Enhanced electrocaloric effect and energy-storage performance in PBLZT films with various Ba2+ content

(100)-oriented Pb_(0.90−x)Ba_xLa_0.10Zr_0.90Ti_0.10O₃ (x=0, 0.02, 0.05 and 0.11) antiferroelectric thick films were deposited on LaNiO₃/Si (100) substrates by the sol-gel process. The influences of Ba²⁺ content on the dielectric properties, electrocaloric effect (ECE), energy-storage performance and leakage current were systematically investigated. With Ba²⁺ content increasing, the temperature (T_m) corresponding to the maximum dielectric constant of the thick films was decreased, while their diffuseness was increased. The maximum ECE ∆T=18.1 °C was obtained in the thick film with x=0.05 at room temperature under ∆E=700 kV/cm. The maximum energy storage density of 42.3 J/cm³ and the corresponding efficiency of 68% was achieved in the film with x=0.11, companied by a power density of 0.53 MW/cm³, due to its high breakdown strength. In addition, a small leakage current density (<10⁻⁵ A/cm²) were attained in these films at room temperature. In conclusion, we believe that this kind of antiferroelctric thick film is a potential candidate for applications in solid cooling devices and the energy-storage systems.     

Effects of Mn doping on dielectric properties and energy-storage performance of Na0.5Bi0.5TiO3 thick films

Lead-free Na_0.5Bi_0.5Ti_1−xMn_xO₃ (NBTMn_x, x=0, 0.01, 0.03 and 0.05) ferroelectric thick films have been fabricated on LaNiO₃/Si(100) substrate by using a polyvinylpyrrolidone-modified sol-gel method and the effects of Mn content on their microstructure, dielectric properties and energy-storage performance were investigated. Compared with the pure Na_0.5Bi_0.5TiO₃ (NBT) thick films, NBTMn_x thick films exhibited a large enhancement in dielectric properties and energy-storage performance. Particularly, a giant recoverable energy-storage density (W) of 30.2 J/cm³ and the corresponding efficiency (η) of 47.7% were obtained in NBTMn_0.01 thick film at 2310 kV/cm. Moreover, the NBTMn_0.01 thick film displayed good energy-storage stability over a large temperature range at different frequency.     

Effects of Sr substitution for Ba on dielectric and energy-storage properties of SrO-BaO-K2O-Nb2O5-SiO2 glass-ceramics

In this work, [xSrO, (1 − x)BaO]-K₂O -Nb₂O₅-SiO₂ (SBKNS, x = 0.2, 0.4, 0.6, 0.8) glass-ceramics were synthesized through the controlled crystallization method. The phase structure, dielectric and energy-storage properties were systematically studied through the Sr substitution for Ba. It was found that the dielectric properties were improved due to the formation of solid liquid phase Sr_0.5Ba_0.5Nb₂O₆. Breakdown strength firstly increases and then decreases, which strongly depends on the variation in interfacial polarization. The highest value of breakdown strength reaches 1828 ± 88 kV/cm for x = 0.4, which is attributed to more uniform and dense microstructure and lower interfacial polarization. Correspondingly, the optimized theoretical energy-storage density reaches up to 17.45 ± 0.74 J/cm³. The maximum of discharged energy-storage density of 1.45 J/cm³ from P-E loop was acquired under electric field of 500 kV/cm. Moreover, discharged power density of the capacitor was evaluated and reached a high value of 1.76 MV/cm³ in pulsed charged-discharged circuit.     

Induced slim ferroelectric hysteresis loops and enhanced energy-storage properties of Mn-doped (Pb0·93La0.07)(Zr0·82Ti0.18)O3 anti-ferroelectric thick films by aerosol deposition

In this study, the high ferroelectric hysteresis loss of (Pb_0·93La_0.07)(Zr_0·82Ti_0.18)O₃ (PLZT 7/82/18) antiferroelectric (AFE) ceramics was reduced by employing a combinatorial approach of Mn acceptor doping followed by thick film fabrication via an aerosol deposition (AD) process. The grains of the as-deposited PLZT 7/82/18 AFE AD thick films were grown by thermal annealing at 550 °C to enhance their electrical properties. Investigation of the electrical properties revealed that Mn-doping results in improved dielectric and ferroelectric properties, increased dielectric breakdown strength (DBS), and energy-storage properties. The Mn-doped PLZT AFE AD films possess a frequency-independent high dielectric constant (ε_r ≈ 660) with low dielectric loss (tan δ ≈ 0.0146), making them suitable candidates for storage capacitor applications. The bipolar and unipolar polarization vs. electric field (P-E) hysteresis loops of PLZT 7/82/18 AFE AD thick films were found to be slimmer than those of their bulk form (double hysteresis) with significantly reduced ferroelectric hysteresis loss, which is attributed to the AD-induced mixed grain structure. The Mn-doped PLZT 7/82/18 AFE AD thick films exhibited a low remnant polarization (P_r ≈ 9.22 μC/cm²) at a high applied electric field (~2750 kV/cm). The energy-storage density and energy efficiency of the Mn-doped PLZT AFE AD thick films were calculated from unipolar P-E hysteresis loops and found to be ~38.33 J/cm³ and ~74%, respectively.     

Enhanced energy storage properties in La(Mg1/2Ti1/2)O3-modified BiFeO3-BaTiO3 lead-free relaxor ferroelectric ceramics within a wide temperature range

A new ternary lead-free (0.67-x)BiFeO₃-0.33BaTiO₃-xLa(Mg_1/2Ti_1/2)O₃ ferroelectric ceramic exhibited an obvious evolution of dielectric relaxation behavior. A significantly enhanced energy-storage property was observed at room temperature, showing a good energy-storage density of 1.66 J/cm³ at 13 kV/mm and a relatively high energy-storage efficiency of 82% at x = 0.06. This was basically ascribed to the formation of a slim polarization-electric field hysteresis loop, in which a high saturated polarization P_max and a rather small remnant polarization P_r were simultaneously obtained. Particularly, its energy storage properties were found to depend weakly on frequency (0.2 Hz–100 Hz), and also to exhibit a good stability against temperature (25 °C–180 °C). The achievement of these characteristics was attributed to both a rapid response of the electric field induced reversible ergodic relaxor to long-range ferroelectric phase transition and a typical diffuse phase transformation process in the dielectric maxima.     

Development of PLZT dielectrics on base metal foils for embedded capacitors

We have deposited Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on nickel and copper substrates to create film-on-foil capacitors that exhibit excellent dielectric properties and superior breakdown strength. Measurements with PLZT films on LaNiO₃-buffered Ni foils yielded the following: relative permittivity of 1300 (at 25 °C) and 1800 (at 150 °C), leakage current density of 6.6 × 10^?9 A/cm² (at 25 °C) and 1.4 × 10^?8 A/cm² (at 150 °C), and mean breakdown field strength ≈2.5 MV/cm. With PLZT deposited directly on Cu foils, we observed dielectric constant ≈1100, dielectric loss (tan δ) ≈0.06, and leakage current density of 7.3 × 10^?9 A/cm² when measured at room temperature.     

Energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-KNbO3 ceramics fabricated by wet-chemical method

0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (BNTBT) and KNbO₃ (KN) powders with average particle size of ∼50 nm and ∼300 nm were synthesized by sol-gel method and hydrothermal method, respectively. Then, (1 − x)(BNTBT)-xKN (BNTBT-KN, x = 0, 0.01, 0.03, 0.05, 0.07) ceramic samples were prepared using these two powder precursors. The structure, dielectric and energy-storage properties of BNTBT-KN ceramics were comprehensively investigated. All the ceramic samples were in single perovskite structure, indicating that KN can completely dissolve into BNTBT within the studied composition range. BNTBT-KN ceramics exhibited a high dielectric constant at room temperature, being in the order of 1430–1550. Ferroelectric hysteresis loops at room temperature became more slim with the increase of KN content, which largely improved energy-storage density and efficiency. For the composition of x = 0.05, the maximum recoverable energy-storage density reached 1.72 J/cm³ under 16.8 kV/mm, which is superior to linear dielectrics and even some Pb-based systems. All these results demonstrate that 0.95BNTBT-0.05KN fabricated by wet-chemical method is a promising lead-free dielectric material for energy-storage capacitors.     

The microstructure,ferroelectric and dielectric behaviors of Na0.5Bi0.5(Ti,Fe)O3 thin films synthesized by chemical solution deposition: Effect of precursor solution concentration

Fe-doped Na_0.5Bi_0.5TiO₃ (NBTFe) thin films were prepared directly on indium tin oxide/glass substrates using a chemical solution deposition method combined with sequential layer annealing. The X-ray diffraction, scanning electron microscopy and insulating/ferroelectric/dielectric measurements were utilized to characterize the NBTFe thin films. All the NBTFe thin films prepared by four precursor solutions with various concentrations of 0.05, 0.10, 0.20 and 0.30 M exhibit polycrystalline perovskite structures with different relative intensities of (l00) peaks. A large remanent polarization (P_r) of 33.90 μC/cm² can be obtained in NBTFe film derived with 0.10 M spin-on solution due to its lower leakage current and larger grain size compared to those of other samples. Also, it shows a relatively symmetric coercive field and large dielectric tunability of 36.34%. Meanwhile, the NBTFe thin film with 0.20 M has a high energy-storage density of 30.15 J/cm³ and efficiency of 61.05%. These results indicate that the electrical performance can be controlled by optimizing the solution molarity.     

CaCu3Ti4O12 ceramics from co-precipitation method: Dielectric properties of pellets and thick films

Dielectric properties of CaCu₃Ti₄O₁₂ (CCTO)-based ceramics and thick films (e ～50 μm) prepared from powders synthesized by a soft chemistry method (co-precipitation) are presented and discussed. The characteristics of pellets and thick films are compared.The pellets exhibit high values of the dielectric permittivity (?_r ～1.4 × 10⁵) and relatively small dielectric losses (tan δ ～0.16) at 1 kHz and room temperature. These properties are independent of the nature of the metallization of the electrodes. In addition, the dielectric permittivity decreases when the diameter of the electrodes of the pellets increases, while the losses remain constant. This result, which is strongly related to the nature of the dielectric material in between the electrodes, constitutes a strong indication that the high dielectric permittivity values observed in this material are not related to an interfacial (electrode material) related mechanism but is an internal barrier layer capacitor (IBLC) type.Very high values of the dielectric permittivity of CCTO thick films are measured (?_r ～5 × 10⁴). The differences in dielectric permittivity between thick films and dense pellets may be attributed to the difference in grain size due to different CuO contents, and to the different reactivity of the materials.     

Dielectric behavior and impedance spectroscopy in lead-free BNT–BT–NBN perovskite ceramics for energy storage

The dielectric behavior, impedance spectroscopy and energy-storage properties of 0.85[(1−x)Bi_0.5Na_0.5TiO₃–xBaTiO₃]–0.15Na_0.73Bi_0.09NbO₃ [(BNT–xBT)–NBN] ternary ceramics were investigated. Temperature dependent permittivity curves displayed two depressed anomalies, resulting in significantly improved dielectric temperature stability. (BNT–9BT)–NBN showed a permittivity of 1680 at 150 °C with Δε/ε_150 °C varying no more than ±10% up to 340 °C. From the complex impedance analysis, grain and grain boundary shared the same time constant. The high temperature resistivity followed the Arrhenius law with E_a=1.7–2.0 eV, suggesting intrinsic band-type electronic conduction. The maximum energy-storage density of all the samples reached 1.1–1.4 J/cm³, accompanied with good temperature stability in the range of 25–140 °C. These results indicate that (BNT–xBT)–NBN system should be a promising lead-free material for energy-storage capacitor applications.     

The effect of annealing on electrical properties of fluorinated amorphous carbon films

Fluorinated amorphous carbon (a–C:F) films have been deposited by electron cyclotron resonance chemical vapor deposition (ECR–CVD) at room temperature using C₄F₈ and CH₄ as precursor gases. The chemical compositions and electrical properties of a–C:F films have been studied by X-ray photoelectron spectroscopy (XPS), capacitance–voltage (C–V) and current-voltage (I–V) measurements. The results show that C–CF_x and C–C species of a–C:F films increase and fluorine content decreases after annealing. The dielectric constant of the annealed a–C:F films increases as a result of enhancement of film density and reduction of electronic polarization. The densities of fixed charges and interface states decrease from 1.6 × 10¹⁰ cm^− 2 and (5–9) × 10¹¹ eV^− 1 cm^− 2 to 3.2 × 10⁹ cm^− 2 and (4–6) × 10¹¹ eV^− 1 cm^− 2 respectively when a–C:F films are annealed at 300 °C. The magnitude of C–V hysteresis decreases due to reduced dangling bonds at the a–C:F/Si interfaces after heat treatment. The conduction of a–C:F films shows ohmic behavior at lower electric fields and is explained by Poole–Frankel (PF) mechanism at higher electric fields. The PF current increases indicative of reduced trap energy when a–C:F films are subjected to higher annealing temperatures.     

High recoverable energy storage density and large piezoelectric response in (Bi0.5Na0.5)TiO3-PbTiO3 thin films prepared by a sol-gel method

Low-lead-content (1-x)(Bi_0.5Na_0.5)TiO₃-xPbTiO₃ (x = 0, 0.05, 0.10, 0.15, 0.25) (hereafter abbreviated as BNT-xPT) thin films were prepared by a sol-gel method, and their crystal structure, dielectric properties, recoverable energy-storage density and piezoelectric response were investigated as a function of PT concentration. Combining the XRD patterns and Raman spectroscopy indicate the phase structures go through rhombohedral (R) – rhombohedral + tetragonal (R + T) – tetragonal (T) evolution with increasing of PT content. A high recoverable energy storage density of 13.02 ± 0.39 J/cm³ was achieved in the BNT-0.10PT thin films due to the high field endurance and significantly enhanced polarizability. Moreover, a superior piezoelectric response (d₃₃^* = 120 ± 5 pm/V) was also obtained in the 10% PT-modified BNT films, which can be attributed to easy polarization rotation due to low polarization anisotropy on the R-T phase boundary. These properties indicate that BNT-0.10PT films might be promising multifunctional materials for piezoelectric micro-actuator and energy storage embedded capacitor applications.     

Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

Preparation and electrical properties of Bi2Zn2/3Nb4/3O7 thin films deposited at room temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited at room temperature on Pt/Ti/SiO₂/Si(1 0 0) and polymer-based copper clad laminate (CCL) substrates by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited in situ with no intentional heating under an oxygen pressure of 4 Pa and then post-annealed at 150 °C for 20 min. It was found that the films are still amorphous in nature, which was confirmed by the XRD analysis. It has been shown that the surface roughness of the substrates has a significant influence on the electrical properties of the dielectric films, especially on the leakage current. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates exhibit superior dielectric characteristics. The dielectric constant and loss tangent are 59.8 and 0.008 at 10 kHz, respectively. Leakage current density is 2.5 × 10^?7 A/cm² at an applied electric field of 400 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on CCL substrates exhibit the dielectric constant of 60 and loss tangent of 0.018, respectively. Leakage current density is less than 1 × 10^?6 A/cm² at 200 kV/cm.     

Low-temperature fabrication of Ba1−xSrxTiO3 thin films with good dielectric properties on platinized silicon substrates

Ba_0.7Sr_0.3TiO₃ (BST) thin films 500 nm in thickness were prepared on technologically desirable Pt/TiO₂/SiO₂/Si(1 0 0) substrates by ion beam sputtering (IBS) and post-deposition annealing method. The effect of annealing temperature on the structural and dielectric properties of BST thin films was systematically investigated. A sharp transition in their tunable dielectric behaviours was observed in good agreement with the evolution of crystal structure from amorphous to crystalline phase. It was demonstrated that the perovskite phase could crystallize in BST films at a very low temperature, around 450 °C. The lowering of perovskite crystallization temperature in the BST films was explained in terms of the high energetic process nature of IBS technique. A high dielectric tunability of 42% at E (electric field intensity) = 500 kV/cm and a low loss tangent of 0.013 at zero bias were both obtained in the 450 °C-annealed film, thereby resulting in the highest figure-of-merit factor among all the different temperature annealed films. Moreover, the 450 °C-annealed film showed superior leakage current characteristics with a low leakage current density of about 10^?4 A/cm² at E = 800 kV/cm.     

Enhanced ferroelectric properties of Ce-substituted BiFeO3 thin films on LaNiO3/Si substrates prepared by sol–gel process

The effects of Ce substitution on the structural and electrical properties of multiferroic BiFeO₃ thin films grown on LaNiO₃/Si(1 0 0) substrates by a sol–gel process have been reported. X-ray diffraction data confirmed the substitutions of Ce into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15%. The dielectric constants of the films increased from 90 to ～260 below 100 kHz with 5% molar Ce substitution and the films showed enhanced dielectric behavior. We observed a substantial increase in the remnant polarization (P_r) with Ce substitution and obtained a maximum value of ～71 μC/cm² by 5% molar Ce incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?6 to 10^?8 A/cm² for 5% molar Ce-substituted films under a field 150 kV/cm. The reduction of dc leakage current of Ce-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.     

X-ray diffraction,dielectric, pyroelectric,piezoelectric and Raman spectroscopy studies on (Ba0.95Ca0.05)0.8875Bi0.075TiO3 ceramic

The (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic composition was prepared using the conventional mixed-oxide technique. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 to 450 K and frequency range from 10² to 2 × 10⁵ Hz, respectively, were studied. The X-ray spectra were investigated by profile refinement technique with the use of specialized software at room temperature, the (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ composition crystallizes in quadratic perovskite structure. The dielectric measurements show classical ferroelectric behavior. The pyroelectric and piezoelectric results confirm the dielectric measurements. The pyroelectric coefficient is about 69.2 nC/cm² K at the transition temperature (T_C = 367 K). The piezoelectric constant is d₃₁ = 31.1 pC/N and the electromechanical coupling factor is k_P = 0.14679. Raman spectra of (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic were taken at various temperatures and measured over the wave number range from 50 to 1000 cm^?1. All the Raman bands were assigned as the transitional modes of Ba²⁺, Ca²⁺, Bi³⁺ and Ti⁴⁺ cations. The temperature evolution of Raman spectra across the transition shows an important evolution characterizing the disorder of the high temperature phase.     

Relaxor behavior and ferroelectric properties of a new Ba4SmFe0.5Nb9.5O30 tungsten bronze ceramic

Unfilled tungsten bronze ceramics with a composition of Ba₄SmFe_0.5Nb_9.5O₃₀ were prepared by the conventional solid-state sintering method. The phase, microstructure, dielectric and ferroelectric properties were studied. Room temperature XRD results indicated that the ceramic occurs in the tetragonal space group P4bm phase with cell parameters of a=b=12.4712(2) Å and c=3.9430(2) Å. The temperature-dependent dielectric properties, XRD data and Raman spectra data indicated that BSFN ceramics exhibit no phase changes from 35 °C to 450 °C. Fitting of a Vogel-Fulcher relationship with an activated energy E_a of 0.11 eV indicates an unambiguous dielectric relaxor state near room temperature. Furthermore, the BSFN ceramics exhibited residual polarization and coercive field of 3.45 µC/cm² and 24.65 kV/cm, respectively.     

Electrohydrodynamic atomization deposition and mechanical polishing of PZT thick films

In this work, electrohydrodynamic atomization deposition, combined with mechanical polishing, was used for the fabrication of dense and even PZT thick films. The PZT slurry was ball-milled and the effect of milling time on the characteristics of the deposited films was examined. A time of 50 h was found to be the optimum milling time to produce dense films. It was found that the PZT thick films presented rough surface after deposition. In order to overcome this drawback the mechanical polishing process was employed on the deposited films. After the mechanical polishing the roughness (Ra) and peak-to-peak height (Rz) of the film surface were decreased from 422 nm to 23 nm and from 5 µm to 150 nm, respectively. Subsequently, an increase of ~10 pC N⁻¹ on piezoelectric constant (d_{33, f}) was obtained. In addition, it was observed that the d₃₃ was increased from 57 pC N⁻¹ to 89 pC N⁻¹ when the thickness was increased from 10 µm to 80 µm.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.