Dielectric Properties Of Na0 Research Articles

Impedance spectroscopy of Na0.5Bi4.50+xTi4Oy (x = ‐0.02, 0, 0.02) ceramics with excellent dielectric properties

AbstractThe electric and dielectric properties of Na0.5Bi4.50+xTi4Oy (x = −0.02, 0, 0.02) prepared by conventional mixed oxide route have been investigated by impedance spectroscopy (IS) over a wide temperature range. Single‐phase bismuth layer‐structured perovskite patterns were observed through X‐ray diffraction of the three samples Na0.5Bi4.5Ti4O15, Na0.5Bi4.48Ti4Oy, and Na0.5Bi4.52Ti4Oy. The results show that the relative permittivity (εr) increases with the increase in temperature and reaches its maximum at about 675℃. With the continuous increase in temperature, the permittivity decreases gradually. Both relative permittivity and dielectric loss show great stability at the low‐temperature zone. The ceramic of x = 0.02 with Ea of 1.09 eV has the maximum oxygen ionic transport number between 600 and 800℃ for all samples. And at this time, it has the maximum electrical conductivity. All the results indicated that Na0.5Bi4.50+xTi4Oy (x = −0.02, 0, 0.02) ceramics were promising base materials for high‐temperature capacitor because of their high dielectric properties.

Combining effects of TiO6 octahedron rotations and random electric fields on structural and properties in Na0.5Bi0.5TiO3

AbstractThe structural and dielectric properties of Na0.5Bi0.5TiO3 (NBT) ceramics and crystals have been investigated and are compared to that of Pb(Zr0.55Ti0.45)O3 (PZT55/45) and Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMNT 72/28) ceramics. X‐ray diffraction (XRD) profiles for (100), (110), (111), (200), (220), and (222) (referred to cubic structure) reveal that the monoclinic structure with Cc space group exists both in the NBT single crystal and ceramics. The diffraction profile obtained with high resolution laboratory XRD for the NBT single crystal can be well described, using Cc model instead of R3c model. The dielectric constant of NBT below Thump shows some similarity to that of PZT45/55 ceramics below 50°C in which oxygen octahedron rotations cause the frequency dispersion of the dielectric constant. The temperature‐dependent dielectric constant for NBT can be deconvolved into two independent processes. The lower temperature process shows a typical relaxor characteristic and follows the Vogel‐Fulcher relationship. The other process at higher temperature shows less frequency‐dependent behavior. Comparing the dielectric constant of NBT with that of PZT55/45 and PMNT72/28 reveals that both oxygen octahedral rotations and random electric fields play an important role in the frequency dispersion of the dielectric constant for NBT relaxor feroelectric.

Growth, microstructure, energy–storage and dielectric performances of chemical–solution NBT–based thin films: Effect of sodium nonstoichimometry

Na0.5+δBi0.5(Ti0.96W0.01Ni0.03)O3 thin films with various Na contents (abbreviated as Na.5+δBTWN, δ = − 3.0, − 1.5, 0, 1.5%) were fabricated on ITO/glass substrates using a chemical–solution process. The effects of Na nonstoichiometry on the microstructure, insulating, ferroelectric and dielectric performances are investigated. The pure perovskite phase can be obtained in Na0.5BTWN and Na0.515BTWN, while for Na0.470BTWN or Na0.485BTWN, the main composition contains secondary phase of TiO2. The grain size increases from 30 nm at δ = − 3.0% to 55 nm at δ = 0%, then decreases to 52 nm with δ = 1.5%. The leakage current of Na0.485BTWN sample is reduced dramatically in comparison with Na0.5+δBTWN (δ = − 3.0, 0, 1.5%). The big recoverable energy–storage density of 63.1 J/cm2 and high energy–storage efficiency of 55.0% can be obtained for Na0.485BTWN due to the improved electric break–down strength and large difference value between the remanent polarization and maximum polarization. Enhanced dielectricity is achieved in Na0.485BTWN with a high tunability of 36.0% and a figure of merit of 4.0 at 450 kV/cm and 500 kHz. These results demonstrated that the crystallization, micrographs and energy storage and dielectric properties of Na0.5Bi0.5TiO3 are highly sensitive to low levels of Na–site nonstoichiometry.

Effects of Nd3+-substitution for Bi-site on the leakage current, ferroelectric and dielectric properties of Na0.5Bi0.5TiO3 thin films

Perovskite Na0.5(Bi1−xNdx)0.5TiO3 (x = 0, 0.01, 0.03, 0.05; xNd: NBT) ferroelectric films were synthesized on indium tin oxide (ITO)/glass substrates via chemical solution deposition. Structural characterization shows the similar phase-pure perovskite structures in all the films and gradually decreased grain sizes with Nd3+ doping amount increasing. For all the films, the leakage behaviors are dominant by the Ohmic conduction in low electric field region and interface-limited Fowler-Nordheim tunneling mechanism in high electric field region. Additionally, the space-charge-limited conduction is involved in 0.03Nd: NBT sample. Compared with the sample of x = 0, the resistivity can be improved through Nd3+-substitution in NBT. Enhanced ferroelectricity can be obtained from the dynamic polarization-electric field test, and the reversible domains switching in film can be confirmed by static dielectric constant-electric field measurement. Especially, the 0.03Nd: NBT possesses optimal electrical performances with a large remanent polarization (Pr = 26.7μC/cm2) and a high dielectric tunability (19.6% at 100kHz).

Dielectric properties of Na0.5BixTi3.98Mg0.02Oy(x=4.48, 4.50, 4.52) ceramics under different Bi contents and sintering temperatures

As a new kind family of lead-free Na0.5Bi0.5TiO3 (NBT) ceramics, bismuth layer-structured ferroelectrics (BLSFs), Na0.5BixTi3.98Mg0.02Oy (x = 4.48, 4.50, 4.52) were synthesized by a conventional mixed oxide route. Studies have found that the dielectric properties of Na0.5Bi4.5Ti4O15 can be optimized through changing the Bi content of the ceramics or Mg-doping on Ti-site under different sintering temperatures. X-ray diffraction analysis indicated that the new material was in a single BLSFs phase. The dielectric constant of Mg-doped Na0.5Bi4.5Ti3.98Mg0.02Oy was improved and dielectric loss of Na0.5Bi4.5Ti3.98Mg0.02Oy changed slowly under 500 °C with the increased sintering temperature. We found that the dielectric properties of the sample sintered at 1120 °C with the highest permittivity of 1122.5 and the lowest dielectric loss of 0.01 were relatively better than those of the other samples. SEM can be better to explain the results of the dielectric spectrum at different sintering temperatures through grain size mechanics. Z* plots showed that Na0.5Bi4.5Ti3.98Mg0.02Oy ceramics are a kind of dielectrics. Thus, Na0.5BixTi3.98Mg0.02Oy (x = 4.48, 4.50, 4.52) can be used as high-temperature capacitors and phase shifter with high dielectric constant, low dielectric loss and wide operating temperature range.

Crystal structure refinement, enhanced magnetic and dielectric properties of Na0.5Bi0.5TiO3 modified Bi0.8Ba0.2FeO3 ceramics

(1-x) Na0.5Bi0.5TiO3–x(Bi0.8Ba0.2FeO3) (x=0.5, 0.6, 0.7, and 0.8) ceramics were synthesized via solid state reaction method. Powder X-ray diffraction investigations performed at room temperature along with Rietveld analysis show all the composites to exhibit a rhombohedral distorted perovskite structure, described by space group R3c. Rietveld refinement confirmed a good agreement between observed and calculated intensities and a low value of goodness of fit (χ2). Magnetic measurements were carried out at room temperature up to a field of 6kOe. Magnetic properties of BBFO modified NBT ceramics are improved with a significant opening in the M–H hysteresis loop at room temperature. Remanent magnetization and coercive field increased with increase of BBFO concentration. The dielectric response of these samples was analyzed in the frequency range 10Hz–7MHz at different temperatures revealing a dispersion in dielectric constant (ε′) and in dissipation factor (tan δ) at lower frequencies. Both ε′ and tan δ increase with increase of BBFO content. The temperature dependence of frequency exponent ′s′ of power law suggests that quantum mechanical tunneling (QMT) model to be applicable at lower temperature and correlated barrier hopping (CBH) mechanism to be appropriate at higher temperature to describe the conduction mechanism in x=0.5 and x=0.6 samples. Further, with increase in BBFO content, the dielectric constant becomes more stable at higher frequencies and temperatures thereby improving the dielectric properties of the material.

Microstructure, piezoelectric, ferroelectric and dielectric properties of Na0.5K0.5NbO3 single crystals prepared by seed-free solid-state crystal growth

ABSTRACTThe Na0.5K0.5NbO3 single crystal was successfully grown by a seed-free solid-state crystal growth method using super-low content of LiBiO3 as a sintering aid. Microstructure, piezoelectric, ferroelectric and dielectric properties were investigated. The results show that well-paralleled lamellar ferroelectric ordering domains structure are present and no crack can be seen inside the single crystal. The best piezoelectric and dielectric properties (at 1 kHz) of d33 = 265 pC/N, Pr = 27.4 μC/cm2, ε = 738, tanδ = 0.04 appear at x = 0.40at% for (1-x)Na0.5K0.5NbO3-xLiBiO3 single crystal. A higher remnant polarization Pr of 36.3 μC/cm2 were obtained at x = 0.45 at%.

Pyroelectric, ferroelectric, piezoelectric and dielectric properties of Na0.5Bi0.5TiO3 ceramic prepared by sol-gel method

Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na0.5Bi0.5TiO3) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na0.5Bi0.5TiO3 was obtained from the precursor gel by heating at 700°C for 2h in air. The BNT ceramic at 1100°C sintering temperature present high crystallinity, good dielectric properties at 1kHz (ε′=885, tan δ=0.03, Tc=370°C), piezoelectric properties (k33=0.39, c33=105GPa, e33=12.6C/m2, d33=120pC/N), high remnant polarization (Pr=47μC/cm2) and pyroelectric coefficient (p=707μC/m2K) and low coercive field (Ec=55kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.

Influence of annealing temperature on the microstructure, leakage current and dielectric properties of Na0.5Bi0.5(Ti,Zn)O3 thin films

Lead-free Na0.5Bi0.5(Ti,Zn)O3 (NBTZn) thin films were deposited on indium tin oxide (ITO)/glass substrates via a metal organic decomposition process and annealed at various temperatures from 450 to 600 °C. The influence of annealing temperature on crystallization and electrical properties were investigated. XRD measurement reveals that the film can be crystallized into single perovskite at an annealing temperature as low as 500 °C. The average grain size of the NBTZn sample increases with increasing the annealing temperature from 500 to 600 °C. The leakage current density also increases with the increase in annealing temperature probably due to the variation content of grain boundaries and oxygen vacancies. Compared with other samples annealed at 500 and 600 °C, the film prepared at 550 °C shows enhanced dielectric properties with a relatively high dielectric tunability of 36.4 % and low dissipation factor of 0.13 at 200 kHz.

Effects of annealing temperature on the microstructure, ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na0.5Bi0.5Ti0.99W0.01O3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620°C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600°C exhibits a relatively large remanent polarization (Pr) of 20μC/cm2 measured at 750kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.

Synthesis and dielectric properties of Na0.5Bi0.5Cu3Ti4O12 ceramic by molten salt method

Na0.5Bi0.5Cu3Ti4O12 (NBCTO) powder was prepared by molten salt method at 700, 750, 800, and 850 °C in NaCl–KCl flux salts, respectively. X-ray diffraction data revealed that the main NBCTO phase of powder was synthesized at a low temperature of 700 °C for 2 h in NaCl–KCl flux, which was reduced by about 250 °C compared with the conventional solid-state reaction method. The evolution of the microstructure was observed by scanning electron microscopy, and the dielectric properties of NBCTO ceramics affected by sintering temperature and sintering time were studied in detail in this paper. The complex impedance plots were also employed to analyze the dielectric properties of NBCTO ceramics. The average grain size of the sintered ceramic increased with the increase in sintering temperature, which lead to the increased dielectric constant of the NBCTO ceramic, whereas the sintering time has affected the dielectric constant slightly. A high dielectric constant of more than 104 and a low loss tangent (tanδ) of 0.06 (at 10 kHz) were obtained for the NBCTO ceramic sintered at 1040 °C for 12 h.

Structural, ferroelectric and dielectric properties of Na0.5Bi0.5(Ti0.98Fe0.02)O3 thin films on different substrates

Na0.5Bi0.5(Ti0.98Fe0.02)O3 (NBTFe) thin films have been prepared on monocrystalline Si, Al-doped ZnO/glass and Pt/TiO2/SiO2/Si substrates by metal organic decomposition combined with sequential layer annealing. The structure, leakage current, ferroelectric and dielectric properties of NBTFe thin films are very sensitive to the using substrates. The NBTFe on Si exhibits a competitive growth mode with various oriented crystallites at different annealing temperature. At 550 °C, the NBTFe on all the substrates crystallize into the pure rhombohedral perovskite structure with an obvious difference in orientation. The electrical measurements were conducted on metal–ferroelectric–semiconductor and metal–ferroelectric–metal capacitors. The NBTFe film on Si exhibits the capacitance–voltage curve with a maximum memory window of 2 V at the applied voltage of ±6 V originated from the ferroelectric polarization. The NBTFe film on Al-doped ZnO/glass shows a round polarization–electric field hysteresis loop due to the large contribution from the leakage current. In contrast, a large remanent polarization (Pr) of 18 μC/cm2 for NBTFe deposited on Pt/TiO2/SiO2/Si can be obtained. Also, the NBTFe thin film on Pt/TiO2/SiO2/Si shows a high er of 313 and low tan δ of 0.1 at 100 kHz.

The structure, ferroelectric and dielectric properties of Na0.5Bi0.5(Ti0.98Mn0.02)O3 thin film prepared by chemical solution decomposition

Na0.5Bi0.5(Ti0.98Mn0.02)O3 (NBTMn) thin film was fabricated on fluorine-doped tin oxide (FTO)/glass substrate via a chemical solution decomposition method. The microstructure and electrical performances of NBTMn thin film were investigated. The XRD pattern reveals that the NBTMn thin film is crystallised into a phase-pure polycrystalline perovskite structure. Also the film possesses a homogeneous structure. Enhanced ferroelectricity is obtained with a large remnant polarisation (Pr) of 19.8 μC/cm2 reflected by polarisation–electric field (P–E) hysteresis loop, which is consistent with the typical butterfly-shaped capacitance–voltage (C–V) curve. At the optimum applied voltage of ±22 V, a maximum value of 27% for dielectric tunability is obtained. Additionally, the NBTMn thin film shows a dielectric constant of 422, dissipation factor of 0.06 and figure of merit of 4.5 at 100 kHz.

Core–shell grain structures and dielectric properties of Na0.5K0.5NbO3–LiTaO3–BiScO3 piezoelectric ceramics

The origins of distinctive compositional dependence of relative permittivity, ɛr, in the Pb-free piezoelectric system (1−x) Na0.5K0.5NbO3–xLiTaO3, x⩽10mol.% modified with BiScO3 have been revealed using transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDX). As the LiTaO3 content increased the Curie peak at ∼370°C in ɛr–T plots became more diffuse, and at x=5mol.% an additional higher temperature peak occurred. TEM-EDX analysis showed the change in dielectric properties at x=5mol.% was due to a change in microstructure: micron-scale grains were replaced by submicron grains exhibiting core–shell chemical segregation. The outer shell was similar to the target solid solution composition, slightly enriched in Bi, Sc and Ta, whilst the core approximated to (Na, K, Li)NbO3 and was responsible for the additional dielectric peak. Examples of a novel three-tier metastable grain structure were observed for certain compositions.

Effects of Zr doping content on microstructure, ferroelectric and dielectric properties of Na0.5Bi0.5TiO3 thin film

Ion-doping is a key factor affecting the microstructure and electrical properties of Na 0.5 Bi 0.5 TiO 3 (NBT) thin film. In this paper, Na 0.5 Bi 0.5 (Ti 1− x Zr x )O 3 ( x =0, 0.01, 0.02, 0.04) thin films were prepared using chemical solution decomposition and the effects of Zr 4+ doping content on crystalline, ferroelectric and dielectric properties were characterized. Compared with the other films, NBT with 2 mol% Zr 4+ doping content exhibits enhanced ferroelectricity with a remanent polarization ( P r ) of 12.3 μC/cm 2 due to the high densification, as well as reduced leakage current and distortion of Ti–O octahedral. The dielectric constant ( ε r ) and dissipation factor (tan δ ) on frequency show small dispersion tendency with ε r of 263 and tan δ of 0.067 at 100 kHz. Also, the capacitance–voltage curve displays a relatively sharp feature with a high dielectric tunability of 61.6%. • NBTZr 0.02 shows a well-defined P–E with a remanent polarization of 12.3 μC/cm 2 . • The high densification and Ti–O distortion favor the enhanced ferroelectricity. • The dependence of ε r on frequency for NBTZr 0.02 film has small dispersion tendency. • At 100 kHz, for NBTZr 0.02 , ε r =263, tan δ =0.067, dielectric tunability=61.6%.

Preparation process, microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 ceramics by a sol–gel method

Effect of concentration, water content (molar ratio of the water and titanium) and pH value of the sol, and sintering temperatures and holding time on microstructure and dielectric properties of Na0.5La0.5Cu3Ti4O12 (NLCTO) ceramics by a sol–gel method were investigated in detail, respectively. It is found that the optimum concentration, the molar ratio of the water and titanium, and pH value of the sol were 1.00 mol/L, 11.0, and 0.3, respectively. The NLCTO ceramics sintered at 1,080 °C for 10 h exhibited more homogeneous microstructure, higher dielectric constant (about 1.1–1.8 × 104) and lower dielectric loss (about 0.051–0.064 at 1–10 kHz). The higher dielectric constant of the NLCTO ceramics might be due to the internal barrier layer capacitor effect. The NLCTO ceramics prepared by the sol–gel method showed two kinds of dielectric relaxation at higher temperature by electric modulus analysis, and two relaxation activation energy values were obtained.

Origin of giant permittivity and high-temperature dielectric anomaly behavior in Na0.5Y0.5Cu3Ti4O12 ceramics

Na0.5Y0.5Cu3Ti4O12 ceramics prepared by the conventional solid-state reaction method under various sintering conditions were found to exhibit a giant dielectric constant over 10 000 around room temperature. Two electrical responses were observed in the combined modulus and impedance plots, indicating the presence of Maxwell-Wagner relaxation. The contributions of semiconducting grains and insulating grain boundaries (corresponding to high-frequency and low-frequency electrical response, respectively) played important roles in the dielectric properties of Na0.5Y0.5Cu3Ti4O12 ceramics. The correlations between grain boundaries resistance and low frequency dielectric loss, grains resistance and the position of dielectric loss peak were addressed. Mixed-valent structures of Cu2+/Cu3+ and Ti3+/Ti4+ had been determined using X-ray photoelectron spectroscopy. Electron hopping between Cu2+ and Cu3+ and electron transport in Ti3+–O–Ti4+ paths were proposed as the origin of the semiconducting nature of Na0.5Y0.5Cu3Ti4O12 ceramics. In particular, high-temperature dielectric anomaly behavior was investigated in detail. A dielectric peak exhibiting relaxor-like behavior was observed around 200 °C, which was linked with the formation of oxygen vacancies. Based on the electric modulus results, this behavior was explored in the light of the defect formation and explained in terms of a competition process depending on the combinational contribution to polarization between n- and p-type carriers rather than a relaxation process.

Structural and Dielectric Properties of Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> Ferroelectric Ceramics

Na0.5Bi0.5TiO3 (NBT) ceramics were synthesized by conventional solid state reaction method. Structural and dielectric properties of these ceramics were investigated. Crystalline phase of sintered ceramics was investigated by X-ray diffraction (XRD). The Rietveld refinement of powder X-ray diffraction revealed that the prepared ceramics exhibit the rhombohedral space group R3c. Dielectric properties of Na0.5Bi0. analyzer.5TiO3 (NBT) ceramics were studied at different temperatures in a wide frequency range using impedance

High permittivity and low dielectric loss of Na0.5Bi0.5−xLaxCu3Ti4O12 ceramics

The phase structure, microstructure and dielectric properties of Na0.5Bi0.5−xLaxCu3Ti4O12 (NBLCTO) ceramics were investigated. La3+ substitution had a great influence on the phase structure and dielectric properties. The results showed that the pure phase could be more easily obtained when substituting La3+ for Bi3+. Under the same processing condition (970°C for 7.5h) and measuring condition (10kHz around room temperature), NBLCTO ceramics with x=0.10 possessed the highest permittivity (1.02×104) and lowest dielectric loss (0.022). The obtained NBLCTO ceramics with x=0.10 also had good frequency stability and good temperature stability (−1.87% to +3.27%) from −60°C to 120°C at both 1 and 10kHz. Complex impedance results revealed that the grain resistance Rg was 7.18Ωcm and the grain boundary resistance Rgb was 1.19×106Ωcm.

Dielectric Properties of Ga-Doped Na0.5K0.5NbO3

In this Article, we investigated the dielectric properties of B-site Ga-doped K0.5Na0.5NbO3 (KNN) in air using AC impedance spectroscopy from room temperature to about 800 °C. Powder X-ray diffraction (PXRD) studies showed the formation of perovskite-type structure with orthorhombic symmetry, √2ap × 4ap × √2ap (where ap is perovskite-type lattice constant) for x = 0.01, 0.1, and 0.13 members of Na0.5K0.5Nb1−xGaxO3. The PXRD result is similar to the parent KNN structure. AC impedance results showed mainly bulk contribution over the frequency range of 0.1 Hz to 1 MHz for the x = 0.01 member, while bulk and grain-boundary contributions were present for x > 0.01 in the same frequency range. Scanning electron microscopy was used to study the effect of microstructure change for Ga3+ substitution in KNN. The inclusion of Ga3+ in KNN showed a significant change in the microstructure. The dielectric properties of Na0.5K0.5Nb1−xGaxO3 were enhanced by increasing the Ga3+ content; among the compounds studied, the x =...