Hans-Peter Abicht

Comparison between bimorphic and polymorphic bending devices

Abstract In the last years a lot of work was done in the field of functionally gradient materials (FGM) especially for their application as monolithic bending devices. For modeling their bending and poling behavior they are mostly treated as a bimorphic structure, although it was shown, that the FGM can have a true gradient or a polymorphic structure. Here we discuss the behavior of a polymorphic structure (PM) consisting of N layers with different piezoelectric properties compared with a bimorphic structure (BM). A finite element method (FEM) modeling shows, that for the same geometrical dimensions and applied voltage the deflection at the end of a cantilever is the smaller the higher the number of layers in the PM. But also for N =11 the deflection is about 70% of the deflection of the BM. On the other hand, the mechanical stresses are clearly smaller the higher the number of layers. This holds valid even when the voltage applied to a PM with N > 2 is raised to such an extent, that the deflection of the PM and the BM are equal. In order to compare the modeling with experimental results a BM and a PM with N =3 based on BaTiO 3 -ceramics were prepared. The bending behavior of both structures was observed and the results seems to support the finite element method modeling.

The influence of different additives and the mode of their addition on the sintering behavior and the properties of semiconducting barium titanate ceramics

Abstract The influence of different additives (TiO 2 , TiO 2 /SiO 2 , CaO/TiO 2 /SiO 2 , 2BaO/TiO 2 /2SiO 2 ) and the mode of their incorporation (spray drying: series 1; mixed-oxide method: series 2) on the sintering behavior and the microstructural and electrical properties of n-doped BaTiO 3 ceramics has been investigated. The incorporation of the additives from their aqueous solution by spray drying produces a homogeneous distribution of the additive in the BaTiO 3 matrix powder by coating the BaTiO 3 particles. This homogeneous distribution significantly lowers the activation energy for the densification process compared with that of the powders of series 2. Dynamic and isothermal dilatometric measurements revealed that the sintering process is considered as a classical solid phase sintering followed by recrystallization of the BaTiO 3 matrix particles by a eutectic melt. The densification process is dominated by sliding processes. These sliding processes are caused by the amorphous layer of the additive and by the defect-rich grain boundary layers of the BaTiO 3 grains generated intermediately by diffusion processes and reactions of the matrix material with the additive forming the secondary phases Ba 2 TiSi 2 O 8 and Ba 4 Ti 13 O 30 , respectively. In series 1, ceramics with a homogeneous microstructure and useful electrical properties (e.g. low resistivity at room temperature) were already produced at a sintering temperature of 1280°C (with SiO 2 -containing additives) due to the homogeneous distribution of the additive. The ceramics of series 2 sintered at the same temperature could only be obtained in poor quality. At higher sintering temperatures the differences between the two series vanished.

Scanning near-field acoustic study of ferroelectric BaTiO3ceramics

Ferroelectric materials have attracted attention in recent years because of the combination of these materials with integrated circuit technology. Although much effort has been made to develop new devices by the use of these materials, there is still much to do to understand the so-called domain effects at submicrometer or even in nanometer range. Although near-field acoustic techniques have achieved considerable progress in this respect recently, a complete understanding of physical effects in the near field of these techniques could not be completed solely by the use of one method, as both ferroelectric materials and near-field acoustic techniques are complicated in nature. A complementary study by two or more techniques will bring a new view to the analyses and characterization of ferroelectric materials and integrated devices. This paper will present complementary investigations on BaTiO3 ceramics by the use of two non-destructive scanning near-field acoustic microscopy techniques on the identical areas of the same sample. A general model for both near-field acoustic techniques on ferroelectric BaTiO3 is presented. Explanations of the results based on present theory will also be discussed in detail.

New evidence for an oxycarbonate phase as an intermediate step in BaTiO3 preparation

A newly developed method of spray hydrolysis of a barium-titanium double alkoxide will be described as an eAcient synthetic route for the preparation of a stoichiometric BaTiO3 powder. During the thermal treatment of the corresponding precursor a barium-titanium oxycarbonate appears as an intermediate. High resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS) at ionization edges (ELNES), along with X-ray powder diAractometry (XRD), Fourier-transformed infrared spectroscopy (FTIR), and thermoanalytical measurements provide evidence of the existence of such an oxycarbonate phase. The comparison of the measured EEL spectra with quantum-mechanical calculations using density functional theory (DFT) reveals that this intermediate phase is characterized by an electronic C-Ti interaction in the crystal lattice and a specific modification of the carbonate bond. # 2000 Elsevier Science Ltd. All rights reserved.

THE INFLUENCE OF SILICON ON MICROSTRUCTURE AND ELECTRICAL PROPERTIES OF LA-DOPED BATIO3 CERAMICS

BaTiO3 positive temperature coefficient of resistance ceramics were prepared with the general composition (La0.002CaxBa0.998−x) (Ti1.01−yMny)O3 ·zSiO2 and sintered in air. The Ca content as well as the amount of doped Mn were varied ranging from 4–20 mol% and 0.02–0.04 mol%, respectively. Up to 4 mol% Si was added using a new method as well as by the classical means as solid silica. In the new method, the desired quantity of Si(OC2O5)4 (Si(OEt)4), contained in dry tetrahydrofurane (THF), was dropped under a slight stream of inert gas into the vigorously stirred aqueous slurry which was manufactured after the calcination process. The addition of Si by this technique was found to result in a homogenization of the microstructure and an improvement in electrical properties. The effect of Si on electrical properties is explained by the influence of the observed second phase on the equilibrium of Ba vacancies. The results of further variation of Ca and Mn contents are presented.

Metal controlled enantioselectivity in the catalytic asymmetric hydrosilylation

The asymmetric hydrosilylation of acetophenone with Ph2SiH2 has been investigated in the presence of (S)-amphos as the chiral ligand in combination with the cyclooctadiene-rhodium(I), -iridium(I), -palladium(II), and -platinum(II) chloride complexes. High activity and optical yields up to 50% ee have been obtained. The product configuration induced by the rhodium system is (S), in all other cases it was (R).

Cyclometallierte Pd- UND Pt-komplexe der (o-lithiobenzyl)diorganophosphine

Abstract The ( o -lithiobenzyl)diorganophosphine o -LiC 6 H 4 CH 2 PR 2 (R  Ph, Me, t-Bu) form the corresponding cyclometalated complexes when allowed to react with MCL 2 · 2Et 2 S (M  Pd, Pt). Under our reaction conditions they appear to be formed in the cis -form only. Mixed cyclometalated species are described as well as the behaviour of some cyclometalated compounds towards HCL, Br 2 and HgBr 2 reactions with n-BuLi. the Ir and MNR spectra of the prepared complexes are discussed.

Synthese und Reaktionsverhalten asymmetrischer Metallacyclen des Palladiums und Platins

The preparation, properties and the complexation behaviour of o-lithiobenzyldiorganoarsines are described. Halogen-bridged binuclear complexes of the type [μ-ClM(o-C6C4CH2ER2)]2 (M = Pd, Pt; E = N,P) react with o-LiC6H4CH2ER2 (E = N, P, As), to form asymmetric metallacycles with two different donor atoms in the molecule. Some physical and chemical properties of these interesting complexes are discussed.

Copper oxide as a sintering agent for barium titanate based ceramics

The purpose of this work was to study the effect of CuO as a versatile sintering agent for BaTiO3 based ceramics. The response is shown to exist in three directions. Firstly, as liquid-phase former at comparatively low temperatures. Hence, the influence of various CuO-based flux formers on the shrinkage behaviour and the microstructure development of the ceramics was investigated. Secondly, the aptitude as an internal susceptor for secondary phase initiated microwave sintering. The use of CuO as a lossy secondary phase leads to an accelerated microwave heating of the ceramics. Thirdly, the addition of CuO to BaTiO3 powders with Ba-excess results in a phase transition cubic → hexagonal at about 1300°C, which is a indication for the incorporation of Cu2+ ions into the BaTiO3 lattice at Ti sites under this conditions.

Ca-containing additives in PTC-BaTiO3 ceramics: effects on the microstructural evolution

Two series of Ca 2+ -modified BaTiO3 ceramics have been prepared of the gross composition La0.002Ba0.998ˇxCaxTi1.01O3.02 (0<x<0.24). In the first series, CaCO3, BaCO3, TiO2 and La2(C2O4)3 .9H2O were used as starting materials. The calcination of mixtures with x40.08 resulted in the formation of the corresponding titanate solid solution (Ba1ˇxCax)TiO3. With values of x higher than 0.08, CaTiO3 was observed as an additional phase. In the second series, a La0.002Ba0.998TiO3 starting powder was hydrothermally recrystallized in Ca(NO3)2 solution. High resolution imaging and analytical methods revealed that the BaTiO3 grains are surrounded by small CaTiO3 crystallites, which influence the evolution of the microstructure of the ceramic in the sintering process strongly by acting as seeds during the recrystallization of the matrix material. Thus, it was possible to optimize the microstructural and electrical characteristics of a ceramic of the second series by adding only 4 mol% Ca, while in case of the first series 16 mol% Ca are necessary. # 2000 Elsevier Science Ltd. All rights reserved.