depressed to room temperature. The evolution behaviors might facilitate our cognition about the mechanism between phase structure and multiple electrical properties of BNT-based ceramics.

Ferroelectric phases coexistence or transition is an important strategy on generating high piezoelectricity. Here, the temperature-induced phase structural evolution correlated with small signal piezoelectric response d33, bias-field piezoelectric activity dmax33(E), unipolar and bipolar strain piezoelectric outputs d*33 in Ba(Ti0.92Sn0.08)O3 (BTS0.08) ceramic was investigated in details. Temperature-driven successive phase transitions from rhombohedral (R) to orthorhombic (O), tetragonal (T), finally to cubic (C) phases took place around 14 °C, 38 °C and 61 °C, respectively. The highest d33 value of 675 pC/N is achieved in the T-C phase transition. However, the O-T phase boundary gives the highest dmax33 = 1170 p.m./V, bipolar d*33 = 822 pm/V and unipolar d*33 = 1318 pm/V. The temperature-driven phase transition exhibits large enhancements in piezoelectric property comparable to that of composition-induced phase boundary. These features suggest an effective method to design high-performance piezoelectrics by tailoring the types of phase boundary.

A-site (Li0.5Sm0.5)2+ substitutions for (Na0.5Bi0.5)2+ of Na0.5Bi0.5TiO3 ceramics were prepared by the conventional solid-state reaction. Structural and electrical properties, including ferroelectric, dielectric, and impedance attributes of the as-prepared ceramics were studied systematically. The new solutions, (1–x)Li0.5Sm0.5TiO3–xNa0.5Bi0.5TiO3, could be roughly separated into three groups in accordance with their electrical polarity as microwave dielectric (x 0.92). An increase in (Na0.5Bi0.5)2+ content had a positive impact on the ferroelectric and dielectric properties. Compositions closest to zero temperature coefficient of resonant frequency(τf) were obtained at x = 0.4, where permittivity(er) was 154 and the microwave quality factor, Q × f was 1560 GHz for the samples sintered at 1125 °C. The highest discharged energy density of 0.92 J/cm3 was achieved at x = 0.9. The loss of Bi3+ during sample processing changed the conductive mechanism from electronic conduction to oxide ion conduction, thus presenting a way to optimize the compositions with various donor and acceptor dopants for better performance in microwave and ferroelectric ceramics.

Mn/Co/Ni-modified BaBiO3-based negative temperature coefficient (NTC) ceramics with the formula, x[(3-y-z)Mn/yCo/zNi-ions]+(1−x)BaBiO3 (x = 0.0–0.4, y = 0.96 and z = 0.48), were synthesized using a conventional solid state reaction. The effects of Mn/Co/Ni-substitute content on the phase structures and composition, microstructures and electrical properties were characterized by X-ray diffraction (XRD), scanning electron microscope and resistance–temperature measurements, respectively. XRD pattern analysis results revealed that the compound phases consisted of a main monoclinal BaBiO3 phase and a secondary phase of Ba(Mn, Co, Ni)O3 solid-solution with a hexagonal structure, which were detected at x = 0.05–0.2. In addition, according to the XRD patterns, the main phase changed from BaBiO3 to a rhombohedral Bi8.11Ba0.89O13.05 phase at x = 0.3, and this phase content increased dramatically as the x value increased to 0.4. For the related electrical properties, all of the samples demonstrated the typical characteristics of NTC thermistors across a relatively wide range of temperatures. The values obtained for B constant (B25/85) and the room-temperature resistivity (ρ25) were in the range of 2297–5235 K and 760 Ω cm−1, 620 kΩ cm, respectively, which implied that the electrical properties of the present ceramic systems could be optimized via various substitutions in the Mn/Co/Ni-ions content. The variable values of ρ25 were affected strongly by the changes in crystal structure and the decrease in charge carrier concentration. These composite ceramic materials are suitable candidates for a variety of NTC thermistor applications due to their widely adjustable electrical properties.

The local heterogeneities and phase transition in the ferroelectric Bi0.5Na0.5TiO3 have a profound impact on the electrical properties. Herein, we have illustrated that the high functional properties involving domain switching and a heterogeneity dependent emerging phase transition are closely associated with intermediate local heterogeneity by comparing the as-prepared and field cycled BNT ceramics. A synergistic role can be triggered by the intermediate metastable ferroelectric state in view of this heterogeneity and associated phase transition with an applied electric field in the freshly prepared specimens. Multiple giant functional responses of colossal piezoelectricity, large electroresistance and dielectric tunability were achieved due to the significant increases in polarization orientations highly related to the metastable ferroelectric state of the localized structure. Particularly, record-setting piezoelectricity with d33* = 17 816 pm V−1 was obtained in the field-induced collaborative interaction. Discovering the catalytic effect of the intermediate metastable ferroelectric state will provide unique opportunities for the design of high-performance materials.

Following increased environmental concerns on the toxicity of lead, the discovery of ultrahigh piezoelectricity in lead-free piezoelectric materials is critical for the substitution of commercial lead zirconate titanate (PZT) ceramics in numerous electronic devices. In this work, a synergistic design strategy is proposed to enhance the piezoelectricity in lead-free piezoelectric materials by flattening the Gibbs free energy density profile, via the coexistence of multiple phases and local structural heterogeneity. This strategic material design approach is based on first-principles calculations combined with Landau phenomenological theory and phase field simulations. Sustainable Stannum-doped BaTiO3 lead-free ferroelectric ceramics are prepared to validate our proposed mechanism, and a giant piezoelectric coefficient d33 > 1100 pC/N is achieved, being the highest value reported in lead-free piezoceramics. The mechanism and paradigm of the excellent piezoelectricity achieved here provides a feasible solution for replacing lead-based piezoelectrics by lead-free counterparts.

The research and development of high-performance lead-free dielectric capacitors with excellent wide temperature stability, large recoverable energy density, ultra-high efficiency, and ultra-high-speed charging and discharging have received extensive attention. However, most lead-free dielectric materials developed at this stage do not meet all these requirements owing to various factors. Herein, a new type of lead-free (1-x)(0.94Bi0.47Na0.47Ba0.06TiO3-0.06CaHfO3)-xBi0.2Sr0.7TiO3 relaxor ferroelectric bulk ceramic was designed and prepared. The doping of Bi0.2Sr0.7TiO3 further refined the sub-micron grains and helped to obtain a wider band gap. Moreover, the ceramic exhibited a polarization response with almost no hysteresis, even under a high electric field because of the large number of randomly distributed nano-scale polar domains. The ceramic with x = 0.4 exhibited an outstanding comprehensive energy-storage performance with an extraordinary Wrec of 6.19 J/cm3 and a superior η of 93.5%. Similarly, another x = 0.45 ceramic also obtained a considerable energy-storage characteristic with an ultra-high η of 94.5% and a large Wrec of 6.02 J/cm3. In addition, the ceramic with x = 0.4 also showed remarkable wide frequency (1–200 Hz) and wide temperature range (20–140 °C) stability. In the pulse charge test, x = 0.4 ceramic exhibited a large discharge energy density of 5.07 J/cm3 under 340 kV/cm and a considerable discharge rate. All these indicate that our work provides a practical and effective idea for the design of application-type dielectric capacitors with an outstanding comprehensive performance.

Na5RE(MoO4)4 (RE = La, Gd, Dy, Er) ceramics have been synthesized by the conventional solid-state reaction method. The crystallizations, microstructures and microwave dielectric properties of Na5RE(MoO4)4 ceramics were also investigated. The room-temperature x-ray diffraction patterns of Na5RE (MoO4)4 ceramics illustrate a tetragonal structure with a I 41/a space group. The grain size of Na5La(MoO4)4 is larger than that of Na5RE(MoO4)4 (RE = Gd, Dy, Er) ceramics, and uneven grains are observed in the systems. Na5RE (MoO4)4 ceramics sintered at 570–690°C for 4 h possess excellent microwave dielectric properties with er = 6.4–8.4, τf = − 27.7–34.3 ppm/°C, and Q × f = 4073–24411 GHz at their optimum sintering temperature. The nonreactivity of Na5Er(MoO4)4 with silver is evidenced by x-ray diffraction, and SEM and EDS analysis reveal that silver can be a co-firable electrode material for the present ceramics.

High visible light transmittance (1 − x)(K0.5Na0.5)NbO3−xSr(In0.5Nb0.5)O3 (KNN−xSIN, x = 0.05, 0.10, 0.15, 0.20, 0.25) lead-free ceramics with excellent electrical properties were synthesized by traditional solid-state method. The effects of Sr(In0.5Nb0.5)O3 doping on the optical properties, microstructure, and electrical performance were analyzed. The results showed that light transmission in KNN−xSIN ceramics was induced by the dense and fine-grain microstructure, the high symmetry of the pseudo-cubic structure as well as typical relaxor behavior of KNN−0.25SIN ceramic. Moreover, KNN−xSIN transparent ceramics with relaxor characteristics possessed permittivity stability over a wide temperature range. Ferroelectric properties were deteriorated gradually with increasing SIN content in virtue of the strengthened relaxor behavior. Its energy storage property was also tailored by the increasing relaxor characteristic. The appearance of a non-Debye type of relaxation was detected through an impedance Cole–Cole plots.

The thermal stability of the piezoelectric properties in BiFeO3 based high-temperature piezoceramics is traditionally investigated through room temperature characterization via thermal annealing measurements, which cannot reflect the actual performance at elevated temperatures. In this work, the microstructures, electrical properties, real-time high-temperature piezoelectric responses and ferroelectric scaling behaviors of 0.7Bi1.05(Fe1-xMgx)O3-0.3BaTiO3 (BFMx-BT) ceramics were studied systematically. Doping with 0.6% Mg resulted in enhanced piezoelectric properties with d33 = 170 pC/N and kp = 0.29 along with a high-temperature stability (Td = 440 °C). With a significant jump near the Td, in situ high temperature piezoelectric responses displayed a distinct behavior different from the ex situ high temperature piezoelectricity. Scaling behaviors were presented by studying the field amplitude and frequency dependence of P-E hysteresis loops areas. The behavior of the real-time high temperature piezoelectricity may provide a new insight into the development of new high-temperature piezoceramics.

Co modified lead-free 0.7BiFeO3− 0.3BaTiO3 (0.7BFO-0.3BT-xCo2O3；x = 0, 0.3, 0.6, 0.9 and 1.2) piezoelectric ceramics were prepared by a conventional solid-state reaction. The effect of Co doping on the structural, piezoelectric properties and leakage current was investigated. A greatly reduced leakage current and dramatically improved piezoelectric properties were achieved in x = 0.3 Co doped ceramic. The maximum d33 = 151 pC/N and kp = 0.32 were obtained at x = 0.3 addition due to the co-effect of maximum applied poling electric field and large grain size. The X-ray photoelectron spectroscopy (XPS) analysis and complex impedance data indicated that the greatly reduced leakage current could be attributed to the effect of suppressing Fe2+ ion formation and promoting grain boundary resistance by Co doping. These results strongly suggest that low concentration of Co doping is a good strategy to improve the resistance and piezoelectric properties simultaneously in BFO-based lead-free piezoceramics.

Effect of Zn site-selected doping on electrical properties, high-temperature stability and sensitivity of piezoelectric response for BiFeO 3 -BaTiO 3 ceramics was investigated. The results revealed that the addition of Zn leaded to an evident modification of the microstructure. The B-site selected doping was a more effective approach in improving piezoelectric properties as well as their thermal stability than those of A-site selected doping. Moreover, the enhanced piezoelectric properties accompanying by excellent high-temperature stability and sensitivity in B-site selected doping ceramics were obtained. The microstructure, domain switching behavior and temperature-dependent piezoelectric response in Zn site-selected doping ceramics were investigated, and their relationships with improving piezoelectric properties and high-temperature stability were explored. These results showed that the B-site selected doping ceramics had excellent piezoelectric properties ( d 33 = 192pC/N) along with a high-temperature stability ( T d = 450 °C).

Crystal structures and microwave dielectric properties of (1-x) LaGaO3-x SrTiO3 (x = 0.4, 0.5, 0.6) and 0.4SrTiO30.6LaGaO3-yCeO2 (y = 0, 0.05, 0.1, 0.2) ceramics were investigated. As the x values increased, the orthorhombic changed to tetragonal perovskite structure at x = 0.6 in LaGaO3-SrTiO3 system ceramics. However, numerous secondary phases were detected in LaGaO3-SrTiO3 system ceramics. Surprisingly, CeO2 additives could effectively suppress formation of secondary phases of 0.4SrTiO3-0.6LaGaO3 ceramics as Ce ions could be incorporated into host crystal lattices, leading to significantly improvement of optimal Q × f values from 35,354 GHz to 62,150 GHz. The Raman spectra exhibited that the modes associated with CeO2 phase became more obvious with increasing CeO2 additives. The 0.4SrTiO30.6LaGaO3-0.05CeO2 ceramics, sintered at 1475 °C/4 h, exhibited superior microwave dielectric properties with er = 32.9, Q × f = 62,150 GHz and τf = − 26.6 ppm/°C.

Lead-free ceramics (1 − x)Bi0.5Na0.5TiO3–xSr0.85Bi0.1TiO3 (BNT–xSBT, x = 0.4, 0.5, 0.6 and 0.7) were prepared by a solid-state reaction process. Coexistence of ferroelectric relaxation at low temperature and Maxwell–Wagner dielectric relaxation at high temperature was revealed for the first time in this system. Meanwhile, hysteresis-free P–E loops combined with a very high piezoelectric strain coefficient (d33) of 1658 pC/N concurrently with large electrostrictive coefficient Q = 0.287 m4C−2 were achieved. The ferroelectric relaxor behavior and large electrostrictive strain might be linked to easy reorientation and reversal of ergodic PNRs and the combined effect of Bi off-center position and lone pair electrons.

Sm2O3-Nd2O3-MgO-CeO2 ceramic systems of the form Sm1-xNdx(Mg0.5Ce0.5)O3 (0.0 ≤ x ≤ 1.0) were synthesized by a conventional solid-state reaction method, and the phase structural characteristics, microstructures, sintering behaviors and microwave dielectric properties were investigated systematically. X-ray diffraction analyses revealed that a cubic fluorite-type structure with Fm-3m (225) space group was identified as the main crystalline phase in the composition range of x = 0.0–1.0, while some secondary phases were also detected in all the Sm1-xNdx(Mg0.5Ce0.5)O3 samples. The phase structural characteristics of Sm2O3-Nd2O3-MgO-CeO2 quaternary ceramic systems were significantly affected by a certain amount of Mg2+ ion volatilization, detected by the typical EDS data. Additionally, both an example of EDS analysis in the second phases regions and some details of the diffraction peaks implied that the unknown phases were mainly composed of MgO phase. Furthermore, for the microwave characteristics, the relative permittivity (er) was closely related to the dense degree and phase compositions, and also, the quality factor (Q × f) had been strongly depended on the compactness and lattice defects in these investigated ceramics. Wherein, after sintering at 1450 °C for 4 h, the x = 0.0 sample demonstrated the excellent microwave dielectric performance: er ∼16.6, Q × f ∼111,280 GHz (at 7.938 GHz) and τf ∼ −56.7 ppm/°C. These results also indicated that the Ce1-xLnxO2-δ (Ln = Sm and Nd) solid solutions could be a good candidate for dielectric resonators, filters and other microwave electronic device applications.

Glass-ceramics with a mass fraction composition (wt%) of 19MgO-23Al2O3-53SiO2-4TiO2-xV2O5 (x = 2.5, 3 and 3.5, abbreviated as samples V2.5, V3 and V3.5) were prepared by two-step heat treatment of the parent glass at selected nucleation and crystallization temperatures for different holding time (2 h and 20 h), respectively. The effects of V2O5 on crystalline phases, microstructures and microwave dielectric properties of the glass-ceramics were investigated in detail. X-ray diffraction (XRD) analyses revealed that the main phases could be identified as α-cordierite and SiO2 phases, and also some amount of μ-cordierite phase and a trace of Al2Si4O10, Mg(VO4)2 and TiO2 phases were also detected in all these glass-ceramics' XRD patterns. In addition, an appropriate V2O5 addition with 3.0–3.5 wt% was found to cause an increase in the content of the precipitated crystalline phases. Based on the EDM observation, a fraction of Ti4 + and V5 + ions were remained in the residual glass matrix of the crystallized specimens. Additionally, the microwave dielectric properties were closely depended on not only the different two-step heat treatment temperatures and holding time, but also the relative densities and degree of crystallization of the glass matrix. Wherein, the fully densified V3 glass-ceramic sample heat-treated at 850 °C/2 h + 950 °C/20 h exhibited a lower dielectric constant (er) of ~ 3.79, a higher quality factor (Q × f) of about 12,520 GHz (at 13.693 GHz) and a near-zero temperature coefficient of resonant frequency (τf) of ~ − 5.4 ppm/°C, which provided a promising candidate for LTCC applications.

Na 2 O-Nd 2 O 3 -CeO 2 ceramic systems of the form Na 3 x − 1 Nd 1 −x CeO 3 ( x = 0.4, 0.5, and 0.6) were prepared via a solid-state reaction method. X-ray diffraction analyses indicated that the samples with x = 0.4, 0.6 and those with x = 0.5 formed Nd 0.25 Ce 0.75 O 1.875 and Nd 0.5 Ce 0.5 O 1.75 solid solutions, respectively, which resulted from a large degree of Na + ion evaporation. Both the Nd 0.25 Ce 0.75 O 1.875 and Nd 0.5 Ce 0.5 O 1.75 phases belonged to the same cubic structure with an Fm-3m (225) space group. Additionally, the microstructures, sintering behaviors, and microwave dielectric properties were considered to be strongly related to the Na content in the Na 3 x − 1 Nd 1 −x CeO 3 ceramics. A relatively large degree of Na + ion evaporation could increase the negative temperature coefficient of the resonant frequency ( τ f ) for these ceramic systems. Moreover, after sintering at 1380 °C for 2 h, the x = 0.6 specimen possessed a low permittivity ( e r ) of approximately 9.13, a moderate quality factor ( Q × f ) of approximately 23,800 GHz (at 9.14 GHz) and a negative τ f value of approximately −61.7 ppm/°C. As a result, it could be a promising microwave dielectric material for achieving a near-zero τ f value by solidifying one or more microwave dielectric ceramics with a high positive τ f value.

This work compared the effects of sintering methods on the structure, dielectric, strain and energy storage properties of (Bi0.5Na0.5)0.94Ba0.06Ti0.965(Mg1/3Nb2/3)0.035O3 (BNBT–0.035MN) lead-free ceramics. The single phase perovskite structure of BNBT–0.035MN ceramics was independent with sintering methods. The ceramics by two-step sintering had smaller grain size and denser microstructure than those of the ceramics by traditional sintering. Compared with traditional sintering, the ceramics by two-step sintering exhibited better energy storage properties. The optimum energy storage density (W = 0.80 J/cm3) and corresponding efficiency (η = 65%) were obtained at 70 kV/cm, while the electric field-induced strain decreased. Dielectric properties of two-step sintering samples were inferior to that of traditional samples, which is related to the grain size effect.

Although tremendous studies have been focused on dielectric ceramics to achieve excellent energy storage and charge-discharge performance, the dielectric ceramics with high comprehensive energy storage properties for pulsed power applications are still in shortage. The large hysteresis came from domain switching process, severely weaken the energy storage and charge-discharge properties. Here, a strategy through ergodic relaxors with high dynamic polar nanoregions (PNRs) featuring with fast discharge rate and high energy storage efficiency was proposed to achieve high energy storage properties and extremely fast discharge speed in ferroelectric ceramic. The ergodic relaxors of Sr0.7Bi0.2TiO3 modified by Na0.73Bi0.09NbO3 (SBT-NBN) ceramics were selected to verify the feasibility of the strategy. Encouragingly, large Wrec of 2.49 J/cm3 together with high η of 89.7% can be achieved simultaneously at 250 kV/cm with the composition of 0.96SBT-0.04NBN. The outstanding stability of energy storage characteristics for temperature (25–125 °C) and frequency (1–100 Hz) was also found in 0.96SBT-0.04NBN ceramics. Besides, 0.96SBT-0.04NBN ceramics also possessed an extremely fast discharge rate (~34 ns), remarkable power density PD (57.3 MW/cm3) as well as high current density CD (955.4 A/cm2) at 120 kV/cm. This work provided an original strategy for high energy storage efficiency and high power density ceramics in pulse power applications.

Bi0·.5Na0·.5TiO3 (BNT)-based lead-free dielectric materials have attracted extensive research in environment-friendly ferroelectrics due to their high dielectric constant and negligible remanent polarisation. In accordance with previous reports, although BNT-based ceramics obtain large recoverable energy storage density (Wrec > 3 J/cm3), they are commonly accompanied with high dielectric breakdown strength (Eb ≥ 200 kV/cm), which is unfavourable to the practical application of dielectric capacitors. In this study, novel (1-x)Bi0·5Na0·5TiO3-xSr0.7Nd0.2TiO3 (BNT-xSNT) materials were designed and fabricated. The introduction of Sr0.7Nd0.2TiO3 decreases the grain size and induces the polar nano regions. An outstanding recoverable energy storage density (Wrec = 3.09 J/cm3) with medium efficiency (η = 77%) is obtained at 182 kV/cm for 0.7BNT–0.3SNT ceramics. Good temperature stability (25–160 °C) and excellent frequency stability (5–200 Hz) are realised at 100 kV/cm. This research provides a promising energy storage ceramic material for pulsed power system applications and serves as reference for the integration and miniaturisation of electronic devices.

Pb-free relaxor ferroelectric materials are attractive because of their fast charge–discharge capability and environmental safety. Here, a series of new-type Pb-free ferroelectric ceramics are designed and fabricated: (1 - x)Bi0.47Na0.47Ba0.06TiO3-xCaHfO3 (abbreviated as BNBT-100xCH). Through the modification of Ca2+/Hf4+ at A/B sites, a wider optical band gap and submicron grains are obtained, and the polar nano regions are induced in the structure. Therefore, an optimal Wrec of 4.2 J/cm3 is obtained for the BNBT-12CH ceramic under 280 kV/cm. In addition, the BNBT-12CH ceramic displays better energy-storage characteristics at high temperatures within the test range of 25–140 °C. All of these features indicate that the modification of BNT-based ceramics by Ca2+/Hf4+ has a significant effect on energy-storage density. This work also offers a novel guidance for the development and application of Hf element.

xSr0.7Ce0.2TiO3–(1 − x)Sr(Mg1/3Nb2/3)O3 ceramics, referred to xSCT–(1 − x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO2, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm−1 splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (e r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm−1 for FWHM of A1g mode Raman peaks suggests to a lower Q × f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450 °C for 4 h illustrates excellent microwave dielectric properties with e r ~ 35.4, Q × f ~ 11282 GHz and τ f ~ 1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.

A series of microwave dielectric ceramics of (1-x) BiVO4 -xLn2/3MoO4 (Ln = Er, Sm, Nd and La; x = 0.06, 0.08, 0.10) sintered below 900 °C were prepared via solid-state reaction. As the x values increase, the monoclinic scheelite continuously changes to a tetragonal structure at x = 0.10. The incorporation of Ln2/3MoO4 into the BiVO4 matrix increases the product (Q × f) of quality factor (Q) and resonance frequency (f), and temperature coefficient (τ f ), but lowers the dielectric constant (e r). Microwave dielectric ceramics with low sintering temperatures (

A novel microwave dielectric ceramics Bi(Sc1/3Mo2/3)O4 with low firing temperature were prepared via the solid reaction method. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and DC conductivity. The Bi(Sc1/3Mo2/3)O4 ceramics showed B-site ordered Scheelite-type structure with space group C2/c. Raman analysis indicated that prominent bands were attributed to the normal modes of vibration of MoO4 2− tetrahedra. The dielectric loss of Bi(Sc1/3Mo2/3)O4 ceramics can be depended strongly the bulk conductivity by DC measurement. The superior microwave dielectric properties are achieved in the Bi(Sc1/3Mo2/3)O4 ceramic sintered at 875 °C/4 h, with dielectric constant ~ 25, Q × f ~ 51,716 GHz at 6.4522 GHz and temperature coefficient of resonance frequency ~ − 70.4 ppm/°C. It is a promising microwave dielectric material for low-temperature co-fired ceramics technology.

By adding a small amount of calcium to the starting composition, Li0.36Nd0.36Bi0.14Na0.14TiO3, oxygen vacancies are suppressed and, therefore, the microwave properties are enhanced. This study not only obtained a kind of ceramic with excellent microwave dielectric properties, e r ∼ 160, Q × f ∼ 1300 GHz and τ f ∼ 10 ppm/°C, but also gives a way to optimize the compositions with various donor and acceptor dopants for better performance in microwave ceramics.

Phase compositions, microstructures and microwave dielectric properties of the MgTiO3 and Mgn+1TinO3n+1 (1 ≤ n ≤ 7, 50) specimens prepared via the conventional solid-state reaction route were investigated. X-ray patterns revealed that a certain amount of the Mgn+1TinO3n+1 phases were detected in the specimens with n = 2–5. Additionally, a visualization of the MgTiO3, Mg2TiO4 unit cell and the considered Mg-Ti-O layered supercells were described, and the layered rhombohedral Mg-Ti-O phases were supposed to make the crystal structure more stable. Both EDS and Raman spectrum analysis results proved that the Mgn+1TinO3n+1 (2 ≤ n ≤ 5) phases indeed existed in the present systems. Besides, the Q×f value was extremely sensitive to the analogical layered phases content and compactness. A relative higher content of Mgn+1TinO3n+1 (2 ≤ n ≤ 5) phases and a well-developed microstructure could cause an extremely low dielectric loss in these ceramic systems. Moreover, some very high Q×f values (>300,000 GHz) could also be achieved for the Mgn+1TinO3n+1 (n = 6, 7) systems as well. Thus, the Mgn+1TinO3n+1 ceramic systems were expected to substitute for conventional MgTiO3 or Mg2TiO4 systems to form some novel microwave dielectric materials with the ultralow dielectric loss.

The structure of the ferroelectrics has been widely studied in order to pursuing the origin of high electromechanical responses. However, some experiments on structure of ferroelectrics have yielded different results. Here, we report that the controversial phase structure is due to the adaptive diffraction of nanodomains which hides the natural crystal structure, and the electric-field-induced phase transition is that the natural crystal structure reappears due to the coalescent nanodomains or ordering nanodomains by applying a high electric field. The temperature dependence of dielectric constant with different measurement frequencies and X-ray diffraction (XRD) patterns of unpoled, poled, and annealing after poled ceramics in Bi0.5Na0.5TiO3–BaTiO3 (BNT–BT) ceramics authenticate the statement. These results provide a new insight into the origin of structural complexity in ferroelectric ceramics, which is related to the key role of nanodomains.

The effect of thermal and electrical histories on structure and dielectric behaviors is studied using 0.95(Bi0.5Na0.5)0.97(Li0.5Nd0.5)0.03TiO3-0.05BaTiO3 (abbreviated as BNTLN0.03-BT5) ceramic as a selected system. Subtle structure change caused by annealing treatment, and pronounced phase transition and domain switching by electrical poling, are observed to occur, respectively. The dielectric constant and its strong frequency dispersion in unpoled samples decrease evidently by electrical poling due to electric field-induced ordered domain. The high temperature Maxwell-Wagner relaxor behavior vanishes by annealing treatment due to the loss of electrical inhomogeneity with interface charging effects. Piezoelectric properties are improved evidently by annealing treatment at 900 °C, implying a new appropriate method to improve piezoelectric properties.

Microwave dielectric ceramics (Ce1−x Bi x )0.2Sr0.7TiO3 (x = 0–0.08) were prepared by conventional solid-state route. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman and impedance spectroscopy techniques. A single perovskite solid solution with cubic structure can be formed over the entire range of x value. Raman analysis discovers that first-order modes are activated by polar defects. With increasing substitution of Bi3+ for Ce3+ ions from x = 0–0.08, the dielectric constant can be improved from 158 to 200 and the product (Q × f) of quality factor (Q) and response frequency (f) decreases from 9531 to 1751 GHz, while the temperature coefficient of resonant frequency increases slightly from 500 to 620 ppm/°C. The impedance analysis revealed that the (Ce1−x Bi x )0.2Sr0.7TiO3 ceramics illustrate electrical heterostructure, which includes grains, grain-layers and grain-boundaries. The mechanism of such electrical heterostructure associated with charge compensation is induced by Bi volatilization at elevated temperature. The presence of the heterogeneous microstructure can deteriorate seriously the Q × f value duo to Bi3+ volatilization at higher sintering temperature. An excellent microwave dielectric properties with dielectric constant ~200, modest Q × f value ~1751 GHz and relatively low temperature coefficient of resonant frequency ~621 ppm/°C can be obtained for the (Ce1−x Bi x )0.2Sr0.7TiO3 with Bi content of x = 0.08, compared with that of (Sr, Ca) TiO3 high-dielectric microwave ceramics. This system will provide a new insight for the fabrication of high-dielectric microwave devices.

Effect of Zn addition on microstructure, electrical properties and temperature stability and sensitivity of piezoelectric properties for 0.7Bi1-xZnxFeO3 −0.3BaTiO3 (abbreviated as BZxF–BT) ceramics was investigated. The improved piezoelectric properties, high-temperature stability and high-temperature sensitivity by in situ and ex situ measuring were obtained by moderate Zn addition. It was demonstrated that the enhancement piezoelectric properties can be attributed to poling induced texturization degree of ferroelectric domains and increased rhombohedral structural distortions. It was proposed that the depoling temperature where the induced small signal piezoelectricity disappears stemmed from the detexturization of preferred orientation domains. The improved piezoelectric responses and high-temperature sensitivity could be attributed to the thermally activated preferred orientation domains. The good piezoelectric properties together with high-temperature stability suggest that BZxF–BT system is a promising material for high temperature piezoelectric applications.

Microwave dielectric ceramics of xLi1/2Ln1/2TiO3-(1-x)Na1/2Bi1/2TiO3 (Ln = Sm, 0.62 ≤ x ≤ 0.68 and Ln = Nd, 0.70 ≤ x ≤ 0.76) were prepared through a conventional solid-state reaction. X-ray diffraction analysis combined with Raman spectra indicated that the matrix phase was a continuous solid solution. The 0.64 Li1/2Sm1/2TiO3-0.36Na1/2Bi1/2TiO3 ceramic showed a very high er of 140.6, a reasonable Q·f values of 1808 Ghz, and a near-zero τf of 5.9 ppm/°C. The 0.72Li1/2Nd1/2TiO3-0.28Na1/2Bi1/2TiO3 ceramic exhibited dielectric properties of er = 151.4, Q·f = 775 Ghz and τf = 10.4 ppm/°C. As the content of Na1/2Bi1/2TiO3 continuously increased, more oxygen vacancies were generated during sample processing, resulting in a higher value of resistance.