Enhanced energy storage performance in Na(1-3x)BixNb0.85Ta0.15O3 relaxor ferroelectric ceramics

High-performance lead-free dielectric containers have excellent energy storage performance such as higher power density and energy density. While being eco-friendly materials, lead-free dielectric materials are more suitable for pulse power systems than other dielectric materials. In this study, Ta⁵⁺and Bi³⁺ ions were introduced into the A site and B site of the NaNbO₃ matrix. The introduction of Bi³⁺ ions induced the formation of a vacancy in the A site, yielding Na_(1-3x)Bi_xNb_0.85Ta_0.15O₃ (NBNT, x = 0.05, 0.08, 0.11, 0.14) ceramics. The recoverable energy density (W_rec) and the energy storage efficiency (η) were highest for the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic, with values of 3.37 J/cm³ and 89% respectively. Batteries employing the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic achieved a current density of 830.4 A/cm², an energy density of 49.8 MW/cm³ and 60.2 ns discharge time. These results show that the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic is an effective energy storage material with broad application prospects.     

Synthesis of (Sr0.85Zn0.15)3(PO4)2:Eu by a modified solid-state reaction and its luminescent properties for ultraviolet light emitting diodes

Using urea, boric acid and polyethylene glycol (PEG) as auxiliary reagents, the novel red emitting phosphors (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ have been successfully synthesized by a modified solid-state reaction. The material has potential application as a fluorescent material for ultraviolet light-emitting diodes (UV-LEDs). The dependence of the properties of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ phosphors upon urea, boric acid and the PEG concentration and the quadric sintered temperature were investigated. The crystallization and particle sizes of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Luminescent measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a red light with a peak wavelength of 616 nm. The results show that the boric acid, urea and the PEG were effective in improving the fluorescent intensity of (Sr_0.85Zn_0.15)₃(PO₄)₂:Eu³⁺ and the optimum molar ratio was 0.1, 8 and 0.021, respectively.     

Piezoelectric properties of Ca-modified Pb0.6Bi0.4(Ti0.75Zn0.15Fe0.10)O3 ceramics

Perovskite-structured Pb_0.6Bi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃ ceramics was reported with high Curie temperature T_C of 705 °C and tetragonality of c/a = 1.10, promising for high temperature applications with large piezoelectric anisotropy. In this paper, it was experimentally demonstrated to ease poling processing and enhance piezoelectricity through substituting lead with calcium of Pb_0.6?xCa_xBi_0.4(Ti_0.75Zn_0.15Fe_0.1)O₃. For the x = 0.18 sample, electromechanical coupling factor ratio of k_t/k_p → ∞, dielectric constant of 380, piezoelectric coefficient d₃₃ of 80 pC/N, mechanical quality factor Q_m of 50 and Curie point T_C of 237 °C were obtained, which exhibits better piezoelectric performance than the (Pb_0.76Ca_0.24)(Ti_0.96(Co_0.5W_0.5)_0.04)O₃. The enhanced piezoelectric response was analyzed with relation to the reduction of tetragonality and Curie temperature.     

Microwave dielectric properties of Ca1.15RE0.85Al0.85Ti0.15O4 (RE=Nd,La, Y) ceramics prepared by the reaction sintering method

Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics were prepared by a reaction sintering method. The sintering behavior, phase composition, microstructure and microwave dielectric performances of ceramics were investigated. X-ray diffraction patterns illustrated that both the Ca_1.15Nd_0.85Al_0.85Ti_0.15O₄(CNAT) and Ca_1.15Y_0.85Al_0.85Ti_0.15O₄(CYAT) ceramics are single-phase structures, and the Ca_1.15La_0.85Al_0.85Ti_0.15O₄(CLAT) ceramic contain LaAlO₃ and CaO phases. The apparent morphology and elemental distribution of the ceramic samples were analyzed by using scanning electron microscope and energy dispersive spectrometer. When the sintering temperature is 1500 °C, the CNAT and CYAT ceramics have the best microwave dielectric properties with ε_r = 19.2, Q × f = 74924 GHz, τ_f = ?1.21 ppm/°C and ε_r = 17.5, Q × f = 27440 GHz, τ_f = ?5.79 ppm/°C, respectively. And the best microwave dielectric properties of ε_r = 17.5, Q × f = 22568 GHz, τ_f = ?14.69 ppm/°C were obtained for the CLAT ceramic sintered at 1525 °C. The reaction sintering method provides a low-cost, economical and straightforward method for the preparation of the Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics, which has promising potential for application.     

High-temperature conductivity,stability and redox properties of Fe3−xAlxO4 spinel-type materials

Iron-based oxides are considered as promising consumable anode materials for high temperature pyroelectrolysis. Phase relationships, redox stability and electrical conductivity of Fe_3?xAl_xO₄ spinels were studied at 300–1773 K and p(O₂) from 10^?5 to 0.21 atm. Thermogravimetry/XRD analysis revealed metastability of the sintered ceramics at 300–1300 K. Low tolerance against oxidation leads to dimensional changes of ceramics upon thermal cycling. Activation energies of the total conductivity corresponded to the range of 16–26 kJ/mol at 1450–1773 K in Ar atmosphere. At 1573–1773 K and p(O₂) ranging from 10^?5 to 0.03 atm, the total conductivity of Fe_3?xAl_xO₄ is nearly independent of the oxygen partial pressure. The conductivity values of Fe_3?xAl_xO₄ (0.1 ≤ x ≤ 0.4) at 1773 K and p(O₂) ～10^?5 to 10^?4 atm were found to be only 1.1–1.5 times lower than for Fe₃O₄, showing high potential of moderate aluminium additions as a strategy for improvement of refractoriness for magnetite without significant deterioration of electronic transport.     

The electrical properties of (Ba,Ca, Ce,Ti, Zr)O3 thermistor for wide-temperature sensor architecture

A series of new negative temperature coefficient (NTC) thermal materials based on (Ba_0.85Ca_0.15)_1-xCe_x/2(Zr_0.1Ti_0.9)O₃ (0.00 ≤ x ≤ 0.20) ceramics were synthesized by a solid-state method. X-ray diffraction, scanning electron microscope and X-ray photoelectron spectroscopy were used to demonstrate the crystal structure, morphology, and composition of the (Ba_0.85Ca_0.15)_1-xCe_x/2(Zr_0.1Ti_0.9)O₃ ceramics, which were composed of solid solution based on the BaTiO₃ phase. The average grain size of doped ceramic samples experienced the process of first decreasing and then increasing. The doping of Ce has reduced the sintering temperature. The temperature-dependent resistance analysis revealed that with the change of doping amount x, the thermal constant B_300/1200 (1.21 × 10⁴–1.13 × 10⁴ K) and the activation energy E_a300/1200 (0.9777–1.0471eV) was initially increased to maximum values at x = 0.05, followed by the decreasing when x > 0.05. It has been established that the concentration of oxygen vacancies is affected by the transition between Ce⁴⁺ and Ce³⁺ provided by high levels of Ce doping. (Ba_0.85Ca_0.15)_1-xCe_x/2(Zr_0.1Ti_0.9)O₃ ceramics exhibited excellent negative temperature characteristics in the range of 300–1200 °C. Moreover, the temperature resistance linearity was improved after samples were aged. Hence, the (Ba_0.85Ca_0.15)_1-xCe_x/2(Zr_0.1Ti_0.9)O₃ ceramics were regarded as a promising material for high-temperature NTC thermistors in a wide temperature range.     

Increase ionic conductivity of a Zn2+/F− synergy Na3Zr2Si2PO12 solid electrolyte for sodium metal batteries

Na₃Zr₂Si₂PO₁₂ (NZSP) solid-state electrolyte is considered one of the most promising solid-state electrolyte because of their excellent electrochemical and thermal stability. Even though, the low conductivity of NZSP solid-state electrolytes hinders practical application. Therefore, an anions/cations co-assisting strategy is proposed by introducing the Zn²⁺ and F⁻. The influence of adding different amounts of Zn²⁺ and F⁻ on the Na⁺ conductivity of NZSP was investigated computationally and experimentally. The Zn²⁺/F⁻ co-assisting (Na_3.3Zr_1.85Zn_0.15Si₂PO₁₂) solid-state electrolyte exhibits the ionic conductivity of 0.722 mS cm⁻¹ at 30 °C, and the activation energy of ∼0.237 eV. Its applicability in a solid-state battery is tested, and the assembled Na/Na₃V₂(PO₄)₃ (NVP) battery exhibits an outstanding electrochemical performance of 98.4% capacity retention after being cycled at 0.5 C. Moreover, DFT calculations also have been used to demonstrate the effect of doping on the crystal structure and space migration energy barrier. This research provides new ideas for improving the electrochemical properties of inorganic solid electrolytes.     

Impedance spectroscopy analysis of Pb5Al3F19

The ac conductivity of Pb₅Al₃F₁₉ between 293 and 743 K has been analyzed within a combined complex impedance, modulus and permittivity formalism. The antiferroelectric phase IV to ferroelastic phase III, and the phase III to paraelastic phase II, transitions have been characterized; the latter is shown to be accompanied by higher F⁻ ion mobility above T=368±5 K. A new dielectric anomaly observed iso-chronously in ε′ (f,T) at 670 K corresponds to an expected, but hitherto unobserved, transition from phase II to the paraelectric prototype phase I of Pb₅Al₃F₁₉.     

Synthesis and coloring properties of novel stablized green Ni0.15MgxAl2(0.85-x)Ti1.15+xO5 pigments

Novel stablized green Ni_0.15Mg_xAl_2(0.85-x)Ti_1.15+xO₅ (0 ≤ x ≤ 0.25) pigments were prepared by solid-state method using Ni₂O₃ as colorant and Mg(CH₃COO)₂‧4H₂O as auxiliary stabilizer. The synthesised pigments were characterized via XRD, XPS, SEM, TEM, UV-Vis, and automatic colorimeters. The results show that Mg-doping increases the oxygen vacancies, resulting in a positive shift of the binding energy of Ni²⁺ irons. The formation of Ni_0.15Mg_xAl_2(0.85-x)Ti_1.15+xO₅ solid solution greatly increases the energy transfer energy and shifts the emission to lower wavelengths (530 nm), corresponding to the visible diffuse reflection of green light. The chromaticity of the pigment changed little (L*=72.51, a*=−18.16, b*=20.94) at 1200 ℃ for 10 h, showing excellent thermal stability. The properties especially excellent thermal stability makes it promising novel green pigments in ceramic industry application.     

High-Qf value and temperature stable Zn2+-Mn4+ cooperated modified cordierite-based microwave and millimeter-wave dielectric ceramics

Cordierite-based dielectric ceramics with a lower dielectric constant would have significant application potential as dielectric resonator and filter materials for future ultra-low-latency 5G/6G millimeter-wave and terahertz communication. In this article, the phase structure, microstructure and microwave dielectric properties of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ (0 ≤ x ≤ 0.3) ceramics are studied by crystal structure refinement, scanning electron microscope (SEM), the theory of complex chemical bonds and infrared reflectance spectrum. Meanwhile, complex double-ions coordinated substitution and two-phase complex methods were used to improve its Q×f value and adjust its temperature coefficient. The Q×f values of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ single-phase ceramics are increased from 45,000 GHz@14.7 GHz (x = 0) to 150,500 GHz@14.5 GHz (x = 0.15) by replacing Al³⁺ with Zn²⁺-Mn⁴⁺. The positive frequency temperature coefficient additive TiO₂ is used to prepare the temperature stable Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ composite ceramic. The composite ceramic of Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ (8.7 wt% ≤ y ≤ 10.6 wt%) presents the near-zero frequency temperature coefficient at 1225 °C sintering temperature: ε_r = 5.68, Q×f = 58,040 GHz, τ_f = ?3.1 ppm/°C (y = 8.7 wt%) and ε_r = 5.82, Q×f = 47,020 GHz, τ_f = +2.4 ppm/°C (y = 10.6 wt%). These findings demonstrate promising application prospects for 5 G and future microwave and millimeter-wave wireless communication technologies.     

Hydrothermal synthesis and sintering of electroceramics

The hydrothermal processing of ultrafine Pb_1·88(Zn_0·3Nb_1·25)O_5·305 and Ba(Mg_0·33Nb_0·67)O₃ powders as well as their sintering behavior at 1000°C were investigated. The morphological analyses on nanometric powders indicated the presence of mesopores in micrometric agglomerates with open cylindrical pores. High dielectric constants were observed, showing normal frequency dispersion and an intrinsic ac relaxation, relatively masked by low frequency conductivity. The sintered ceramics presented lower dielectric permittivities than the hydrothermal powders, and a classical Cole–Cole plot could be obtained for the Pb_1·88(Zn_0·3Nb_1·25)O_5·305 electroceramic for frequencies above 10³ Hz.     

Microwave dielectric properties of Ca1.15Sm0.85Al0.85Ti0.15O4 ceramics prepared by reaction sintering

In the present work, a high quality (Q) Ca_1.15Sm_0.85Al_0.85Ti_0.15O₄ (CSAT) ceramic was prepared via reaction sintering (RS) method. The phase structure, surface morphology, packing fraction (PF), and valence bond of the ceramic were systematically investigated. By studying the X-ray diffraction (XRD) pattern of the ceramic, it was determined to exhibit a single-phase tetragonal structure with the dimensions of a = b = 3.6943(13)Å and c = 12.0320(23)Å and volume of V = 164.22(10) ų. The influence of the intrinsic quality loss factor on the Q × f value was investigated by calculating the PF. Simultaneously, the bond valence of the samarium (Sm) sites was evaluated to elucidate the relationship with the temperature coefficient of resonant frequency (τ_f). The CSAT ceramic was sintered at 1550 °C for 6 h and exhibited exceptional characteristics in terms of the relative dielectric constant (ε_r) = 17.5, quality factor (Q × f) = 66700 GHz, and τ_f = ?6.93 ppm/^°C. These results highlighted the excellent suitability of the RS method for preparing CSAT ceramics with outstanding microwave dielectric properties.     

Enhanced energy storage performance and thermal stability in relaxor ferroelectric (1-x)BiFeO3-x(0.85BaTiO3-0.15Bi(Sn0.5Zn0.5)O3) ceramics

Lead-free (1-x)BiFeO₃-x(0.85BaTiO₃-0.15Bi(Sn_0.5Zn_0.5)O₃) [(1-x)BF-x(BT-BSZ), x=0.45-0.7] ceramic samples were prepared by solid phase sintering. It is revealed that the pure single-phase perovskite structure can be obtained in samples with x ≥ 0.6. With increasing x, the measured ferroelectric hysteresis loop becomes gradually slimmed in accompanying with reduced remnant polarization, and a clear ferroelectric-relaxor transition at x = 0.65 is identified. Furthermore, the measured electric breakdown strength can be significantly enhanced with increasing x, and the optimal energy storage performance is achieved at x = 0.65, characterized by the recoverable energy storage density up to ≈3.06 J/cm³ and energy storage efficiency as high as ≈92 %. Excellent temperature stability (25°C–110°C) and fatigue endurance (>10⁵ cycles) for energy storage are demonstrated. Our results suggest that the BF-based relaxor ceramics can be tailored for promising applications in high energy storage devices.     

Electronic transition,ferroelectric and thermoelectric properties of bismuth pyrostannate Bi2(Sn0.85Cr0.15)2O7

The ferroelectric properties of bismuth pyrostannate Bi₂(Sn_0.85Cr_0.15)₂O₇ in the high-temperature region are established. The linear thermal expansion coefficient, electrical resistance, impedance, I?V characteristics, capacitance, loss-angle tangent, charge, and thermopower of the investigated material are measured in the temperature range of 300?700 K at frequencies of 10²?10⁶ Hz. Anomalies of the thermal expansion coefficient and hodograph spectrum variation in the region of polymorphic phase transitions are observed. The high resistance and change of the hopping conductivity for the tunnel-emission are found. The hysteresis in the electric field dependence of polarization is established. The change in the thermopower sign with temperature is revealed. The obtained experimental data are explained in the framework of the model of migration polarization by charged chromium ions.     

Synergetic tuning of electrical/thermal transport via dual-doping in Bi0.96−xMgxPb0.06CuSeO

The layered oxyselenides BiCuSeO was recently discovered as potential thermoelectric. Our result reveals that the substitute for atom Bi³⁺ by Pb²⁺ & Mg²⁺ in (Bi₂O₂)²⁻ play an important role in electrical transport properties. The maximum electrical conductivity obtained is 460 Scm⁻¹ for Bi_0.84Mg_0.10Pb_0.06CuSeO at RT, highly above the 15 Sm⁻¹ for BiCuSeO. In synergy with low thermal conductivity (0.6-0.4 Wm⁻¹ K⁻¹) and large thermopower (300-500 μVK⁻¹), the highest ZT is achieved about 0.80 at 873 K for Bi_0.88Mg_0.06Pb_0.06CuSeO.     

Dielectric Tunability,Dielectric Relaxation,and Impedance Spectroscopic Studies on (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 Lead‐Free Ceramics

Dielectric and impedance spectroscopies were employed to study the electrical behavior of (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (abbr. BCTZ) lead‐free ceramic. The dielectric properties versus dc bias electric field experiment revealed high dielectric tunability (> 65%) as well as figure of merit (> 27) at 10 kHz and room temperature. At elevated temperature range, a dielectric loss peak was observed and verified to be correlate of oxygen vacancy relaxation. The impedance spectra studies indicate that the ceramic is a mixed ionic conductor of p‐type nature at the paraelectric phase and, the grain and total conductivity at 600°C reaches 6.0 × 10^?5 and 2.0 × 10^?5 S/cm, respectively.     

Utilization of Ag ions to improve room-temperature TCR of La0.85-xSr0.15AgxMnO3 polycrystalline ceramics

In this work, silver-doped La_0.85-xSr_0.15Ag_xMnO₃ (LSAMO, 0.05 ≤ x ≤ 0.20) polycrystalline ceramics were prepared by the sol-gel method. The experimental characterization of ceramics revealed that Ag ions were bounded with the lattice matrix. The resistivity and the corresponding peak temperature coefficient (TCR) of LSAMO ceramics were systematically tuned by changing the Ag dopant content. Adjusting the proportion of Ag enabled one to vary the metal-insulator transition temperature (T_MI) for LSAMO specimens in a wide range, and their peak resistivity temperature (T_p) was increased from 299.6 to 335.7 K. At the same time, the peak TCR value achieved its maximum of 15.2% K^?1 at the doping molar ratio x of 0.15 and the peak resistivity temperature (T_k) of 294.1 K. In addition, the electrical transport was described in the context of the small polaron hopping (SPH) model and the phenomenological percolation model (PP) over the metal-insulator transition region. Under the combined action of the Jahn-Teller (JT) effect, the double exchange (DE) mechanism and the PP model, LSAMO ceramics possessing high TCR at room temperature were obtained by varying the amount of Ag doping. The observed properties suggest LSAMO material can be used in advanced uncooled infrared bolometers.     

Enhanced thermoelectric properties of CNT dispersed and Na-doped Bi2Ba2Co2Oy composites

The thermoelectric properties of Bi₂Ba₂Co₂O_y and Bi_1.975Na_0.025Ba₂Co₂O_y+x wt% carbon nanotubes (CNT; x=0.00, 0.05, 0.10, 0.15, 0.5, and 1.0) ceramic samples synthesised by the solid-state reaction method were investigated from 300K to 950K. Na doping with a small amount played an important role in reducing resistivity and slightly reduced the Seebeck coefficients and the thermal conductivity. The CNT dispersant increased resistivity, but the thermal conductivity was reduced remarkably. In particular, the Bi_1.975Na_0.025Ba₂Co₂O_y+1.0wt% CNT sample exhibited an ultralow thermal conductivity of 0.39 W K⁻¹ m⁻¹ at 923K. This was attributed to the point defects caused by Na doping and the interface scattering caused by the CNT dispersant. The combination of Na doping and CNT dispersion had better effects on thermoelectric properties. The Bi_1.975Na_0.025Ba₂Co₂O_y+0.5wt% CNT sample exhibited a better dimensionless figure of merit (ZT) value of 0.2 at 923K, which was improved by 78.2%, compared with the undoped Bi₂Ba₂Co₂O_y sample.     

Ultrahigh energy storage density in Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics by introducing a relaxor end-member

Dielectric ceramics with relaxor characteristics are promising candidates to meet the demand for capacitors in next-generation pulse devices. In this work, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT)-based lead-free ceramics with an ultrahigh recoverable energy storage density (W_rec) were designed and fabricated by introducing the relaxor end-member of Bi(Zn_2/3Ta_1/3)O₃ (BZT). The addition of BZT disrupted the ferroelectric (FE) long-range order and triggered an FE-to-relaxor FE (RFE) phase, leading to the formation of locally polar nano-regions (PNRs) and significantly inhibiting grain growth. Meanwhile, the presence of PNRs with good thermal stability improved the temperature stability of both the dielectric constant (ε') and W_rec. More importantly, the breakdown electric field strength was significantly improved up to ∼640 kV/cm, resulting in an ultrahigh W_rec of ∼7.11 J/cm³ for the 8%BZT doped BCZT (BCZT-BZT8) ceramic. Furthermore, the BCZT-BZT8 ceramic exhibited excellent charge/discharge performances (C_D ∼ 458.4 A/cm², P_D ∼ 50.4 MW/cm³, W_D ∼ 1.354 J/cm³, t_0.9 ∼ 320 ns) with good thermal stability in the temperature range of 298–373 K. The defect chemistry of the BCZT-BZT8 was explored using electron paramagnetic resonance (EPR) spectroscopy which revealed an EPR signal (g ∼ 1.955), associated with oxygen vacancies. The above findings indicate that the novel composition of BCZT-BZT8 has great prospects in energy storage capacitor applications.     

Enhanced energy storage and discharge-charge performance by changing glass phase content in potassium sodium niobate glass-ceramics

(1-x) (K₂O–Na₂O–2Nb₂O₅)-x (2BaO–Nb₂O₅–2SiO₂) glass-ceramics with x = 0.10, 0.15, 0.20, 0.25 have been successfully prepared by traditional melting method. XRD and microstructure analysis demonstrate that all glass-ceramics are crystallized into uniform Na_0.9K_0.1NbO₃ and K₂(NbO)₂(Si₄O₁₂) ferroelectric crystalline phase. Increasing x promotes the formation of Ba₂NaNb₅O₁₅ phase with a tungsten bronze structure. Raman and complex impedance data confirmed that Ba²⁺ is introduced to repair the disruption of the glass network and make carrier migration difficult when x = 0.15. Thus, the x = 0.15 glass-ceramic sample possesses a maximum calculated energy storage density of 2.32 J/cm³ under 820 kV/cm because of a high degree of polymerization (DOP) glass network structure. Moreover, the pulsed discharge-charge tests are carried out to evaluate actual energy storage performance.