Robert Haberkorn

Sol-Gel Synthesis of Nano-Scaled BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 Oxides via Single-Source Alkoxide Precursors and Semi-Alkoxide Routes

Sol-gel synthesis of nano-sized BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO3 and BaZrO3) and three (for BaTi0.5Zr0.5O3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide synthesis was performed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000°C. At temperatures below 1000°C, BaCO3 and small amounts of other undesired phases (e.g., BaTi2O4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTA measurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthesis route. Among alkoxide derived powders, crystalline BaTi0.5Zr0.5O3 phase is formed at 400°C while complete crystallisation of BaMO3 ceramics occurs around 600°C. The cubic to tetragonal phase transition for BaTiO3 is clearly observed at relatively low-temperature of 800°C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysis and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity.

Pitfalls in the synthesis of nanoscaled perovskite type compounds. Part I: Influence of different sol-gel preparation methods and characterization of nanoscaled BaTiO3

Abstract Different sol–gel routes are compared for the synthesis of nanoscaled BaTiO 3 with respect to the reaction paths and the quality of the products. The various precursor systems differ largely in their behaviour during decomposition imposing quite different procedures for their thermal treatment. It is shown that the compositional homogeneity during the process of synthesis, which is the target of sol–gel methods, may well be destroyed by the formation of intermediate compounds. It will only be restored after prolonged heating at higher temperatures where the crystallite sizes will in general have left the nanoregime. Due to such pitfalls the desired properties of the products with narrow size distributions will not always be ensured when working according to such recipes and the products obtained will behave quite differently in fabrication procedures like shaping and sintering of workpieces.

Sol–gel preparation and characterization of manganese-substituted superconducting YBa2(Cu1−xMnx)4O8 compounds

In this work the effect on the structural and superconducting properties of YBa2Cu4O8 (Y-124) of replacing Cu by Mn was studied. Multimetallic oxide powders with the composition of YBa2(Cu1−xMnx)4O8 (x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) have been prepared by a simple aqueous sol–gel method at an oxygen pressure of 1 atm starting from an aqueous mixture of the metal acetates. Homogeneous gels were achieved by complexing copper ions by tartaric acid before the gelation process. Thermal decomposition of the gels was studied by thermogravimetry. Effects of manganese substitutions on the properties of compounds were studied by X-ray powder diffraction, TG analysis, IR spectroscopy and resistivity measurements. These data indicated that the transition temperature of superconductivity drastically decreases upon Mn substitution, and that superconductivity is lost at 3% of Mn substitution level. XRD measurements showed that the structure of the Y-124 phase is also largely affected even at low manganese-substitutional levels.

Specification of microstructure and characterization by scattering techniques

Publisher Summary This chapter focuses on one major aspect of this task of preparation, investigation, and optimization of nanostructured materials, namely, determining the average size and size distribution of the (nano)crystalline building blocks of a nanostructured material. These objects may be densely packed or embedded in a matrix, with any degree of correlation in their spatial arrangement. There are two basic experimental approaches to measuring the sizes of crystalline objects in the interior of a nanostructured material: direct imaging by transmission electron microscopy (TEM) and indirect determination by X-ray or neutron diffraction. Following a summary of the basic parameters used to specify the microstructure of a crystalline material, the basic kinematical theory governing the diffraction of radiation from samples containing nanometer-sized crystalline units have been presented. Simple equations form the basis for the various methods described in the chapter for determining microstructural parameters from diffraction data. Finally, several of these methods have been applied to the characterization of the microstructure of a nanostructured TiN sampled and compared with the results obtained from a TEM investigation of the same material.

Pitfalls in the synthesis of nanoscaled perovskite type compounds. Part II: Influence of different sol-gel preparation methods and characterization of nanoscaled mixed crystals of the type Ba1−xSrxTiO3 (0⩽x⩽1)

Abstract The preparation of mixed crystals Ba1−xSrxTiO3 (0⩽x⩽1) by an acetate based sol-gel method was monitored by TG/DTA, TG–MS and XRD with respect to the reaction paths and the quality of the products. Depending on x, there is a more or less pronounced segregation of the alkaline earth compound leading at first to by-products richer in Ba than the perovskite phase itself. Chemical homogeneity will only be restored after prolonged heating at high temperatures where the primary crystallites of the ABX3 compound will have left the nanoregime and new ones will be formed during the decomposition of the by-products giving a more bimodal size distribution. Due to such pitfalls the desired properties of the products and especially their physical characteristics important for use in electrical devices will not always be ensured.

SYNTHESIS AND CRYSTAL STRUCTURE OF RB6PB5CL16

The synthesis of a hitherto unknown 6 : 5 phase in the quasi-binary system RbCl/PbCl2 and its structure deter- mination is reported. The compound Rb6Pb5Cl16 crystallizes in the tetragonal space group P4/mbm with a large variety of different coordination polyhedra for the cations. Special fea- ture of the structure is a statistical distribution of Rb and Pb at one of the cation sites with a ratio of 1 : 3 as defined by electroneutrality. There is no evidence for symmetry reduc- tion by ordering.

Synthesis of perovskite type compounds via different routes and their X-ray characterization

Abstract Perovskite type compounds may be synthesized via different routes, which will yield nanocrystalline material, if certain temperatures are not exceeded while annealing, calcinating or decomposing. In the case of BaTiO3 this temperature is at about 800°C. Solid state reactions, decomposition of metal organic compounds and sol-gel processing have been used to prepare BaTiO3 and other perovskite type compounds. Sol-gel processes, followed by calcination, proved to be proper methods in preparing nanocrystalline powder because they need rather low temperatures during calcination. But not all sol-gel processes are suitable in the same manner. Lattice constants, resulting phases and properties may also depend on crystallite size or annealing temperature.

Fe16Nb6Si7 and Fe16Ta6Si7: New D8a phases synthesized by the crystallization of mechanically alloyed amorphous powders

Abstract Ternary phases with the cubic D8 a structure (isostructural to Mg 16 Cu 6 Si 7 ) were identified in both the Fe–Nb–Si and Fe–Ta–Si systems. They form during the crystallization of mechanically alloyed amorphous materials and are thermally stable during heat treatments up to 90 h at 1050°C. The X-ray powder diffraction data were evaluated (i) by local line fit, and (ii) by Rietveld analysis. Mossbauer spectroscopy was used to complement the XRD results and to show the absence of magnetic ordering above 77 K.

On the Photocatalytic Performance of Indium Tantalate and its Modifications

Abstract The photocatalytic activity of InTaO4 has been studied regarding the effect of a substitution of In by Ni, of the performance of NiO as well as Ag2O as co-catalysts, and especially of the products of different methods of preparation (solid state reaction and/or sol-gel process) and their particle sizes. Solid state reactions and sol-gel procedures were used to synthesise different products for the catalytic reaction in a reactor vessel equipped with amercury UV lamp. The optical properties and the band gap values of the different products were evaluated by reflectance spectroscopy, and the microstructure parameters of the crystalline products were determined by an elaborate profile analysis of the X-ray diagrams. The evolution of H2 and O2 under irradiation was quantified by a GC setup. The causes for the deviations of the performance of these catalysts from the values reported elsewhere are discussed.

Calcium phosphate phase transition in the presence of Aminosilane

Calcium phosphate has been the point of interest for in vitro gene delivery for many years because of its biocompatibility and straight forward application. However, there are some limitations regarding in vivo administration of these particles mostly because of vast agglomeration of the particles and lack of strong bond between the particles and pDNA. We introduced a simple single step method to functionalize calcium phosphate nanoparticles with Aminosilanes having a different number of amine groups. The nanoparticles were characterized chemically and structurally and their toxicity and interaction with pDNA were studied as well. Results revealed that different crystalline phase of calcium phosphate nanoparticles (Brushite and Hydroxyapatite) with a size below 150 nm were prepared, depending on conditions of synthesis and phase, each with a narrow size distribution. The aminosilane agents caused oriented nucleation and growth of crystallites and can decrease the pH for producing hydroxyapatite phase. The phenomenon could be revealed with the presence of anisotropy in the structure of synthesized hydroxyapatite. The number of amine groups in the Aminosilane agent could change the phase transition pH. Brushite particles revealed to have stronger interaction with pDNA mostly because of their higher positive surface charge. Both particles showed blood compatibility and negligible toxicity. Transfection experiment revealed the capability of both brushite and hydroxyapatite particles to transfect A549 and HEK293 cells. The new modified nanoparticles can be stored in a dried state and re-dispersed easily at the time of administration. Moreover, the transfection efficiency is higher in comparison with conventional calcium phosphate. This study showed the impact of presence and type of the modifying agent on the crystal structure and the amount of surface functionalization of nanoparticles, which in consequence influenced their interaction with cells.