Barium titanate characterization by differential scanning calorimetry

Differential scanning calorimetry (DSC) was used to characterize barium titanate formed after decomposition of barium titanyl oxalate. Three different methods of the oxalate precipitation reaction were used to prepare barium titanyl oxalate which after calcinations result in barium titanates with different barium to titanium ratio (A/B). It appears that two factors have effect on Curie temperature: barium to titanium ratio and mechanical stress introduced by milling.     

Ultrafine Barium Titanate Powders via Microemulsion Processing Routes

Three processing routes have been used to prepare barium titanate powders, namely conventional coprecipitation, single-microemulsion coprecipitation using diether oxalate as the precipitant, and double-microemulsion coprecipitation using oxalic acid as the precipitant. A single-phase perovskite barium titanate was obtained when the double-microemulsion-derived oxalate precursor was calcined for 2 h at a temperature of as low as 550°C, compared to 600°C required by the single-microemulsion-derived precursor. A calcination for 2 h at >700°C was required for the conventionally coprecipitated precursor in order to develop a predominant barium titanate phase. It was, however, impossible to eliminate the residual TiO₂ impurity phase by raising the calcination temperature, up to 1000°C. The microemulsion-derived barium titanate powders also demonstrated much better powder characteristics, such as more refined crystallite and particle sizes and a much lower degree of particle agglomeration, than those of the conventionally coprecipitated powder, although they contained ∼0.2 wt% BaCO₃ as the impurity phase.     

Preparation of Stoichiometric Fine Lead Barium Titanate Powder

Lead barium titanate powder with 0.03–0.15 μm particle sizes was prepared from lead barium titanyl oxalate which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical factor in preparing the barium titanyl oxalate was the reaction time. It was necessary to allow 2–4 h to synthesize the oxalate to get a single-phase barium titanate. The critical factors in preparing the lead titanyl oxalate were pH and the concentration of the solution. It was necessary to adjust the pH to around 0.5 and the concentration to <0.08 M . When lead barium titanyl oxalate is prepared, low pH, low concentration, and a long reaction time are necessary.     

Alkoxide-Hydroxide Route to Syntheltize BaTiO3-Based Powders

When preparing homogeneous, fine barium titanate powders, the major difficulty is to avoid the spontaneous self-condensation between the Ti-OH groups. In the usual way of preparing fine barium titanate powders, chelating agents (citrate, oxalate) or simply unidentate ligands (alkoxy or carboxyl groups) are used to complex titanium atoms. Another way is to mix barium and titanium precursors in a strongly basic medium. The condensation between the Ti(OH)^2-₆Ba²⁺ species directly gives the perovskite compound. Using an alkoxide-hydroxide route, a homogeneous Ba-Ti solution was prepared that completely advanced by condensation between the Ti(OH)^2-₆Ba²⁺ species and led to a controlled-stoichiometry powder. Concerning pure barium titanate, dried powders exhibited the cubic perovskite structure, and a direct sintering at 1150°C, without calcination, led to highly dense BaTiO₃ bodies with fine-grained uniform microstructure (1 μm) that exhibited a high permittivity value at room temperature ( K = 5400). The alkoxide-hydroxide method was also used to prepare dense alkaline-earth perovskite ceramics with complex compositions.     

一种钛酸钡制备方法实验研究

以硫酸法钛白生产过程中的中间产品工业钛液（TiOSO4）为钛源,通过常温水解获得正钛酸,经草酸溶解获得草酸氧钛酸,再与氯化钡共沉淀得到草酸氧钛酸钡,高温煅烧后制备得到电子级钛酸钡产品。实验确定最佳制备条件：钛液水解pH为2.5～3.5,草酸氧钛酸生成温度和草酸氧钛酸钡共沉淀温度均选择50～70 ℃,共沉淀pH为2.5,煅烧温度为800 ℃,煅烧时间为2 h。分析结果表明,以工业钛液为钛源生产钛酸钡的成本明显低于偏钛酸。     

Density functional theory investigation of site predilection of Fe substitution in barium titanate

The site predilection and effects of the impurity in the form of Fe (II) and Fe (III) in the tetragonal barium titanate lattice were systematically determined by density function theory calculations. All electron calculation was carried out in the local density approximation (LDA). It is shown that both Fe (II) and Fe (III) prefer to substitute at the titanium site with oxygen vacancy compensation as a result of lowest substitution energy. Effect of Fe dopant both in form of Fe (II) and Fe (III) at titanium site with oxygen vacancy compensation lead to change in electrical property in terms of energy band structure of the tetragonal barium titanate lattice.     

Effect of Composition and Size of Crystallite on Crystal Phase in Lead Barium Titanate

Lead titanate, barium titanate, and lead barium titanate powders (>99.9% pure), the particle size of which varied from 0.03 to 0.15 μm depending on the calcination temperature and the composition, was prepared from barium lead titanyl oxalate, which was previously prepared by reacting high-purity ammonium titanyl oxalate with barium and lead acetate. The critical crystallite size of BaTiO₃ powder from the cubic to the tetragonal phase is around 1 μm. Pb_0.3Ba_0.7TiO₃ powder with an average size of 0.057 μm showed the tetragonal phase.     

Factors Affecting the Preparation of Barium Titanyl Oxalate Tetrahydrate

Several experiments have been conducted to investigate the preparation of barium titanyl oxalate tetrahydrate (BTO). Differential thermal analysis and thermogravimetric analysis were employed to investigate the thermal decomposition, and an X-ray diffractometer and a transmission electron microscope were used to analyze the phases and crystalline states. It has been found that BTO is a nonstoichiometric compound, in which barium hydrogen oxalate hydrate was inserted by the titanium species. Moreover, it has been shown that a mixture would from rather than BTO, depending on pH, mixing order, and oxalate solution.     

13C NMR Study of the Solution Chemistry of Barium Titanium Citrate Gels Prepared Using the Pechini Process

The chemistry of the initial precursor solutions of the barium titanate citrate gel prepared using the Pechini process was characterized by carbon nuclear magnetic resonance spectroscopy (¹³C NMR). Several experiments have been conducted to investigate the effect of the order of adding the species in the initial precursor solutions on synthesis of the barium titanium citrate gel. Based on the data from ¹³C NMR and photoacoustic Fourier-transform infrared spectroscopy (PA-FTIR) in previous work, it was found that the alcoholic and terminal carboxyl ligands of citric acid (CA) chelating with titanium ions are deprotonated. Esterification has a significant influence on the reaction of the species in the solution. Reaction mechanisms of the species in the precursor solution have been detailed. The possible molecular structures of Ti-CA and a barium titanate mixed-metal CA complex are proposed.     

空心钛酸钡的制备及其形成机理

以二氧化钛（TiO₂）和八水合氢氧化钡[Ba（OH）₂·8H₂O]为原料,采用水热合成法,成功制备出具有四方相晶型和空心形貌结构的钛酸钡粉体。利用透射式电子显微镜（TEM）和X射线衍射（XRD）对样品的形貌结构和晶型做了表征,通过研究反应过程中钛酸钡粉体的结构和晶型随时间的变化过程,对空心钛酸钡的形成机理做了详细的探讨,并考察了不同反应温度和钡浓度对钛酸钡粉体结晶和生长的影响。研究结果表明：反应温度和钡浓度会影响钛酸钡粉体的晶型和形貌,并以此提出了一种空心钛酸钡的形成机理;当反应温度为180 ℃、钡浓度为3.0 mmol/L时,能获得粒径分布均匀的四方相晶型的空心钛酸钡粉体。     

Alternative Route for Synthesis of Barium Titanyl Oxalate: Molecular Precursor for Macrocrystalline Barium Titanate Powders

An important molecular precursor to barium titanate, namely, barium titanyl oxalate [BaTiO(C₂O₄)₂.4H₂O], has been synthesized by an alternative route. An alcoholic solution containing 1 mol of butyl titanate monomer [(C₄H₉O)₄Ti] is reacted with alcoholic solution containing 2 mol of oxalic acid (H₂C₂O₄:2H₂O) to form an intermediate soluble oxalotitanic acid [H₂TiO(C₂O₄)₂.nH₂O]. The oxalotitanic acid in alcoholic medium is subjected to cation exchange reaction with aqueous solution containing equimolar barium acetate to form an insoluble barium titanyl oxalate (BTO) in yields of 80–85% at room temperature. The pyrolysis of BTO in air at T .750°C/5 h produced barium titanate (BT) powders.     

Phase development of barium titanate from chemically modified-amorphous titanium (hydrous) oxide precursor

A synthesis procedure for barium titanate involving a chemically modified titanium precursor has been developed. Using a titanium isopropoxide precursor modified with acetylacetone and barium acetate, coprecipitated gels were obtained by addition to a KOH solution. Direct precipitation of cubic BaTiO₃ from such precursor suspensions was obtained under hydrothermal conditions. The pH value was found to be a critical reaction parameter such that production of phase pure BaTiO₃ required high pH (>13.0), a finding consistent with thermodynamic predictions of the Ba–Ti–H₂O stability system and prior hydrothermal syntheses. It was determined that phase-pure barium titanate can be synthesized at temperatures as low as 50 °C and that higher reaction temperatures accelerate the crystallization process. The particle size of the synthesized powder ranged from 50 to 350 nm for the synthesis conditions explored in the current work.. It was demonstrated that particle size can be controlled by proper selection of the hydrothermal synthesis conditions such as reaction concentration, temperature, and time. The chemically modified synthesis produces barium titanate more rapidly at lower reaction temperatures than previously reported for similar syntheses.     

Properties of lanthanum doped BaTiO3 produced from nanopowders

Pure and barium titanate (BT) powders doped with different lanthanum concentration were prepared by the polymeric precursor method (Pechini process) which was carried out as a three-stage process from organometallic complexes. Sintering of pressed powders was performed at 1300 °C for 2, 4 and 8 h. XRD analysis showed cubic BT powders with crystallite sizes between 20 and 25 nm and tetragonal crystal structure of BT ceramics. The influence of sintering time on grain growth was fairly obvious. It was found that lanthanum doping has significant effect on powders particle size and ceramics grain size. The influence of lanthanum concentration on grain size inhibition, improving the dielectric properties of BT ceramics was detected. The relation between sintering time, grain size, structure and electrical properties of the BT ceramics was analyzed.     

Preparation of Spherical, Solid Barium Titanate Particles with Uniform Composition at High Precursor Concentration by Spray Pyrolysis

Hydrolysis-assisted spray pyrolysis (HASP) using dimethyl oxalate as hydrolyte was found to be applicable to precipitation of solid, spherical BaTiO₃ powder with uniform composition when the stock solution concentration was high (>1.0 M ). Solid, dense powder with uniform composition was successfully obtained because barium titanium oxalate was prepared from partial hydrolysis of dimethyl oxalate and coprecipitation of oxalate with barium and titanium during the hydrolysis–precipitation process, and then the oxalate particles became seeds in the following process. The sintered sample from the as-prepared BaTiO₃ powder led to a higher dielectric constant and lower loss.     

Processing of Positive Temperature Coefficient Thermistors

The controlled addition of impurities such as lanthanum in barium titanate and barium strontium titanate systems results in thermistor materials which have large positive temperature coefficients of resistance over controlled temperature ranges. The resistivity in these systems is sensitive to the concentration of the trace additives, to undesirable impurities in the raw materials, and to the sintering and maturing conditions. Ceramic procedures well adapted to prepare these thermistors reproducibly have been developed.     

Preparation and characterizations of tetragonal barium titanate powders by hydrothermal method

Tetragonal barium titanate powder with an average particle size of 80 nm has been successfully prepared by a hydrothermal process at 240 °C for only 12 h. The influence of processing parameters on the phase and the particle size of hydrothermally derived BaTiO₃ powders was investigated. Increasing NaOH excess concentration and decreasing the initial titanium tetrachloride concentration promote to increase the particle size and are benefit for preparation of tetragonal BaTiO₃ powder, while increasing the reaction temperature and time also obtain same result. There is a relationship between the particle size and the phase of BaTiO₃ powder and a critical size of transformation of cubic-BaTiO₃ to tetragonal-BaTiO₃. In the present work the critical size was 80 nm and finer than other previous works.     

Preparation of BaTiO3 nanopowders by the solution combustion method

Barium titanate was synthesized by the method of exothermal combustion in solutions using barium nitrate, titanium dioxide (TiO₂) and titanyl nitrate (TiO(NO₃)₂) as sources of titanium and barium and reducing agents such as glycine (C₂H₅NO₂), carbamide (СН₄N₂O) and glycerol (C₃H₅(OH)₃). In an effort to form a barium titanate phase, the materials synthesized using titanium dioxide were subjected to additional calcination at 800 °С. With titanyl nitrate the use of glycine and carbamide enabled carrying out a single-step synthesis of barium titanate. The obtained materials have pseudo-cubic lattice and are characterized by high stability of properties in a wide range of temperatures and frequencies of the electromagnetic field.     

Stabilization Effect in Lead Lanthanum Titanate Ceramics During Aging in Ferroelectric Phase

The reverse transformation (from ferroelectric to paraelectric phase) temperature in aged ferroeletric lead lanthanum titanate ceramics is measured precisely by differential scanning calorimetry (DSC). It is observed that the transformation temperature increases with increasing aging time, indicating ferroelectric phase is stabilized by aging. This behavior is similar to those in ferroelectric single crystal barium titanate. The origin of the stabilization effect in the system is discussed with respect to the diffusion of point defects.     

Preparation of BaTi4O9 from Oxalates

A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC₂O₄·0.5H₂O and TiO(OH)₂·1.5H₂O in a molar ratio of 1:4. Crystallized BaTi₄O₉ was obtained by the thermal decomposition of a precipitate precursor at 1300°C for 2 h in air. The dimensions of the powder calcined at 1000°C are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300°C are of the order of 10 to 30 μm. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE₀₁₁ mode. Excellent microwave characteristics for BaTi₄O₉—ɛ= 38 ± 0.5, Q = 3800–4000 at 6–7 GHz and τ _f = 11 ± 0.7 ppm/°C—were found.     

Piezoresistivity in PTCR Barium Titanate Ceramics: I, Experimental Findings

Positive temperature coefficient of resistance (PTCR) barium titanate is the active material in a ceramic sensor which employs piezoresistivity to detect changes in applied stress. High-purity, chemically prepared barium titanate is donor-doped with 0.30 at.% lanthanum, and <0.10 at.% of a transition-metal counterdopant may be added to enhance the PTCR effect. Tape-cast sheets of undoped and PTCR BaTiO₃ are laminated to produce a three-layer "trilaminate"—a sintered structure which has two semiconducting PTCR layers separated by an insulating layer. The trilaminate is stressed in a four-point bend configuration (placing one semiconducting layer completely in tension, the other in compression), and the resistivities for both stress states are measured concurrently as functions of applied stress and temperature. Results are presented for various semiconducting layer compositions and sintering conditions.