Lead-free alkali niobates Na0.5K0.5NbO3 (NKN) ceramics, with significantly enhanced ferroelectric remanent polarization (Pr), were prepared using Spark Plasma Sintering (SPS). Three types of boundaries were observed in the ceramics, being grain boundaries between faceted grains, domain boundaries that separate ferroelectric domains inside individual grains, and nanoscale sub-grain boundaries that reveal the nano-scale mosaicity of individual grains. Part of the sub-grain boundaries were from initial powder particles. The other sub-grain boundaries were built by ordered coalescence of nano-crystals during rapid SPS process. It was worthwhile to emphasize that the ordered coalescence of nano-crystals in bulk ceramics during sintering takes place and completes within minutes. These sub-grain features would disappear at higher temperature by long time sintering. Rapid Spark Plasma Sintering allowed us to capture this transient microstructure. The significantly enhanced ferroelectric Pr of NKN was attributed to nanoscale sub-boundaries, which stimulated the dynamics of ferroelectric domain formation and switching.

A new tungsten bronze in the Sb-W-O system has been prepared in a solid state reaction from Sb2O3, WO3 and W metal powder. The average structure was determined by single crystal X-ray diffraction. SbxWO3+y (x~0.11) crystallizes in the orthorhombic space group Pm21n (no. 31), a = 27.8135(9) Å, b = 7.3659(2) Å and c = 3.8672(1) Å. The structure belongs to the (n)-ITB class of intergrowth tungsten bronzes. It contains slabs of hexagonal channels formed by six WO6 octahedra. These slabs are separated by three layers of WO6 octahedra that are arranged in a WO3-type fashion. The WO6 octahedra share all vertices to build up a three-dimensional framework. The hexagonal channels are filled with Sb atoms to 80% and additional O atoms. The atoms are shifted out of the center of the channels. Exit-wave reconstruction of focal series of high resolution-transmission–electronmicroscope (HRTEM) images combined with statistical parameter estimation techniques allowed to study local ordering in the channels. Sb atoms in neighbouring channels tend to be displaced in the same direction, which is in agreement with total energy calculations on ordered structure models, but the ratio of the occupation of the two possible Sb sites varies from channel to channel. The structure of SbxWO3+y exhibits pronounced local modulations.

A newly developed gentle ion beam polishing technique was established for preparing of cross sections of dental implants feasible for high resolution scanning electron microscope investigation. This approach was applied to investigate the interfacial microstructure between newly formed bone and dental implants with modified surfaces extracted after in vivo test in adult miniature pigs. The results obtained so far reveal that it has become possible to analyze the bone coherence to implants besides measuring the bone coverage. The amount and density of the mineralized extra cellular matrix has found to be different in different sub-microscopic regions around the implant. From our observations, it can be seen that new bone grows from the existing bone and advances towards the implant surface by in growth mechanism. The images also reveal that new bone is formed directly at the implant surface; we propose a deposition mechanism to explain this. Eventually the in grown and the deposited bone connect to give a good anchorage of the implant. This achievement bears implication for understanding osseointegration at microscopic level.

An exceptional high ferroelectric remnant polarization (P-r) was observed in BaTiO3 ceramics owing to the formation of micron-sized grains possessing nano-scale mosaicity. Such a structural hierarchy was developed via a novel crystal-growth mechanism, namely ordered coalescence of nano-crystals achieved by synergetic atomic epitaxial growth and self-assembly of nano-crystals. The accommodating lattice defects in sub-grain boundaries due to the imperfect assembly of nano-crystals significantly contribute to the P-r enhancement by stimulating the dynamics of ferroelectric domain formation and switching. This finding defines a new approach to nanopowder sintering leading to enhanced properties sensitive to lattice defects.

A novel open-framework silicogermanate SU-JU-14 (Stockholm University-Jilin University-Number 14), vertical bar NH3CH2CH2NH3 vertical bar(3)[Ge6.40Si0.60O15(OH)](2)[Ge0.73Si3.27O8], was synthesized by using ethylenediamine as the structure-directing agent under solvothermal conditions. Single-crystal structure analysis reveals that the crystal structure of SU-JU-14 consists of extended 24-ring channels built from [(Ge,Si)(7)O12O6/2(OH)](3-) [(Ge,Si)(7)] clusters and unbranched zweier silica double chains [Ge0.73Si3.27O4O8/2]. Charge neutrality is achieved by diprotonated ethylenediamine guest molecules. The structure consists of stacking faults of layered arrays in two different configurations along the a-axis. SU-JU-14 was characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, nuclear magnetic resonance, inductively coupled plasma, and thermogravimetric analyses. Crystallographic data: monoclinic, space group C2/c, and unit cell parameters: a = 35.625 (7) angstrom, b = 28.580 (6) angstrom, c = 10.403 (2) angstrom, and beta = 98.30 (3)degrees.

A core-shell zeolite composite consisting of a single-crystal FAU-type zeolite (zeolite X) as the core and the LTA-type zeolite (zeolite A) as the shell has been synthesized. The growth of the zeolite shell has been studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and single crystal X-ray diffraction. Cross-sections for SEM and TEM studies were prepared by argon ion cross-section polishing (CP) and focused ion beam (FIB), respectively. The results show that crystals of zeolite A grew epitaxially and uniformly on zeolite X with well-defined orientation relationships. Three possible models of the X-A interface have been proposed, all indicating that the pores in zeolites X and A are interconnected. The different techniques used for studying the composite materials are described in detail, which are general and can be applied for studying other composite materials.

Piezoelectric ceramics of the composition Na0.5K0.5NbO3 (NKN) with grain sizes in the range of 0.2–1 μm were fabricated by spark plasma sintering. Ferroelectric domain size decreases with decreasing grain size and non‐180° ferroelectric domains walls were still visible in 200 nm sized grains. The Curie point of the ceramics was grain size independent. This suggests that the critical grain size for a single domain single grain structure for NKN is <200 nm. Optimized processing conditions enabled ceramics of high densities (>99.5% theoretical density) to be made at T≥850°C. For the dense ceramics (grain size ≥350 nm), the room temperature dielectric constant and coercive field increased with decreasing grain size. The remnant polarization was grain size independent. The material sintered at 850°C is a very good candidate for lead‐free piezoelectric applications because of its high piezoelectric constant (d33=160 ± 2 pC/N).

PURPOSE:The objective of this study was to assess the use of ion beam polishing for preparing cross sections suitable for high-resolution scanning electron microscope (SEM) investigation of dental implants with a brittle porous oxide layer and of bone/implant interfaces.MATERIALS AND METHODS:Thirteen Nobel Biocare TiUnite implants were placed in minipigs. After 4 weeks, the implant and surrounding bone were removed en bloc and the implant was cut axially into two halves. The cross section was then polished with an argon ion beam. Additionally, ion beam-polished cross sections were prepared from four as-received implants. Ion beam-polished surfaces were studied with a field emission SEM (FE-SEM).RESULTS:With FE-SEM, up to 1 mm along the interface of ion beam-polished implant surfaces can be studied with a resolution of a few nanometers. Filled and unfilled pores of the porous TiUnite coating can be distinguished, providing information on pore accessibility. Implant-bone interfaces can be analyzed using backscattered electron images, where titanium, the oxide layer, mineralized extracellular matrix, and osteocyte lacunae/resin/soft tissue can easily be distinguished as a result of atomic number contrast and the sharp boundaries between the different materials. Filled and unfilled pores can be distinguished. Characterization of local chemistry is possible with energy dispersive X-ray spectrometry, and bone growth into small pores (< 1 μm) can be unambiguously confirmed.CONCLUSION:FE-SEM complements the established methods for the characterization of interfaces and bridges the wide gap in accessible length scale and resolution between the observations of mechanically polished interfaces by optical or scanning electron microscopes and the observation of focused ion beam-milled sections in a transmission electron microscope.

Rapid cooling of an aluminosilicate-zirconia melt after laser sintering results in the formation of zirconia nano-crystals and dendritic zirconia crystals embedded in a glass matrix. The nano-cryst ...

BaTiO 3 –Cu composite powders were prepared via an alkoxide-mediated synthesis approach. As-synthesized BaTiO 3 nanoparticles were as small as 40 nm and coated partially larger Cu particles of approximately 1 μm in size. Thermogravimetric analysis (TGA) and dilatometry revealed a gradual increase in weight loss and retarded shrinkage with the increase of Cu addition. BaTiO 3 –Cu composites were successfully densified by spark plasma sintering (SPS). The microstructures show an average grain-size for BaTiO 3 of around 100 nm and a crystallite size of about 1 μm for the Cu inclusions. The AC conductivity of the BaTiO 3 –Cu composites increased with increasing Cu content or with temperature. The dominant electrical conduction mechanism in SPSed BaTiO 3 –Cu composites changed from migration of oxygen vacancies to band conduction of trapped electrons in oxygen vacancies with the increase of Cu content.

Spark plasma sintering (SPS) was used to densify BaTiO3–Ni composite powders to relative densities above 92.8%. With the increasing Ni content, a decrease in relative density is observed, suggesting that Ni hampers the consolidation process. The microstructures of the BaTiO3–Ni composites were of duplex character. The crystallite size of the BaTiO3‐grains was around 100 nm in average. The ceramic matrix phase of BaTiO3 surrounded Ni inclusions of approximately 1 μm in diameter that were completely incorporated without the formation of any elongated metallic filaments. The ac conductivity of these BaTiO3–Ni composites increased with increasing Ni content and with temperature. The dominant conduction mechanisms in SPSed BaTiO3–Ni composites showed quite a complicated behavior. A gradual change from band conduction of trapped electrons in oxygen vacancies to a hopping‐type motion of small polarons between Ti4+ and Ti3+ is suggested to occur, when the Ni content increases. The influence of oxygen vacancies and other lattice defects on the electrical properties of BaTiO3–Ni composites is discussed.

A software-based method for collecting precession electron diffraction (PED) patterns is described. The PED patterns are obtained on a computer controlled transmission electron microscope. A series of electron diffraction (ED) patterns are collected as still ED frames at equal intervals, while the electron beam is precessed by one period (360°) around the optical axis. A PED pattern is obtained by combining the different ED frames, which resembles the sampling of a conventional PED pattern. Since intermediate ED frames are collected, it is possible to perform different post-processing strategies on the ED data. This can be used for geometric corrections to obtain accurate integrated intensities. The alignments and data collection are fully automated and controlled by software. The data quality is comparable to what can be achieved using specialized hardware for precession. The PED data can be used for structure solution and refinement with reasonably good R-values.

237 Laves phases have the general composition AB2 and form one of the largest groups of intermetallic compounds with more than 1400 known examples. They crystallize in three structure types: cubic MgCu2 (C15), hexagonal MgZn2 (C14) and hexagonal MgNi2 (C36). In the first half of the last century it was shown in the pioneering works of J. B. Friauf [1,2], F. Laves [3,4], G. E. R. Schulze [5], F. C. Frank and J. S. Kasper [6,7], that the Laves phases can be regarded as tetrahedrally close packed structures of components A and B with tetrahedral interstices only. The ideal ratio of the radii, based on a hard-sphere model, is rA/rB = (3/2) with two kinds of coordination type polyhedra. The Frank-Kasper polyhedron Z16 surrounding the A atoms has 4 six-fold A vertices and 12 five-fold B vertices, whereas the icosahedron surrounding the B atoms has 6 five-fold A and 6 five-fold B vertices. The structure types C15, C14 and C36 can be regarded as polytypes with c3, h2, and (ch)2 stacking sequences in Jagodzinski-Wyckoff notation [8] of one common slab composed of tetrahedra and truncated tetrahedra [9]. The A atoms form a four-connected network interpenetrated by a six-connected network of the B atoms. Approximately 25% of the binary Laves phases exhibit considerable homogeneity ranges [10]. Laves phases have been studied intensely to understand the fundamental aspects of phase stability. However, simple factors governing the crystal structure type of geometric (rA/rB) and electronic (valence electron concentration, vec, and electronegativity difference, A– B) nature have proven to be helpful in predicting the occurrence and stability of the Laves phases in strictly limited cases [11, 12] only. In general, phase stability and properties of Laves phases are difficult to forecast, especially the origin of the homogeneity ranges and disorder phenomena. In order to understand the nature of Laves phases, studies on a number of Nb-TM alloy systems with TM = Cr, Mn, Fe and Co are in progress by combining experimental and theoretical methods. Since January 2006 this work is part of an interinstitutional research initiative of the Max Planck Society with the Max Planck Institutes for Metals Research and for Solid State Research in Stuttgart, the “Max-Planck-Institut für Eisenforschung” in Düsseldorf and the Max Planck Institute for Chemical Physics of Solids in Dresden as members. The results discussed here are based on the preparatory work [13-17] related to the proposal of the project. The binary system Nb–Co is particularly suitable to throw light on the stability of the polytypes due to the coexistence of the C14, C15 and C36 Laves phases. The homogeneity ranges of the Laves phasThe Nature of Laves Phases: An Explorative Investigation of the Nb-Co System Daniel Grüner, Frank Stein , Martin Palm , Joachim Konrad , Tadahiro Yokosawa , Alim Ormeci, Walter Schnelle, Osamu Terasaki , Yuri Grin, and Guido Kreiner

A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high‐resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain‐ and defect‐free surface generated by gentle ion milling, pronounced orientation contrast is observed.

We present a quantitative investigation of data quality using electron precession, compared to standard selected-area electron diffraction (SAED). Data can be collected on a CCD camera and automatically extracted by computer. The critical question of data quality is addressed–can electron diffraction data compete with X-ray diffraction data in terms of resolution, completeness and quality of intensities?

Possible methods for collecting complete 3D electron diffraction data from crystals much smaller than 1μm 3 are described.Data can be collected on a CCD camera and automatically extracted by computer.The critical question of data quality is addressed -can electron diffraction data compete with X-ray diffraction data in terms of resolution, completeness and quality of intensities?

Nuclear magnetic resonance (NMR) experiments are a local probe of the electronic environment of nuclear spins. The signal of elements in non-magnetic compounds with nuclear spin I = 1⁄2 is dominated by chemical shielding or Knight shift. For I > 1⁄2 an additional contribution due to the coupling of the nuclear quadrupole moment with the electric field gradient has to be considered as a source of information [1]. Atomic disorder changes the local environments of the atoms and therefore, the electric field. This may result in resolvable NMR signals or in a broadening of the line shape. Two examples will be given: the first one is focused on atomic disorder in Cu1–xAl2, and the second example illustrates the influence of chemical bonding on NMR in the stannides M4Sn4 of the alkali metals (M = Na, K, Rb, Cs).