Effects of intense plastic straining on the structure of barium,lead, and cadmium titanates

Under the action of intense plastic straining (IPS), barium titanate (BaTiO₃) exhibits a phase transition from the tetragonal to cubic structure, while lead titanate (PbTiO₃) shows a tendency to such a transformation. In cadmium titanate (CdTiO₃), the IPS induces a transition from the perovskite to ilmenite phase.     

Fabrication of BaTiO3 nanoparticles and its formation mechanism using the high temperature mixing method under hydrothermal conditions

Barium titanate (BaTiO₃) single-crystalline nanoparticles have been prepared via high temperature mixing method (HTMM) under hydrothermal conditions. The crystallized products were characterized by X-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), Raman spectra, transmission electron microscopy (TEM). The BaTiO₃ nanoparticles can be prepared at dilute KOH as compared with the method mixed at room temperature. The results show that the stoichiometric BaTiO₃ nanoparticles were synthesized at [Ba/Ti]_solution = 1. The high temperature will significantly narrow the solubility difference between the barium and titanium sources and leads to a burst nucleation from the solution. The defect mechanism is used to illustrate the time-dependent transformation from cubic to tetragonal phase.     

Water-based sol–gel nanocrystalline barium titanate: controlling the crystal structure and phase transformation by Ba:Ti atomic ratio

Highly stable, water-based barium titanate (BaTiO₃) sols were developed by a low cost and straightforward sol–gel process. Nanocrystalline barium titanate thin films and powders with various Ba:Ti atomic ratios were produced from the aqueous sols. The prepared sols had a narrow particle size distribution in the range 21–23 nm and they were stable over 5 months. X-ray diffraction pattern revealed that powders contained mixture of hexagonal- or perovskite-BaTiO₃ as well as a trace of Ba₂Ti₁₃O₂₂ and Ba₄Ti₂O₂₇ phases, depending on annealing temperature and Ba:Ti atomic ratio. Highly pure barium titanate with cubic perovskite structure achieved with Ba:Ti = 50:50 atomic ratio at the high temperature of 800 °C, whereas pure barium titanate with hexagonal structure obtained for the same atomic ratio at the low temperature of 500 °C. Transmission electron microscope revealed that the crystallite size of both hexagonal- and perovskite-BaTiO₃ phases reduced with increasing the Ba:Ti atomic ratio, being in the range 2–3 nm. Scanning electron microscope analysis revealed that the average grain size of barium titanate thin films decreased with an increase in the Ba:Ti atomic ratio, being in the range 28–35 nm. Moreover, based on atomic force microscope images, BaTiO₃ thin films had a columnar-like morphology with high roughness. One of the highest specific surface area reported in the literature was obtained for annealed powders at 550 °C in the range 257–353 m²g⁻¹.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Synthesis of single-crystal barium titanate nanorods transformed from potassium titanate nanostructures

Single-crystal barium titanate (BaTiO₃) nanorods were synthesized by a hydrothermal reaction using precursors of potassium titanate (K₂O·nTiO₂, n = 4 or 6) nanostructures. The precursors of potassium tetratitanate (K₂Ti₄O₉) and potassium hexatitanate (K₂Ti₆O₁₃) nanostructures were prepared by a sol-gel method in which a growth of K₂O·nTiO₂ (n = 4 or 6) nanorods was induced by a role of pre-crystallized K₂O phase at defined heating temperatures. The specific morphologies of BaTiO₃ nanorods featured with flat or stepped surfaces and rectangular or polygonal cross-section, were obtainable by selecting the structure of precursors.     

Synthesis of BaTiO<Subscript>3</Subscript> powder from barium titanyl oxalate (BTO) precursor employing microwave heating technique

Cubic barium titanate (BaTiO₃) powder was synthesized by heating barium titanyl oxalate hydrate, BaTiO(C₂O₄)₂·4H₂O (BTO) precursor in microwave heating system in air at 500°C. Heating BTO in micro-wave above 600°C yielded tetragonal form of BaTiO₃. Experiments repeated in silicon carbide furnace showed that BaTiO₃ was formed only above 700°C. The product obtained was cubic.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

Effects of doping with La and Mn on the crystallite growth and phase transition of BaTiO3 powders

The effects of La and Mn dopants on the crystallite growth and the phase transformation of BaTiO₃ powders were studied. The barium titanate powders were obtained by calcining barium titanyl oxalate tetrahydrate in the temperature range 800 to 1200 °C. Crystallite growth of BaTiO₃ powders was promoted by the use of Mn dopant due to the increase of oxygen vacancies. The dissolution of La dopant into BaTiO₃ structure may decrease the oxygen vacancies so that the growth of BaTiO₃ crystallites is inhibited at high temperature ( 900 °C). When the crystallite size is small, the barium titanate can exist as a cubic phase due to the manifestation of the surface energy. Undoped cubic BaTiO₃ powders can be stable at a size < 30 nm. Doping with La and Mn would bring the crystallite size for the cubic-to-tetragonal phase transformation to 100 nm, resulting from the presence of cation or oxygen vacancies.     

Synthesis, characterization and dielectric properties of europium-doped barium titanate nanopowders

Europium-doped cubic barium titanate (BT) nanocrystals with % [Eu/Ti] mol ratio varying from 0.05 to 0.25 were prepared through hydrothermal route. The nano nature of these powders was confirmed by XRD and TEM studies. Pellets were prepared after calcining the powders at 1000 °C for 2 h. These pellets were annealed at 200, 500, 700 and 1000 °C for 2 h at each temperature and used for dielectric measurements. Raman spectra of two typical pellets with %[Eu/Ti] Eu/Ti mol ratios of 0.15 and 0.25 showed all the peaks characteristic of tetragonal BaTiO₃. Pure BT showed a low dielectric constant (DC) with a value of 398. Doping with small amounts of Eu resulted in many fold increase of DC values. A maximum value of 10576 at 1 KHz frequency was observed for the sample with % [Eu/Ti] mol ratio of 0.15. Lowering of Curie temperature T_c (95 to 110 °C) was observed for pure as well as Eu-doped barium titanate.     

UV-visible spectra of perovskite iron-doped Ba0.72Sr0.28TiO3

The ultraviolet-visible spectra of the pure barium strontium titanate (Ba_0.72Sr_0.28TiO₃) and the Fe³⁺-doped Ba_0.72Sr_0.28TiO₃ were measured. The pure barium strontium titanate exhibited an ultraviolet (UV) absorption effect. The addition of Fe₂O₃ resulted in an increase of absorption wavelength. This red-shift effect was very strong even though the amount of Fe³⁺ was very small. The similar phenomenon was also observed in pure BaTiO₃ and Fe³⁺-doped BaTiO₃. The UV-absorption behavior was discussed in terms of Fe³⁺ replacing Ti⁴⁺ in the titanate with perovskite structure.     

Design and development of SnO decorated BaTiO3 heterostructure device platform for ethanol vapor detection

Herein, we reported the SnO decorated BaTiO₃ heterostructure as well as pristine BaTiO₃ based ethanol gas sensing properties examined. Barium titanate (BaTiO₃) and tin oxide (SnO) materials have been successfully synthesized by the hydrothermal alkaline solution technique. Structural investigations carried out by X-ray diffraction (XRD) analysis suggested the cubic phase of BaTiO₃ and the tetragonal SnO phase of the materials. Transmission electron microscopy (TEM) suggested irregular nanospheres of BaTiO₃ and micro sheets of SnO. The macroporous nature of BaTiO₃ and mesoporous nature of SnO were confirmed through Brunauer–Emmett–Teller (BET) analysis.   The fabricated device of BaTiO₃/SnO heterostructure shows sensor response of 10% with the fast response/recovery time of 1.9/1.6 s at the operating temperature of 150 °C for 500 ppm of ethanol vapor. The highest performance for the BaTiO₃/SnO heterostructure device was found to be sensor performance of 343% for 500 ppm of ethanol vapor with fast response time of 2.4 s at the operating temperature of 250 °C and it shows excellent sensor response at higher temperature. 

     

Microwave synthesis of nano-sized barium titanate

Nano-sized barium titanate powders have been synthesized by microwave processing at 2.45 GHz. Using barium titanyl oxalate (BTO) as a precursor, microwave processing was carried out by heating the precursor to a temperature between 600 °C and 750 °C with different heating rates from 10 °C/min to 20 °C/min without isothermal holding. X-ray diffraction analysis indicates that the decomposed product at 680 °C was pure cubic BaTiO₃. The BET specific surface area of barium titanate powder, after microwave heating to 680 °C, was 14.2 ± 0.5 m²/g, corresponding to an average particle size of 70 nm. This particle size was confirmed by the scanning electron microscopy (SEM). Parallel study shows that the conventional heating in a regular resistance furnace using a similar heating schedule did not result in complete conversion of BTO. This study shows that the microwave processing significantly accelerated the decomposition of barium titanyl oxalate and reduced the temperature of barium titanate nano-powder formation, resulting in nano-sized pure cubic barium titanate powder.     

Investigating the vibration damping behavior of barium titanate (BaTiO<Subscript>3</Subscript>) ceramics for use as a high damping reinforcement in metal matrix composites

We have examined factors that affect the vibration damping behavior of the ferroelectric ceramic barium titanate (BaTiO₃) by measuring its low frequency (0.1–10 Hz) damping loss coefficient (tan δ) using dynamic mechanical analysis. In monolithic BaTiO₃, tan δ was found to increase with temperature up its Curie temperature (T _C), beyond which the damping capability exhibited a sharp drop. The abrupt drop as temperatures increase beyond T _C has been attributed to the disappearance of ferroelastic domains as the crystallographic structure of BaTiO₃ transforms from tetragonal to cubic. At temperatures below T _C, the damping coefficient is further shown to increase with decreasing frequency of the imposed vibration, and in microstructures with a high degree of tetragonality and large domain densities. Data further indicate that tan δ values tend to decrease with the number of cycles that are imposed; however, initial values can be restored if the material is allowed to age following loading.     

Mechanochemical synthesis of BaTiO<Subscript>3</Subscript> from barium titanyl oxalate

The effect of mechanochemical processing in air and water on the physicochemical transformations of barium titanyl oxalate has been studied using X-ray diffraction, thermal analysis, FTIR spectroscopy, temperature-programmed argon desorption, and particle size measurements. The results demonstrate that mechanochemical processing of barium titanyl oxalate in air leads to the formation of structurally imperfect barium titanate. During subsequent air calcination at 550°C, this material transforms into well-crystallized cubic BaTiO₃, whereas thermal decomposition of barium titanyl oxalate only yields cubic BaTiO₃ starting at 800°C. Mechanochemical processing in water leads to partial amorphization of barium titanyl oxalate, and conversion of the product to BaTiO₃ requires heat treatment at 700°C. All of the BaTiO₃ samples obtained via mechanochemical processing have a larger specific surface in comparison with samples prepared by conventional calcination of barium titanyl oxalate or other known processes.     

X-ray diffraction and microstructural studies on hydrothermally synthesized cubic barium titanate from TiO2-Ba(OH)2-H2O system

In our earlier studies synthesis of pure barium titanate (BT) from TiO₂-Ba(OH)₂-NH₃ system was reported. This work describes a novel route for preparing cubic barium titanate from TiO₂-Ba(OH)₂-H₂O system without addition of any mineraliser. The experimental parameters varied were: reaction time (half-an-hour to 3 h), reaction temperature (80 to 150 °C) and [Ba/Ti] ratio (0.92 to 1.64). The progress of reaction for formation of BT was monitored by analyzing the X-ray diffraction data obtained under different processing conditions. Mono-phasic barium titanate powder having a mean crystallite diameter (MCD) of 26 nm along (101) plane was formed when the reaction was carried out for 3 h at 150 °C. The estimated strains on the planes of the BT nano-crystals were found to be negligible. The microstructure of pure BT showed the particles to be of single crystallite nature with average size matching with the MCD value calculated from the XRD data.     

Preparation of monodispersed spherical barium titanate particles

Spherical barium titanate particles with cubic phase were synthesized by a low-temperature hydrothermal reaction. Firstly, The method of hydrolysis of titanium tetrachloride was used for producing spherical TiO₂ particles (0.45–1.5 μ m) with various concentrations of TiCl₄(0.05–0.2 M) and volume ratios of acetone to water solutions (RH = 0–4). These TiO₂ particles were converted to barium titanate by a hydrothermal conversion in a barium hydroxide solution. The size and morphology of the TiO₂ particles was controlled by the volume ratio of acetone to water (RH ratio) in the mixed solvent. At the RH ratio of 3, the morphology of TiO₂ particles was very uniform and discrete. These TiO₂ particles were in the anatase phase and were converted to the rutile phase when the calcination temperature increased to 700∘C and above. Uniform and spherical barium titanate particles were successfully synthesized from the as-prepared TiO₂ particles by using a hydrothermal reaction in a barium hydroxide solution. The Ba/Ti ratios, reaction temperature, and reaction time did not influence the size and morphology of BaTiO₃ particles, but increased the concentration of unfavorable salts such as Ba(OH)₂ and BaCO₃. The high purity BaTiO₃ particles could be obtained by washing with formic acid to remove the unfavorable salts. The size and morphology of the BaTiO₃ particles remained the same as those of the TiO₂ particles, confirming the in-situ transformation mechanism for the conversion of TiO₂ to BaTiO₃. The as-synthesized particles were cubic phase and transformed to tetragonal phase after calcinations at 1150∘C for 1 h. The mean density of the pellets sintered at 1300∘C for 2 h was 5.86 g/cm³ and accounted for 97.34% of the theoretical density.     

Phase transitions in the (BaTiO3)x/(BiFeO3)1−x composite ceramics: Dielectric studies

Dielectric studies were carried out for composite ceramics (BaTiO₃)_x/(BiFeO₃)_1−x (0 < x < 1) within a temperature range 23–450 °C. Linear permittivity studies at various frequencies showed the emergence of peaks near the temperatures of the ferroelectric phase transition in the BaTiO₃ grains and of the antiferromagnetic phase transition in the BiFeO₃ grains. The positions of the peaks did not depend visibly on frequency. The permittivity peaks near the antiferromagnetic phase transition shifted to low temperature with increasing the barium titanate fraction which suggests the reduction of the Neel temperature. The decrease in the Neel temperature in the composite ceramics was confirmed by measurements of the temperature dependence of the third harmonic generation.     

Effect of BaTiO3 additive on the electrical properties of Na0.50Bi0.50TiO3 lead free ceramics

The near morphotropic phase boundary (MPB) compositions of lead-free piezoelectric ceramics based on sodium bismuth titanate (Na_0.50Bi_0.50TiO₃: NBT) and barium titanate (BaTiO₃: BT) were carefully investigated by conventional high temperature mixed-oxide method. All the ceramics exhibit single phase rhombohedral symmetry. The frequency (100 Hz to 1 MHz) and temperature (Room temperature–500 °C) dependence of impedance spectroscopy of (1 − x)Na_0.50Bi_0.50TiO3–xBaTiO₃ (x = 0.0, 0.06, 0.07 and 0.08) ceramics were investigated by impedance analyzer. The frequency explicit plots of Z″ versus frequency at various temperatures show peaks in the higher temperature range (>400 °C). The compounds show dielectric relaxation, which is found to be of non-Debye type and the relaxation frequency shifted to higher side with increase in temperature. The activation energy values obtained for different BT content suggest that the electrical conduction in NBT is mainly due to the mobility of the ionized oxygen defects.     

Ceramic/natural rubber composites: influence types of rubber and ceramic materials on curing,mechanical, morphological,and dielectric properties

Influence of different types of rubber and ceramic material on cure characteristics, mechanical, morphological, and dielectric properties of natural rubber (NR) vulcanizate was studied. Two types of ferroelectric ceramic materials: barium titanate (BaTiO₃) and lead titanate (PbTiO₃) were prepared by solid-state reaction with calcinations at 1100 °C for 2 h. The ceramic powders were then characterized by X-ray diffraction (XRD), particle size analyzer, and SEM techniques. Ceramic/rubber composites were then prepared by melt mixing of rubber and ceramic powders. Two different types of NR (i.e., epoxidized NR [ENR] and unmodified NR) and two types of ceramic powders (i.e., BaTiO₃ and PbTiO₃) were exploited. It was found that incorporation of ceramic powders in rubber matrix and the presence of epoxirane rings in ENR molecules caused faster curing reaction, and higher delta torque but lower elongation at break. This is attributed to lower mobility of molecular chains and higher interaction between ENR molecules. Furthermore, SEM results revealed that the BaTiO₃ composites showed finer and better distribution of the particles in the rubber matrix than that of the PbTiO₃ composite. This caused superior mechanical properties of the BaTiO₃ composites. Furthermore, higher dielectric constant and loss tangent was observed in the ENR/BaTiO₃ composites.     

The dielectric and photochromic properties of defect-rich BaTiO3 microcrystallites synthesized from Ti2O3

We report here the synthesis of barium titanate (BaTiO₃) microcrystallites by using Ti₂O₃ powders as the raw material through a modified hydrothermal method. The BaTiO₃ contains abundant (1 1 1) twinned microcrystallites, along with a large amount of oxygen vacancies and Ti³⁺ cations. It is considered that (1 1 1) twins nucleate and grow from the face-shared TiO octahedra of rhombohedral Ti₂O₃. This unique BaTiO₃ structure presents lower phase transition temperature than normal BaTiO₃ and exhibits reversible photochromic effects under UV and NIR irradiation.