54081603
Rare-earth Element-bearing Apatites and Oxyapatites
A number of prepared alkaline-earth-rare-earth silicates and germanates also have the structure of apatite type. The fifth chapter of this book then continues with descrip‐ tion of synthetic compounds of apatite structure. Attention will be directed to descrip‐ tion of rare-earth element bearing apatites and oxyapatites. The structure, properties and preparation of apatite-type silicates, germanates and borates were described. This chapter gives also description of oxygen-rich apatites, which are promising material for electrolytes in solid oxide fuel cells and sensors and explain the basic concepts between structure and conductivity of these compounds. The additional information about application of apatites is given in the last chapter of this book. Furthermore, N-apatite, REE vanadocalcic apatite and apatite type yttrium phosphates were described.
97862573
Ionic conductivity of apatite-type rare-earth silicates prepared by mechanical milling
Abstract Apatite-type silicates, R E 10 − x ( Si O 4 ) 6 O ′ 2 + y (RE = La, Nd, Gd and Dy), were prepared by mechanical milling (MM) starting from stoichiometric mixtures of the constituent oxides, RE2O3 and SiO2. XRD patterns collected after grinding the starting mixtures in a planetary ball mill for 9 h contain only the characteristic reflections of the target materials. The electrical properties were analyzed on sintered pellets by using impedance spectroscopy and the isothermal conductivity data were successfully fitted to a Jonscher-type empirical expression σ′(ω) ∝ ωn with a decreasing fractional exponent n as the RE3+ cation size increases. Activation energies for oxygen migration were found to decrease and conductivity to increase as the size of the RE3+ cation increases with the highest conductivity values obtained for the apatite-type lanthanum silicate. In addition, we also show that the electrical properties of the as-prepared materials are influenced by the silicon source used in their synthesis.
92866920
Surface and Nanomolecular Catalysis
Characterization of Heterogeneous Catalysts Z. Ma and F. Zaera Catalysis by Metal Oxides K.T. Ranjit and K.J. Klabunde Colloidal Nanoparticles in Catalysis H. Bonnemann and K.S. Nagabhushana Microporous and Mesoporous Catalysts W. Schmidt Skeletal Catalysts A.J. Smith A Scientific Method to Prepare Supported Metal Catalysts J.R. Regalbuto Catalysis and Chemical Reaction Engineering S. Hocevar Structure and Reaction Control at Catalyst Surfaces M. Tada and Y. Iwasawa Texturology V. Fenelonov and M. Melgunov Understanding Catalytic Reaction Mechanisms: Surface Science Studies of Heterogeneous Catalysts W.T. Wallace and D.W. Goodman High-Throughput Experimentation and Combinatorial Approaches in Catalysis S.A. Schunk, O. Busch, D.G. Demuth, O. Gerlach, A. Haas, J. Klein, and T. Zech Heterogeneous Photocatalysis V.I. Parvulescu and V. Marcu Liquid-Phase Oxidations Catalyzed by Polyoxometalates N. Mizuno, K. Kamata, and K. Yamaguchi Asymmetric Catalysis by Heterogeneous Catalysts S.M. Coman, G. Poncelet, and V.I. Parvulescu
97587065
Room-temperature synthesis of apatite-type lanthanum silicates by mechanically milling constituent oxides
Apatite-type lanthanum silicates have been successfully prepared at room temperature by dry milling hexagonal A−La2O3 and either amorphous or low cristobalite SiO2. Milling a stochiometric mixture of these chemicals in a planetary ball mill with a moderate rotating speed (350 rpm), allows preparing the target phase in only 6 h although longer milling times are needed to eliminate all SiO2 traces. The mechanically activated chemical reaction proceeds faster when using amorphous silica than low cristobalite as silicon source and pure phases are obtained after only 9 and 18 h respectively. As obtained powder phases are not amorphous and show an XRD pattern as well as IR and Raman bands characteristic of the lanthanum silicate.
94298805
Synthesis of Ga-doped Ge-based apatites: Effect of dopant and cell symmetry on oxide ion conductivity
Apatite-type rare earth silicates/germanates are attracting significant interest as a new class of oxide ion conductors. For the germanates, La{sub 9.33+x}(GeO{sub 4}){sub 6}O{sub 2+3x/2}, it has been shown that, depending on composition, the cell can be either hexagonal or triclinic, with evidence for reduced low temperature conductivities for the latter, attributed to increased defect trapping in this lower symmetry cell. In this paper the effect of Ga doping on the cell symmetry and conductivity is reported, with the observation of triclinic cells across the series La{sub 10}(GeO{sub 4}){sub 6-x}(GaO{sub 4}){sub x}O{sub 3-x/2}. Through co-doping with Y on the La site, i.e. La{sub 8}Y{sub 2}(GeO{sub 4}){sub 6-x}(GaO{sub 4}){sub x}O{sub 3-x/2}, it is shown that hexagonal cells are obtained, and the dependence of the conductivity on oxygen content/Ga content is discussed. In particular it is shown that the stabilisation of the hexagonal cell through Y doping enhances the low temperature conductivity.
95639230
Influence of iron on the synthesis and stability of yttrium silicate apatite
Abstract The stability of yttrium silicate apatite has been investigated by studying the influence of iron as a “stabilising cation” and also by using different synthesis routes. The formation of apatite in samples has been followed by X-ray diffraction and by 29Si MAS NMR spectroscopy. The apatite phase appears to be stable at high temperatures (≈1700 °C) especially when heated in a nitrogen atmosphere; it can also occur in a metastable state when heated in air at lower temperatures; ≈1600 °C if prepared from a Y2O3SiO2 mixture or in the range 950 °C
95741453
Electrical properties of iron doped apatite-type lanthanum silicates
Abstract The effect of Fe doping on the electrical properties of lanthanum silicates was investigated. The apatite-type lanthanum silicates La 10 Si 6− x Fe x O 27− x /2 ( x =0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via sol-gel process. The unit cell volume increased with Fe doping because the ionic radius of Fe 3+ ion is larger than that of Si 4+ ion. The conductivities of La 10 Si 6− x Fe x O 27− x /2 first increased and then decreased with the increasing of Fe content. The increase of the conductivity might be attributed to the distortion of the cell lattice, which assisted the migration of the interstitial oxygen ions. The decrease of the conductivity might be caused by the lower concentration of interstitial oxygen ions. The optimum Fe doping content in lanthanum silicates was 0.6. La 10 Si 5.4 Fe 0.6 O 26.7 exhibited the highest ionic conductivity of 2.712×10 −2 S/cm at 800 °C. The dependence of conductivity on oxygen partial pressure p (O 2 ) suggested that the conductivity of La 10 Si 6− x Fe x O 27− x /2 was mainly contributed by ionic conductivity.
96165357
Single crystal growth and oxide ion conductivity of apatite-type rare-earth silicates
Abstract Rare-earth silicate with an apatite structure is a new type of oxide ion conductor, the electrical conductivity of which is higher at relatively low temperatures than that of stabilized zirconia. Single crystals are indispensable in order to reveal the intrinsic bulk properties such as anisotropy of electrical conductivity. This paper reviews our recent research work on single crystals growth by the floating zone method and electrical properties of this material, including reinvestigation of phase relations in Nd 2 O 3 –SiO 2 system and structure refinement using neutron diffraction. A possible mechanism for the oxide ion conduction is proposed based on the existence of cation vacancies.
118549313
Symmetry and Condensed Matter Physics: A Computational Approach
Preface 1. Symmetry and physics 2. Symmetry and group theory 3. Group representations: concepts 4. Group representations: formalism and methodology 5. Dixon's method for computing group characters 6. Group action and symmetry projection operators 7. Construction of the irreducible representations 8. Product groups and product representations 9. Induced representations 10. Crystallographic symmetry and space-groups 11. Space groups: Irreps 12. Time-reversal symmetry: color groups and the Onsager relations 13. Tensors and tensor fields 14. Electronic properties of solids 15. Dynamical properties of molecules, solids and surfaces 16. Experimental measurements and selection rules 17. Landau's theory of phase transitions 18. Incommensurate systems and quasi-crystals References Bibliography Index.
93334923
Anisotropy of oxide-ion conduction in apatite-type lanthanum silicate
Abstract The anisotropy of oxide-ion conduction was clarified for the apatite-type La9.33 + 2x(SiO4)6O2 + 3x (0.01 ≤ x ≤ 0.13). We synthesized the polycrystalline materials of apatite by the isothermal heating of the sandwich-type La2Si2O7/La2SiO5/La2Si2O7 diffusion couples at 1873 K for 100 h. The resulting polycrystals were subsequently characterized using optical microscopy, X-ray diffractometry and impedance spectroscopy. The individual c-axes of the crystallites were appreciably aligned along the diffusion direction, while their a-axes were, around the common c-axis direction, oriented randomly. We obtained the impedance spectroscopy data of the polycrystalline electrolyte, the planar electrodes of which were parallel to the common c-axis. Thus, the obtained bulk conductivity ( σ ¯ bulk ⊥ c) corresponds to the average value of those perpendicular to the c-axis, which steadily increased from 1.6 × 10− 5 to 3.8 × 10− 4 S/cm with increasing temperature from 623 to 848 K. The bulk conductivity parallel to the c-axis (σbulk ‖ c) that was determined in a previous study was, when compared at the same temperature, necessarily higher than the corresponding σ ¯ bulk ⊥ c value; the magnitude of anisotropy (σbulk ‖ c / σ ¯ bulk ⊥ c) steadily decreased with increasing temperature from 2.1 × 102 at 623 K to 4.5 × 101 at 823 K. The activation energy of σ ¯ bulk ⊥ c was 0.71 eV, which is almost twice that of σbulk ‖ c (0.35 eV).
96330086
Oxygen ionic and electronic transport in apatite ceramics
The development of novel oxygen ion conducting solid electrolytes is of great interest for high-temperature electrochemical applications such as solid oxide fuel cells (SOFCs). This work was focused on the study of transport properties of apatite-type La 10 Si 6-x Fe x O 27-x/2 (x= 1-2). Single-phase apatite ceramics with density higher than 98% were prepared by the standard solid-state synthesis route. The materials were characterized by X-ray diffraction, dilatometry, impedance spectroscopy and faradaic efficiency measurements. The total conductivity and Seebeck coefficient were studied as function of the oxygen partial pressure varying in the range 10 -16 Pa to 50 kPa. The ionic conductivity of apatite phases was found to increase with oxygen content. In air, the ion transference numbers of La 10 Si 6-x Fe x O 27-x/2 (x= 1.0-1.5) at 700-950 °C are higher than 0.99, whilst the p-type electronic contribution to the total conductivity of La 10 Si 4 Fe 3 O 26 is about 3%. Mossbauer spectroscopy showed that the coordination of iron cations, which are all trivalent within the detection limits, increases with oxygen intercalation in the lattice. Reducing p(O 2 ) below 10 -8 Pa leads to a decrease in the ionic transport and growing n-type electronic contribution, the role of which increases with iron additions. The average thermal expansion coefficients in air are (8.2-9.9) x 10 -6 K -1 at 100-1000 °C.
137558742
Mössbauer spectroscopy in materials science
Preface. I: Chemistry, Mineralogy and Metallurgy. Structure and Properties of Tin-Doped Metal Oxides F.J. Berry, et al. The Kinetics of the Phase Transition in Ferrosilicon System O. Helgason, et al. Fluoride-Ion Conductors Derived from the Fluorite Type G. Denes, et al. The Ba1-xSnxCl1+yF1-y Solid Solution A. Muntasar, G. Denes. The Mechanism of beta-Fe2O3 Formation by Solid-State Reaction between NaCl and Fe2(SO4)3 R. Zboril, et al. Mossbauer Measurements of Solid Solutions (FexCr1-x)2O3, 0 Spectrometry Applied to Iron-Based Nanocrystalline Alloys I J.-M. Greneche, M. Miglierini. Mossbauer Spectrometry Applied to Iron-Based Nanocrystalline Alloys II M. Miglierini, J.-M. Greneche. Radiation Damage of Nanocrystalline Materials J. Sitek, J. Degmova. Disordered Nanocrystalline Fe-Sn Alloys E.P. Yelsukov, et al. Iron Nanoparticles in X and Y Zeolites Prepared by Reduction with NaN3 K. Lazar, et al. Quasielastic Mossbauer Scattering in Stable Icosahedral AI-Cu-Fe Quasicrystals R.A. Brand, et al. IV: Experimental Techniques and Data Processing. Quasi-Elastic Processes Studied by Methods Sensitive to the Momentum and Energy Transfer K. Ruebenbauer. Synchrotron Mossbauer Reflectometry in Materials Science D.L. Nagy, et al. Site Preference of57Co in Fe-Si Alloys after Grain Boundary Diffusion O. Schneeweiss, et al. High Pressure Mossbauer Spectroscopy M.P. Pasternak, R.D. Taylor. The Challenge of an Automatic Mossbauer Analysis P.A. de Souza Jr., V.J. Garg. Evaluation of Experimental Data: Lineshape and Goodness of Fit G. Pedrazzi, et al. CONFIT for WINDOWS(R) 95 T. Zak. YAP:Ce Scintillation Detector for Transmission Mossbauer Spectroscopy M. Mashlan, et al. The Mossbauer Spectrometer as a Virtual Instrument M. Mashlan, et al. Calib
96649926
Ionic conductivity and fuel cell properties of apatite-type lanthanum silicates doped with Mg and containing excess oxide ions
Abstract Enhancement of the ionic conductivity of lanthanum silicate-based apatites is examined with emphasis on optimizing the La composition and the Mg doping level at the same time. La10Si5.8Mg0.2O26.8 and La9.8Si5.7Mg0.3O26.4 show the highest level of the ionic conductivities among apatite silicates, 8.8 and 7.4 × 10− 2 S cm− 1 at 800 °C, respectively, with a very low level of activation energy (0.42–0.43 eV). Their conductivities are higher than yttria stabilized zirconia (YSZ) below 900 °C and even comparable to Sr and Mg doped lanthanum gallate (LSGM) below 550 °C. A solid oxide fuel cell using La9.8Si5.7Mg0.3O26.4 as an electrolyte with Ni–ceria cermet anode and Sr doped lanthanum cobaltite cathode exhibits a remarkable improvement in power generation compared to previous data using Pt electrodes. Structural investigation by the Rietveld analysis on the powder X-ray diffraction pattern shows significant enlargement of the bottleneck triangle sizes of the conduction channel with the Mg doping.
137490245
Introduction to Materials Science and Engineering
Introduction What Is Materials Science and Engineering? Fundamental Principles Atomic and Molecular Bonding Crystal Structures Polymorphism Labeling Directions and Planes Determination of Structure and Composition Using X-Rays What Is Next? Problems Crystalline Imperfections and Diffusion Cloudy and Clear Ice Experiments Imperfections-Good or Bad? Solid Solutions Point Defects Line Defects Planar Defects Precipitates as Three-Dimensional Defects Amorphous Solids Temperature Dependence of Defect Concentration Atomic Diffusion Applications of Impurity Diffusion Diffusion in Biological Systems What Is Next? Appendix: Vacancy Concentration versus Temperature Problems Electrical Properties of Metals and Semiconductors World of Electronics Definitions and Units Classical Model of Electronic Conduction in Metals Resistivity Rules for Dilute Metallic Alloys Energy Band Model for Electronic Conduction Intrinsic Semiconductors Extrinsic Semiconductors Selected Semiconductor Devices Electron Tunneling Thin Films and Size Effects Thermoelectric Energy Conversion Electrical Signaling in Neurons: Lessons from Mother Nature Appendix: Ohm's Law and Definitions Problems Mechanical Properties Gossamer Condor and Gossamer Albatross Definitions and Units Basic Facts Plastic Deformation Dislocations Plastic Deformation of Polycrystalline Materials Recovery of Plastically Deformed Metals Fracture Mechanical Properties, Surface Chemistry, and Biology Materials Selection: Mechanical Considerations Biomedical Considerations Problems Phase Diagrams Rocket Nozzles Phase Diagram for a Single-Component System: Graphite/Diamond Phase Diagram for a Common Binary System: NaCl + H2O Phase Diagram for a Binary Isomorphous System: Ni + Cu Binary Eutectic Alloys: Microstructure Development Zone Refining Application of Phase Diagrams in Making Steels Shape Memory Alloys Phase Transformation in Biological Systems: Denaturation of Proteins Application of Phase Diagrams in Making Nanocrystalline Materials Phase Diagrams for Dentistry Problems Ceramics and Composites Recipe for Ice Frisbees Crystal Structures Imperfections Mechanical Properties Toughening of Ceramics Electrical, Magnetic, Optical, and Thermal Applications Mechanical Properties of Composites Biomedical Applications Problems Polymers Rubber Band Experiments Polyethylene as a Typical Polymer Beyond Polyethylene: Polymer Structures Common Polymers and Typical Applications Solid Solutions (Copolymers) Crystallinity Mechanical Properties Crystallization, Melting, and Glass Transition Temperatures Rubber Band Mystery Unveiled Fire Retardants for Polymers Selected Electro-Optical Applications Polymer and Life Sciences Problems Corrosion and Oxidation of Metals and Alloys Silverware Cleaning Magic Conventional Example of Corrosion Electrode Potentials Influence of Concentration and Temperature on Electrode Potentials Power by Corrosion: The Cu-Zn Battery The Hydrogen Fuel Cell Rusting of Iron Conditions for Corrosion Rate of Corrosion Corrosion Control Oxidation A Few Examples for Thought Common Batteries Problems Magnetic Properties Flashlight without Batteries Tiny Magnets for Data Storage Magnetism Fundamentals and Definitions Diamagnetic and Paramagnetic Materials Magnetic Materials: Ferromagnetism and Antiferromagnetism Magnetic Materials for Power Generation Magnetic Materials for Data Storage Magnetostriction Medical, Surveying, and Materials Applications Magnetic and Force Shields Problems Thin Films Why Thin Films? Deposition of Thin Films Structure and Morphology Selected Properties and Applications Biomedical Applications Appendix: Obtaining the Projected Area of Contact in Nanoindentation Experiments Problems Bibliography Index
118217760
The Crystal Lattice: Phonons, Solitons, Dislocations, Superlattices
Prefaces. PART I: INTRODUCTION. Geometry of crystal lattice. PART II: CLASSICAL DYNAMICS OF A CRYSTAL LATTICE. Mechanics of a one-dimensional crystal. General analysis of vibrations of monoatomic lattices. Vibrations of polyatomic lattices. Frequency spectrum and its connection with the Green's function. Acoustics of elastic ssuperlattices: Phonon crystals. PART III: QUANTUM MECHANICS OF CRYSTALS. Quantization of crystal vibrations. Interaction of excitations in a crystal. Quantum crystals. PART IV: DEFECTS. Point defects. Dislocations and disclinations. Linear crystal defects. Localization of vibrations. Localization of vibrations near extended defects. Elastic field of dislocations in a crystal. Dislocation dynamics. Bibliography. Index.
132335187
Deformation of Earth Materials: An Introduction to the Rheology of Solid Earth
Much of the recent progress in the solid Earth sciences is based on the interpretation of a range of geophysical and geological observations in terms of the properties and deformation of Earth materials. One of the greatest challenges facing geoscientists in achieving this lies in finding a link between physical processes operating in minerals at the smallest length scales to geodynamic phenomena and geophysical observations across thousands of kilometers. This graduate textbook presents a comprehensive and unified treatment of the materials science of deformation as applied to solid Earth geophysics and geology. Materials science and geophysics are integrated to help explain important recent developments, including the discovery of detailed structure in the Earth’s interior by high-resolution seismic imaging, and the discovery of the unexpectedly large effects of high pressure on material properties, such as the high solubility of water in some minerals. Starting from fundamentals such as continuum mechanics and thermodynamics, the materials science of deformation of Earth materials is presented in a systematic way that covers elastic, anelastic, and viscous deformation. Although emphasis is placed on the fundamental underlying theory, advanced discussions on current debates are also included to bring readers to the cutting edge of science in this interdisciplinary area. Deformation of Earth Materials is a textbook for graduate courses on the rheology and dynamics of the solid Earth, and will also provide a much-needed reference for geoscientists in many fields, including geology, geophysics, geochemistry, materials science,mineralogy, and ceramics. It includes review questions with solutions, which allow readers to monitor their understanding of the material presented.
94890522
Structure and ionic conductivity of reactively sputtered apatite-type lanthanum silicate thin films
Abstract La–Si–O thin films with Si/(La + Si) atomic ratios ranging from 0.36 to 0.43 were produced by magnetron sputtering in a reactive Ar/O discharge gas. The as-deposited films have large X-ray diffraction peak characteristic of quasi-amorphous materials and oxygen contents from 29 to 35 at.%. The Apatite-type lanthanum silicate phase was formed in all the as-deposited films upon annealing at 900 °C for 1 h. The lanthanum silicate films obtained by annealing the as-deposited films with lower Si/(La + Si) atomic ratios have a preferential orientation with the c-axis perpendicular to the substrate while low intensity diffraction peaks ascribed to La2Si2O7 phase were detected in the films deposited with higher Si content. The preferentially oriented films have higher activation energy and lower ionic conductivity as the ionic conductivity measurements were performed in the direction perpendicular to the c-axis. The highest ionic conductivity was obtained for the film deposited with a Si/(La + Si) atomic ratio of 0.42, with a value of 1.2 × 10− 2 S·cm− 1 at 750 °C.
96785790
Luminescence of alkaline earth yttrium and lanthanum phosphate-silicates with apatite structure
Abstract The following compositions having the apatite structure were prepared: MeII2+xMeIII8−x(SiO4)6−x(PO4)×O2, (0≤×≤6) (I) MeII3+xMeIII6−x(SiO4)6−x(PO4)×,(0≤×≤1.5)(II) MeII4+xMeIII6−x(SiO4)6−x(PO4)×O,(0≤×≤6)(III) with MeII = Ca, Sr, Ba, Mg, Zn or Cd and MeIII = Y or La. Among these are several new compounds; e.g., Zn2La8(SiO4)6O2, BaMgY8(SiO4)6O2, Zn2Y8(SiO4)6O2, Cd2Y8(SiO4)6O2, Ca4La5(SiO4)5(PO4) and Ba4La5 (SiO4)5(PO4). The crystallographic parameters were determined and their luminescence studied. The most efficient activator proved to be trivalent antimony, especially in compositions of type I. At 77°K an emission band at about 400 nm was observed in many of the apatites.
95586588
Synthesis and characterisation of lanthanum germanate-based apatite phases
Abstract La germanate apatite-based materials, La 9.33 + x (GeO 4 ) 6 O 2 + 1.5x , are good oxide ion conductors but there are uncertainties over the solid solution limits, the defect crystal structure and conductivity variations with composition and temperature. Volatilisation of GeO 2 during synthesis is increasingly important for temperatures above ∼1300 °C. The solid solution range at 1100 °C is ∼0.17 ≤  x  ≤ ∼0.50 at which temperature GeO 2 loss appears not to be significant. With increasing x , the symmetry changes from hexagonal to triclinic; for high x compositions, high temperature X-ray diffraction shows a gradual triclinic to hexagonal transition over the range 600–800 °C. Conductivity data of the high x solid solutions also show evidence of the phase transition region, with lower activation energy and higher conductivity in the high temperature hexagonal structure. The extent of, and structural changes within, the apatite domain in the LaO 1.5 –GeO 2 –SrO ternary system at 1100 °C have been studied and single-phase samples are obtained for La 9.33 + x − 2y / 3 Sr y (GeO 4 ) 6 O 2 + 1.5x y  = 1.0 with x  = 0.17 and 0.34. The hexagonal to triclinic transition is clearly associated with increasing oxygen content rather than filling the La sites by addition/substitution of Sr into the structure.
11401910
Synthesis of hexagonal lanthanum germanate apatites through site selective isovalent doping with yttrium
Abstract Apatite-type lanthanum silicates/germanates have been attracting considerable interest as a new class of oxide ion conductors, whose conductivity is mediated by oxide ion interstitials. For the germanates, it has been shown that, depending on composition, the cell can be either hexagonal or triclinic, with evidence for reduced low-temperature conductivities for the latter, attributed to increased defect trapping in this lower symmetry cell. In this paper we show that site selective doping of Y into the triclinic apatite-type oxide ion conductors, La 9.33+ z (GeO 4 ) 6 O 2+3 z /2 (0.33 ≤  z  ≤ 0.67) results in a hexagonal lattice for the complete series with correspondingly enhanced low-temperature conductivity.
22280113
Doping strategies to optimise the oxide ion conductivity in apatite-type ionic conductors.
The apatite-type phases, La(9.33+x)(Si/Ge)(6)O(26+3x/2), have recently been attracting considerable interest as potential electrolytes for solid oxide fuel cells. In this paper we report results from a range of doping studies in the Si based systems, aimed at determining the key features required for the optimisation of the conductivities. Systems examined have included alkaline earth doping on the rare earth site, and P, B, Ga, V doping on the Si site. By suitable doping strategies, factors such as the level of cation vacancies and oxygen excess have been investigated. The results show that the oxide ion conductivities of these apatite systems are maximised by the incorporation of either oxygen excess or cation vacancies, with the former producing the best oxide ion conductors. In terms of samples containing cation vacancies, conductivities are enhanced by doping lower valent ions, Ga, B, on the Si site. The presence of higher valent ions on these sites, e.g. P, appears to inhibit the incorporation of excess oxygen within the channels, and so limits the maximum conductivity that can be obtained. Overall the results suggest that the tetrahedral sites play a key role in the conduction properties of these materials, supporting recent modelling studies, which have suggested that these tetrahedra aid in the motion of the oxide ions down the conduction channels by co-operative displacements.
92644413
Transition Metal Compounds
1. Localised and itinerant electrons in solids 2. Isolated transition metal ions 3. Transition metal ions in crystals 4. Mott-Hubbard vc charge-transfer insulators 5. Exchange interaction and magnetic structures 6. Cooperative Jahn-Teller effect and orbital ordering 7. Charge ordering in transition metal compounds 8. Ferroelectrics, magnetoelectrics and multiferroics 9. Doping of correlated systems and correlated metals 10. Metal-insulator transitions 11. Kondoeffect, mixed valence and heavy fermions Appendix A. Some historical notes Appendix B. A layman's guide to second quantization Appendix C. Phase transitions and free energy expansion: Landau theory in a nutshell.
94609592
Hydrothermal synthesis of new alkali silicates I. Potassium neodymium phases
Hydrothermal techniques have been used to synthesize potassium neodymium silicates as potential new fast ion conductors (FICs). Alkali silicates are interesting both scientifically and technologically as FICs because of their typically open framework structures and the unique possibilities for crystal chemical tailoring. We describe here the growth conditions for eight phases, K_3NdSi_3O_8(OH)_2, K_3NdSi_7O_(17), K_5NdSi_9O_(22), K_8Nd_3Si_(12)O_(32)OH, K_3NdSi_6O_(15) (Bb * *), K_3NdSi_6O_(15) (Pbam), K_2NdSi_4O_(10)OH, and KNd_9(SiO_4)_6O_2 the first four of which have no known isomorphs. Syntheses has been carried out employing an aqueous solution of KOH, K_2CO_3, K_2B_4O_7, KF, or KHF_2 as the solvent, and either a glass of high silica content, 4K_2O-Nd_2O_3-17SiO_2, or a mixture of Nd_2O_3, vitreous SiO_2 and K_2CO_3 as the precursor material. Pressures, temperatures, and solution molarities utilized ranged from 0.3 to 1.4 kbar, from 350 to 600 ° C, and from 0 to 10 M, respectively. Experiments, performed both isothermally and under the influence of a temperature gradient, proceeded for 5 to 20 days. Phases were identified using electron microprobe composition measurements and X-ray single-crystal and powder diffraction methods. Most phases were produced under well-defined conditions and synthesis was characterized by a tendency to crystallize compounds of low silica content and hence low connectivity of the SiO_4 tetrahedra in the crystal structure at high molarities, high temperatures, and, to some extent, high pressures. Of the eight phases listed, six were obtained as crystals large enough for X-ray structure determination and conductivity measurements along at least one crystallographic axis.
95837825
Synthesis and characterization of strontium–lanthanum apatites
Two series of strontium-lanthanum apatites, Sr{sub 10-x}La {sub x}(PO{sub 4}){sub 6-x}(SiO{sub 4}) {sub x}F{sub 2} and Sr{sub 10-x}La {sub x}(PO{sub 4}){sub 6-x}(SiO{sub 4}) {sub x}O with 0 {<=} x {<=} 6, were synthesized by solid state reaction in the temperature range of 1200-1400 deg. C. The obtained materials were characterized by powder X-ray diffraction, infrared absorption spectroscopy and solid {sup 31}P Nuclear Magnetic Resonance. Pure solid solutions were obtained within a limited range of unsubstituted phosphate and silicate apatites. A variation of the lattice parameters was observed, with an increase of a and a decrease of c parameters, related to the radius of the corresponding substituted ions.
97010811
Synthesis and structure of nanocrystalline mixed Ce–Yb silicates
Graphical abstract: - Highlights: • New method of synthesis of nanocrystalline mixed lanthanide silicates is proposed. • Formation of A-type (Ce{sub 1−y}Yb{sub y}){sub 2}Si{sub 2}O{sub 7} in well dispersed Ce{sub 1−x}Yb{sub x}O{sub 2−(x/2)}–SiO{sub 2} system. • Formation of Yb{sub y}Ce{sub 9.33−y}(SiO{sub 4}){sub 6}O{sub 2} in agglomerated Ce{sub 1−x}Yb{sub x}O{sub 2−(x/2)}–SiO{sub 2} system. - Abstract: This work presents results of studies on synthesis and structure of mixed, nanocrystalline Ce–Yb silicates. Using TEM, XRD and FTIR we showed that heat treatment of nanocrystalline Ce{sub 1−x}Yb{sub x}O{sub 2−(x/2)} (x = 0.3, 0.5) mixed oxide supported on amorphous silica in reducing atmosphere, results in formation of Ce–Yb mixed silicates. Dispersion of the oxide on the silica surface and thus a local lanthanide/Si atomic ratio determines the stoichiometry of the silicate. Oxide crystallites uniformly dispersed on the silica surface transformed into A-(Ce{sub 1−y}Yb{sub y}){sub 2}Si{sub 2}O{sub 7} disilicate, while the agglomerated nanoparticles converted into Yb{sub y}Ce{sub 9.33−y}(SiO{sub 4}){sub 6}O{sub 2} oxyapatite silicate as an intermediate phase.
53414950
SYNTHESIS AND STUDY OF YTTRIALITE
The rare earth pyrosilicates, Rg3+SizOz 1Br+:Sc,In,REl where RE:Lu,Yb,Tm,Er, Ho,Y,Dy, and Gd) were synthesized at temperatures from 900-1600"c in air. A solidsolution series exists between SczSirOz (thortveitite) and B-YzSizOz at 1300'C in air and at 700oC under 2.5 kbar. The compositional range from YzSiOs-YzSLOz-YzSiaOg was investigated at temperatures from 900 to 1500'c. "High-yttrialite" was identified as a-(Y,RE)gSizOz from the results of recrystallization of the natural minerals and by direct synthesis from sodium-free gels both in air and under water pressure. The phase described as ,,low yttrialite" is a compiex silicate of approximate formula R(Y,RE)5Si6or where R includes ions of great variety, such as H+, Na+, Fe2+, Mg2+, Mn2+, p":+, A13+, Tha+ and
96777392
Rare earth silicates with the apatite structure
Abstract Complete series of apatite like compounds RE9.33□0.67[SiO4]6O2, LiRE9[SiO4]6O2, NaRE9[SiO4]6O2 have been synthesized with RE: La → Lu. From anisotropic response of the unit-cell dimensions suggestions are made on the cation distribution on the (4f)- and (6h)-lattice sites. Crystal data on (Mg, Ca, Sr, Ba)2RE8[SiO4]6O2 and (Ca, Sr, Ba, Pb)4RE6[SiO4]6(OH)2 are also included in the structural discussion.
98614363
Advances in the structure and microstructure determination of yttrium silicates using the Rietveld method
Abstract The Y2O3–SiO2 1:1 composition doped with a weak concentration of europium ions was prepared with the sol–gel technique and the products studied by X-ray diffraction as a function of temperature in the range from 900 to 1300 °C, using the method of Rietveld for quantitative evaluation of amorphous and crystalline evolving phases. The amorphous profile of the yttrium oxyorthosilicate glasses has been described following the “Rietveld for Disordered Materials” method and subsequently included in the patterns of semicrystalline samples that have been heat-treated for temperatures above 900 °C at 1000, 1100, 1150, 1200 and 1300 °C. The quantitative evaluation of the amorphous phase is obtainable from the Rietveld approach equivalent to the method after Ruland. This enabled us to study in fine detail the structural rearrangements and growth mechanisms that take place during the crystal-to-amorphous transformation in terms of coordination numbers, average interatomic distances, average crystallite size and microstrain and to identify the polymorphous transformation involving the Y2SiO5 phase from low-to-high-temperature forms, as well as some minor quantities of other phases namely α-Y2Si2O7 phase, Y2O3 and Y4.67(SiO4)3O.
97923593
Preparation and properties of yttrium magnesium silicate with apatite structure
A new phase of yttrium magnesium silicate having the apatite structure was prepared at 1500°C in air. Its chemical composition can be varied from (Y4Mg)Si3O13 to (Y4∼3.3Mg1∼1.3)Si3∼3.4O13. Hexagonal unit cell dimensions ao and co of (Y4Mg)Si3O13 are 9.298 ± 0.002A and 6.635 ± 0.001A respectively and its axial ratio c/a is 0.714. It is optically uniaxial negative with ϵ = 1.810 ± 0.005, ω = 1.820 ± 0.005, ω − ϵ = 0.010. Cleavages parallel and perpendicular to the c-axis were recognized.
53418903
STRONTIUM IN THE APATITE STRUCTURE: STRONTIAN FLUORAPATITE AND BELOVITE-(Ce)
Strontium is one of the most common substituents in apatite; the presence and behavior of Sr in apatite-group phases are of considerable significance in geology, materials science and biology. The atomic arrangements in strontian fluorapatite (1.18 Sr atoms per 10 Ca sites) and belovite-(Ce) [ideally Sr 6(REE2Na2)(PO4)6F2] have been refined to R values of 0.016 and 0.014, respectively, in order to examine the incorporation of Sr in apatite and apatite-group minerals. In strontian fluorapatite, Sr is ordered at the Ca(2) site, and no dissymmetrization from P63/m results from the substitution; expansion of the Ca(2) site accom
135509599
Glass Ceramic Technology
Principles of Designing Glass-Ceramics. Advantages of Glass-Ceramic Formation. Factors of Design. Crystal Structures and Mineral Properties. Nucleation. Crystal Growth. Composition Systems for Glass-Ceramics. Alkaline and Alkaline-Earth Silicates. Aluminosilicates. Flourosilicates. Silicophosphates. Iron Silicates. Phosphates. Others Systems. Microstructure Control. Solid-State Reactions. Microstructure. Control of Key Properties. Methods and Measurements. Applications of Glass-Ceramics. Technical Applications. Consumer Applications. Optical Applications. Medical and Dental Glass-Ceramics. Electrical and Electronic Applications. Architectural Applications. Coatings and Solders.
137014566
X-ray data for new Y-Si-Al-O-N glass ceramics
Abstract Since the 1970s an increasing number of crystalline oxynitrides have been observed as grain boundary phases in sialon ceramics. In particular, the well-known four- and five-component phases in the Y-Si-Al-O-N system have been accepted as the total picture in this system and the potential for new phases has not been considered. However, with further development of sialon glasses and glass ceramics, post-preparative heat-treatment has revealed a number of previously uncharacterised crystalline phases occurring particularly at temperatures below 1200 °C, Three such phases are discussed, IW, Q and D, all of which have been observed previously by other researchers but without X-ray diffraction data; Q-phase occurs in some rare earth as well as yttrium sialon systems. All these phases can be produced only within a limited temperature range and are critically dependent on starting composition and heat-treatment temperature, so the present data will complement those already existing for devitrified sialon glass products, with potentially more phases yet to be identified.
137174044
Phase diagrams in advanced ceramics
W.H. Rhodes, Phase Chemistry in the Development of Transparent Polycrystalline Oxides. J.J. Brown, Jr., The Use of Phase Diagrams to Predict Alkali Oxide Corrosion of Ceramics. W.B. Johnson and A.S. Nagelberg,Application of Phase Diagrams to the Production of Advanced Composites. T-Y. Tien, Use of Phase Diagrams in the Study of Silicon Nitride Ceramics. A.J. Pyzik and A.M. Hart, The Use of Phase Studies in the Development of Whiskers and Whisker-Reinforced Ceramics. Chapter References. Subject Index.
137098709
Classic and Advanced Ceramics: From Fundamentals to Applications
Preface INTRODUCTION TO CLASSIC CERAMICS Ceramics through the Ages, and Technological Progress Classification of Ceramics MINERALOGY, STRUCTURE, AND GREEN PROCESSING OF CLAY MINERALS Natural Clay Minerals Synthetic Raw Materials Processing and Forming of Clay Powders Rheology of Clay Particle Suspensions Drying of Green Clay Bodies IMPORTANT CERAMIC PHASE SYSTEMS Fundamentals of Phase Diagrams Phase Systems with Ceramic Relevance MINERALOGY AND CHEMISTRY OF THE CERAMIC FIRING PROCESS Introduction Crystallography of the Thermal Transformations of Kaolinite Thermal Transformations in Illitic Clays Thermal Transformations and Phase Formation in the System MgO-CaO-Al2O3-SiO2 Thermal Transformations and Phase Formation in the System MgO-(Fe2O3)-Al2O3-SiO2 MINERALOGY AND CHEMISTRY OF CEMENTS Historical Development Portland Cement High Performance Concrete (HPC) Environmental Impact and Concrete Recycling Future Developments and Outlook INTRODUCTION TO ADVANCED CERAMICS General Properties of Advanced Ceramics Current World Market Situation Recent US and Global Forecasts OXIDE CERAMICS: STRUCTURE, TECHNOLOGY, AND APPLICATIONS Alumina Zirconia Titania ELECTROCERAMIC MATERIALS Introduction Physics of Dielectric Materials Ferroelectric Ceramics Microwave Ceramics Pyroelectric and Piezoelectric Ceramics Electro-Optic Ceramics Selected Application of Electroceramic Materials and Devices SUPERCONDUCTING CERAMICS Introduction Definitions Historical Developments Material Classification Crystal Chemistry Theory Materials Processing Application of Ceramic Superconductors Outlook and Future Developments BIOCERAMIC MATERIALS Introduction The Concept and Definition of Biocompatibility The Interaction of Implant Materials and Living Tissue: A Basic Approach Mechanical Properties of Advanced Bioceramics: Alumina versus Zirconia Selected Bioceramic Materials Performance Requirements and Quality Control of Ceramic Femoral Ball Heads Future Developments and Outlook NON-OXIDE CERAMICS: STRUCTURE., TECHNOLOGY, AND APPLICATIONS Introduction Carbides Nitrides ADVANCED CERAMIC APPLICATIONS AND FUTURE DEVELOPMENT TRENDS Design of Monodisperse Ceramic Powders Ceramic Processing in a Microgravity Environment Powder Preparation under Reduced Gravity Ceramic Powder Synthesis by SHS Nanosized Ceramic Powders Future Development Trends APPENDIX A: Construction of the Phase Diagram of a Binary System A-B with Ideal Solid Solution APPENDIX B: Thermodynamics of Displacive Phase Transformation APPENDIX C: Radial Electron Density Distribution (RED) Function APPENDIX D: Thermodynamics of Spinodal Decomposition of Crystals APPENDIX E: Theory of Superconductivity
138767206
Oxidation and Microstructure of Sintered Silicon Nitride
Three sintered silicon nitrides with different kinds of grain boundary phase were oxidized and the changes in microstructure were examined. The material with glassy grain boundary phase exhibited the highest oxidation rate. The additive cations in the grain boundary migrated to the surface oxide scale, and beneath the scale, the decrease of glass phase were observed. The material with crystallized grain boundary phase of Mg-sialon and Mg2SiO4 also showed the high oxidation rate. The decomposition of Mg-sialon was observed in the subscale and its constituents migrated to the scale. The material with crystallized grain boundary phase of N-diopside and small amount of N-apatite produced the lowest oxidation rate. The migration of grain boundary constituents to the scale was very slow. It is considered that the oxidation resistance of sintered silicon nitride is determined by the diffusion flux of the additive cations to the scale.
95997602
Synthesis and physicochemical study of new rare-earth-containing vanadocalcic oxyapatites
Abstract In vanadocalcic oxyapatite Ca 10 (VO 4 ) 6 O□, the pair (Ca 2+ , □) can be substituted by the pair (Ln 3+ , 1/2O 2− ) (Ln 3+ is a rare-earth ion). In theory, this substitution allows for introducing up to two rare-earth ions into the apatitic lattice. However, a limitation of this substitution depending on the nature of rare-earth was observed. Thus, this substitution is maximum in the case of La 3+ and Pr 3+ ions and leads to lanthanum or praseodym dioxyapatites Ca 8 Ln 2 (VO 4 ) 6 O 2 (Ln = La, Pr). With regards to rare earths such as neodym, samarium, europium, gadolinum, and terbium, the Ln 3+ content limit varies from one rare earth to another. It decreases when the rare-earth ionic radius declines.
96785790
Luminescence of alkaline earth yttrium and lanthanum phosphate-silicates with apatite structure
Abstract The following compositions having the apatite structure were prepared: MeII2+xMeIII8−x(SiO4)6−x(PO4)×O2, (0≤×≤6) (I) MeII3+xMeIII6−x(SiO4)6−x(PO4)×,(0≤×≤1.5)(II) MeII4+xMeIII6−x(SiO4)6−x(PO4)×O,(0≤×≤6)(III) with MeII = Ca, Sr, Ba, Mg, Zn or Cd and MeIII = Y or La. Among these are several new compounds; e.g., Zn2La8(SiO4)6O2, BaMgY8(SiO4)6O2, Zn2Y8(SiO4)6O2, Cd2Y8(SiO4)6O2, Ca4La5(SiO4)5(PO4) and Ba4La5 (SiO4)5(PO4). The crystallographic parameters were determined and their luminescence studied. The most efficient activator proved to be trivalent antimony, especially in compositions of type I. At 77°K an emission band at about 400 nm was observed in many of the apatites.
95407006
Humidity-sensitivity of yttrium substituted apatite ceramics
Abstract The humidity-sensitivity of yttrium substituted calcium oxyhydroxyapatites, was studied. The logarithm of the electrical resistance of the present sensors was decreased linearly with increasing relative humidity (RH) from 30 to 65%. The resistance of [Ca 9.0 Y 1.0 ](PO 4 ) 6 [O 1.5 ▭ 0.5 ] with the largest OH vacancy content was about one order of magnitude lower than that of calcium hydroxyapatite. It was found that the larger ratio of surface hydroxyl groups per unit surface area in the sample, the lower the resistance and the higher the amount of OH vacancies.