Characterization of Transparent Fluorapatite Ceramics Fabricated by Spark Plasma Sintering.

Highly optically transparent polycrystalline fluorapatite ceramics with hexagonal crystal structures were fabricated via a liquid-phase synthesis of fluorapatite powder, followed by spark plasma sintering (SPS). The effect of sintering temperature, as observed using a thermopile, on the optical transmittance and microstructure of the ceramics was investigated in order to determine suitable sintering conditions. As a result, high optical transmittance was obtained in the SPS temperature range of 950-1100 °C.

Malate-aided selective crystallization and luminescence comparison of tetragonal and monoclinic LaVO:Eu nanocrystals.

With malate (Mal2-) as a new type of chelate, tetragonal (t-) and monoclinic (m-) structured LaVO4:Eu crystals (∼10-60 nm) were selectively crystallized as nanosquares and nanorods via a hydrothermal reaction at 200 °C for 24 h. The effects of the Mal2-:(La,Eu)3+ molar ratio, solution pH and Eu3+ content on the phase structure and crystal morphology were systematically investigated and elucidated. The competition between OH- and Mal2- toward rare earth ions was discussed to play a critical role in phase selection, and the t-phase can only be fabricated at pH ∼ 6-8 with the assistance of Mal2-.

Transparent non-cubic laser ceramics with fine microstructure.

Transparent polycrystalline ceramics with cubic crystal structure have played important roles in a wide variety of solid-state laser applications, whereas for non-cubic structures, single crystal only has been used. For further progress in optical technologies, effective materials beyond the current limitations are necessary. Here we report a new type of non-cubic ceramic laser material that overturns conventional common sense.

Morphology Tailoring of ZnWO Crystallites/Architectures and Photoluminescence of the Doped RE Ions (RE = Sm, Eu, Tb, and Dy).

Tartrate (Tar) was originally employed in this work as a chelating/structure-directing agent for hydrothermal crystallization of ZnWO, where the decisive roles of Tar/Zn/WO molar ratio, solution pH (7-10), and the use of ethylene glycol (EG) cosolvent in phase/morphology evolution were deciphered in detail. It was unambiguously manifested that Tar may remarkably retard the intrinsically preferred [001] growth of ZnWO, transform 1D nanorods to 0D nanoparticles and then to 2D platelets, and meanwhile induce face-to-face alignment of the platelets to form spheroidal, ellipsoidal and snowflakelike 3D architectures, where the 2D crystallites were revealed to develop via oriented attachment (colattice) of non-(00) facets. A lower solution pH and excessive WO were clearly shown to enhance and offset the effect of Tar, which led to ellipsoidal assemblies of substantially larger 2D crystallites and suppressed 2D growth/3D assembly of ZnWO crystallites, respectively.

Multi-Color Luminescent m-LaPO:Ce/Tb Monospheres of High Efficiency via Topotactic Phase Transition and Elucidation of Energy Interaction.

Monoclinic (m-) structured (LaCeTb )PO phosphor monospheres ( x = 0-0.12) of excellent dispersion and morphology uniformity were calcined (≥600 °C) from their precipitated precursor spheres (∼2.0 μm) of a hexagonal (h-) structure for efficient and multicolor luminescence.

Mechanisms and Characterization of the Pulsed Electron-Induced Grafting of Styrene onto Poly(tetrafluoroethylene-co-hexafluoropropylene) to Prepare a Polymer Electrolyte Membrane.

During the pulsed-electron beam direct grafting of neat styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) substrate, the radiolytically-produced styryl and carbon-centered FEP radicals undergo various desired and undesired competing reactions. In this study, a high-dose rate is used to impede the undesired free radical homopolymerization of styrene and ensure uniform covalent grafting through 125-μm FEP films. This outweighs the enhancement of the undesired crosslinking reactions of carbon-centered FEP radicals and the dimerization of the styryl radicals.

Selective Crystallization of Four Tungstates (LaWO, LaWO, LaWO, and LaWO) via Hydrothermal Reaction and Comparative Study of Eu Luminescence.

Hydrothermal reaction at 200 °C was systematically undertaken in wide ranges of solution pH (4-13) and W/La molar ratio ( R = 0.5-2), without using any organic additive, to investigate the effect of hydrothermal parameter on product property and the underlying mechanism. Combined analysis by X-ray diffraction (XRD), inductively coupled plasma (ICP) spectroscopy, elemental mapping, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that either a decreasing pH or increasing R value yielded a product richer in W and, conversely, richer in La.

Two-step crystallization of a phase-pure Ln(OH)NO·nHO layered compound for the smallest Ln ions of Tm, Yb and Lu, anion exchange, and exfoliation.

Crystallization of the Ln(OH)NO·nHO layered hydroxide (LLnH) is the most difficult for the three smallest lanthanide ions of Tm, Yb and Lu. By applying a novel two-step crystallization technique, which involves chemical precipitation at a freezing-temperature of ∼4 °C and subsequent Ostwald ripening at 50 °C for Tm and Yb and 65 °C for Lu, the three compounds have been obtained in a phase-pure form without the use of any mineralizer. The resulting LTmH and LYbH (n ∼ 1.

EDTA-assisted phase conversion synthesis of (GdRE)PO nanowires (RE = Eu, Tb) and investigation of photoluminescence.

Hexagonal (GdRE)PO·HO nanowires ~300 nm in length and ~10 nm in diameter have been converted from (GdRE)(OH)NO·HO nanosheets (RE = Eu, Tb) in the presence of monoammonium phosphate (NHHPO) and ethylene diamine tetraacetic acid (EDTA). They were characterized by X-ray diffraction, thermogravimetry, electron microscopy, and Fourier transform infrared and photoluminescence spectroscopies. It is shown that EDTA played an essential role in the morphology development of the nanowires.

Transparent polycrystalline cubic silicon nitride.

Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties.

Effect of sintering temperature on optical properties and microstructure of translucent zirconia prepared by high-pressure spark plasma sintering.

Aiming to characterize the effect of sintering temperature on transparency of zirconia, we have evaluated the optical properties and microstructure of translucent cubic zirconia prepared by high-pressure spark plasma sintering (SPS) at 1000-1200 C. Color centers (oxygen vacancies with trapped electrons) and residual pores were primary defects in the samples. In SPS samples, the total forward transmittance and in-line transmittance are mainly affected by color centers with a limited contribution from residual pores; in contrast, the changes in reflectance are only related to the porosity.