Nb-doped BaTiO3 Research Articles

Space-charge-induced colossal dielectric constant and large flexoelectricity in Nb-doped BaTiO3 ceramics

Donor doping can increase the dielectric constant of a material by several orders of magnitude due to induced space charge causing interfacial polarization. Giant dielectric properties and interface polarization are also both expected to greatly enhance the flexoelectric behavior of a material. In this work, a typical flexoelectric ceramic material, BaTiO3, was selected and donor doped using elemental Nb. Compared with the nominal BaTiO3 ceramic, the dielectric constant and flexoelectric coefficient of the Nb-doped BaTiO3 ceramics were significantly improved. The transverse flexoelectric coefficient of 0.3 mol. % Nb-BaTiO3 was found to increase to nearly 40 times the nominal value, reaching 387 μC/m. The results indicate that the giant dielectric response, and therefore the giant flexoelectric response, is the result of the combined effects of internal barrier-layer capacitance and surface barrier-layer capacitance. This study not only deepens the understanding of the semiconductor macro-dielectric effect and the flexoelectric mechanism caused by doping, but it also provides a feasible strategy for the design of giant dielectric/flexoelectric response materials and related devices with high dielectric constants and flexoelectric coefficients.

Electrochemical Synthesis of Nb-Doped BaTiO3 Nanoparticles with Titanium-Niobium Alloy as Electrode.

In this paper, Nb-doped BaTiO3 nanoparticles (BaNb0.47Ti0.53O3) were prepared using an electrochemical method in an alkaline solution, with titanium-niobium alloy as the electrode. The results indicated that under relatively mild conditions (normal temperature and pressure, V < 60 V, I < 5 A), cubic perovskite phase Nb-doped BaTiO3 nanoparticles with high crystallinity and uniform distribution can be synthesized. With this increase in alkalinity, the crystallinity of the sample increases, the crystal grain size decreases, and the particles become more equally dispersed. Furthermore, in our study, the average grain size of the nanoparticles was 5−20 nm, and the particles with good crystallinity were obtained at a concentration of 3 mol/L of NaOH. This provides a new idea and method for introducing foreign ions under high alkalinity conditions.

Efficient Production of Solar Hydrogen Peroxide Using Piezoelectric Polarization and Photoinduced Charge Transfer of Nanopiezoelectrics Sensitized by Carbon Quantum Dots.

Piezoelectric semiconductors have emerged as redox catalysts, and challenges include effective conversion of mechanical energy to piezoelectric polarization and achieving high catalytic activity. The catalytic activity can be enhanced by simultaneous irradiation of ultrasound and light, but the existing piezoelectric semiconductors have trouble absorbing visible light. A piezoelectric catalyst is designed and tested for the generation of hydrogen peroxide (H2O2). It is based on Nb‐doped tetragonal BaTiO3 (BaTiO3:Nb) and is sensitized by carbon quantum dots (CDs). The photosensitizer injects electrons into the conduction band of the semiconductor, while the piezoelectric polarization directed electrons to the semiconductor surface, allowing for a high‐rate generation of H2O2. The piezoelectric polarization field restricts the recombination of photoinduced electron–hole pairs. A production rate of 1360 µmol gcatalyst −1 h−1 of H2O2 is achieved under visible light and ultrasound co‐irradiation. Individual piezo‐ and photocatalysis yielded lower production rates. Furthermore, the CDs enhance the piezocatalytic activity of the BaTiO3:Nb. It is noted that moderating the piezoelectricity of BaTiO3:Nb via microstructure modulation influences the piezophotocatalytic activity. This work shows a new methodology for synthesizing H2O2 by using visible light and mechanical energy.

Electrochemical Synthesis of Nb-Doped Batio3 Nanoparticles with Titanium-Niobium Alloy as Electrode

Electrochemical Synthesis of Nb-Doped Batio3 Nanoparticles with Titanium-Niobium Alloy as Electrode

Prediction of Strong Converse Magnetoelectric Effect in Nb‐Doped BaTiO3‐Based Polar Metals

The origin of the converse magnetoelectric (CME) effect in the Nb‐doped BaTiO3 (NBTO) polar metal is investigated by density functional theory. Unlike the Fe doping system, where the magnetic moment is chiefly contributed by eg orbitals of the Fe atom, the magnetic moment of the NBTO system is mainly contributed by the dxz/dyz orbitals of Ti (Nb) atoms and highly depends on the polarization intensity. When the in‐plane compressive strain η ≤ −2%, the magnetic moment of the NBTO system is zero because electrons predominantly occupy the dxy orbitals. However, the switching process of the ferroelectric polarization induces a strong CME effect with significant magnetic moment changes. Especially, the magnetic moment changes in the NBTO system with the compressive strain η ≤ −2%, which is dozens of times of that of the unstrained NBTO system. These results are useful for designing new ultrafast and low‐power information storage devices with remarkable electrically controlled magnetism.

Flash sintering of barium titanate

A novel technique of low temperature and fast sintering is expected to meet the productive requirements of reducing energy consumption and improving efficiency. In this work, a dense Nb-doped BaTiO3 ceramic is obtained by a sintering method applying a direct current electrical field of 140 V cm−1 for 30 s at 1055 °C. In particular, the rapid densification mechanism of flash sintering Nb-doped BaTiO3 ceramic is explained by a model about liquid film which is formed by wetting at particle contacts, due to the Joule heating runaway. It is believed that the capillary forces generated from liquid film play a dominant role during flash sintering, which ensure the compaction of local particles and achieve the densified specimen in a relatively short time.

Enhanced resistive memory in Nb-doped BaTiO3 ferroelectric diodes

In this study, we report on enhanced resistive memory in BaTiO3-based ferroelectric diodes due to the doping of donors. A large ON/OFF current ratio of ∼2000, about two orders of magnitude higher than that of Au/BaTiO3/SrRuO3, is achieved in a Au/Nb:BaTiO3/SrRuO3 diode at room temperature. This can be ascribed to the enhanced ferroelectric-modulation on the potential barrier at the Nb:BaTiO3/SrRuO3 interface associated with the (NbTi4+5+)· donors, which gives rise to an efficient control of device transport between a bulk-limited current in the ON state and an interface-limited Schottky emission in the OFF state. In contrast, the resistance switching is suppressed in a Au/Fe:BaTiO3/SrRuO3 device since the (FeTi4+3+)′ acceptors suppress semiconducting character of the BaTiO3 thin film and make the polarization-modulation of the band diagram negligible. The present work facilitates the design of high-performance resistive memory devices based on ferroelectric diodes with controllable charged defects.

An effective optimization strategy and analysis for BaTiO3–Na0.5Bi0.5TiO3 system with colossal permittivity

Colossal permittivity (CP, ε＞104) behavior in BaTiO3–Na0.5Bi0.5TiO3 (BT-NBT) ceramics has been studied, which showed extremely high permittivity up to ~105. Dielectric properties of samples showed Debye-like relaxations in the frequency range 20Hz–30MHz. Two different polarizations located in grain boundaries and grains respectively are responsible for the CP behavior and the models of defect charge compensation achieved by niobium doping are proposed to explain the phenomenon of abnormal variation of dielectric constant.By using defect engineering, a Nb-doped BaTiO3 ceramics with stable colossal permittivity (εr =1.3×104 at 1kHz and room temperature)，high bulk resistivity (>1010Ω·cm) as well as relative low dielectric loss (tanδ~0.06) has been obtained over a wide temperature range of −55–150°C, satisfying IEA X8R specification, which has a potential application prospect in high capacity solid supercapacitor.

Effect of Sintering Time on Dielectric Properties of Barium Titanate and Nb Doped Barium Titanate

Barium titanate (BaTiO3) with its perovskite structure is a promising dielectric material for many applications such as transducers, actuators, high-k dielectrics and multilayer ceramic capacitors (MLCC). In this study, we have investigated the effect of sintering time on dielectric properties of BaTiO3 and Nb-doped BaTiO3. BaTiO3 was doped with 0.3 mol % niobium oxide (Nb2O5). At first, nanosized pure BaTiO3 and Nb2O5 doped BaTiO3 were milled, dried and pressed into pellets to prepare green samples. Then, the samples were sintered at 1275°C for different time periods ranging from 2 to 5 hrs. Single stage sintering was adopted for the densification of prepared samples. Microstructure of the sintered samples was investigated employing Field-emission scanning electron microscope (FESEM). Dielectric properties of the samples were measured using an impedance analyzer. Finally, a correlation was established between the dielectric properties of the sintered samples and their microstructure. Nb has shown to provide strong inhibiting effect after sintering the samples in the range of 2 to 5 hours at 1275°C thereby, resulted in higher dielectric properties of doped BaTiO3 ceramics compared to that of pure BaTiO3. The best room temperature dielectric constant of 7200 was obtained for Nb doped BaTiO3 sintered at 1275°C for five hours. Such improved dielectric constant is attributed to the optimum grain size of about 1 micron at this sintering temperature.

Nb-doped BaTiO3–(Na1/4Bi3/4)(Mg1/4Ti3/4)O3 ceramics with X9R high-temperature stable dielectric properties

Nb2O5 doped 0.8BaTiO3–0.2(Na1/4Bi3/4)(Mg1/4Ti3/4)O3 (0.8BT–0.2NBMT) polycrystalline ceramics were prepared by solid state reaction method. 0.8BT–0.2NBMT samples were observed to possess two dielectric peaks, which were attributed to the formation of core–shell structure (Huang et al. in J Eur Ceram Soc 36:533–540, 2015). Longer sintering induced uniform distributions of the additives. The introduction of Nb2O5 into 0.8BT–0.2NBMT could obviously bring about the improvement of the dielectric temperature stability, the degradation of the dielectric loss at room temperature and the decrease of the sintering temperature. The 0.8BT–0.2NBMT ceramics doped with 2.0 at% Nb2O5 could satisfy the temperature range of the X9R (−55 to 200 °C, △C/C25°C = ±15% or less) characteristics, with a moderate dielectric constant of 1130, low dielectric loss of 0.7%, low sintering temperature of 1050 °C and insulation resistivity of 5 × 1012 Ω cm at room temperature, which might be promising for practical use in multilayer ceramic capacitors. The inhomogeneous distribution and the existence of the secondary phases were responsible for this excellent dielectric temperature characteristic. The complex impedance analysis was introduced to elaborate the conduction mechanism.

Effects of ultrasonication and conventional mechanical homogenization processes on the structures and dielectric properties of BaTiO3 ceramics

The effects of the homogenization process on the structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics have been investigated using an ultrasonic homogenization and conventional mechanical methods. The reagents were homogenized using an ultrasonic processor with high-intensity ultrasonic waves and using a compact mixer-shaker. The components and crystal types of the powders were determined by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The complex permittivity (ε′, ε″) and AC conductivity (σ′) of the samples were analyzed in a wide frequency range of 20Hz to 2MHz at room temperature. The structures and dielectric properties of pure and Nb-doped BaTiO3 ceramics strongly depend on the homogenization process in a solid-state reaction method. Using an ultrasonic processor with high-intensity ultrasonic waves based on acoustic cavitation phenomena can make a significant improvement in producing high-purity BaTiO3 ceramics without carbonate impurities with a small dielectric loss.

Nb-doped BaTiO3-(Bi0.5Na0.5)TiO3 ceramics with core-shell structure for high-temperature dielectric applications

Nb-doped 0.90BaTiO3-0.10(Bi0.5Na0.5)TiO3 temperature-insensitive ceramics with novel core-shell structure were sintered at low temperature by the conventional solid-state reaction method. The beneficial role of Nb in facilitating the formation of core-shell structure because of chemical inhomogeneity is verified, which is responsible for the weak temperature dependence of dielectric properties. Temperature dependence of permittivity measured at different frequencies shows high frequency dispersion at low temperature, while without relaxor characteristic at high temperature. The Vogel–Fulcher model was adopted to study the relaxor behaviour of Nb-doped 0.90BaTiO3-0.10(Bi0.5Na0.5)TiO3 ceramics at low temperature. The samples with an addition of 1.5 mol% Nb2O5 provide a temperature coefficient of capacitance meeting the requirements of the X9R characteristic, and result exhibits an optimum dielectric behaviour of εr ∼1900, tanδ ∼1.8% at room temperature, making the material a promising candidate for high temperature applications.

Microstructure defects mediated charge transport in Nb-doped epitaxial BaTiO3 thin films

Nb-doped BaTiO3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal–semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.

Effects of a donor concentration on the structure of Nb-doped nano-sized BaTiO3 powders prepared by microwave-hydrothermal synthesis methods

BaTi1–xNbxO3 compounds (with x = 0.00, 0.01, 0.03, 0.06, and 0.09) are synthesized by the microwavehydrothermal (MH) method. The donor concentration effect on the structural properties is investigated. The new MH method is used instead of the previous solid state reaction for the BaTiO3+Nb2O3 system. In the MH process, as the niobium incorporation rate increases, the particle growth substantially slows down. The synthesis of Nb-doped BaTiO3 is investigated under the MH conditions subjected to 150°C for only 2 h using C16H36O4Ti (tetra-n-butyl orthotitanate), Ba(OH)2∙8H2O, and NbCl5 as Ba, Ti, and Nb sources respectively. For the phase evolution studies, X-ray diffraction patterns are analyzed and Raman spectroscopy is performed. The transmission electron microscope and the field emission scanning electron microscope images are taken for the detailed analysis of the grain size, surface, and morphology of the compound.

Microwave-hydrothermal synthesis of Nb-doped BaTiO3 nanoparticles under various conditions

Tetragonal BaTiO3 powders were synthesized by the microwave-hydrothermal (MH) method. The effects of the reaction time and temperature on the MH synthesis were investigated. Typical experiments were performed with a solid state reaction for the system BaTiO3 + Nb2O3 at a high temperature. In the MH method, at a shorter time and lower temperature, the rate of the formation of tetragonal BaTiO3 and of the growth of particles went down substantially. The microwave heating can be very fast and uniform through a self-heating process that results from the direct absorption of the microwave energy in the reaction mixture. The synthesis of Nb-doped BaTiO3 has been investigated under MH conditions in the temperature range of 120–180°C for 1–3 hours using C16H36O4Ti, BaH2O2 · 8H2O, and NbCl5 as Ba, Ti and Nb sources, respectively. In the phase evolution studies, the X-ray diffraction measurements and Raman spectroscopy were employed. The Transmission Electron Microscope and the Field Emission Scanning Electron Microscopy images were taken for the detailed analysis of the grain size, surface, and morphology. The MH method was applied for the synthesis of Nb-doped BaTiO3 via provided advantages of the fast crystallization and decreased crystallite size. The nucleation rate should have been high because of a high heating rate in microwave heating processes.

Effect of Donor Dope Ions, Compaction Pressures and Sintering Temperatures on PTCR and Dielectric Properties of BaTiO&lt;sub&gt;3&lt;/sub&gt;

Donor doped BaTiO3 is a well known PTCR material. Many PTCR theories have been written but none of them can completely explain the PTCR property. In this work, BaTiO3 samples doped with Sb, La, Nb and Pb ions and compacted under various uniaxial pressures were examined. Results show that Sb and La-doped BaTiO3 have PTCR properties corresponding to Heywang and Jonker models to a greater degree than Nb-doped BaTiO3. Moreover, it was found that La and Nb-doped Ba1-xPbxTiO3 samples sintered at l000-1100°C have good PTCR properties while samples of the same composition sintered at 1150-1200°C have fair to poor PTCR properties. The PTCR properties in these materials do not correspond to Heywang and Jonker models. The resistivity change in these materials at Curie’s point is relatively lower than the resistivity change at other temperatures.

Effect of Mn and Nb Doped BaTiO3 in the Dielectric Properties in the Ba(Mn1/2Nb1/2)xTi1−xO3

Polycrystalline samples of BaTi1−x(Mn0.5Nb0.5)xO3 with x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.175 have been synthesized by the high-temperature solid-state reaction technique. The effects of cationic substitution of manganese and niobium for titanium at B sites of the BaTiO3 perovskite lattice on symmetry and dielectric properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 K to 500 K and frequency range from 100 Hz to 2 × 105 Hz were studied. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. TC or Tm decreases when both manganese and niobium are introduced into the lattice of BaTiO3. High dielectric constant of around 9000 at TC = 280 K was found for Ba Ti0.925(Mn0.5Nb0.5)0.075O3 ceramic. A relaxor ferroelectric with ΔTm = 60 K and \( \varepsilon_{\rm{r}}^{\prime } \) of about 3500 at 10 kHz with Tm = 150 K was found for the BaTi0.85(Mn0.5Nb0.5)0.15O3 sample.

The PTCR Performance of Nb-Doped BaTiO&lt;sub&gt;3&lt;/sub&gt;-NBT Ceramics

In this paper, Nb-doped BaTiO3-(Na0.5Bi0.5)TiO3(BBNT-Nb) based PTCR ceramic material has been prepared using high purity Nb2O5, Bi2O3, Na2CO3,TiO2and BaTiO3powders as starting materials, and its structural and electrical properties are investigated. The results indicated that the Nb2O5dopant is helpful not only to promote the formation of tetragonal BBNT structure without any second phase, but also to decrease the room-temperature resistivity. For the 0.10at% Nb-doped BBNT material with BNT content 35mol%, the properties of room-temperature resistance of 104Ω·cm, temperature coefficient (αk) of 6.3%/°C, PTCR anomaly lg(Rmax/Rmin) of 3.6 and Curie temperature (Tc) of 193°C are obtained.

Effects of Nb2O5 doping on the microstructure and the dielectric temperature characteristics of barium titanate ceramics

In this work, the effects of Nb2O5 addition on the dielectric properties and phase formation of BaTiO3 were investigated. A core–shell structure was formed for Nb-doped BaTiO3 resulted from a low diffusivity of Nb5+ ions into BaTiO3 when grain growth was inhibited. In the case of 0.3–4.8 mol% Nb2O5 additions, two dielectric constant peaks were observed. The Curie dielectric peak was determined by the ferroelectric-paraelectric transition of grain core, whereas the secondary broad peak at lower temperature was due to strong chemical inhomogeneity in Nb-doped BaTiO3 ceramics. The dielectric constant peak at Curie temperature was markedly depressed with the addition of Nb2O5. On the other hand, the secondary dielectric constant peak was enhanced when sintered above 1280 °C for higher Nb2O5 concentrations (≥1.2 mol%). The Curie temperature was shifted to higher temperatures, whereas the transition temperature corresponding to the secondary peak moved to lower temperatures as increasing the amount of Nb2O5 more than 1.2 mol%. The decrease of this lower transition temperature was assumed to be closely related with the secondary phase formation when Nb concentration greater than 1.2 mol%. From XRD analyses, a large amount of secondary phases was observed when Nb2O5 amount exceeded 1.2 mol%. The coefficients of thermal expansion of Nb-doped BaTiO3 were increased with increasing Nb2O5 contents, resulting in large internal stress between cores and shells. Therefore, the shift of Curie temperature to higher temperatures was attributed to internal stress resulting from the formation of a core–shell structure and a large amount of secondary phase grains.

Sintering Behavior of Pure and Nb-Doped BaTiO&lt;sub&gt;3&lt;/sub&gt; Powder Prepared by High-Gravity Reactive Precipitation

Sintering behavior of pure and Nb-doped barium titanate powders prepared by high-gravity reactive precipitation (HGRP) process was investigated. A thermal dilatometer was employed to monitor the sintering shrinkage continuously during sintering. TEM and SEM were used to characterize the microstructures of the samples. The experimental results confirmed that Nb-doped BaTiO3 ceramics sintered at 1220°C for 2 h reached a larger densification of 97.0% relative density compared with 94.6% of pure BaTiO3 ceramics sintered at 1265°C for 2 h, and Nb-doped BaTiO3 ceramics had a smaller grain size (1.2μm) than that of pure BaTiO3 ceramics (2μm).