Dielectric properties and electrical behaviors of tunable Bi1.5MgNb1.5O7 thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on Au-coated Si substrates by rf magnetron sputtering. We systematically investigated the structure, dielectric properties and voltage tunable property of the films with different annealing temperatures. The relationships of leakage current and breakdown bias field with annealing temperature were firstly studied and a possible explanation was proposed. The deposited BMN thin films had a cubic pyrochlore phase when annealed at 550 °C or higher. With the increasing of annealing temperature, the dielectric constant and tunability also went up. BMN thin films annealed at 750 °C exhibited moderate dielectric constant of 106 and low dielectric loss of 0.003–0.007 between 10 kHz and 10 MHz. The maximum tunability of 50% was achieved at a bias field of 2 MV/cm. However, thin films annealed at 750 °C had lower breakdown bias field and higher leakage current density than films annealed below 750 °C. The excellent physical and electrical properties make BMN thin films promising for potential tunable capacitor applications.     

Investigation on Tunable Performance of BMN/BST Multilayer and BMN–BST Composite Thin Films

The BMN/BST multilayer and BMN–BST composite thin films have been fabricated by pulsed laser deposition on Au/TiO_x/SiO₂/Si substrate. The multilayer thin films comprising one, two, and four periodic compositional Bi_1.5MgNb_1.5O₇/Ba_0.6Sr_0.4TiO₃ (BMN/BST) layers (PCBLs) have been elaborated with the final same thickness. The four PCBLs show the largest dielectric constant of ~168 and tunability of 40.6% at a maximum applied bias field of 0.67 MV/cm and the lowest loss tangent of ~0.006, whereas the figure of merit (FOM) is 72. The BMN–BST composite thin films exhibit medium dielectric constant of ~238, low loss tangent of ~0.0053, and superior tunable dielectric properties at room temperature. Calculations of tunability and FOM display a maximum value of 49.3% at 670 kV/cm and ~88, respectively.     

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

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

Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents of (1−x)Ba(Mg1/3Nb2/3)O3–xBaSnO3 Solid Solutions

Microwave dielectric ceramics of (1?x)Ba(Mg_1/3Nb_2/3)O₃‐xBaSnO₃ [(1?x)BMN‐xBS] with high quality factors was synthesized by the solid‐state reaction method. The effects of BaSnO₃ additions (x = 0–0.2) on the sinterability, crystal structures, microwave dielectric properties, and microwave dielectric loss mechanisms of BMN were investigated systematically. The degree of 1:2 cation ordering was decreased with increasing Sn content and eventually faded away as x ≥ 0.1, where the low‐temperature relaxations disappeared coincidently through the thermally stimulated depolarization current technique. It was supposed to be the short‐range misplacements of the B‐site cations within the long‐range ordered structure. Meanwhile, the high‐temperature relaxations associated with the in‐grain oxygen vacancies were found in all the title compounds. Though the concentrations of oxygen vacancies of 0.8BMN‐0.2BS were higher than BMN, high Q × f values could also be obtained even in the absence of 1:2 cation ordering. Specifically, the excellent characteristics like ε_r = 29.02, Q × f = 90 000 GHz and τ_f = 6.3 ppm/°C were achieved in the specimens of x = 0.2 sintered at 1450°C.     

Relaxor Ferroelectric BaTiO3–Bi(Mg2/3Nb1/3)O3 Ceramics for Energy Storage Application

Perovskite solid solution ceramics of (1 ? x)BaTiO₃–xBi(Mg_2/3Nb_1/3)O₃ (BT–BMN) (x = 0.05–0.2) were synthesized by solid‐state reaction technique. The results show that the BMN addition could lower the sintering temperature of BT‐based ceramics. X‐ray diffraction results reveal a pure perovskite structure for all studied samples. Dielectric measurements exhibit a relaxor‐like characteristic for the BT–BMN ceramics, where broadened phase transition peaks change to a temperature‐stable permittivity plateau (from ?50°C to 300°C) with increasing the BMN content (x = 0.2), and slim polarization–electric field hysteresis loops were observed in samples with x ≥ 0.1. The dielectric breakdown strength and electrical resistivity of BT–BMN ceramics show their maxima of 287.7 kV/cm and 1.53 × 10¹³ Ω cm at x = 0.15, and an energy density of about 1.13 J/cm³ is achieved in the sample of x = 0.1.     

Sol–Gel Synthesis and Characterization of Na0.5Bi0.5TiO3–NaTaO3Thin Films

Thin films with the composition 70 mol% Na_0.5Bi_0.5TiO₃ + 30 mol% NaTaO₃ were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low‐ (kHz–MHz) and microwave‐frequency (15 GHz) ranges were investigated. In the low‐frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature‐stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between ?25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO₂/TiO₂/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.     

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.     

Dielectric Properties of Sol–Gel‐Derived Bi12SiO20 Thin Films

In this paper the dielectric properties of crack‐free, Bi₁₂SiO₂₀ thin films were investigated. The films were prepared on Pt/TiO₂/SiO₂/Si and corundum substrates using the sol–gel method. The formation of a pure Bi₁₂SiO₂₀ phase was observed at a temperature of 700°C. The Bi₁₂SiO₂₀ thin films, heat treated at 700°C for 1 h, had a dense microstructure with an average roughness (R_a) of 50 nm. The dielectric properties of the film were characterized by using both low‐ and microwave‐frequency measurement techniques. The low‐frequency measurements were conducted with a parallel capacitor configuration. The dielectric constant and dielectric losses were 44 and 7.5 × 10^?3, respectively. The thin‐film dielectric properties at the microwave frequency were measured using the split‐post, dielectric resonator method (15 GHz) and the planar capacitor configuration (1–5 GHz). The dielectric constant and the dielectric losses measured at 15 GHz were 40 and 17 × 10^?3, respectively, while the dielectric constant and the dielectric losses measured with the planar capacitor configuration were 39 and 65 × 10^?3, respectively.     

Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films

Bismuth magnesium niobate (Bi_3/2MgNb_3/2O₇, BMN) thin films were prepared on bare SiO₂/HR-Si and Pt/TiO₂/SiO₂/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO₂/Si substrate with a BMN/SiO₂ interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO₂ interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.     

Influence of rare-earth La3+ ion doping on microstructural,magnetic and dielectric properties of Mg0.5Ni0.5Fe2-xLaxO4 (0 ≤ x ≤ 0.1) ferrite nanoparticles

A series of La³⁺ ion doped magnesium nickel ferrites, Mg_0.5Ni_0.5Fe_2-xLa_xO₄ (0 ≤ x ≤ 0.1) having a cubic spinel structure were prepared by the co-precipitation method. Various characterization techniques, including X-ray diffractometer (XRD), high resolution transmission electron microscopy (HR-TEM), electron spin resonance (ESR) and vibrating sample magnetometer (VSM) were used to investigate structural and magnetic properties. The average crystallite size decreases and lattice parameter increases with La³⁺ ion doping and lie in the range of 12–7 nm and 8.347–8.361 Å respectively. Analysis of ESR spectra reveals that, g-value with La³⁺ ion addition decreases from 2.57 to 2.12. The saturation magnetization and the coercivity decrease with increasing rare-earth content. Magnetic-hysteresis (M − H) loop shifts from a ferromagnetic to a superparamagnetic nature with La³⁺ ion addition. The dielectric study was carried out in the frequency range of 1 KHz to 4000 KHz and temperature ranging 30 °C–350 °C using the impedance analyzer. The dielectric constant decreases with increasing frequency and the La³⁺ ion concentration. The dielectric loss of the sample increases with increasing temperature. The magnetic properties of the synthesized nanoparticles make them a potential material for stable ferrofluid application and the low tangent loss value makes these material a potential candidate for frequency-based applications.     

热处理对 Ba0.6Sr0.4TiO3 厚膜介电性能的影响

采用柠檬酸盐法制备了Ba_(0.6)Sr_(0.4)TiO_3粉体,通过丝网印刷法制备了Ba_(0.6)Sr_(0.4)TiO_3厚膜,研究了在空气气氛中进行热处理前后厚膜样品的介电性能。研究结果表明,在空气气氛中进行热处理可以有效地提高厚膜样品的介电性能。经过1000°C热处理,厚膜样品在10 kH z下的介电损耗由1.7%降为1.1%,其优质系数由33提高到55。     

Novel BiFeO3–BaTiO3–Ba(Mg1/3Nb2/3)O3 Lead‐Free Relaxor Ferroelectric Ceramics for Energy‐Storage Capacitors

A novel lead‐free relaxor ferroelectric ceramic of (0.67?x)BiFeO₃–0.33BaTiO₃–xBa(Mg_1/3Nb_2/3)O₃ [(0.67?x)BF–0.33BT–xBMN, x = 0–0.1] was prepared by a solid‐state reaction method. A relatively high maximum polarization P_max of 38 μC/cm² and a low remanent polarization P_r of 5.7 μC/cm² were attained under 12.5 kV/mm in the x = 0.06 sample, leading to an excellent energy‐storage density of W ~1.56 J/cm³ and a moderate energy‐storage efficiency of η ~75%. Moreover, a good temperature stability of the energy storage was obtained in the x = 0.06 sample from 25°C to 190°C. The achievement of these characteristics was basically attributed to an electric field induced reversible ergodic to ferroelectric phase transition owing to similar free energies near a critical freezing temperature. The results indicate that the (0.67?x)BF–0.33BT–xBMN lead‐free realxor ferroelectric ceramic could be a promising dielectric material for energy‐storage capacitors.     

Dielectric properties of SrTiO3/LaNiO3 composite structure prepared by “sol-gel” method

In this work, Pt/SrTiO₃(STO)/LaNiO₃(LNO) and Pt/STO/Pt structures were fabricated on Si substrates using sol–gel method. Dielectric tunability characteristics of these two structures are investigated over temperature range of 300–80 K. As temperature decreases, relative dielectric constant and tunability of STO films in both structures increase linearly, while loss tangent (tan?) decreases. STO prepared on LNO exhibits better crystallinity and dielectric tunability than that prepared on Pt. Furthermore, LNO top pole array with 0.2 mm diameter was prepared on STO/LNO using photosensitive sol–gel method, resulting in LNO/STO/LNO structure with symmetric electrode. Dielectric tunability tests reveal that, compared with Pt/STO/LNO structure, LNO/STO/LNO structure exhibits similar tunability, lower tan?, higher figure-of-merit (FOM) values, and better tunability symmetry. Relative dielectric constant, tunability (350 kV/cm), and FOM are approximately 391, 60%, and 142.6 at 80 K, respectively. Further analysis shows that because of Schottky barrier at Pt/STO interface, the FOM and tunability symmetry of Pt/STO/LNO structure are worse than those of LNO/STO/LNO structure. These results demonstrate that LNO electrode performs better than conventional inert metal electrodes.     

Synthesis and Thermal,Structural, Dielectric,Magnetic and Magnetoelectric Studies of BiFeO3‐MgFe2O4 Nanocomposites

Spinel–perovskite magnetoelectric (ME) nanocomposites xMgFe₂O₄–(1?x)BiFeO₃, x = 0.1, 0.2, 0.3, and 0.4 were synthesized by sol‐gel method and characterized by differential thermal analysis, X‐ray diffraction analysis, dielectric and magnetic measurements. The samples were calcined at various temperatures and then the effect of annealing temperature on structural and magnetic properties was studied. From transmission electron microscopy, the average crystal size was found to be 30–50 nm. The magnetic behavior is found to be dependent on annealing temperature and magnesium ferrite content. The dielectric behavior with frequency and temperature has been modified with the induction of magnesium ferrite. The relative change of dielectric constant with magnetic field was observed in the nanocomposites. This relative change of magnetic field‐induced dielectric constant can also be expressed by Δε ~ γM² (where γ is magnetoelectric coupling coefficient).     

Ferroelectric properties of compressively strained epitaxial SrTiO3 films on sapphire

Magnetron sputtered and laser deposited SrTiO₃ thin films are deposited on CeO₂ buffered sapphire substrates. Their structural and ferroelectric properties are analyzed and possible (mutual) correlations between these properties are investigated. It is shown, that the biaxial compressive strain imposed by the substrate on the ferroelectric films leads to a considerable increase of the Curie temperature, as well as the dielectric constant and the tenability of these films in technically relevant temperature regimes. Generally, the dielectric constant and the tuning decreases with increasing strain. However, the ferroelectric phase transition of the SrTiO₃ films is shifted to higher temperatures compared to that of single crystalline SrTiO₃. As a consequence, the dielectric constant of the films is larger than that of undistorted SrTiO₃ single crystals for small strain (Δa/a < 0.005) and temperatures above the Curie temperature. Furthermore, a linear dependence of the loss tangent and the tunability on the dielectric constant is observed, which indicates, that all three properties are affected by the same mechanism that itself is affected by the lattice strain.     

Sol‐gel derived TiNb2O7 dielectric thin films for transparent electronic applications

To reduce power consumption of transparent oxide‐semiconductor thin film transistors, a gate dielectric material with high dielectric constant and low leakage current density is favorable. According to previous study, the bulk TiNb₂O₇ with outstanding dielectric properties may have an interest in its thin‐film form. The optical, chemical states and surface morphology of sol‐gel derived TiNb₂O₇ (TNO) thin films are investigated the effect of postannealing temperature lower than 500°C, which is crucial to the glass transition temperature. All films possess a transmittance near 80% in the visible region. The existence of non‐lattice oxygen in the TNO film is proposed. The peak area ratio of non‐lattice oxygen plays an important role in the control of leakage current density of MIM capacitors. Also, the capacitance density and dissipation factor were affected by the indium tin oxide (ITO) sheet resistance at high frequencies. The sample after postannealing at 300°C and electrode‐annealing at 150°C possesses a high dielectric constant (>30 at 1 MHz) and a low leakage current density (<1 × 10^?6 A/cm² at 1 V), which makes it a very promising gate dielectric material for transparent oxide‐semiconductor thin film transistors.     

Frequency and Temperature‐Independent Electrical Transport Properties of 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass‐Ceramics

The temperature (300–973 K) and frequency (100 Hz–10 MHz) response of the dielectric and impedance characteristics of 2BaO‐0.5Na₂O–2.5Nb₂O₅–4.5B₂O₃ glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz–10 MHz) and temperature (300–600 K). The temperature coefficient of dielectric constant was 8 ± 3 ppm/K in the 300–600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal‐glass interface, leading to a high value of effective dielectric constant especially for the samples heat‐treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (P_r) increased with the increase in crystallite size.     

Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films

Polyimide composite films were prepared by mixing the BaTiO₃ particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO₃ particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO₃ content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO₃ content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Annealing effects on the microstructure and magnetic properties of Y3Fe5O12 films deposited on Si/SiO2 substrates by RF magnetron sputtering

Crack-free Yttrium iron garnet (Y₃Fe₅O₁₂, YIG) thin films were successfully deposited on Si/SiO₂ substrates by RF magnetron sputtering, through controlling the annealing temperature and cooling rate during post-annealing process. The annealing condition dependences of crystallinity, microstructures and magnetic properties of YIG films were investigated. With the increase of the annealing temperature, the saturation magnetization of YIG films increases and the coercive field decreases, while the ferromagnetic resonance (FMR) linewidth becomes wider. The films annealed at 750 °C with cooling rate of 1 °C/min are crack-free and present excellent comprehensive performances, the corresponding coercive field is 32 Oe and the FMR linewidth is 57 Oe at 9.4 GHz. These results indicate that high-quality crack-free YIG films with excellent magnetic properties can be achieved on Si/SiO₂ substrates by controlling the annealing process, which makes it more convenient to fabricate low-loss microwave integrated devices.     

Effects of Ni2+ substitution on the structure and dielectric properties of Bi1.5MgNb1.5O7 cubic pyrochlores

The dielectric properties of bismuth-based cubic pyrochlores strongly depend on the environment of the A-site ions, e.g. the Ni²⁺ ions doped into Bi_1.5MgNb_1.5O₇ (BMN) pyrochlores for tailoring dielectric properties. Both BMN and Bi_1.5NiNb_1.5O₇ (BNN) ceramics exhibit a cubic pyrochlore structure with preferential (222) planes. However, {442} reflections are observed in BNN pyrochlores, revealing an off-center displacement of A and O' ions. The dielectric constant of BNN pyrochlores is lower than that of BMN pyrochlores, besides BNN pyrochlores have a larger dielectric loss (0.002) than BMN pyrochlores (0.0007). Ni-doping results in a loose and flexible structure contributing positively to the dielectric tunability, besides creating a large amount of oxygen vacancies. The higher amount of oxygen vacancies increases the dielectric loss of BNN pyrochlores. However, BNN pyrochlores exhibit enhanced temperature stability, with a temperature coefficient of –57 ppm/^oC, which is significantly better than that of BMN pyrochlores (–362 ppm/^oC).