Synthesis of barium strontium titanate nanorods in reverse microemulsion

Perovskite Ba_0.7Sr_0.3TiO₃ nanorods were synthesized in Triton X-100 reverse microemulsion at room temperature and characterized by XRD, ICP-AES, ED and TEM. The Ba_0.7Sr_0.3TiO₃ nanorods with a diameter of 60-100 nm and a length of 450-1200 nm showed a single-crystalline tetragonal structure. The size of nanorods was effectively tuned by changing w value (molar ratio of water to surfactant), aging time and reactant concentration.     

Physical and electromechanical properties of barium zirconium titanate synthesized at low-sintering temperature

Barium zirconium titanate or (Ba(Zr_xTi_1 − x)O₃, BZT) was prepared using homogeneous BZT powders derived from a sol-gel process. With a sintering aid, the firing temperature for the BZT ceramics was lower by about 30%, meanwhile, the electromechanical properties of the material were not degraded. Crystallographic phases of the BZT system were identified by the XRD data and Raman spectra and we found that the orthorhombic-perovskite BZT ceramic with x = 0.05 has the best dielectric and piezoelectric properties.     

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.     

Magnetically anisotropic barium ferrite thin films on sapphire by sol-gel process

Hexagonal barium ferrite (BaM) thin films have been prepared by sol-gel technique involving spin coating and annealing in air. Different ratios of Ba to Fe, different annealing temperatures and different annealing time are explored. X-ray diffraction shows that the films have been epitaxially grown on the sapphire (001) plane with [100] direction of BaM parallel to [110] of Al₂O₃, and the c-axes of them being parallel, while magnetic measurements show magnetically anisotropic loops with in-plane and out-of-plane intrinsic coercivity of 87.5 kA/m and 230.8 kA/m, respectively.     

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.     

Molten-salt synthesis of tetragonal micron-sized barium titanate from a peroxo-hydroxide precursor

Barium titanate (BaTiO₃) was produced from an barium-titanate-peroxo-hydroxide precursor material in NaCl-KCl and Na₂SO₄-K₂SO₄ salt mixtures or fluxes at temperatures up to 1080 °C via the molten-salt synthesis (MSS) method. Beside the different salt mixtures several other parameters were studied to determine the effect on the particle morphology. A relatively fast heating rate and a relatively high salt to precursor ratio resulted in a highly faceted morphology. The effect of the salt flux was clearly seen in the morphology of BaTiO₃ obtained by MSS at 1080 °C. Cube-shaped particles were observed for the chloride-flux-grown BaTiO₃ while hexagonal-shaped flat particles were observed for the sulfate-flux-grown BaTiO₃. BaTiO₃ particles produced in the chloride-flux were either {1 0 1} or {0 0 1} faceted. The hexagonal surface of the sulfate-flux-grown BaTiO₃ was {1 1 1} faceted.     

Characterization and microstructure of highly preferred oriented lead barium titanate thin films on MgO (100) by sol-gel process

Highly preferred oriented lead barium titanate (Pb_1−x,Ba_x)TiO₃ thin film, with particular emphasis on (Pb_0.5,Ba_0.5)TiO₃, can be obtained by spin-coating on MgO (100) substrate by using the precursor sol, which was synthesized from acetylacetone chelating with titanium isopropoxide and ethylene glycol as a solvent, in the sol-gel process. Film thickness, pyrolysis temperature and heating rate were studied systemically to investigate their influences on the formation of preferred oriented thin films. The highly preferred (001)/(100) oriented thin film could be obtained by the pyrolysis of wet film at 500 °C and annealing at 600 °C at a slow heating rate of 5 °C/min. It is confirmed that the tetragonal perovskite structure of the titanate ceramic decreases with an increase of Ba content in (Pb_1−x,Ba_x)TiO₃. The (001)/(100) oriented films were synthesized from all compositions between x = 0.2 and x = 0.8, at a crystallization temperature of 600 °C. In particular, for the Ba content in the range of x = 0.50.6, highly preferred (001)/(100) planes were observed.     

Electrical and optical properties of chemical solution deposited barium hafnate titanate thin films

We have investigated the electrical and optical properties of Ba(Hf_xTi_1 − x)O₃ (x = 0, 0.1, 0.2, 0.3, 0.4) (BHT) thin films deposited on platinized silicon and fused quartz substrates. Analyses of the X-ray diffraction patterns reveal that with the increase in Hf contents there is a systematic increase of the lattice constants of BHT films. Irrespective of the measurement frequencies the dielectric constants was found to be systematically decreased, whereas their frequency dispersion was found to be reduced with increasing Hf contents. The leakage current data measured using a metal-insulator–metal configuration reveal that the Schottky emission is the dominant leakage current mechanism in these films. BHT films, deposited on transparent fused quartz substrates, were also characterized in terms of their optical properties. For this purpose the transmittance of the undoped as well as Hf doped barium titanate thin films was measured as a function of wavelength in the range of 290 nm to 800 nm. The transmission spectra were analysed to estimate the wavelength dependence of the refractive indices/extinction coefficients as well as the variation of optical band gap of these films. With the increase of Hf contents, a systematic increase of the band gap [from 3.65 eV (undoped film) to 4.15 eV (40 at.% Hf doped barium titanate film)] was observed. The reduction of the leakage current with increasing hafnium substitution is discussed on the basis of an increasing Schottky barrier height and due to a simultaneous increase in the band gap of the material.     

Large-scale synthesis of nanocrystals of barium titanate and other titanates through solution-phase processes

We reported a large-scale synthesis of nanocrystals of BaTiO₃, SrTiO₃, PbTiO₃, Sr_xBa_1−xTiO₃ through low-temperature and solution-phase processes without any surfactant. The series of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Samples obtained were of high purity, consisting of nanoparticles with fine crystallinity and uniformity as well as good dispersibility in ethanol. This method might also offer an effectively new way to synthesis other titanate nanocrystals with perovskite structure in the future.     

Dependence of the refractive index grating in photorefractive barium titanate on intensity

The interference pattern of light waves creates a refractive index modulation in photorefractive media. This process is relatively well described by the theory (Kukhtarev equations) but deviations are found. Therefore, experimental methods are used in order to characterise the processes. The influence of the absolute intensity as well as the intensity ratio of the interfering waves on the refractive index modulation are studied in a two-wave mixing arrangement. Especially for the dependence on the absolute intensity the interesting relation Δn=f(I_abs)I_abs was found that is not predicted by the theory. Nevertheless, this experimental approximation can be used in calculations in order to minimise the error.     

Low temperature synthesis of aluminium titanate by an aqueous sol-gel route

Formation of aluminium titanate (AT) has been achieved at low temperature through sol-gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2-3 μm.     

Dielectric and microstructural properties of barium titanate hafnate thin films

Barium titanate hafnate (BaTi_1−xHf_xO₃, 0 ≤ x ≤ 0.25) thin films have been deposited by a chemical solution method on copper foil substrates. The films were crystallized at 900 °C and in a reducing atmosphere to prevent substrate oxidation. Perovskite phase formation was identified for each composition, accompanied by an increased pseudocubic lattice parameter. Temperature dependent dielectric measurements revealed a decreasing phase transition temperature and peak permittivity with increasing hafnium level. The decrease in permittivity resulted from grain size reduction with increasing hafnium content. Compositions containing 25 mol% barium hafnate display a deviation from Curie-Weiss behavior indicating the onset of relaxor behavior.     

Characterization and photoluminescence studies on hydrothermally synthesized Mn-doped barium titanate nano powders

Manganese doped cubic barium titanate nanocrystals with [Mn/Ti] mole percent varying from 0.1 to 3 were prepared through hydrothermal route at 150 °C. The mean crystallite diameters obtained for different Mn concentrations varied within 26 to 30 nm. TEM of a typical sample showed most of the particles as single crystallites (particle size 15-40 nm) with some weakly agglomerated particles. The photo luminescent (PL) spectra of each sample showed a sharp peak in the blue band centered approximately at 464 nm and a weaker peak in the green band centered nearly at 494 nm. The luminescent efficiency passed through maxima for the sample with 2% [Mn/Ti] molar ratio. Effect of calcination temperature in the range of 200 to 600 °C on PL spectra showed that the intensity of peak corresponding to blue region decreased with the increase in calcination temperature from 200 to 600 °C and for the sample calcined at 600 °C, only a broad peak corresponding to green luminescence region was observed.     

Effect of temperature schedule on the particle size of barium titanate during solid-state reaction

Nano-sized BaTiO₃ particles were synthesized by a solid-state reaction in air using a 2-step heat treatment process. The dependence of the particle size and tetragonality (=c/a) on the temperature schedule was investigated. The temperature was held for 10 h at an intermediate temperature before heating to the target temperature of 1000°C for 1 h. Although more heat was consumed, the powders synthesized by the 2-step heat treatment method showed a much smaller particle size with higher tetragonality than those produced by direct heating. For example, the mean particle size was <100 nm at a holding temperature ranging from 500-700 °C, while it was 246 nm for direct heating to the same target temperature of 1000 °C. This was explained by the enhanced nucleation rate during temperature holding stage based on the TG/DTA and high temperature XRD results.     

Low temperature fabrication of barium titanate hybrid films and their dielectric properties

A method for incorporating BT nano-crystalline into barium titanate (BT) films is proposed for a low temperature fabrication of high dielectric constant films. BT nanoparticles were synthesized by hydrolysis of a BT complex alkoxide in 2-methoxyethanol (ME)/ethanol cosolvent. As the ME volume fraction in the cosolvent (ME fraction) increased from 0 to 100%, the particle and crystal sizes tended to increase from 13.4 to 30.2 nm and from 15.8 to 31.4 nm, respectively, and the particle dispersion in the solution became more improved. The BT particles were mixed with BT complex alkoxide dissolved in an ME/ethanol cosolvent for preparing a precursor solution that was then spin-coated on a Pt substrate and dried at 150 °C. The dielectric constant of the spin-coated BT hybrid film increased with an increase in the volume fraction of the BT particles in the film. The dissipation factor of the hybrid film tended to decrease with an increase in the ME fraction in the precursor solution. The hybrid film fabricated at a BT fraction of 30% and an ME fraction of 25% attained a dielectric constant as high as 94.5 with a surface roughness of 14.0 nm and a dissipation factor of 0.11.     

Synthesis and properties of manganese-doped barium titanate

An oxalate route for the production of BaTiO₃ has been modified to incorporate Mn (upto 2%) as a dopant and the reaction sequence has been studied. The resulting Mn-doped BaTiO₃ exhibits a dielectric constant with an increasing insensitivity to temperature and applied a.c. field as the Mn content is increased. These samples possess a high electrical resistivity even after treatment in hydrogen at 1100°C and are therefore suitable as dielectric for multilayer capacitors with base metal electrodes.     

改进的sol-gel工艺制备细晶Ba0.6Sr0.4TiO3陶瓷及其介电性能的研究

用改进的sol-gel工艺制备了细晶钛酸锶钡(Ba0.6Sr0.4TiO3,BST)陶瓷块体,研究了BST陶瓷的结晶与介电性能.在这种改进sol-gel的工艺中,用传统的固相反应煅烧形成BST粉体,经高能球磨制备BST纳米陶瓷粉体,再将一定质量的纳米粉体加入到相同化学组成的BST的溶胶液中,经普球球磨12h后,制备成悬浮性好,分散均匀的浆料.浆料可用来制备BST陶瓷,并在1200℃保温2h烧结成瓷,结果显示,BST陶瓷块体结构致密,晶粒尺寸在0.15～2μm之间.分析了样品的介电性能和晶粒尺寸对材料介电性能的影响.介电温谱显示,在0℃,100kHz时,相对介电常数为2500,介电损耗为0.02;并且存在明显的弥散相变.     

Novel synthesis of aligned Zinc oxide nanorods on a glass substrate by sonicated sol-gel immersion

For the first time, aligned ZnO nanorod structured thin films have been synthesized on a glass substrate, which had been coated with an Al-doped ZnO thin film, using the sonicated sol-gel immersion method. These nanorods were found to have an average diameter of 100 nm and an average length of 500 nm, with hexagonal wurtzite phase grew preferentially along the c-axis direction. A sharp ultra-violet (UV) emission centred at 383 nm corresponding to the free exciton recombination was observed in a room temperature photoluminescence (PL) spectrum. The prepared ZnO nanorod structured thin film is transparent in the visible region with an average transmittance of 78% in the 400-800 nm wavelength range and high absorbance properties in the UV region (< 400 nm). The results indicate that the prepared ZnO nanorods are suitable for ultra-violet photoconductive sensor applications.     

Synthesis of barium titanate nanoparticles via a novel electrochemical route

An electrochemical route from Ti metal plate in KOH and Ba(OH)₂ electrolyte at room temperature is first established for the synthesis of BaTiO₃ nanoparticles. Anodic sparks play a key role, and KOH concentration is one of the most significant factors which affect the appearance of anodic sparks in this method. XRD patterns show that the powder obtained in our study is a pure perovskite phase BaTiO₃ with a cubic structure, whose size and morphology are subsequently studied by TEM. The mean diameter of the particles is 13.8 nm and the standard deviation (S.D.) fitted is 6.26 nm. It is also found that the mean size of the obtained nanoparticles increase from 13.8 nm to 168.0 nm, when 60 vol.% absolute ethanol is replaced by distilled water as the solvent of the electrolyte.     

乙醇热法合成纳米钛酸钡及其形成机理的研究

研究了常压下以偏钛酸和氢氧化钡为原料，乙醇为溶剂制备纳米钛酸钡粉末的工艺条件。结果表明反应原料的钡钛比1.0：反应温度79℃；反应时间6h；pH值11为最佳制备条件．通过对在最佳条件下所得产物的XRD分析，表明钛酸钡粉体为立方相，a值约为4．028,TEM分析表明，分散的钛酸钡纳米粒子呈方形，平均粒径约20nm；ED分析表明，钛酸钡纳米粒子为多晶结构，其中有少量的单晶存在，通过对不同反应时间合成的产物的XRD分析，认为本法合成的钛酸钡为原位转变形成机理。