Bi2O3-Modified Ceramics Based on BaTiO3 Powder Synthesized in Water Vapor

Bi2O3 was investigated in the role of a modifier for BaTiO3 powder synthesized in a water vapor atmosphere at 200 °C and 1.55 MPa. Modification was aimed at increasing the sinterability of the powder as well as improving the structural and dielectric properties of the obtained ceramics. The morphology and phase contents of the synthesized BaTiO3 powder were controlled by the methods of SEM and XRD. Properties of pure and Bi-doped BaTiO3 ceramics were comprehensively studied by XRD, SEM, dielectric spectroscopy, and standard approaches for density and mechanical strength determination. Doping with Bi2O3 favored BaTiO3 ceramic densification and strengthening. The room-temperature dielectric constant and the loss tangent of Bi-doped BaTiO3 were shown to stabilize within the frequency range of 20 Hz to 2 MHz compared to non-doped material. The drop of dielectric constant between room temperature and Curie point was significantly reduced after Bi2O3 addition to BaTiO3. Bi2O3 appeared to be an effective modifier for BaTiO3 ceramics produced from non-stoichiometric powder synthesized in water vapor.

Preparation and Sintering Behaviour of a Fine Grain BaTiO3 Powder containing 10 mol% BaGeO3

The formation of solid solutions of the type [Ba(HOC2H4OH)4][Ti1-xGex(OC2H4O)3] as Ba(Ti1-x/Gex)O3 precursors and the phase evolution during thermaldecomposition of [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) are described herein. The 1,2-ethanediolato complex 1 decomposes above 589 °C to a mixture of BaTiO3 and BaGeO3. Aheating rate controlled calcination procedure up to 730 °C leads to a nm-sizedBa(Ti0.9/Ge0.1)O3 powder (1a) with a specific surface area of S = 16.9 m2/g, whereas aconstant heating rate calcination at 1000 °C for 2 h yields a powder (1b) of S = 3.0 m2/g. Theshrinkage and sintering behaviour of the resulting Ba(Ti0.9/Ge0.1)O3 powder compacts incomparison with nm-sized BaTiO3 powder compacts (2a) has been investigated. A 2-stepsintering procedure of nm-sized Ba(Ti0.9/Ge0.1)O3 compacts (1a) leads below 900 °C toceramic bodies with a relative density of ³ 90 %. Furthermore, the cubic ? tetragonal phasetransition temperature has been detected by dilatometry and the temperature dependence ofthe dielectric constant (relative permittivity) has also been measured.

Shrinkage mechanism and phase evolution of fine-grain BaTiO3 powder compacts containing 10 mol% BaGeO3 prepared via a precursor route

The shrinkage mechanism of BaTiO3 powder compacts containing 10 mol%BaGeO3, synthesized by a precursor route and a conventional mixed-oxide method, aredescribed herein. The calcination of a barium titanium germanium 1,2-ethanediolato complexprecursor - [Ba(HOC2H4OH)4][Ti0.9Ge0.1(OC2H4O)3] (1) - at 730 °C leads to a nm-sizedBa(Ti0.9/Ge0.1)O3 powder (1a) (SBET = 16.9 m2/g) consisting of BaTiO3 and BaGeO3. Whereasthe conventional mixed-oxide method yields a powder (2) with a specific surface area of SBET= 2.0 m2/g. Powder compacts of 1a start to shrink at 790 °C and the shrinkage rate reaches amaximum at 908 °C. Dense ceramic bodies can be obtained below the appearance of theliquid melt (1120 °C), therefore the shrinkage of 1a can be described by a solid-state sinteringmechanism. Otherwise the beginning of the shrinkage of powder 2 is shifted to highertemperatures and the formation of the liquid melt is necessary to obtain dense ceramic bodies. Isothermal dilatometric investigations indicate that the initial stage of sintering is dominatedby sliding processes. XRD investigations show that below a sintering temperature of 1200 °Cceramic bodies of 1a consist of tetragonal BaTiO3 and hexagonal BaGeO3, whereastemperatures above 1200 °C lead to ceramics containing orthorhombic BaGeO3, and atemperature of 1350 °C causes the formation of a Ba2TiGe2O8 phase. The phase evolution ofceramic bodies of 2 is similar to 1a, however a Ba2GeO4 phase is observed below atemperature of 1100 °C.

Thermal analysis of formation of nano-crystalline BaTiO3 using Ba(NO3)2 and TiO2

The reaction of Ba(NO3)2 with TiO2 was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000?C and in nitrogen atmosphere. It was found that the formation of BaTiO3 takes place above 600?C and that precursor mixing time and heating rate have no effect on the reaction temperature. BaTiO3 powder was prepared by calcination of Ba(NO3)2 and TiO2 precursor mixture at 800?C for 8 h. X-ray diffraction analysis of the synthesized BaTiO3 confirmed the formation of tetragonal phase with lattice parameters a = 3.9950?0.0003? and c = 4.0318?0.0004?. Thermal analysis of the synthesized BaTiO3 powder showed weight loss within temperature range 40-1000?C of only 0.40%. This small amount of weight loss was connected with some impurity phase, and identified as BaCO3 using Fourier transform infrared (FTIR) technique.