La-doped BaTiO3 Research Articles

The Piezocatalytic Degradation of Sulfadiazine by Lanthanum-Doped Barium Titanate.

Piezocatalysis, a heterogeneous catalytic technique, leverages the periodic electric field changes generated by piezoelectric materials under external forces to drive carriers for the advanced oxidation of organic pollutants. Antibiotics, as emerging trace organic pollutants in water sources, pose a potential threat to animals and drinking water safety. Thus, piezoelectric catalysis can be used to degrade trace organic pollutants in water. In this work, BaTiO3 and La-doped BaTiO3 were synthesized using an improved sol-gel-hydrothermal method and used as piezocatalytic materials to degrade sulfadiazine (SDZ) with ultrasound activation. High-crystallinity products with nano cubic and spherical morphologies were successfully synthesized. An initial concentration of SDZ ranging from 1 to 10 mg/L, a catalysis dosage range from 1 to 2.5 mg/mL, pH, and the background ions in the water were considered as influencing factors and tested. The reaction rate constant was 0.0378 min-1 under the optimum working conditions, and the degradation efficiency achieved was 89.06% in 60 min. La-doped BaTiO3 had a better degradation efficiency, at 14.98% on average, compared to undoped BaTiO3. Further investigations into scavengers revealed a partially piezocatalytic process for the degradation of SDZ. In summary, our work provides an idea for green environmental protection in dealing with new types of environmental pollution.

Impedance Spectroscopy of Fe and La-Doped BaTiO3 Ceramics

A wide range of the interesting properties of electroceramics Ba0.996La0.004Ti0.999O3 (BLT4) undoubtedly deserves differentiation and optimization. For this purpose, the corresponding donor oxide dope Fe2O3 was introduced in excess quantities into the base ceramics. In this way, an innovative ceramic material with the general formula of Ba0.996La0.004Ti1−yFeyO3 (BLTF), for y = 0.001, 0.002, 0.003, 0.004, has been produced. The crystal structure of BLTF ceramics was investigated using X-ray diffraction. The diffraction peaks in XRD confirm the formation of the tetragonal perovskite phase. The electrical properties of BLTF ceramics have been tested using impedance spectroscopy, in the frequency range of 20 Hz–2 MHz and the temperature range of 20–580 °C. To gain absolute certainty on the consistency of the measured data, the obtained impedance spectra were analyzed using the Kramers–Kronig method. The usage of an equivalent circuit, proposed by the authors, allowed grain and grain boundary resistivity to be obtained. Based on the diagram of the natural logarithm of the mentioned resistivity versus the reciprocal absolute temperature, the activation energies of the conductivity processes have been determined. The values of activation energies indicated that the admixture of iron introduced into the BLT4 ceramics played a crucial role in the conductivity of grains and intergranular borders.

Impact of the change in charge compensation mechanism on the electrical, dielectric, and structural properties of La-doped BaTiO3 ceramics

La-doped BaTiO3 ceramics are essential materials in electronic devices, finding applications in multilayer ceramic capacitors and positive temperature coefficient thermistors. While the electrical properties of La-doped BaTiO3 have been investigated, the impact of its room-temperature resistivity anomaly on dielectric properties remains unclear. We synthesized pristine and La-doped BaTiO3 (0.1 – 0.5 mol%) powders via hydrothermal methods, and then sintered bulk samples. Their resistivities (DC and AC), Curie temperature, room-temperature dielectric constant, and lattice volume with varying La doping concentrations were characterized. Beyond 0.3 mol%, the shift from electronic to ionic charge compensation mechanisms resulted in abrupt changes in resistivities, Curie temperature, and dielectric constant near 0.3 mol%. Given minimal changes in average grain size and relative density near 0.3 mol% La, the dominant factor influencing the dielectric constant peaking near this concentration was the shift in charge compensation mechanism.

Pressure Coupled Lanthanide Ion Doping to Enhance Optical Properties in BaTiO3.

Self-trapped excitons (STEs) typically give broadband photoluminescence emission with a large Stokes shift, which is important for the enhancement of the optical properties of materials. Here, low-dimensional La-doped BaTiO3 nanocrystals with defects are prepared using supercritical CO2 (SC CO2). The generation of the STEs is facilitated by doping La3+ ions and introducing CO2 pressure, which effectively enhance the luminescence intensity of BaTiO3. This discovery shows that the La ion doping concentration can modulate the photoluminescence of BaTiO3 nanocrystals under pressure. This work deepens the understanding of the influence of rare-earth-doped luminescent materials under pressure and provides insight to improve the capabilities of optical devices.

Abnormal grain growth and electrical properties of Ba-excessive La-doped BaTiO3 ceramics prepared from nanopowder synthesized by sol-gel method

Abnormal grain growth and electrical properties of Ba-excessive La-doped BaTiO3 ceramics prepared from nanopowder synthesized by sol-gel method

Engineering Electro-Optic BaTiO3 Nanocrystals via Efficient Doping.

Electro-optic (EO) modulators provide electrical-to-optical signal conversion relevant to optical communications. Barium titanate (BaTiO3 ) is a promising material system for EO modulation in light of its optical ultrafast nonlinearity, low optical loss, and high refractive index. To enhance further its spontaneous polarization, BaTiO3 can be doped at the Ba and Ti sites; however, doping is often accompanied by ion migration, which diminishes EO performance. Here, donor-acceptor doping and its effect on EO efficiency are investigated, finding that La-doped BaTiO3 achieves an EO coefficient of 42 pm V-1 at 1kHz, fully twice that of the pristine specimen; however, it is also observed that, with this single-element doping, the EO response falls off rapidly with frequency. From impedance spectroscopy, it is found that frequency-dependent EO is correlated with ion migration. Density functional theory calculations predict that the ion-migration barrier decreases with La3+ doping but can be recovered with further Mn2+ doping, a finding that prompts to prevent ion migration by incorporating Mn2+ into the Ti-site to compensate for the charge imbalance.

The Quantizable Contribution of Epdd, Sblc, and Iblc Effects to Colossal Permittivity in La-Doped Batio3 Ceramic

The Quantizable Contribution of Epdd, Sblc, and Iblc Effects to Colossal Permittivity in La-Doped Batio3 Ceramic

BaTiO3-based thermistor hollow fibers prepared using a phase inversion spinning process for energy efficient gas sorption

Positive temperature coefficient of resistivity (PTCR) hollow fibers that exhibit self-regulating heating characteristics have potential applications in temperature-swing adsorption systems (TSA), such as CO2 recovery and drying of compressed air. La-doped BaTiO3 hollow fibers displaying a PTCR effect were produced by phase inverting a casting solution consisting of N-methly-2-Pyrrolidone, polymethyl methacrylate, polyvinylpyrrolidone, BaTiO3, TiO2, and La2O3 through a spinneret into a coagulating waterbath. This was followed by polymer debinding, high temperature sintering between 1350−1400 °C and annealing in air at 1175 °C to produce hollow fibers of the composition Ba0.9975La0.0025TiO3. Hydrothermal synthesis was implemented to deposit an adsorbent porous zeolite X layer within the hollow fiber lumen, which was confirmed by electron dispersive X-ray spectroscopy and CO2 adsorption at 0 °C. Hence, these materials can be applied to energy efficient TSA gas separation processes. The results are discussed in terms of hollow fiber microstructure, adsorption characteristics and electrical properties.

Electrochemical Synthesis of La-Doped BaTiO₃ Nanopowders.

Electrochemical synthesis has been presented as a powerful technique to produce nanoparticles. However, it has been especially focused on noble metal particles, while few studies have been done on oxides production. On the other hand, when partially doped with trivalent cations at the barium sublattice, BaTiO₃-based ceramics are well known to exhibit semiconductive character, accompanied by a positive temperature coefficient of resistivity (PTCR). Here, we synthesized pure and La-doped BaTiO₃ nanoparticles electrochemically using a metallic titanium electrode as a Ti source. The powder synthesis was made in an electrochemical cell coupled to a thermostatic bath under mild conditions (ambient temperature and pressure) with an electrical potential up to 50 V and current of 3.2 A. In these conditions, the synthesized powders present nanometric size, confirmed by transmission electron microscopy images. The pseudo-cubic BaTiO₃ phase is confirmed by X-ray diffraction and Raman spectroscopy techniques. To check the quality, the powders were sintered at 1250 °C and the ceramics achieved a relative density of 95%. The BaTiO₃:La sintered ceramics present a PTCR jump of up to three orders of magnitude on resistivity with minimum value at room temperature of 105 Ω·cm.

Strain effects on conductivity and charge transport in La-doped BaTiO3 thin films

We investigate how epitaxial strain affects the conductivity and charge transport of Ba0.6La0.4TiO3 (BLTO) films deposited by pulsed laser deposition. Depositing BLTO films with thicknesses varying from 14.1 to 95.9 nm gives differing epitaxial strains, with a maximum strain up to ~6% for the thinnest film of 14.1 nm. Transport measurements demonstrate that film thickness (i.e. epitaxial strain) affects the conductivity, carrier mobility, and concentration. Measurements of resistivity versus temperature demonstrate that all the BLTO films undergo a distinct semiconductor-metal phase transition, and the transition temperature TSM also depends clearly on strain. For all the films, the charge transport follows the small-polaron hopping mechanism below TSM and the thermal phonon scattering mechanism above TSM. These results prove that strain in epitaxial films strongly affects the conductivity and charge transport of traditional insulating ferroelectric oxide films.

Effect of sintering atmosphere on the electrical properties of lanthanum doped barium titanate: an impedance spectroscopic study

The electrical properties of 0.1 mol% La-doped BaTiO3 was investigated by impedance spectroscopy after sintering the sample in air and H2 at 1350 °C. H2-sintered sample showed more semiconducting nature than air-sintered one due to a higher level of oxygen loss accompanied by reduction of Ti4+ to Ti3+. The overall resistance of the sample decreased with rise in temperature and change of sintering atmosphere from oxidizing to reducing. The higher value of activation energy obtained from Arrhenius activated hopping frequency fH for H2-sintered sample describes the delayed onset of frequency-dispersion in the conductivity curves than the air-sintered sample. The conductivity relaxation was studied in the light of frequency-dependence of the imaginary part of electric modulus and scaling studies of the real and imaginary parts of Z* elucidating the thermally activated relaxation dynamics.

Conductivity, charge transport, and ferroelectricity of La-doped BaTiO3 epitaxial thin films

La-doped BaTiO3 thin films (BLTO) were deposited by pulsed laser deposition, and a comprehensive investigation on their conductivity, charge transport, and ferroelectricity was carried out. Resistivity-temperature (T) measurements demonstrate that the conductivity of Ba1−xLaxTiO3 (x = 0.05, 0.1, 0.2, 0.3, and 0.4) films can be largely regulated in a wide range. The BLTO film exhibits typical semiconductor conduction behavior for x ⩽ 0.3, whereas a typical metallic conduction behavior was observed for x = 0.4 at T > 240 K. The La doping concentration x also plays an important role on the charge transport mechanisms. For x ⩽ 0.3, the charge transport follows small-polaron hopping at low temperature (T < 300 K) and thermal excitation at high temperature (T ⩾ 300 K). While the charge transport for x = 0.4 changes from small-polaron hopping to thermal phonon scattering with the increase of temperature. Piezo-force microscopy measurements reveal that BLTO films exhibit ferroelectricity for La doping concentration x up to 0.4. These results demonstrated that La doping plays an important role in regulating the conductivity and charge transport in BLTO films. More importantly, we revealed experimentally that macro metallic conduction and ferroelectricity can coexist in the La-doped BaTiO3 epitaxial thin films.

Study of La-doped barium titanate ceramics obtained by laser sintering technique

This work studies the influence of laser sintering on the semiconducting properties of La-doped BaTiO3 (BTL) ceramics. The BTL powders were synthesized using a solid-state reaction method and sintered via a new laser sintering technique. In this technique, a CO2 laser is used as the main heating source and no atmosphere control was employed. The BTL laser-sintered ceramics exhibited high relative density and a crack-free homogeneous microstructures after sintering at a laser power density of 5.0 W/mm2 for 30 s. The samples exhibited a positive temperature coefficient of resistivity (PTCR) increase of two orders of magnitude, and a room-temperature resistivity of 105 Ω.cm, even when sintered in an open atmosphere. X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and UV-Vis and impedance spectroscopy techniques were employed and results provided.

Effects of BaCO3 addition on the microstructure and electrical properties of La-doped barium titanate ceramics prepared by reduction-reoxidation method

Effects of trace BaCO3 addition were investigated on microstructure and electrical properties of La-doped BaTiO3 ceramics prepared via reduction-reoxidation method. The addition of BaCO3 could effectively facilitate the densification and grain growth of ceramics. SEM images suggested that numerous pores presented in ceramics due to the decomposition of BaCO3 to expel generated CO2 gas. The presence of pores promoted reoxidation of the reduced ceramics. As a result, lowering room-temperature (RT) resistivity and improving PTCR jump were simultaneously achieved as suitable amount of BaCO3 was added. An optimal addition of 0.3mol% BaCO3 led to a low RT resistivity of about 28Ωcm and a PTCR jump up to 103.7 after ceramics were fired at 1100°C in high-purity N2 and reoxidized at 800°C in air.

Crystal structure, dielectric, ferroelectric and energy storage properties of La-doped BaTiO3 semiconducting ceramics

Polycrystalline La-doped [Formula: see text] [Formula: see text] [[Formula: see text]] ceramics (denoted as BTO,BLT1,BLT2,BLT3) were synthesized by conventional solid-state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. XRD and Raman spectra revealed single-phase tetragonal perovskite crystalline structure. Well-saturated polarization–electric field ([Formula: see text]) hysteresis loops were observed with the measurement frequency of 50 Hz at room temperature and confirmed ferroelectric nature of these ceramics and a high recoverable electrical energy storage density of 0.350 J/cm3 with energy efficiency [Formula: see text], which is useful in energy storage capacitor applications. Dielectric studies revealed anomalies around 415–420 K and near the Curie temperature. The latter is attributed to the ferroelectric to paraelectric phase transition. Better dielectric performances were obtained for La-doped samples sintered at 1350°C for 4 h. Grain growth is inhibited with lanthanum (La) incorporation into the BTO lattice. Room temperature semiconducting behavior with positive temperature coefficient of resistivity (PTCR) behavior at [Formula: see text] is attributed to electron compensation mechanism.

Super-broad temperature stability achieved by la-doped BaTiO3–Bi0.5 Na0.5TiO3–Nb2O5 based ceramics

BaTiO3–Bi0.5Na0.5TiO3–Nb2O5–ZnO–Glass ceramics with La2O3 addition, were prepared and studied to satisfy super-broad temperature stability (from −55 to 325 °C, capacitance variation rate based on C20°C is within ±15 %). With the addition of 0.4 mol% La2O3, a remarkable high ceiling working temperature of 325 °C has been achieved. Meanwhile, the sample has good dielectric and electrical properties at room temperature (er = 2,121, tanδ = 1.82 %, ρV = 1.63 × 1011 Ω cm). La iron can substitute for Ti iron as La3+. The substitution decreases the spontaneous polarization of BaTiO3, and then weakens the ferroelectricity of BaTiO3. As a result, the temperature stability of the samples is improved obviously. The maximum of TCC value was reduced from 24 to only 7 % by doping 0.4 mol% La2O3. This substitution also gave rise to the densification of the system.

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.

Effects of Ag–La codoping on structure and electrical properties of BaTiO3 powder

Ag–La codoped BaTiO3 powders were prepared by sol–gel technology after the preparation of Ag-doped and La-doped BaTiO3 powders. Variations in the structure, constitution, morphology, and electrical properties of the modified BaTiO3 powders were characterized. It can be concluded that Ag–La codoping decreases the resistivity of the modified powders more significantly than Ag doping and La doping, respectively. The sample with the lowest resistivity was obtained by codoping with 0.1 at.% Ag and 0.3 at.% La, where the resistivity decreased to 7.13 × 102 Ω m from the value of 4.30 × 109 Ω m of the undoped powder. X-ray diffractometry (XRD) and Fourier-transform infrared (FTIR) analyses indicate that the main phase of the codoped powders transitions from tetragonal to cubic with increasing La doping content. Scanning electron microscopy (SEM) observations illustrate that codoping makes the particles distribute more equably. The relationship between the resistivity and the structure of the doped BaTiO3 powders is discussed based on defect chemistry.

Electric Properties of La3+ Doped BaTiO3 Ceramics

Barium titanate ceramic BaTiO3 (BT) has been investigated extensively because of scientific interest as well as various applications to electronic devices. When pure BaTiO3 is highly resistive at room temperature (ρ > 1010 Ωcm). However its electrical resistivity can be dramatically lowered by some dopants, like rare earth elements [1, 2]. In the present research lanthanum-doped BT ceramics described by the general formula Ba1-x La x Ti1-x/4O3, for x = 0.001 and x = 0.003, was prepared by free sintering method. The electrical properties of (BLT) materials were studied by impedance spectroscopy with a Quadtech 1920-type precision LCR meter and parameters of the phase transition were determined. The equivalent circuit method was applied to fit the experimental data. The possibility of application of La-doped BT ceramics for fabrication of piezoresistive transducers sensitive for small stress load are also discussed in the present paper.

Effects of La content on the properties of Ba1−xLaxTiO3 powders prepared by spray pyrolysis

Nano-sized Ba1−xLaxTiO3 (0 ≤ x ≤ 0.03) powders were prepared by ultrasonic spray pyrolysis from the spray solution with citric acid. The mean sizes of the primary particles decreased from 110 nm to 59 nm when the x of the Ba1−xLaxTiO3 powders was changed from 0 to 0.03. The BET surface areas of the powders changed from 9.1 m2/g to 16.9 m2/g. The pure BaTiO3 and La-doped BaTiO3 powders had both tetragonal and cubic crystal structures. The average grain size of the sintered BaTiO3 specimen was 2.8 µm, while those of the La-doped BaTiO3 pellets ranged from 1.04 µm to 0.68 µm according to the doping concentrations of La. The dielectric constant of Ba1−xLaxTiO3 (0.01 ≤ x ≤ 0.03) pellets ranged from 2500 to 3855 when sintered at 1280 °C.