Fabrication of Three-Dimensional Micro Photonic Crystals of Resin-Incorporating TiO2 Particles and their Terahertz Wave Properties

Three-dimensional (3D) photonic crystals with a diamond structure made from 40 vol% TiO₂–acrylate dielectric composites were formed by means of a CAD/CAM micro-stereolithography system. The lattice constant of the diamond unit cell was 500 μm and the forming accuracy was 10 μm. The photonic band gap in the Γ–X 〈100〉 direction measured by terahertz-time-domain spectroscopy appeared at 280–360 GHz, which agreed fairly well with the band gap calculated by the plane wave expansion method.     

Fabrication of Ceramic Photonic Crystals with Diamond Structure for Microwave Applications

A process for fabricating three-dimensional photonic crystals composed of SiO₂–TiO₂-based ceramics with a diamond structure was investigated. An epoxy structure having an inverse diamond configuration was fabricated by stereolithography, a rapid prototyping method. The epoxy structure was infiltrated with a ceramic slurry and then cold isostatically pressed. After sintering at 670°C for 5 h in air, the epoxy was burned off, leaving behind the desired structure of a ceramic photonic crystal. The calculated band diagram indicated that an absolute photonic band gap for all wave vectors existed. The measurement of transmission in the 〈100〉 direction from 10 to 20 GHz showed that a complete band gap formed at about 14.7–18.5 GHz. The magnitude of the maximum attenuation was as large as 30 dB at 17 GHz, which indicated that the fabricated structure worked well as a photonic crystal.     

Band Gap Modification of Diamond Photonic Crystals by Changing the Volume Fraction of the Dielectric Lattice

Photonic crystals with a diamond structure of epoxy lattices in which TiO₂-based ceramic particles are dispersed were fabricated by stereolithography. The periodicity of the lattice was designed to reflect electromagnetic waves in the gigahertz range. The volume fraction (β) of the dielectric lattice medium was modified from 14% to 33% by changing the rod diameter of the lattice. The photonic band gap was observed along Γ-L 〈111〉, Γ-X 〈100〉, and Γ-K 〈110〉 directions and the complete photonic band gap was formed at over β= 20%. The width of the forbidden gap increased gradually when the β increased over 14%, and reached 2.4 GHz at β= 33%. These results agreed with the band calculation using the plane wave expansion method.     

Fabrication of TiO2–SiO2 Photonic Crystals with Diamond Structure

Ceramic photonic crystals with diamond structure were fabricated using stereolithography and successive sintering. The green body of an epoxy resin incorporating 10 vol% TiO₂–SiO₂ was formed by stereolithography and then heated in air at 1100°–1400°C for 2 h. The sintered products maintained the diamond structure with a linear shrinkage ratio of about 57% and a porosity of 38%. The ceramic photonic crystal with eight unit cells showed a photonic band gap at the center frequency of 23.5 GHz. This fabrication method of three-dimensional (3D) ceramic photonic crystals is applicable to other 3D structural ceramics and does not require any molding techniques.     

Microfabrication of Three-Dimensional Photonic Crystals of SiO2–Al2O3 Ceramics and Their Terahertz Wave Properties

Dense three-dimensional microphotonic crystals of SiO₂–Al₂O₃ ceramics were fabricated using microstereolithography and successive sintering process. The forming dimensional tolerance for a 50 vol% ceramic paste is 10 μm and sintering shrinkage is around 12%. Diamond-type photonic crystals with lattice constants of 500 and 125 μm were formed and sintered successfully. The band gaps of the samples were measured and compared with the theoretically calculated band diagram.     

Fabrication of Metallodielectric Photonic Crystals with a Diamond Structure and their Microwave Properties

Three-dimensional (3D) metallodielectric photonic crystals with a diamond structure were fabricated in order to investigate the formation of stop bands and the absorption ability for microwaves with the dielectric absorbing media embedded into the 3D metal lattice. First, the metallic photonic crystals were prepared by filling the epoxy molds formed by stereolithography with a metal alloy having a low melting point of 70°C, followed by removal of the molds. The metallodielectric photonic crystals were then fabricated by infiltrating the porous metal crystal with a SiC/polyester mixture. The lattice constant of photonic crystals was 15 mm. The effects of different aspect ratios of diamond lattice rods, number of metallic lattice units along Γ-L 〈1 1 1〉, Γ-X 〈1 0 0〉, and Γ-K 〈1 1 0〉 directions, and metallodielectric samples along the Γ-X 〈1 0 0〉 direction on the formation of stop band and microwave absorption ability were investigated in the frequency range from 3 to 30 GHz. Metallodielectric photonic crystals formed showed good absorption ability. The measured transmission spectra of the metallic and metallodielectric crystals agreed well with the simulation of the transmission line modeling method.     

Strengthening of Alkali Halides by Divalent-Ion Additions

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca²⁺, Sr²⁺, and Ba²⁺ were tested mechanically. In the solution-treated condition, the yield strength, σ _v , as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca²⁺, NaBr:Ca²⁺, and NaBr:Sr²⁺ systems. In addition, correlation was good between σ _v , and the Knoop hardness number, H , obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σ _v = C ( H–H ₀), where C ≅ 0.21 for all four halide families and H₀ is near the hardness value of the pure halides. Furthermore, H ₀≅5×10⁻³E₁₁₁, the Young's modulus in the 〈111〉 direction. Hence σ _v ≅0.21 H –10⁻³E₁₁₁.     

Preparation of 〈110〉-Textured BaTiO3 Ceramics by the Reactive-Templated Grain Growth Method Using Needlelike TiO2 Particles

Dense, highly 〈110〉-textured BaTiO₃ ceramics were prepared by the reactive-templated grain growth method. Needlelike TiO₂ (rutile) particles with their needle axis parallel to 〈001〉 were used as reactive template particles. Slurry containing an equimolar mixture of TiO₂ and BaCO₃ was tape cast to form a green compact, in which TiO₂ particles were aligned with their needle axis parallel to the casting direction. Calcination of the green compact changed TiO₂ particles into BaTiO₃ grains with their 〈110〉 direction parallel to the casting direction, for which the topotaxial relation of was responsible. Sintering yielded a dense, highly textured BaTiO₃ compact.     

Microwave Absorption in Photonic Crystals Composed of SiC/Resin with a Diamond Structure

Three-dimensional photonic crystals were fabricated by infiltrating an epoxy mold with a SiC/polyester mixture. The epoxy molds with normal or inverse diamond structures were formed by stereolithography. The size of the mold was 45 mm × 18 mm × 18mm, and the lattice constant of the photonic crystals was 18 mm. The effects of the epoxy mold type, aspect ratio (the ratio of height and diameter of a diamond lattice rod), and number of sample units on the formation of photonic band gap (PBG) and microwave absorption ability along the 〈100〉 direction were studied. The attenuations of microwave transmission and reflection were measured through the photonic crystal samples at a frequency range of 3–12 GHz with a network analyzer. The results obtained suggest that the combination of the absorbing material SiC and diamond structure has a dual effect to form a PBG with a high absorption ability.     

High Strain, 〈001〉 Textured 0.675Pb(Mg1/3Nb2/3)O3–0.325PbTiO3 Ceramics: Templated Grain Growth and Piezoelectric Properties

Lead magnesium niobate–lead titanate, 0.675Pb(Mg_1/3Nb_2/3)O₃–0.325PbTiO₃ (PMN–32.5PT) ceramics were textured (grain-oriented) in the 〈001〉-crystallographic direction by the templated grain growth process. The textured PMN–32.5PT ceramics were produced by orienting {001}-SrTiO₃ (ST) platelets (∼10 μm in diameter and ∼2-μm thickness) in a submicron PMN–32.5PT matrix. The templated growth of 〈001〉-oriented PMN–32.5PT grains on the ST platelets resulted in textured ceramics with ∼70% Lotgering factor and >98% theoretical density. Unlike most lead-based ceramics, excess PbO was not needed for sintering or grain growth. Based on unipolar stain-field measurements at 0.2 Hz, the textured samples displayed >0.3% strain at 50 kV/cm. Low-field d ₃₃-coefficients of >1600 pC/N (<5 kV/cm) were measured directly from unipolar measurements. The low drive field d ₃₃-piezoelectric coefficient of the highly textured samples is two times greater than polycrystalline PMN–32.5PT.     

Iron and Spinel Precipitation in Iron-Doped Sapphire

Single crystals of Al₂O₃ containing 0.5 wt% Fe were exposed to low p o₂ atmospheres at 1500°C to produce precipitate phases. Analytical TEM identified the precipitate phases as spinel (hercynite) and iron, with the following orientation relationships: 〈001〉_Fe‖〈2 2 01〉_s with {1 1 0}_Fe‖{11 2 0}_s, 〈111〉_Fe‖〈10 1 0〉_s with {0 1 1}_Fe‖ (0001)_s, and 〈1 1 0〉_H‖〈01 1 0〉_s with {111}_H‖ (0001)_s. The three phase fields observed — (Fe, Al)₂O₃, spinel +α-Al₂O₃, and iron +αAl₂O₃— are in accordance with phase stability diagrams. Precipitation kinetics indicate that oxygen is mobile in the reduced region of the crystal.     

Large Pyroelectric Effect in Relaxor-Based Ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

The pyroelectric properties of (1− x )Pb(Mg_1/3Nb_2/3)O_{3− x} PbTiO₃ (PMN− x PT) single crystals with various compositions and orientations have been investigated using a dynamic method. Excellent pyroelectric performances can be achieved in 〈111〉-oriented rhombohedral PMN− x PT (0.24≤ x ≤0.30) crystals, where the measurement direction corresponds to the polar axis of the crystal. At room temperature, the pyroelectric coefficient and the detectivity figure of merit ( F _d ) for the 〈111〉-oriented PMN–0.28PT single crystal are 8.55 × 10⁻⁴ C·(m²·K)⁻¹ and 9.89 × 10⁻⁵ Pa^−1/2 (100 Hz), respectively, superior to those of the widely used pyroelectric materials. They are also weak temperature dependent and nearly independent of frequency. These outstanding pyroelectric performances make the single crystals a promising candidate for uncooled infrared detectors and thermal imagers.     

C70 Nanowhiskers Fabricated by Forming Liquid/Liquid Interfaces in the Systems of Toluene Solution of C70 and Isopropyl Alcohol

C₇₀ whiskers with submicrometer diameters (C₇₀ nanowhiskers, or C₇₀NWs) have been successfully fabricated by forming liquid/liquid interfaces in systems that involve a toluene solution of C₇₀ and isopropyl alcohol. Transmission electron microscopy observations show that the C₇₀NWs have a 〈110〉 growth axis and that the intercluster distance of C₇₀ molecules in the C₇₀NWs are shortened by ∼3%, compared with that of face-centered cubic C₇₀ crystals in the 〈110〉 close-packed growth direction, which indicates the formation of strong chemical bonds between the C₇₀ molecules. It is suggested that the C₇₀ molecules are polymerized, with their short axis parallel to the growth axis of the C₇₀NWs, from observation via high-resolution transmission electron microscopy.     

Growth of Single Crystals of BaTiO3 by Exaggerated Grain Growth

Grain-growth experiments with steep temperature gradients and with polycrystalline aggregates seeded with single crystals were carried out to explore the feasibility of growing large crystals of BaTiO₃ in the solid state. It is shown that both methods resulted in a large increase in size of crystals normally obtained by sintering but that the rapid grain-boundary motion resulted in high porosity. Definite orientation dependence of grain-boundary velocity is demonstrated, and growth in a 〈110〉 direction was found to be at least as fast as 2 mm per hour.     

Deformation and Cracking in Ge–Sb–Se Chalcogenide Glasses During Indentation

Deformation and cracking behavior of Ge–Sb–Se binary and ternary chalcogenide glasses of varying average covalent coordination number, 〈 r 〉, was studied by indenting with Vickers and Brinell microindenters using static and recording machines, and subsequent analysis using a non-contact profilometer. Vickers-produced cracks were the smallest around the GeSe₄ composition (〈 r 〉=2.4) after unloading, hence the indentation toughness was a maximum and the brittleness a minimum at 〈 r 〉=2.4. Brinell-created pond (crater) depth, the mound (pile-up) height, and the radial fractures originating from the mounds displayed minima in the binaries, presumably due to maximized elastic recovery around 〈 r 〉=2.4. Consequently, Brinell hardness computed from the unloaded depth ( H _BD) showed a maximum around GeSe₄. The maximized elastic recovery around GeSe₄ is consistent with Phillips' optimized connectivity arguments. GeSe₄ resembles the "anomalous" SiO₂ glass for deformation and cracking behavior. Surprisingly, many of the extrema were nearly non-existent in the ternary glasses. The apparent contrast to the binary glasses is not understood.     

Review and Chemical Thermodynamic Representation of 〈U1–zCezO2±x〉 and 〈U1–zLnzO2±x); Ln = Y, La; Nd, Gd

The entire data base for the dependence of the nonstoichiometry, x , on temperature and chemical potential of oxygen (oxygen potential) in 〈U_{1– z} Ce _z O_{2+ x} 〉 and 〈U_{1– z} Ln _z O_{2+ x} 〉 was retrieved from the literature and represented by a thermodynamic method. The method reproduces the behavior of the experimental data and also results in partial molal Gibbs free energy quantities that are useful for any thermodynamic calculation involving these nonstoichiometric phases. The behavior of these systems is also compared with that for 〈U_{1– z} Pu _z O_{2± x} 〉.     

Decoration of Dislocations by the Precipitation of Alumina in MgO · 2.9Al2O3 Spinel

A thermal etching technique is developed to reveal dislocations in MgO · nAl₂O₃ (n=2.9) single crystals decorated by Al₂O₃ precipitation. Large plastic deformation leads to a larger density of thermal etch pits. Also, dense arrays of pits, parallel to the traces of slip planes with a surface, are observed around a Vickers identation. The cracks developed by an indentation run selectively along the 〈100〉 directions and accompany dislocations arrayed in the possible slip planes.     

Fabrication and Microwave Properties of Three-Dimensional Photonic Crystals With a Diamond Structure Composed of Ceramic Spheres in Resin

Three-dimensional photonic crystals with a diamond structure composed of YSZ (3 mol% Y₂O₃-stabilized ZrO₂) spheres in a resin matrix were fabricated by using stereolithography. The lattice constant was 12 mm and the diameter of the spheres was 5 mm. These photonic crystals made of ceramic spheres showed complete photonic band gaps at around 12 GHz between the eighth and ninth bands. The propagation characteristics of microwaves agreed well with the calculated results using the plane wave expansion method.     

High-Temperature Precipitation Hardening of Two-Phase Y2O3-Partially-Stabilized ZrO2 Single Crystals: A First Report

Precipitation hardening was observed in two-phase (cubic plus tetragonal) Y₂O₃-partia1ly-stabilized ZrO₂ single crystals deformed at 1400°C. Slip was activated on (001) 〈110〉, primarily in Luders bands.     

π-Rotation Faults in Hexagonal BaTiO3

Planar defects in the metastably retained h-BaTiO₃ exhibiting α-fringe pattern have been characterized via transmission electron microscopy (TEM). The eligible fault vectors were determined by adopting the invisibility criteria of 2πg·R = 0 or 2 n π augmented by high-resolution imaging. Three stacking faults, F₁, F₂, and F₃, of the extrinsic nature have been fully analyzed. The eligible fault vectors for faults F₁ and F₃ contained a basal component respectively of ⅓[0001] and ⅙[0001] and a common prismatic component of ⅓〈10[1-macr]0〉. However, only three of the 〈10[1-macr]0〉 vectors are the eligible prismatic component for the fault vectors R_F1=⅓[0[1-macr]11], ⅓[10[1-macr]1], and ⅓[[1-macr]101], and R_F3=⅙[02[2-macr]1], ⅙[2[2-macr]01], and ⅙[[2-macr]021] that have fulfilled the invisibility criteria. On the other hand, all fault vectors R_F21=⅙〈[4-macr]223〉 for fault F₂, containing six vectors of the 〈[2-macr]110〉 family, is eligible. Unlike the faults of πR_F=⅙〈[2-macr]203〉 found in the D0₁₉ intermetallics of Ni₃Sn and Co₃W, neither fault F₁ nor F₃ is the π-rotation type. Fault F₂, however, is a π-rotation fault since a 60°-rotation clockwise about [0001] has produced another eligible fault vector.