Single crystals of the title Ag-substituted calcium magnesium germanide, CaMg1-xAgxGe [x = 0.13 (3)] were obtained from the reaction of the corresponding elements at high temperature. The compound crystallizes with the TiNiSi structure type (Pearson code oP12) and represents an Ag-substituted derivative of the Zintl phase CaMgGe in which a small fraction of the divalent Mg atoms have been replaced by monovalent Ag atoms. All three atoms in the asymmetric unit (Ca, Mg/Ag, Ge) occupy special positions with the same site symmetry (.m.). Although the end member CaAgGe has been reported in an isomorphic superstructure of the same TiNiSi type, higher Ag content in solid solutions could not be achieved due to competitive formation of other, perhaps more stable, phases.

New cuprate systems related to high temperature superconductors have been investigated and are reviewed. The synthesized samples have been studied mainly by transmission electron microscopy, energy-dispersive spectrometry and X-ray powder diffraction, in order to determine composition and structure of the formed phases.

The following compounds were studied: Bi14Cu10Nb16O7 and Bit 7Cuo.2Ti2.006.8, both of cubic pyrochlore-type structure; BiNbs.4015, a tetragonal tungsten bronze type compound; Bi2/3Cu3Ti4012, a perovskite-related phase; Ba4CuYW2012, with a perovskite based unit cell; LaSrCuGaOs and LaCaCuGaOs, both of brownmillerite type and some related phases obtained by aliovalent substitution; R2Hg04 (R = La, Nd, Sm, Eu and Gd), with a new type of structure; and HgBa^RCugOy (R = La, Nd, Eu, Eu+Ca, Gd, Dy and Y), new "Hg-1212" type phases with a structure related to that of the thallium superconductor TlBa2CaCu207.

The structural features of these compounds of relevance to superconductivity are also discussed.

Commercial nanocrystalline yttrium aluminum garnet (nc-YAG) powders were used for fabrication of dense and transparent YAG by spark plasma sintering (SPS). Spherical 34 nm size particles were densified by SPS between 1200 and 1500 degrees C using 50 and 100 MPa pressures for 3, 6, and 9 min durations. Fully dense and transparent polycrystalline cubic YAG with micrometer grain size were fabricated at very moderate SPS conditions, i.e. 1375 degrees C, 100 MPa for 3 min. Increase in the SPS duration and pressure significantly increased the density especially at the lower temperature range. The observed microstructure is in agreement with densification by nano-grain rotation and sliding at lower densities, followed by curvature driven grain boundary migration and normal grain growth at higher densities. Residual nanosize pores at the grain boundary junctions are an inherent microstructure feature due to the SPS process.

Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.

Polycrystalline ceramics are brittle at room temperature but may deform by dislocation slip processes at higher temperatures, where T >= 0.5 T-M (T-M, the melting temperature), leading to strain hardening, i.e. the total strain to rupture is limited. We show that mutual sliding of nanometer grains and atomic transport along their boundaries enables low-temperature metal-like plasticity in nanocrystalline ceramics. Compression of fully dense MgO nanoceramics at temperatures as low as 700 degrees C (0.31 T-M) exhibited stress-strain curves with no strain hardening.

In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12-xN16-xO2+x) spanning a compositional range up to x approximate to 3, we examine the incorporation of Al and O by Si-29 and Al-27 magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and Al-27 triple-quantum MAS (3QMAS). The 3QMAS spectra reveal Al-27 signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. Si-29 NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4-xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.

While performing molecular-dynamics simulations of a simple monatomic liquid, we observed the crystallization of a material displaying octagonal symmetry in its simulated diffraction pattern. Inspection of the atomic arrangements in the crystallization product reveals large grains of the beta-Mn structure aligned along a common fourfold axis, with 45° rotations between neighboring grains. These 45° rotations can be traced to the intercession of a second crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose primitive cell has lattice parameters a=b=c=a_{beta-Mn}, alpha =beta =90°, and gamma =45°. This secondary phase adopts a structure which appears to have no known counterpart in the experimental literature, but can be simply derived from the Cr3Si and Al3Zr4 structure types. We used these observations as the basis for an atomistic structural model for octagonal quasicrystals, in which the beta-Mn and the secondary phase structure unit cells serve as square and rhombic tiles (in projection), respectively. Its diffraction pattern down the octagonal axis resembles those experimentally measured. The model is unique in being consistent with high-resolution electron microscopy images showing square and rhombic units with edge-lengths equal to that of the beta-Mn unit cell. Energy minimization of this configuration, using the same pair potential as above, results in an alternative octagonal quasiperiodic structure with the same tiling but a different atomic decoration and diffraction pattern.

This study has been carried out to investigate the influence of process parameters upon the material characteristics during the conversion of UFg to UO2 powder, and the importance of variation in these charcteristics for the final quality of the sintered pellets. The first process step is a precipitation of ammonium uranyl carbonate (AUC) from UFg, ammonia and carbon dioxide. In this step the most important characteristic is the particle size distribution, which is determined by the concentration of the reacting species and by the temperature.

The reducing capacity of the atmosphere, the heating rate and the final temperature influence the specific surface area, the stoichiometry and the crystallite size, obtained in the reduction of AUC to UO2 powder.

The studies also reveal that the reaction path from AUC to UO2 is very complex. Intermediates such as amorphous UO3, CÏ-UO3, uranium oxide hydrates, U4O9 and U30g can under certain conditions exist, transiently during this operation. The reaction path actually followed very strongly influences the powder characteristics.

Methods to study sinterability and sintering kinetics have also been employed. Quasi-isothermal dilatometry (QID), has been used to find the rate controlling mechanism in the initial stage of sintering, and to evaluate the activation energy in the different atmospheres and diffusion coefficients.

Full-scale experiments have verified the findings; coarse, inactive powders accumulate high defect concentations during pressing, leading to a relatively high defect frequency after sintering. Finer powders, which are still coarser than a certain minimum, however give the strongest green pellets with the best sinterablity. This type of powders also yields high quality sintered pellets with low defect frequencies.

Mid infrared, far-infrared and Raman spectroscopic studies, combined with force field analyses, were performed for the 1 hydrated platinum(II) and palladium(II) ions and cis-diammineplatinum(II) complex in acidic aqueous solutions. Simplified Density Functional Theory (DFT) calculations were made for the equatorial plane of the platinum complexes. Careful subtraction of solvent spectra allowed a number of 'internal' modes of coordinated H2O and NH3 to be determined as weak residual bands. The [Pt(OH2)(6)](2+) and [cis-Pt(NH3)(2)(OH2)(4)](2+) complexes were found to be six-coordinated with four ligands strongly bound in an equatorial plane. The assignments of the vibrational modes in the equatorial plane could be performed on the basis of the experimental observations and by comparison with metal-ligand vibrations of square-planar complexes, aided by normal coordinate calculations. For the weakly coordinated axial aqua ligands, the low wavenumber range and the polarizibility properties allowed the assignments of the bands at about 365 and 325 cm(-1) to the stretching modes of one short and one longer Pt - O* bound to axial aqua ligands, respectively. A similar picture with even less strongly bound axial water molecules emerges from Raman spectroscopy data for the hydrated palladium(II) ion, [Pd(OH2)(6)](2+). The results are consistent with a description of the [Pt(OH2)(6)](2+) and [Pd(OH2)(6)](2+) aqua ions in C-4v symmetry, and with the [cis-Pt(NH3)(2)(OH2)(4)](2+) complex in the Cs point group, and also in qualitative agreement with the structures devised from previous extended X-ray absorption fine structure (EXAFS) measurements.

Highly dense La2CuO4 ceramics have been prepared by the spark plasma sintering technique. Temperature dependence of electrical conductivity indicates that La2CuO4 ceramics sintered at over 875 degrees C exhibit a metal-like behavior, which should be ascribed to the special La2CuO4 crystal structure and its correlation splitting of the half-filled d(x2-y2) band. Our experimental data indicate that all of the La2CuO4 samples exhibit positive thermoelectric power in the whole measuring temperature range, indicating that the majority of charge carriers are holes. It is desirable to obtain good thermoelectric performance for this system by optimizing the electrical properties and reducing the thermal conductivity.

By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d(33) piezoelectric coefficient of BLT ceramics gradually reduces up to 350 degrees C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d(33) above the permittivity peak, T-m, show that the BLT ceramic has relaxor-like behavior.

The transport of oligomeric molecules in silica spheres with cylindrical mesopores has been quantified and related to the features of the internal structures in the spherical particles and the interactions at the polymer-pore interface. An emulsion-solvent-evaporation method was used to produce silica spheres having cylindrical mesopores with an average pore diameter of 6.5 nm. The transport of dextran molecules (fluorescently tagged) with molecular weights of 3000 and 10000 g/mol were quantified using confocal laser scanning microscopy (CLSM). The intraparticle concentrations profiles in the dextran-containing spheres were flat at all times, suggesting that the underpinning diffusion is not fully isotropic and the release is controlled by the pores close to the external surface of the spheres. The release of dextran into the solution is characterized by an initial burst, followed by a long-term sustained release. This behaviour cannot be described by a spherical model with a single diffusion constant (or a surface-induced mass transfer resistance). The release follows a logarithmic time-dependency that can be described by a Temkin model.

A new phase, BaNb_6.3(1)Ti_3.6(1)O₁₆, has been synthesised. Electron diffraction studies indicate an hexagonal substructure with unit cell parameters a ≈ 8.9 Å and c ≈ 9.5 Å. In some of the ED patterns superstructure reflections are present, indicating a supercell with a = √3 · a_sub and c = c_sub. However, X-ray single-crystal diffraction studies of a crystallite yielding reflections corresponding to the supercell revealed it to be monoclinic, with the unit cell parameters a = 26.811(2) Å, b = 15.4798(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°. The average crystal structure was refined, using the subcell with a = 8.937(2) Å, b = 15.479(2) Å, c = 9.414(2) Å, β = γ = 90° and α = 90.0(3)°, space group Cm11, and Z = 4, to R_I = 3.24% and R_wI = 3.44%. The structure can be described as an hexagonal close packing layers of Nb₆ octahedra, Ba, and O atoms (A1, A2) and layers of O atoms (B1, B2), appearing in the packing sequence: A1B1A2B2. The Nb₆ octahedra are found in isolated Nb₆O₁₂O₆ clusters, and the Ti atoms in Ti₃O₁₃ and Ti₃O₁₀ units in octahedral and tetrahedral voids formed by O atoms, respectively. The Ti positions were found to be only partly occupied. Microanalysis indicates that some Nb atoms are located in the Ti₃ triangles. A model is presented that interprets these not fully occupied Ti₃ triangles as a result of a superimposing of three different structures. Two of these consist of two fused Ti₃O₁₃ units, forming an Ti₆O₁₉ unit, and a Ti₃O₁₀ unit, while the third consists of alternating Ti₃O₁₃ units.

All sintering techniques have their advantages and disadvantages. In this contribution it will be shown that the SPS technique is very well suited for the task to prepare nano-structured ceramics. In this contribution the processing strategy used to obtain nano-sized ceramics of Bi4Ti3O12, BaTiO3, and SrTiO3, respectively, will be discussed in some detail and outline the procedure that allow us to define a ""kinetic window"" within which it is possible to densify these nano-powders into fully dense compacts containing grains of almost the same size as the staring powders. We have up to day consolidated some 20 different of nano-sized powders into fully dense compacts having grain sizes exceeding those of the starting powders by factors ranging from 1.5 to 6. The grain growth factor varies with the grain size of the starting powder, i.e. if the starting powder has a grain size in the range 60-100 nm the obtained compacts normally have grain sizes in the range of 150-250 nm. With decreasing grain size of the starting powder, e. g. 10-30 run, the grain growth factor is increasing from 1.5-2.5 to 4-6. These observations are in line with the common knowledge that the driving force for reduction of the interfacial area is much smaller for 100 run sized precursor powders than for 10 nm ones.

A new binary phase, Cu10In7, was found during the investigation of the eta-phase field in the Cu-In system. Single crystals Cu10In7 were grown from a melt under an inert atmosphere. The compound crystallizes in the monoclinic space group C2/m with cell parameters a = 13.8453(2) angstrom, b = 11.8462(1) angstrom, c = 6.7388(1) angstrom and beta = 91.063(1). The structure is based on a unit of face-sharing octachedra consisting of five Cu4In2 octahedra terminated by Cu5In octahedra at both ends. The crystal Structure is closely related to the Cu11In9 structure type.

The crystal structure of the new phase, Ca2Ag1.83Al0.67Ge1.50 (1) (1) was determined by single-crystal X-ray diffraction, after the compound was obtained by high temperature synthesis technique. 1 crystallizes with the NbCoB type structure in the orthorhombic space group Pmmn (no. 59) with unit cell parameters: a = 20.505(1) angstrom, b = 4.3807(2) angstrom, c = 7.2211(3) angstrom, V = 648.65 angstrom(3) (Z = 5). The structure of the title compound represent a rare intergrowth of the well known KHg2 (or CeCu2) and Fe2P type structures.

Although free from structural disorder, the new intermetallic compound Cd_13−xIn_ySb₁₀ (see figure) displays similarly low thermal conductivity values as disordered thermoelectric β-Zn₄Sb₃ with an isostructural framework.

Cd_13−xIn_ySb₁₀ (x≈2.7, y≈1.5) was synthesized in the form of mm-sized crystals from reaction mixtures containing excess cadmium. The intermetallic compound crystallizes in the rhombohedral space group Rm with a=12.9704(4), c=12.9443(5) Å, V=1886.0(1) ų, Z=3 and is isostructural to thermoelectric β-Zn₄Sb₃ and β-Cd₄Sb₃. However, in contrast to these last two compounds Cd_13−xIn_ySb₁₀ is free from interstitial atoms and does not display any temperature polymorphism. The electrical resistivity of Cd_13−xIn_ySb₁₀ is considerably higher than that of Zn₄Sb₃ and Cd₄Sb₃ although the temperature behavior remains that of a metal. The thermal conductivity of Cd_13−xIn_ySb₁₀ is low, with room-temperature magnitudes around 0.8 W m⁻¹ K⁻¹, which is comparable to disordered or complex structured Cd₄Sb₃ and Zn₄Sb₃.

Magnetoelectric (ME) composite structures of Pb(Zr_0.52Ti_0.48)O₃ (PZT) and CoFe₂O₄ (CFO) were prepared by directly growing PZT films on highly dense CFO ceramics via a simple solution spin coating, rather than by conventional high-temperature cofiring. An obvious ME response, which had the same bias-dependent trend as the piezomagnetic coefficient of CFO ceramics, was observed in such film-on-bulk ceramic composites. It was found that the PZT films showed a good ferroelectric feature, and the ME response of the composites strongly depended on the resistivity of the CFO ceramics as both a substrate and a bottom electrode. The results suggest plenty of room for further enhancing the ME response of such films-on-ceramic substrate composites.

This thesis describes the synthesis and characterisation of alkoxides in the Er-M systems, where M = Al, Ti and Zr. The compounds found have been characterised by IR, UV-Vis DSC and single-crystal X-ray diffraction techniques and by chemical behaviour. It is shown that UV-Vis spectra can be used as an analytical tool to distinguish between different Er-containing alkoxides.

Two homometallic erbium isopropoxides have been synthesised. The first (1) is assumed to be a solvated non-oxo-alkoxide, which decomposes almost quantitatively to Er₅O(OPrⁱ)₁₃ when it is evaporated or partially hydrolysed. Er₅O(OPrⁱ)₁₃ can also be synthesised directly in high yields, using a reaction that involves partial hydrolysis. The reactivity of Er₅O(OPrⁱ)₁₃ is demonstrated by the reaction with Al₄(OPrⁱ)₁₂. The Nd analogues are also presented.

The structures of two different compounds in the Er-Al-isopropoxide system have been determined: Er₂Al₂(OPrⁱ)₁₂(HOPrⁱ)₂ and ErAl₃(OPrⁱ)₁₂, and a fourth[SGIW1] compound with the approximate Er-to-Al ratio 3:1 has also been found. ErAl₃(OPrⁱ)₁₂ could be syntesised using Er₅O(OPrⁱ)₁₃ as erbium source. This reaction was monitored by UV-Vis measurements and by IR studies of evaporated samples at different stages in the reaction. In the Er-Ti-ethoxide system only one compound could be isolated: Er₂Ti₄O₂(OEt)₁₈(HOEt)₂, and partial hydrolysis was necessary in order to reach high yields. Synthesis under strictly anhydrous conditions produced only non-isolable compound(s). When using isopropanol in stead of ethanol, another oxo-alkoxide was formed: Er₄TiO(OPrⁱ)₁₃.

In the Er-Zr-isopropoxide system, the compound Er₂Zr₂O(OPrⁱ)12(HOPrⁱ)₃ is obtained both under anhydrous conditions and after partial hydrolysis. No alkoxides with higher Zr content are formed in this system.

Most of the structural fragments, i.e. the M-O core structures (M = Er, Al, Ti and Zr) found in the different erbium-containing alkoxides, are rather common in both homometallic and heterometallic alkoxides. Examples of these fragments are: the square pyramidal M₅O core, the C_2h configuration (M₄O₆₂) and the "butterfly configuration" (M₄O). Er₂Al₂(OPrⁱ)₁₂(HOPrⁱ)₂ is exceptional in containing the rarely seen linear arrangement of the M-O core.