Papers by Keyword: Tetragonality

Abstract: Sand-milling machine was firstly utilized to crush and disperse the raw materials. A homogenous and well-dispersed mixture of TiO₂ and BaCO₃ (<30nm) was obtained. The solid state reaction temperature can be reduced by 200°C for nanosized reactants compared with coarse ones. In order to increase tetragonality of nanosized BaTiO₃, an innovative two-step calcination method, which includes solid state reaction process between reactants at a low temperature T₁ and phase transition process at a high temperature T₂, was subsequently adopted. The microstructure evolution of BaTiO₃ by two-step calcination was investigated as a function of T₂ and corresponding dwelling time t₂. Pure-perovskite BaTiO₃ nanopowders with the mean particle size as small as 75nm and tetragonality (c/a ratio) higher than 1.0096 could be fabricated by two-step calcination through altering T₂ and/or its dwelling time t₂.

Abstract: Structure–property relationship has been performed in the lanthanum-modified lead–zirconate–titanate (PLZT) with a lanthanum content 8 and Zr/Ti ratio 40/60. The X-ray diffraction analysis, scanning electron microscopy, and sintering behavior have evidently demonstrated that it is possible to tailor the structural properties of PLZT 8/40/60. Structure of PLZT 8/40/60 had pure perovskite with tetragonal without secondary phase. Tetragonality (c/a) was observed in the range of 1.01093-1.02095. SEM micrographs were shown a development of mean grain size to clarify the development of grain after sintering processing. The result shows that increasing of sintering temperature resulted in mean grain size increasing from 1.70 to 3.08 μm. Ferroelectricity of PLZT ceramics were normal ferroelectric and dielectric constant increased with the increasing sintering temperature.

Abstract: This paper describes the relationship between sintering time conditons, tetragonality from phase formation, dielectric and ferroelectric characteristics of tetragonal PLZT (lanthanum modified lead zirconate titanate) ceramics with the pressureless sintering conditions. Ferroelectric compounds of Pb_0.92La_0.08(Zr_0.4,Ti_0.6)_0.98)O_3, PLZT 8/40/60, were prepared using mixed-oxide synthetic route via a rapid vibro-milling method. X-ray diffraction, is used to observe the tetragonality characteristic and the presence of pyrochlore. When sintering time was increased (≥ 8 hours), pyrochlore was developed. It can be observed that with the increased sintering time, it were changed the structure and ferroelectric behavior of the PLZT ceramics.

Abstract: We studied the crystallographic of Barium Zirconium Titanate thin films with Aluminum doped (BZAT). These films were prepared by sol-gel process and followed by spin coating. The sintering temperature is taken at 800°C and 900°C. We found that the crystallographic system of BZAT thin films have tetragonal structure with the lattice parameter slightly changed by various Aluminum partial substitution. When 0.01 Al moles added, the grain size of the films is 29.42 nm at 800°C. The sintering temperature 900°C increased the grain size into 50.95 nm. We also calculated the spontaneous polarization theoretically and we found the optimum value of BZT thin film with 0.01 mole Al heated at 800°C, is 0.143 C/m². This way, we could predict that the film has ferroelectric phase.

Abstract: Structural changes induced by oxygen vacancies in tetragonal phase BaTiO₃ are studied with first principles calculations within density functional theory. In our calculations, the incorporation of oxygen vacancies greatly decreases c/a ratio of the tetragonal phase BaTiO₃, and a phase transition from tetragonal to cubic phase occurs when the incorporation of the oxygen vacancies reaches about 4%. Our results also shows that the generation of the oxygen vacancies slightly increases the volume of BaTiO₃, and the increases are typically less than 0.5% even in heavily reduced conditions.

Abstract: BaTiO3 powders with particle size 0.1μm were made by solid state synthesis. To make high tetragonality BaTiO3 powder, mixture of TiO2 and BaCO3 was calcined in vacuum condition. And to make low tetragonality BaTiO3 powder, the mixture was calcined in air condition. With each powder, MLCCs with Ni-internal electrode were fabricated. Relationships between temperature and relative dielectric constant of MLCCs’ dielectric layers were analyzed and their dielectric grains were observed by TEM-EDS. As the result, MLCC made from high tetragonality BaTiO3 powder had good temperature characteristics and core-shell dielectric grains.

Abstract: Nano-sized BaTiO3 powders with narrow size distribution and the high tetragonality were attempted to synthesize by the rotary-hydrothermal process in water system, using two kinds of commercial anatase-type TiO2 (ST21/ST01) with different particle size and Ba(OH)2. The rotary-hydrothermal syntheses were done with the rotary-speed of 20 revolutions per minute at 523 K for 24 h. Highly- and mono-dispersed BaTiO3 powders were successfully synthesized by applying the rotary-hydrothermal process. For rotary-hydrothermal synthesis, it was found that the average size, tetragonality, and quality of the BaTiO3 particle strongly depended on the particle size of the starting material. In the case of using ST01 as a starting material, BaTiO3 nano-powders mainly composed of coarse-faceted particles (average particle size = ca.100 nm) with the tetragonal phase and very little lattice defects were successfully synthesized.

Abstract: (Pb1-xSrx)TiO3 (PST) (x=0.25, 0.50) powders were synthesized by a mixed oxide solid-state reaction method under various calcination temperatures (600-1100oC). Powder samples were characterized using thermogravimetric (TGA), differential thermal analysis (DTA), x–ray diffractrometer (XRD) and scanning electron microscopy (SEM). The results showed that a single-phase of PST for x=0.25 and 0.50 powders was successfully obtained with a calcination condition of 950 oC for 2 h with a heating/cooling rate of 5oC/min. The TGA-DTA results corresponded to the XRD investigation. The lattice parameter a increased whilst the lattice parameter c decreased with increasing calcination temperatures. The tetragonality of powders decreased with an increase of calcination temperatures. The average particle size of the powders increased with the increase of calcination temperature.

Abstract: (Pb0.925Ba0.075)TiO3 (PBT) ceramics have been prepared using a mixed oxide technique. The phase formation and morphology were studied in detail via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The pure tetragonal perovskite structure was discovered with calcination temperatures above 800 oC. The percentage of perovskite phase and particle size tends to increase with the increasing of calcination temperatures. The PBT ceramics sintered at various temperatures belonged to a pure tetragonal perovskite phase. The average grain sizes increased from 0.90 to 6.44 µm with the increase of sintering temperatures from 1100 to 1200 oC. The highest density was obtained from the sample that sintered at 1150 and 1200 oC

Abstract: In this work, we studied the effect of excess PbO doping on lead barium titanate [(Pb0.925Ba0.075)TiO3; (PBT)] ceramic. PBT was prepared via a mixed oxide method with various PbO levels (-3, 0, 1, 3, 5 and 10 wt.%). The excess PbO was added to compensate the loss from evaporation during calcination and sintering at 800 oC and 1150 oC. It was found that lead barium titanate powders indexed in a tetragonal structure. Impurity phases of lead oxide (PbO), titanium oxide (TiO), and lead dioxide (PbO2) were detected in the calcined powders with higher than 1 wt% of excess PbO. The impurity phase was not obtained in any ceramic samples. The c/a ratios decreased with an increasing excess of PbO in both calcined powders and sintered pellets. The average particle size and the average grain size of the PBT increased with the increase of PbO. The shrinkage plots showed a maximum peak for the 1 wt.% sample which was also the most dense sample.