Optical and electric properties of strontium bismuth tantalate thin films

High quality SrBi₂Ta₂O₉ ferroelectric thin films were fabricated on platinized silicon using pulsed laser deposition. The optical properties of the thin films were studied by spectroscopic ellipsometry from the ultraviolet to the infrared region. Optical constants, n ∼ 0.25 in the infrared region and n ∼ 2.18 in the visible spectral region, were determined through multilayer analyses on their respective pseudodielectric functions. The band-gap energy is estimated to be 4.14 eV. It was found that the leakage current mechanism of the film was from bulk limited Poole-Frenkle emission to interface-controlled Schottky emission with applied field increasing, and that the breakdown field of the film had a negative linear variation with the logarithm of the electrode area.     

Nanostructures of bismuth sulphide: synthesis and electrical properties

Bismuth ammonium citrate complex (C24H20Bi4O28 x 6NH3 x 10H2O) interacted with sodium sulphide (Na2S) in presence of beta-cyclodextrin (beta-CD) yielding Bi2S3 nanospheres. Solvothermal treatment of the bismuth complex and dimethyl sulphoxide (DMSO) produced Bi2S3 nanorods. Reaction conditions were optimized to investigate the morphology evolution of the product. Electrical properties of the nanorods were monitored in details.     

Preparation,electrical, thermal and mechanical properties of near-stoichiometric lithium tantalate wafers

Journal of Materials Science: Materials in Electronics - Near-stoichiometric lithium tantalate (NSLT) crystal wafers were prepared by a vapour transfer equilibrium (VTE) method. The electrical,...     

Phase formation kinetics of nanoparticle-seeded strontium bismuth tantalate powder

Strontium bismuth tantalate (SBT) having composition of Sr_0.7Bi_2.3Ta₂O₉ has been prepared through sol-gel method using their corresponding metal alkoxides as precursors. Seeded SBT powder was prepared by the addition of 5 wt% of nanometer-sized SBT particles to the sol followed by pyrolysis. Differential thermal analyses (DTA) were performed on the unseeded and seeded powder and Aurivillius phase formation temperatures were found to be reduced by 60°C in the seeded ones. Non-isothermal kinetic analyses were applied to the DTA results to obtain activation energy and Avrami exponent values for the Aurivillius phase formation in unseeded and seeded samples. The activation energy for the Aurivillius phase formation was found to be 268 kJ/mol for the seeded ones, while 375 kJ/mol for the unseeded ones, which plays a major role for the enhanced kinetics in the seeded ones. The Avrami exponent values for the Aurivillius phase formation in unseeded and seeded ones were determined as 2.80 and 1.15, respectively, revealing different nucleation and crystal growth mechanisms.     

Grain-oriented fabrication of bismuth titanate ceramics and its electrical properties

The concept of grain-oriented fabrication in ceramics, which utilizes anisotropy either in morphology or some specific property of the particle, is reviewed. A fabrication method, which maximizes the grain orientation, is described for Bi(4)Ti(3)O(12 ). The process utilized plate-like morphology of Bi(4)Ti (3)O(12) particles and yielded a ceramic with an X-ray density of 95.4% and an unprecedented value of 100% for Lotgering's orientation factor in the direction of orientation. The dielectric and piezoelectric properties of this ceramic are described and compared to single crystal values. Complex impedance analysis of the ceramics was used to explain the dielectric relaxations at elevated temperatures. The use of grain-oriented fabrication as a practical technique for making polycrystalline ceramics with electrical properties close to those of single crystals (in the direction of orientation) is emphasized. The use of grain-oriented Bi(4)Ti(3)O(12) ceramics as a high-temperature piezoelectric transducer is suggested.     

Studies of the electrical properties of bismuth oxide films

A detailed study has been made of the resistivity , activation energy ΔE, Hall coefficient R_H, mobility μ, thermoelectric power and TCR of vacuum-deposited films of bismuth oxide evaporated from silica and molybdenum boats in the temperature range 78°–525°K. The electrical parameters of these films differed considerably from those of oxidized films and this difference has been attributed to the dissociation of the bismuth oxide and the formation of intermediate products.     

Ce-doped bismuth ferrite thin films with improved electrical and functional properties

Bi_1?xCe_xFeO₃ (BCFO) thin film capacitors (x = 0 to 0.2) are fabricated on indium tin oxide coated corning glass substrate by chemical solution deposition method. X-ray diffraction results show a partial phase transition from rhombohedral to tetragonal structure induced in BCFO thin film having preferred (110) orientation with increase in Ce dopant concentration. Current density–field (J–E) characteristics indicate that the leakage current density reduces by several orders of magnitude in Ce-doped BFO thin films resulting from smaller grain sizes and smoother surfaces. Space-charge-limited current and Fowler–Nordheim tunneling are identified as dominating leakage behavior in BCFO thin film capacitors at moderate and high field regions, respectively. Enhanced ferroelectric response with well-saturated (P–E) hysteresis loop is observed for Bi_0.88Ce_0.12FeO₃ thin film having high remnant polarization (P _r—127 µC/cm²) at an applied field of 1080 kV/cm. Bi_0.88Ce_0.12FeO₃ thin film exhibiting well-defined capacitance–field (C–E) butterfly loop with dielectric loss (tan δ—0.03) measured at 10 kHz suggested good ferroelectric properties with high tunability of about 88 %.     

Influence of samarium doping on structural and dielectric properties of strontium bismuth tantalate ceramics derived by molten salt synthesis route

Layered Sr(Bi_1?xSm_x)₂Ta₂O₉ ceramics with x ranging from 0 to 0.10 (10 mol%) were fabricated by the low temperature molten salt synthesis route. X-ray powder diffraction studies revealed that the single phase orthorhombic layered perovskite structure is retained in all these compositions. Scanning electron microscopic studies on these ceramics confirmed the presence of well packed equiaxed plate shaped grains. The dielectric and electrical conductivity properties were studied in the 100 Hz–1 MHz frequency range at 300 K. Interestingly, the 10 mol% samarium doped SrBi₂Ta₂O₉ ceramics exhibited high dielectric constant (ε_r = 155) and low dielectric loss (0.00298) compared to those of other compositions. The electrical conductivity of undoped and samarium doped ceramics increased linearly with increase in frequency.     

Size effect in the electrical properties of thin epitaxial bismuth films

The thickness dependence of the electrical properties of thin epitaxial bismuth films (of thickness 0.2–3 μm) was studied at 4.2 and 77 K. The size effect theory developed by Mayadas and Shatzkes was modified so that it could be applied to a system with two carriers (electrons and holes). The thickness dependence of the carrier densities was also taken into account.The specularity parameter P at the surface and the reflection coefficient R at the grain boundaries were determined to be 0.7 and 0.2–0.3 respectively. It should be noted that the effect of scattering of the carriers at the grain boundary planes parallel to the electric field could not be neglected.     

Preparation, sintering, and microstructures of strontium barium bismuth tantalate layered perovskite ceramics

The solid solutions of Ba-doped SrBi₂Ta₂O₉ layered perovskite ceramic powders have been successfully prepared via a two-step process using BiTaO₄ as a precursor. The lattice constants of the solid solutions monotonically increase with increasing barium-ion content. The sinterability of (Sr_1–xBa_x)Bi₂Ta₂O₉ powders is significantly improved by increasing the barium-ion content. When the specimens with high barium-ion contents are sintered at 1100°C, they thermally decompose to form rod-like grains and the matrix expands, leading to a lower density. The addition of barium ions to SrBi₂Ta₂O₉ also results in significant variation in the morphology of the sintered specimens and the occurrence of c-axis preferred orientation which is ascribed to the anisotropic growth of plate-like grains. The precise control of the barium-ion content as well as the sintering conditions is critical for obtaining densified barium-ion doped SrBi₂Ta₂O₉ ceramics with a pure, layered perovskite structure.     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Effect of iron on the electrical properties of lead–bismuth glasses

Semiconducting oxide glasses of the system (80 − x)Bi₂O₃–20PbO–xFe₂O₃, where x = 5, 10 and 15 mol.%, were prepared and investigated for dielectric properties in the frequency range 120–100 KHz and temperature range 300–550 K. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron. The ac conductivity results suggest that the correlated barrier hopping (CBH) is dominant in ac conductivity.     

Optical and electrical properties of multiferroic bismuth ferrite thin films fabricated by sol-gel technique

Single-phase multiferroic BiFeO₃ thin films have been prepared on LaNiO₃/Si(100) and Si(100) wafer via sol-gel technique. The films are polycrystalline with preferring orientation of (101). The film has a conspicuous absorption in the blue and green light region, and band gap of 2.74 eV. The refractive index and the extinction coefficient of the film is about 2.36 and 0.06 at 600 nm, 2.26 and close to zero in the range of 800-1200 nm, respectively. The films also exhibit favorable ferroelectric and dielectric properties. A large photo induced open-circuit voltage was observed, indicating that the film exhibits photovoltaic behaviours.     

Dc electrical properties and conduction mechanisms of Al-clay based composite resistors

We studied the electrical properties of composite resistors fabricated from materials of natural origin based on Al-kaolinite clay mixture. Our electrical measurements and microstructural studies reveal the effect of annealing schedule, insulating particle size and composition on the resistance of the cermet. We measured small values of activation energy of conduction from temperature dependence of resistance and compared these values of activation energy with those obtained from microstructural examinations using electron microscopy. The small activation energy in the range of 0.53–1.24 μeV obtained suggests conduction by direct or quantum mechanical tunneling between conducting grains. All the resistors were observed to show a negative TCR with some possessing TCR as low as 50 ppm/°C in magnitude, which further confirms the tunneling conduction process. The variation of resistivity with the volume fraction of the metallic phase was found to follow a percolative conduction expression of the form R(X) = R_M(x − x_c)^−t, with the critical exponent t and critical concentration x_c showing a significant dependence on firing temperature. We found that the critical exponent assumed a value of t = 2.0 ± 0.8, which is different from a universal value of 2.0. This was shown to result from tunneling- percolating nature of the cermet.     

Preparation and humidity-sensing properties of nanostructured potassium tantalate thin films

Nanostructured potassium tantalate (KT) thin films are prepared using a sol–gel process and the humidity-sensing behaviors of the films are investigated. The films possessed nano-sized grains and nanoporous structure. The KT film annealed at 500 °C showed high humidity sensitivity with nearly three orders change in the resistance during the relative humidity variation from 20% to 90%. The humidity-sensing behaviors of the thin films with annealing temperature are discussed.     

The influences of bismuth antimony additives and cobalt manganese dopants on the electrical properties of ZnO-based varistors

This paper investigates the influences of additive contents and the additive ratio to dopants on the electrical characteristics of ZnO-based varistors. Bismuth and antimony are chosen as the additives while cobalt and manganese are selected as the dopants in this study. Our previous works discussed the influences of the initial additive content on the electrical characteristics of ZnO-based varistors without considering the dopant content and the weight loss during processing and sintering. Therefore, in this study, we fabricated varistors with same initial formula after sintering for 1, 3 and 5 h, respectively. The sintering temperatures were 950 and 1100 °C. After sintering, the additive content and dopant content of the varistors were measured using an inductively coupled plasma-atomic emission spectrometer (ICP). The experimental results showed that when the additive-content varies from 1.44 to 3.59 at % and the dopant/additive ratio changes from 0.16 to 0.69, the nonlinear coefficient, α, reaches up to 48 and the breakdown field E_bk is to 895 V mm⁻¹. The average grain size is 2.7 μm. The α value is higher with the higher additive-content and the lower dopant/additive ratio and vice versa. The breakdown field E_bk is increased with the additive-content increasing and sintering temperature lowering at a given dopant-content. The grain size is increased with the increase in sintering temperature while the bismuth concentration decreased. The observed effects are related to the quality of grain boundaries and the conductivity of grains.