Large recoverable energy density with excellent thermal stability in Mn‐modified NaNbO3‐CaZrO3 lead‐free thin films

Effect of Mn dopant on energy storage properties in lead‐free NaNbO₃?0.04CaZrO₃ (NNCZ) thin films was investigated. The leakage current was largely suppressed, whereas dielectric constant, breakdown fields, and the difference between maximum polarization and remnant polarization were improved significantly by Mn doping, resulting in a large enhancement of energy storage performance. A large recoverable energy storage density of ~19.64 J/cm³ and an excellent thermal stability (from 30 to 160°C) were simultaneously achieved in the NNCZ thin film with 1 mol% Mn addition. Our results ascertain the great potential of NNCZ lead‐free thin films for the applications in energy storage devices over a wide temperature range.     

Improved piezoelectricity and energy storage performance simultaneously achieved in [001]-preferentially oriented Bi0.5Na0.5TiO3–BaTiO3–BiMnO3 thin films grown on Nb-doped SrTiO3 single-crystalline substrates

The control of grain orientation by introducing Nb-doped SrTiO₃ single crystalline substrates is an effective way to improve piezoelectric and ferroelectric properties of thin films. Therefore, in this work, 0.99(0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃)–0.01BiMnO₃ thin films were coated on Pt(111)/TiO_x/SiO₂/Si(001) polycrystalline substrates and Nb-doped SrTiO₃ single crystalline substrates, respectively. The Nb-doped SrTiO₃ single crystalline substrates can affect the orientation of the BNT–BT–0.01BMO thin films, promote the grain growth, reduce the leakage current, and form an interfacial layer between the thin film and the substrate, and a comparatively larger converse piezoelectric coefficient (46.49 pm·V^?1), a high energy storage density (56.5 J cm^-3), and a high energy storage efficiency (79.4 %) were therefore simultaneously achieved in the thin films grown on Nb-doped SrTiO₃ single crystalline substrates, promising the oriented thin films broad application prospects.     

High energy storage density achieved in Bi3+-Li+ co-doped SrTi0.99Mn0.01O3 thin film via ionic pair doping-engineering

The demand for lead-free dielectric capacitors with rapid charge-discharge ability and high energy storage density is increasing owing to the rapid development of electronic equipment. Lead-free Sr_1-x(Bi_0.5Li_0.5)_xTi_0.99Mn_0.01O₃ (x = 0.02, 0.025, 0.03, 0.035) thin films grown on Pt/Ti/SiO₂/Si substrates were prepared by sol-gel method. A huge enhancement in polarization was found in Bi³⁺-Li⁺ co-doped SrTiO₃ thin films. The large lattice distortion and local broken-symmetry due to formation of Bi³⁺-Li⁺ ionic pairs are responsible for ferroelectricity and high polarization. The maximum polarization (42.1 μC/cm²) and largest energy storage density of 47.7 J/cm³ at 3307 kV/cm were both achieved in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film. Moreover, an excellent temperature-dependent stability was also obtained in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film from 30 to 110 °C.     

Structural,electric and multiferroic properties of Sm-doped BiFeO3 thin films prepared by the sol–gelprocess

Pure polycrystalline Bi_1−xSm_xFeO₃ (BSFO) (x=0–0.12) thin films were successfully prepared on FTO/glass substrates by the sol–gel method. The influence of Sm doping on the structure, dielectric, leakage current, ferroelectric and ferromagnetic properties of the BSFO films was investigated. X-ray diffraction analysis and FE-SEM images both reveal a gradual rhombohedra to pseudo-tetragonal phase transition with the increase of Sm dopant content. On one hand, a proper amount of Sm doping can decrease the leakage current densities of the BSFO thin films. On the other hand, excess Sm substitution for Bi will lead to multiphase coexistence in the film, the lattice inhomogeneity results in more defects in the film, which can increase the leakage current density. The result shows that defects in the complexes lead to electric domain back-switching in the BSFO_x=0.06 thin film, resulting in a decreased dielectric constant, leakage current and remanent polarization. The BSFO_x=0.09 thin film is promising in practical application because of its highest dielectric constant, remanent polarization and remanent magnetization of 203–185, 70 μC/cm² and 1.31 emu/cm³, respectively.     

Studies on NO2 gas sensing properties of sprayed Co1−xMnxFe2O4 (0≤x≤0.5) spinel ferrite thin films

The Co_1−xMn_xFe₂O₄ (0≤x≤0.5) spinel ferrite thin films were deposited on quartz substrates by chemical spray pyrolysis technique. The effect of Mn substitution on to the structural, electrical, dielectric and NO₂ gas sensing properties of cobalt ferrite thin films was studied. The X-ray diffraction analysis reveals that deposited films exhibit spinel cubic crystal structure. The lattice constant increases with the increase in Mn²⁺ content. The decrease in resistivity with increase in temperature suggests that the films have a semiconducting nature. The room temperature dielectric properties such as dielectric constant (ε′), loss tangent (tanδ), dielectric loss (ε′′) and AC conductivity have been studied in the frequency range 20 Hz–1 MHz. The film shows the highest sensor response at moderately low (150 °C) operating temperature. The effect of operating temperature, gas concentration, film selectivity and substitution of Mn on to gas response is carefully studied. The manganese substituted cobalt ferrite films are extremely selective towards NO₂ with a 20 times gas response compared with other gases. The gas response achieved nearly 92% of its initial value after 150 days, indicating good stability of the films.     

Large enhancement of energy storage density in (Pb0.92La0.08)(Zr0.65Ti0.35)O3/PbZrO3 multilayer thin film

(Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT), PbZrO₃ (PZO) films, and type A and type B PLZT/PZO multilayer thin films were deposited on Pt(111)/TiO_x/SiO₂/Si substrates by sol-gel method, where type A and type B films stand for PLZT/PZO/PLZT/PZO/PLZT/PZO and PLZT/PZO/PLZT/PLZT/PZO/PLZT multilayer thin film, respectively. Compared to the PLZT and PZO film, enhanced breakdown field strength and improved energy storage density were obtained in type A and B multilayer thin films. A superior energy storage density of 29.7 J/cm³ with the energy storage efficiency of 50.8% was achieved in type B multilayer thin film, corresponding to 81% enhancement compared with the energy storage density of PLZT films (16.4 J/cm³). Additionally, the type B multilayer thin film exhibits a good thermal stability up to 160 °C and excellent fatigue endurance after 10⁷ charging-discharging cycles. The enhanced energy storage performance of type B multilayer thin film shows promise and may stimulate further researches on energy storage applications of multilayer dielectric thin films.     

Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

Simultaneously achieved high-energy storage density and efficiency in (K,Na)NbO3-based lead-free ferroelectric films

With the development of advanced electrical and electronic devices and the requirement of environmental protection, lead-free dielectric capacitors with excellent energy storage performance have aroused great attention. However, it is a great challenge to achieve both large energy storage density and high efficiency simultaneously in dielectric capacitors. This work investigates the energy storage performance of sol-gel-processed (K,Na)NbO₃-based lead-free ferroelectric films on silicon substrates with compositions of 0.95(K_0.49Na_0.49Li_0.02)(Nb_0.8Ta_0.2)O₃-0.05CaZrO₃-x mol% Mn (KNN-LT-CZ5-x mol% Mn). The appropriate amount of Mn-doping facilitates the coexistence of orthorhombic and tetragonal phases, suppresses the leakage current, and considerably enhances the breakdown strengths of KNN-LT-CZ5 films. Consequently, large recoverable energy storage density up to 64.6 J cm⁻³ with a high efficiency of 84.6% under an electric field of 3080 kV cm⁻¹ are achieved in KNN-LT-CZ5-5 mol% Mn film. This, to the best of our knowledge, is superior to the majority of both the lead-based and lead-free films on silicon substrates and thus demonstrates great potentials of (K,Na)NbO₃-based lead-free films as dielectric energy storage materials.     

Temperature Stable Dielectric Behavior of Sol–Gel Derived Compositionally Graded SrTiO3/Na0.5Bi0.5TiO3/SrTiO3 Thin Films

Polycrystalline sol–gel‐derived SrTiO₃/Na_0.5Bi_0.5TiO₃/SrTiO₃ (ST/NBT/ST) thin films were designed to achieve the electrical isolation of the NBT, and to mediate the temperature dependency of the dielectric properties. Proper thermal annealing of particulate phase enabled us to achieve compositionally graded elemental profiles between individual ST and NBT layers. The dielectric and ferroelectric properties were investigated with respect to the electrical behavior of the monophasic ST and NBT thin films. The dielectric characteristics of the multilayer thin film were marked by a temperature stable behavior (temperature coefficient of dielectric constant of 780 ppm/°C) in the measured ?50°C to 200°C range, frequency‐independent response at room temperature and improved dielectric loss characteristics compared with the NBT; however, on the expense of decreased permittivity and a reduced ferroelectric stability. Nevertheless, stable dielectric properties were achieved and properties of multilayer may well be exploited in functional devices that demand insensitive operation over wide temperature and frequency ranges.     

Relaxor transition and properties of Mn-doped SrxBa1−xNb2O6 ferroelectric ceramics

Pure and Mn-doped Sr_xBa_1−xNb₂O₆ (SBN) ceramics were prepared by the conventional solid state reaction method and their morphology, phase structure, relaxor behavior, ferroelectric and energy storage properties were investigated to reveal the effects of Mn doping on their properties. The results show that all the samples are single tetragonal tungsten bronze structure and the Mn element having few influences on their microstructures. The dielectric constant of pure SBN samples shows a classical relaxor behavior with obvious frequency dispersion and fits well with the Vogel–Fulcher law. However, the dielectric constant of Mn-doped samples does not show frequency dispersion. Then the relaxor behaviors of both pure and doped samples were further investigated by fitting the dielectric constant to the modified Curie-Weiss law. It was found that the diffusion parameters (γ) of Mn-doped samples are close to those pure samples, which indicates that the Mn-doped samples still have relaxor characteristics even without the classical dielectric frequency dispersion. Compared with the pure samples, the Mn-doped samples have a slimmer polarization-electric field (P-E) hysteresis loop, which can also prove their relaxor behaviors. The investigations of energy storage properties reveal that the Mn-doped samples have a higher energy storage density and efficiency.     

Effects of composition and stacking sequence on dielectric properties of the multilayered (Pb,Sr)TiO3 thin films for tunable device application

Multilayered (Pb_1−xSr_x)TiO₃ (PST(x)) thin films consisted of uniform, PST(x) and heterostructure, PST(x)–PST80 were synthesized by coating the solutions with different Sr contents (50 ≤ x, Sr(mol%) ≤80), respectively. Their structural and dielectric properties were investigated in terms of composition and stacking sequence of each film. Among uniform PST(x) thin films, the PST60 films showed the highest dielectric constant and tunability, while so lower figure of merit which is an important parameter for microwave tunable device application was obtained due to relatively higher dielectric loss. In an effort to bring down the dielectric loss, the PST(x) thin films were alternately coated with PST80 thin layer. Dielectric properties of the heterostructured PST(x)–PST80 films were found to be dependent on the intrinsic dielectric values of each film composition and corresponding phase transition temperature shift effect. Furthermore, surface roughness became smoother by inserting PST80 thin layer, resulting in decrease in dielectric loss. In case of the PST60–PST80 heterostructured film, despite of slight decrease in tunability, the figure of merit on account of lowered dielectric loss was effectively improved (>40%), compared to that of the uniform PST60 film.     

Reduced leakage current,enhanced energy storage and dielectric properties in (Ce,Mn)-codoped Ba0.6Sr0.4TiO3 thin film

Ba_0.6Sr_0.4TiO₃, Ce-doped Ba_0.6Sr_0.4TiO₃, Mn-doped Ba_0.6Sr_0.4TiO₃, (Ce,Mn) co-doped Ba_0.6Sr_0.4TiO₃ (abbreviated as BST, BSTCe, BSTMn, BSTCeMn) thin films were deposited on LaNiO₃(LNO)/Si substrates. The effects of ion doping on the microstructure and electrical properties of BST-based thin film have been researched and discussed. The X-ray diffraction pattern shows that each sample has pure perovskite phase structure with high (l00) peaks. The microstructure of each film is quite dense with uniform size. Compared with pure BST, improved insulating properties can be found in ion-doped BST thin films. For all the films, Ohmic conduction, space charge limited conduction and interface-limited Fowler-Nordheim tunneling should be the main conduction mechanisms within different electric field regions. For the case of BSTCeMn thin film, it possesses enhanced energy storage performance with a recoverable energy storage density (18.01?J/cm³) and a energy storage efficiency (75.1%) under 2000?kV/cm. This can be closely related to the small remanent polarization value (P_r=?1.89 μC/cm²), large maximum polarization value (P_max=?28.08?μC/cm²) as well as big maximum electric field (2000?kV/cm). Also, it exhibits a large dielectric constant of 405 and a small dissipation factor of 0.075 at 500?kHz.     

The study of BiCrxFe1−xO3 thin films synthesized by sol–gel technique

Cr-doped bismuth ferrite (BiCr_xFe_1?xO₃, BCFO) thin films were prepared by a sol–gel method with the value of x varying from 0 mol% to 10 mol%. The structures of the BCFO thin films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis was employed to represent the surface and cross-sectional morphologies of the thin films. Dielectric, electrical, ferroelectric and magnetic properties were measured by HP4294A, Keithley 4200, RT6000 and 6700 Magnet Controller at room temperature, respectively. The dielectric behaviour and insulation are improved in 3% Cr-doped BFO thin film which may be due to the reduced concentration of oxygen vacancies by 3% Cr doping.     

Energy storage properties of low concentration Fe-doped barium strontium titanate thin films

Ba_0.7Sr_0.3Fe_xTi_1?xO₃ (x = 0, 0.004, 0.008, 0.01, 0.015) ceramic thin films were prepared on platinized silicon wafers via sol-gel deposition method. Significant enhancement of grain size and dielectric constant were observed when x<0.008, accounting for effectively enhanced polarization, and beneficial for the energy storage applications. Excessive iron doping resulted in reduced grain size and deteriorated energy storage properties. The optimal energy storage behavior was achieved in samples with x=0.008, exhibiting a high discharged energy density of 7.6 J/cm³.     

Low Dielectric Loss and Good Dielectric Thermal Stability of xNd(Zn1/2Ti1/2)O3–(1−x)Ba0.6Sr0.4TiO3 Thin Films Fabricated by Sol–Gel Method

xNd(Zn_1/2Ti_1/2)O₃–(1?x)Ba_0.6Sr_0.4TiO₃ (xNZT–BST) thin films were fabricated on Pt/Ti/SiO₂/Si substrates by sol–gel method with x = 0, 3%, 6%, and 10%. The structures, surface morphology, dielectric and ferroelectric properties, and thermal stability of xNZT–BST thin films were investigated as a function of NZT content. It was observed that the introduction of NZT into BST decreased grain size, dielectric constant, ferroelectricity, tunability, and significantly improved dielectric loss and dielectric thermal stability. The corresponding reasons were discussed. The 10%NZT–BST thin film exhibited the least dielectric loss of 0.005 and the lowest temperature coefficient of permittivity (TCP) of 3.2 × 10^?3/°C. In addition, the figure of merit (FOM) of xNZT–BST (x = 3%, 6%, and 10%) films was higher than that of pure BST film. Our results showed that the introduction of appropriate NZT into BST could modify the dielectric quality of BST thin films with good thermal stability. Especially for the 3%NZT–BST thin film, it showed the highest FOM of 33.58 for its appropriate tunability of 32.87% and low dielectric loss of 0.0098.     

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.     

Structure and dielectric characteristics of continuous composition spread Ba1−xSrxTiO3 thin films by combinatorial pulsed laser deposition

Ba_1−xSr_xTiO₃ (0≤x≤1, BST-x) continuous composition spread thin films were grown on SrTiO₃ substrates buffered by La_0.9Sr_1.1NiO₄ (LSNO) electrodes using combinatorial pulsed laser deposition. The effects of Sr concentration on the structure and dielectric properties of the Au/BST-x/LSNO capacitors were investigated. X-ray diffraction patterns and reciprocal space maps revealed that both the in-plane and out-of-plane BST-x lattice parameters decreased with the increment of Sr content. Impedance measurements showed that the dielectric constant and tunability simultaneously changed with Sr concentration and reached the maximum at about x=0.5, which is comparable to that of BST-x individual thin films or bulks. Our results showed the large potential of combinatorial method in optimizing materials properties and even finding new materials.     

Dielectric,ferroelectric, and energy storage properties in dysprosium doped sodium bismuth titanate ceramics

In this work, Na_0.5(Bi_1-xDy_x)_0.5TiO₃ (0?≤?x?≤?15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy³⁺ into Sodium Bismuth Titanate (Na_0.5Bi_0.5TiO₃) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (??/?_(150?°C) ≤?±?15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2?J/cm³ obtained for 2%Dy composition at 200?°C. The obtained results are very promising for energy storage capacitors operating at high temperatures.     

Influence of deposition parameters on the dielectric properties of rf magnetron sputtered Ba(ZrxTi1−x)O3 thin films

Ba(Zr_xTi_1−x)O₃ (BZ_xT_1−x in short) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering and their dielectric properties have been characterized as a function of sputtering parameters. The BZ_xT_1−x thin films are amorphous when sputtered at rf power (R_p)=100 W and substrate temperature (S_T)=300 °C. The crystalline phase of the BZ_xT_1−x thin films appears when the substrate temperature increases from 300 to 400 and 500 °C, respectively, and the films have a high degree of (100) preferred orientation. The dielectric constant decreases with increasing measurement temperature, irrespective of the rf power and Zr content of the BZ_xT_1−x thin films. The BZ_0.3T_0.7 thin films have a low dielectric loss tangent irrespective of the sputtering parameters. The dielectric constant of the BZ_0.3T_0.7 thin film increases with increasing Zr·(Zr+Ti)⁻¹ ratio and deposition temperature but decreases with increasing working pressure. Besides, the dielectric constant suddenly increases from 244.0 to 284.1 when the rf power increases from 100 to 130 W, then it decreases from 284.1 to 270.0 when the rf power increases from 130 to 160 W. The dielectric constant also suddenly increases from 164.1 to 281.5 when the sputtering gas contains O₂ from 0 to 10%, but its variation is insignificant when the sputtering gas contains O₂ from 10 to 20%.     

N-doping SrTiO3@SrCO3 heterostructure electrode: Synthesis,electrochemical characterization,and varistor application

Optical traditional techniques, such as diffusive reflectance spectroscopy, are used to confirm absorption behavior modification after anion doping process. However, the doping process in some materials as a SrTiO₃ semiconductor was not clearly proved in different anions doping cases through traditional techniques. In this case, supporting technique as electrochemical measurements could prove a great help in elucidating the doping process modifications in the semiconductor material. In this paper, the electrochemical characterization was applied to analyze changes in energy bands produced by N-doping in SrTiO₃@SrCO₃ composite thin film electrodes. SrTiO₃@SrCO₃ and N-doped SrTiO₃@SrCO₃ nanoparticles were first characterized by X-ray diffraction to confirm a perovskite crystalline structure in both materials, whereas diffusive reflectance spectroscopy was used to demonstrate that no modification in the absorption spectrum is evident after doping. The thin films were observed by FESEM/SEM, and its deposition parameters were electrochemically evaluated. The electrochemical profiles of SrTiO₃@SrCO₃ and N doped SrTiO₃@SrCO₃ thin film electrodes were compared in dark and under UV-C light to determine the photocurrent. These measurements presented distinct results for the undoped and the doped materials, such as modification in photocurrent under UV-C illumination. SrTiO₃@SrCO₃ composite electrodes show important characteristics which could be classified as a potential candidate in varistor uses, especially in the low-voltage protection system. The presented results confirm that electrochemical methods are useful to analyze the synthesis efficiency to produce N-doped structures.