Undoped BaTiO3 Research Articles

Magnetic and nonlinear optical properties of BaTiO3 nanoparticles

In our earlier studies the BaTiO3 samples were processed at higher temperatures like 1000oC and explained the observed magnetism in it. It is found that the charge transfer effects are playing crucial role in explaining the observed ferromagnetism in it. In the present work the samples were processed at lower temperatures like 650oC-800oC. The carrier densities in these particles were estimated to be ∼ 1019-1020/cm3 range. The band gap is in the range of 2.53eV to 3.2eV. It is observed that magnetization increased with band gap narrowing. The higher band gap narrowed particles exhibited increased magnetization with a higher carrier density of 1.23×1020/cm3 near to the Mott critical density. This hint the exchange interactions between the carriers play a dominant role in deciding the magnetic properties of these particles. The increase in charge carrier density in this undoped BaTiO3 is because of oxygen defects only. The oxygen vacancy will introduce electrons in the system and hence more charge carriers means more oxygen defects in the system and increases the exchange interactions between Ti3+, Ti4+, hence high magnetic moment. The coercivity is increased from 23 nm to 31 nm and then decreased again for higher particle size of 54 nm. These particles do not show photoluminescence property and hence it hints the absence of uniformly distributed distorted [TiO5]-[TiO6] clusters formation and charge transfer between them. Whereas these charge transfer effects are vital in explaining the observed magnetism in high temperature processed samples. Thus the variation of magnetic properties like magnetization, coercivity with band gap narrowing, particle size and charge carrier density reveals the super paramagnetic nature of BaTiO3 nanoparticles. The nonlinear optical coefficients extracted from Z-scan studies suggest that these are potential candidates for optical imaging and signal processing applications.

Field-assisted sintering of undoped BaTiO3: Microstructure evolution and dielectric permittivity

Abstract We report, for first time, how electric fields influence the sintering of undoped BaTiO 3 , a ferroelectric material, and how this process affects the microstructure and the dielectric properties. Flash sintering is achieved at a furnace temperature of 688 °C under a field of 500 V cm −1 , producing specimens that are 94% dense. As a consequence, the grain size is much finer than in conventional sintering, which is shown to influence the Curie temperature and dielectric permittivity. Data obtained at different strengths of the electrical field, and current limits imposed on the specimen are presented in the form of a “processing map” that separates the safe region, where sintering is uniform, from the fail region, where the current flow in the sample becomes localized. The map illustrates that ceramics can respond by different mechanisms, with the dominant mechanism changing with the strength of the electrical parameters.

PTCR anomaly in barium-titanate-based composites

We have identified a PTCR anomaly in undoped BaTiO3 (BT) ceramics. This anomaly was ascribed to a disconnection of the semiconducting grains, due to dimensional changes of the BT grains at the Curie point, in a composite composed of two constituent BT phases, one with a low electrical resistivity and the other with a high electrical resistivity. The composite exhibits a significant PTCR effect of three orders of magnitude at the Curie temperature.Using a similar approach, a PTCR anomaly was observed in a composite where copper was used as the conductive matrix, while BT particles were used as the second constitutive phase in the composite, acting as a circuit-breaker, and disconnecting the continuous conducting phase at the Curie temperature.

Low temperature synthesis and characterization of lanthanide-doped BaTiO3 nanocrystals

The vapor diffusion sol-gel (VDSG) method was employed for the room-temperature synthesis of ~10 nm, aliovalently doped 0.4, 0.8, and 1.6 mol% La:BaTiO3 and 0.4, 0.6, and 1.2 mol% Dy:BaTiO3 nanocrystals. Maximum ensemble relative permittivities of 176 and 208 were observed in the 0.8 mol% La:BaTiO3 and the 1.2 mol% Dy:BaTiO3 nanocrystals, respectively, relative to 89 for undoped BaTiO3 (at 1 MHz, 25 °C) due to local disorder induced by aliovalent substitution.

Optical properties of sonochemically synthesized rare earth ions doped BaTiO3 nanophosphors: Probable candidate for white light emission

Undoped BaTiO3 and doped BaTiO3:RE (where RE=Sm3+, Ce3+, Dy3+, Tb3+and Eu3+) nanophosphors were synthesized sonochemically and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX (energy dispersive X-ray spectroscopy) and photoluminescence (PL) spectrophotometry. The resultant nanophosphors are single phase and rod shaped. The doped samples showed multicolor emission on single wavelength excitation. The luminescence decay curves for all the BaTiO3:RE3+ (RE3+=Eu3+, Dy3+, Sm3+, Tb3+) samples fitted well into bi-exponential decay fit indicating availability of the dopant ions on surface and core regions of the sample. In case of the double doped BaTiO3:Sm3+(2.5%):Tb3+(2.5%) sample, the green emission from Tb3+ was almost negligible. However, addition of Ce3+ ions in the Sm3+ and Tb3+ double doped host yielded relatively stronger green emission which has been assigned to energy-transfer between the Ce3+ and Tb3+ ions. The CIE coordinates of this triple doped BaTiO3:Ce3+(2%): Tb3+(2%):Sm3+(1%) sample lie in the white light region of the chromaticity diagram and has a quantum efficiency of 58%. Thus, this sample shows promise as good phosphor material for new lighting devices.

Complex diffusion behavior of oxygen in nanocrystalline BaTiO3 ceramics

(18)O/(16)O exchange annealing and subsequent Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis is used to investigate oxygen transport in dense, nanocrystalline (average grain size d ≈ 300 nm) ceramics of nominally un-doped BaTiO3. Isotope penetration profiles are obtained as a function of temperature, 973 < T/K < 1173, at an oxygen activity aO2 = 0.20 and as a function of oxygen activity, 0.002 < aO2 < 0.20, at T = 1073 K. All isotope profiles show the same unusual shape: a flattened profile over the first ∼10(2) nm, followed by a short, conventional diffusion profile. We demonstrate that the entire isotope profile can be described quantitatively by a numerical solution to the diffusion equation based on an increase in the local oxygen diffusion coefficient close to the surface. This position-dependent increase is attributed to additional oxygen vacancies that are generated by diffusion of chlorine impurities out of the ceramics. The presence of chlorine derives from the chemical route necessary to produce nanometric powders: it thus indicates a new manner in which nanocrystalline ceramics may differ from their microcrystalline counterparts.

Catalytic efficiency of some novel nanostructured heterogeneous solid catalysts in pyrolysis of HDPE

Abstract In the present study, the catalytic conversion of high density polyethylene (HDPE) to useful products has been investigated in the presence of BaTiO 3 based catalysts in a micro steel reactor at 350 °C and 30 min reaction time. The catalysts, including BaTiO 3 , Pb/BaTiO 3 , Co/BaTiO 3 and Pb–Co/BaTiO 3 were prepared in the laboratory by reactive calcination method and characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-rays (EDX), Surface Area Analyzer (SAA) and X-rays Diffractometry (XRD). The product yields (over all yields and yields of liquid, gas and coke/residue) as a function of individual catalyst concentration was studied. The result indicated a promising effect of the catalysts used on conversion to liquid products and their composition in term of carbon range (C 6 – >C 30 ) & hydrocarbon group types (paraffin's, olefins, naphthenics, and aromatics). Among the catalysts used, Pb–Co/BaTiO 3 gave the maximum yield of liquid products (86%) when used in 1 wt % loading. The same catalyst gave the average yield (20–25%) of different range hydrocarbons i.e. C 6 –C 12 , C 13 –C 16 , C 17 –C 20 and C 20 –C 30 . Inversely, the un-doped BaTiO 3, favored the formation of C 6 –C 12 and C 13 –C 16 range hydrocarbons, whereas Pb doped BaTiO 3 and Co doped BaTiO 3 enhanced the yield of C 13 –C 16 , and C 20 –C 30 range hydrocarbons. Regarding the hydrocarbon group types, all catalysts significantly increased the formation of paraffins and reduced olefins and naphthenes.

Lead-Free Oxide Thin Films for Gas Detection

In view to develop gas sensors, a first generation of lead-free thin films was deposited by different techniques on commercial Si and Al2O3 substrates. During our research project, the correlation between the micro structure of films, the structure of the embedded sensors and the applied temperature range, is being studied. In the first year, doped and undoped BaTiO3, KNbO3 and ZnO thin films have been deposited by sol-gel and PLD techniques. BT and BST films have shown a polycrystalline structure with very fine and regular grains, while disoriented grains with an average size ranging from 50 to 200 nm were observed on the KNbO3 film surface, and ZnO films exhibited a columnar growth. All films were characterized and finally embedded to make semiconductor gas sensors which have been tested under different gases. In this first generation of sensors, ZnO sensors have shown encouraging preliminary results under CO and H2S gases. Keywords : thin films, lead-free oxide, sensor, gas.

Lead-Free Oxide Thin Films for Gas Detection

In view to develop gas sensors, a first generation of lead-free thin films was deposited by different techniques on commercial Si and Al2O3 substrates. During our research project, the correlation between the micro structure of films, the structure of the embedded sensors and the applied temperature range, is being studied. In the first year, doped and undoped BaTiO3, KNbO3 and ZnO thin films have been deposited by sol-gel and PLD techniques. BT and BST films have shown a polycrystalline structure with very fine and regular grains, while disoriented grains with an average size ranging from 50 to 200 nm were observed on the KNbO3 film surface, and ZnO films exhibited a columnar growth. All films were characterized and finally embedded to make semiconductor gas sensors which have been tested under different gases. In this first generation of sensors, ZnO sensors have shown encouraging preliminary results under CO and H2S gases. Keywords : thin films, lead-free oxide, sensor, gas.

Determination of electronic and ionic conductivity in mixed ionic conductors: HiTEC and in-situ impedance spectroscopy analysis of isovalent and aliovalent doped BaTiO3

The ionic and electronic conductivities of nonstoichiometric BaTiO3 (undoped, Ca-doped, and Zr-doped BaTiO3–δ) ceramics were investigated through high temperature equilibrium conductivity (HiTEC) and in-situ impedance measurements at various equilibrium conditions with different oxygen partial pressures over a temperature range of 950–1050 °C. Contribution of mobile oxygen vacancies on the electrical conductivity has been determined by HiTEC measurement as a function of oxygen partial pressure; the electrical conductivity with mobile oxygen vacancies shows a broad transition from p-type to n-type, and thereby there is an increase of the minimum conductivity at the n–p transition point. Through combining in-situ impedance spectroscopy measurements with the HiTEC measurements, it was confirmed clearly that the mobile oxygen vacancy contributes to the total conductivity, and the oxides become mixed conductors around the n–p transition regime (minimum electronic conductivity regime). It was found that Warburg impedance can be observed at the condition of tion/telectronic ≳ 0.05 in the temperature range of 950–1050 °C and pO2 range of 0.95–10− 16 atm. The ionic conductivity varied with the concentration of extrinsic oxygen vacancies and dopants, and the activation energy for mobility of oxygen vacancy in Ca-doped BaTiO3–δ was found to be 1.04 ± 0.05 eV using the two techniques in a very good agreement.

Shallow donor level associated with hydrogen impurities in undoped BaTiO3

The influence of hydrogen impurities on the electronic properties of undoped BaTiO3 was studied from a microscopic point of view using the muon spin rotation and relaxation technique. Electron localization around an implanted positive muon, by analogy a hydrogen impurity, was observed below ∼80 K. The effective electron binding energy was estimated to be ∼10−2 eV, indicating that the hydrogen-induced defect forms a shallow donor level. At room temperature, the weakly bound electron is excited into the conduction band and behaves as a free carrier, which causes insulation degradation undesirable for capacitor applications.

Effect of a Boron Additive on the Microstructure and Dielectric Properties of BaTiO&lt;sub&gt;3&lt;/sub&gt; Thin Films Formed by Nanocrystal Deposition

Highly crystallized BaTiO3 thin films were fabricated by a nanocrystal sintering process. Boron alkoxide was introduced into a slurry of Mn-doped BaTiO3 nanocrystals with particle sizes of 5-7 nm. The deposited nanocrystal film on a (111)-oriented Pt/TiO2/Al2O3 substrate was sintered at a low temperature of 800 °C and the obtained film had highly densified and oriented microstructures. We found that the boron additive enhanced the grain growth of nanoparticles and as a result the dielectric constant of the thin film increased to 1100 at 10 kHz, which is much higher than that of undoped BaTiO3 thin films.

Energetics of Donor‐Doping, Metal Vacancies, and Oxygen‐Loss in A‐Site Rare‐Earth‐Doped BaTiO3

AbstractThe energetics of La‐doping in BaTiO3 are reported for both (electronic) donor‐doping with the creation of Ti3+ cations and ionic doping with the creation of Ti vacancies. The experiments (for samples prepared in air) and simulations demonstrate that ionic doping is the preferred mechanism for all concentrations of La‐doping. The apparent disagreement with electrical conduction of these ionic doped samples is explained by subsequent oxygen‐loss, which leads to the creation of Ti3+ cations. Simulations show that oxygen‐loss is much more favorable in the ionic‐doped system than undoped BaTiO3 due to the unique local structure created around the defect site. These findings resolve the so‐called “donor‐doping” anomaly in BaTiO3 and explain the source of semiconductivity in positive temperature coefficient of resistance (PTCR) BaTiO3 thermistors.

Enhancement in electro-strain behavior by La3+ substitution in lead free BaZr0.05Ti0.95O3 ceramics

Recently, lead-free piezoelectric ceramics have widely attracted interest among the research community, as they are considered to be potential substitutes for lead-based ceramics which causes environmental pollution due to the presence of hazardous lead oxide in them. In the present study we have synthesized La doped Ba1−x/2Lax/3(ZryTi1−y)O3 (x=0–0.06 in steps of 0.02; y=0, 0.05) ceramics by the conventional solid-state reaction method. Results reveal that electric field induced strain increases from ∼0.08% to ∼0.18% (at 40kV/cm applied field) for x=0.02 and y=0.05 of lanthanum and zirconium substitution respectively compared to undoped BaTiO3. It was also observed that, sample with 2mol% lanthanum could sustain higher electric field upto 120kV/cm during strain measurement (without electrical breakdown) and results showed highest strain value of ∼0.3% in this system.

Study of Ferroelectric Hysteresis Scaling Exponents in Aged Polycrystalline BaTiO3

The evolution of electric field dependent dynamic ferroelectric hysteresis area of aged and de-aged un-doped polycrystalline BaTiO3 (BTO) is studied. It is observed that the field exponent of aged sample is significantly different as compared to de-aged BTO at low strengths of applied electric field. The observations are discussed in terms of orientation of defect dipoles and it is suggested that the relation between hysteresis area (A) and the electric fields in aged samples is of the form⟨A⟩∝(E±EI ) n , where E is the applied electric field; EI is the internal bias field generated due to defect diploes and n is the scaling exponent.

Chemical investigation of Fe3+/Nb5+-doped barium titanate ceramics

Abstract Renewed interest in the perovskite ferroelectric barium titanate (BaTiO 3 ) has been driven by the introduction of large recoverable electrostrain in doped BaTiO 3 -based materials. Our previous work demonstrated that the potential for high-performance in Pb-free ferroelectrics based on BaTiO 3 was confirmed in Fe 3+ /Nb 5+ -doped BaTiO 3 systems. It is well documented that the electronic behavior of BaTiO 3 is intimately related to the chemical state of the constituents. However, information regarding the chemical states of the ions of the Fe 3+ /Nb 5+ -doped BaTiO 3 ceramics is currently unavailable. Consequently, this study describes the chemical state of sintered hybrid Fe 3+ /Nb 5+ -doped BaTiO 3 ceramics, compared with undoped BaTiO 3 ceramics derived from the same processing. Analysis by X-ray photoelectron spectroscopy (XPS) showed that the binding energy of Ti indicates the presence of more than one component of Ti within the doped BaTiO 3 ceramics, but only one component of Ti within the undoped BaTiO 3 ceramics. Unlike Ti, the XPS spectra indicates that more than one type of barium and oxygen species exist in both undoped and doped BaTiO 3 ceramics.

Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

Theoretical Analysis of Oxygen Vacancy Formation in Zr-Doped BaTiO3

One of the most serious problems for the development of multilayer ceramic capacitors (MLCCs) is that their electrical resistance decreases under long-term DC voltage. Oxygen vacancy migration in BaTiO3 is thought to be one cause of this deterioration. In this study, to understand this mechanism, quantitative analysis of the oxygen vacancy formation energy [Ef(VO)] in Zr-doped and undoped BaTiO3 was performed. The Ef(VO) of Zr-doped BaTiO3 was higher than that of undoped BaTiO3 because the valence of Ti in undoped BaTiO3 easily changed from +4 to +3 owing to oxygen vacancy formation, compared with that in Zr-doped BaTiO3. We also prepared undoped (BaTiO3) and Zr-doped (BaZr0.05Ti0.95O3) ceramic samples sintered under reducing atmosphere (T = 1573 K pO2 = 10-13 MPa). BaZr0.05Ti0.95O3 remained an insulator, but BaTiO3 showed semiconducting behavior. This experimental result corresponds well to theoretical results of first-principles calculations.

Application of BaTiO3 as anode materials for H2S-containing CH4 fueled solid oxide fuel cells

Undoped BaTiO3 perovskite oxide is more effective than SrTiO3 and La2Ti2O7 oxide as anode catalyst in SOFC fueled with H2S-containing methane. Electrochemical performance, impedance spectroscopy and other characterizations show that pure BaTiO3 is a good anode catalyst for conversion of methane in SOFC, especially in H2S-containing atmospheres. Compared with SrTiO3 and La2Ti2O7 samples, the BaTiO3−based fuel cell has higher resistance to carbon deposition, better electrochemical performance and much higher stability during long term operation. A maximum power density of 135 mW cm−2 was achieved at 900 °C with 0.5% H2S–CH4 in a fuel cell having a 300 μm thick YSZ electrolyte. High catalytic activity for methane conversion, mixed electronic and ionic conductivity, and the surface basicity of BaTiO3 unexpectedly provides promising performance as anodes in SOFC.

Comprehensive dielectric performance of bismuth acceptor doped BaTiO3 based nanocrystal thin film capacitors

We present a novel approach to preparing bismuth acceptor doped barium titanate nanocrystal formulations that can be deposited in conjunction with polymers in order to prepare a thin film nanocomposite dielectric that exhibits desirable capacitor characteristics. Exploring the limits of dielectric function in nanocomposites is an important avenue of materials research, while paying strict attention to the overall device quality, namely permittivity, loss and equivalent series resistance (ESR). Pushing capacitor function to higher frequencies, a desirable goal from an electrical engineering point of view, presents a new set of challenges in terms of minimizing interfacial, space charge and polarization effects within the dielectric. We show the ability to synthesize BaTi0.96Bi0.04O3 or BaTi0.97Bi0.03O3 depending on nominal molar concentrations of bismuth at the onset. The low temperature solvothermal route allows for substitution at the titanium site (strongly supported by Rietveld and Raman analysis). Characterization is performed by XRD with Rietveld refinement, Raman Spectroscopy, SEM and HRTEM. A mechanism is proposed for bismuth acceptor substitution, based on the chemical reaction of the alkoxy-metal precursors involving nucleophilic addition. Dielectric analysis of the nanocrystal thin films is performed by preparing nanocrystal/PVP 2–2 nanocomposites (no annealing) and comparing BaTi0.96Bi0.04O3 and BaTi0.97Bi0.03O3 with undoped BaTiO3. Improvements of up to 25% in capacitance (permittivity) are observed, with lower loss and dramatically improved ESR, all to very high frequency ranges (>10 MHz).