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Dense and transparent ceramic samples of a (Gd,Y)3Al2Ga3O12:Ce scintillator were obtained by using stereolithography-based Digital Light Processing (DLP) 3D printing for compacting, subsequent burnout, and pressureless sintering. The effects of stoichiometric deviations and green body compaction methods (uniaxial pressing versus DLP 3D printing) on the optical, luminescent, and scintillation properties of ceramics were analyzed. An excess of Y and Gd in the composition led to an increase in transmittance and to the acceleration of the scintillation kinetics. Moreover, transparent ceramics made of 3D-printed green bodies were found to be superior in light yield to the samples, which were prepared from the same powders and densified by uniaxial pressing. [ABSTRACT FROM AUTHOR]

For complete and reproducible recovery of a high-pressure polymorph of zinc oxide, rock-salt ZnO (rs-ZnO), nanostructured wurtzite ZnO (w-ZnO) is typically used as a precursor for high-pressure synthesis. In the case of polycrystalline w-ZnO, only small amounts (less than 30 vol%) of disordered/nanosized rs-ZnO were occasionally observed in the recovered products. Here we report the conditions for the synthesis of single-phase rs-ZnO from microcrystalline (40–50 μm) w-ZnO powder at 7.7 GPa and 2000 K. The complete recovery of metastable rs-ZnO is possible only by using multianvil apparatus for quasi-hydrostatic (triaxial) compression/decompression and pyrolytic boron nitride as a pressure medium. Single-phase rs-ZnO was produced as colorless nanocrystalline well-sintered bulks with Vickers hardness up to 7 GPa – the record value for ZnO due to a fortunate combination of Hall–Petch nanostructuring effect and high intergranular purity. This unexpected phenomenon can be related to the mechanism of the direct and reverse phase transitions in ZnO, which requires "uniaxial" tensile deformation. Texture analysis of the recovered samples, as well as previous kinetic studies and ab initio simulation of strain–structure relationships, strongly support this model. Thus, 3-axial decompression is a more efficient tool – neglected until now – for reproducible recovery of high-pressure ZnO-based materials than the nature of the w-ZnO precursor and the presence of isostructural rock-salt phases. [ABSTRACT FROM AUTHOR]

The production of scintillating ceramics can require the utilization of the phosphorus compounds at certain stages of 3D-printing, such as vat polymerization, applied for the formation of green bodies before sintering. The effect of phosphorus additive on the microstructure, optical, and scintillation parameters of Gd1.494Y1.494 Ce0.012Al2Ga3O12 (GYAGG:Ce) ceramics obtained by pressureless sintering at 1650 °C in an oxygen atmosphere was investigated for the first time. Phosphorus was introduced in the form of NH4H2PO4 into the initial hydroxycarbonate precipitate in a wide concentration range (from 0 to 0.6 wt.%). With increasing of phosphorus concentration, the density and the optical transmittance of garnet ceramics show a decrease, which is caused by an increase in the number of pores and inclusions. The light yield of fast scintillation, which is caused by Ce3+ ions, was found to be affected by the phosphorus additive as well. Moreover, an increase in phosphorescence intensity was recognized. [ABSTRACT FROM AUTHOR]

Metastable ZnO—Lin−2MeOn−1 (Me = Sc3+, Ti4+, Ta5+) solid solutions with a rock-salt structure were synthesized through the solid-state reaction of ZnO with Lin−2Men+On−1 (n = 3, 4, 5) complex oxides at 7.7 GPa and 1300–1500 K. In all investigated systems, single-phase rock-salt solid solutions can be quenched down to ambient conditions in a wide (up to 80 mol% ZnO) concentration range. The phase composition, thermal stability, and thermal expansion of the recovered rock-salt solid solutions were studied by synchrotron powder X-ray diffraction. At ambient pressure, these solid solutions exhibit high thermal stability (up to 1000 K), with the decomposition temperature and decomposition products depending on the nature of the multiple charge cations. [ABSTRACT FROM AUTHOR]

Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under pressures up to 34 GPa at room temperature. No pressure-induced structural phase transition was observed, while strong pressure shift of Raman bands towards higher wavenumbers has been revealed. IR spectroscopy as a complementary technique has been used in order to completely describe the phonon modes of r-BS. All experimentally observed bands have been compared with theoretically calculated ones and modes assignment has been performed. r-BS enriched by 10B isotope was synthesized, and the effect of boron isotopic substitution on Raman spectra was observed and analyzed. [ABSTRACT FROM AUTHOR]

Here we propose a new approach to the synthesis of single-phase boron phosphides (BP and B12P2) by mechanochemical reactions between boron phosphate and magnesium/magnesium diboride in the presence of an inert diluent (sodium chloride). The proposed method is characterized by the simplicity of implementation, high efficiency, low cost of the product, and good perspectives for large-scale production. [ABSTRACT FROM AUTHOR]

Melting of boron subphosphide (B12P2) to 26 GPa has been studied byin situsynchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and by quenching and electrical resistance measurements in a toroid-type high pressure apparatus. B12P2melts congruently, and the melting curve has a positive slope of 23(6) K/GPa. No solid-state phase transition was observed up to the melting in the whole pressure range under study. [ABSTRACT FROM PUBLISHER]

A synthesis route to rock salt zincoxide (rs-ZnO),high-pressure phase metastable at ambient conditions, has been developed.High-purity bulk nanocrystalline rs-ZnO has beensynthesized from wurtzite (w) ZnO nanopowders at7.7 GPa and 770–820 K and, for the first time, recovered atnormal conditions. Structure, phase composition, and thermal phasestability of recovered rs-ZnO have been studied bysynchrotron X-ray powder diffraction and X-ray absorption spectroscopy(XANES and EXAFS) at ambient pressure. Phase purity of rs-ZnO was achieved by usage of w-ZnO nanoparticleswith a narrow size distribution as a pristine material synthesizedby various chemical methods. At ambient pressure, rs-ZnO could be stable up to 360 K. The optical properties of rs-ZnO have been studied by conventional cathodoluminescencein high vacuum at room and liquid-nitrogen temperatures. The nanocrystalline rs-ZnO at 300 and 77 K has shown bright blue luminescenceat 2.42 and 2.56 eV, respectively. [ABSTRACT FROM AUTHOR]

The present study demonstrates the possibility of fabricating zirconia parts with a complex shape and internal architecture using a low-cost stereolithography-based technique. One of the critical steps in ceramics stereolithography is the preparation of a photo-curable slurry with properties that fulfill specific requirements, such as having a low viscosity, high solids loading and appropriate curing characteristics. Slurries with different acrylic monomers and ceramic fillers were studied concerning their rheological and curing behavior. New formulations based on mono- and tri-functional acrylic monomers revealed the following excellent rheological properties: The viscosity of the mono-/tri-acrylate-based slurry with 75 wt.% of zirconia was 1.6 Pa·s at 30 s−1. Zirconia stabilized with 3 mol.% yttria was found to be more favorable than zirconia with 8 mol.% yttria for slurry preparation, because of its lower surface area and higher tapped density. It was shown that the cure depth of the suspensions was suitable for printing objects with a 50 µm layer thickness, good interlayers connection and surface finishing. [ABSTRACT FROM AUTHOR]

Here we propose a new approach to the synthesis of single-phase boron phosphides (BP and B12P2) by mechanochemical reactions between boron phosphate and magnesium/magnesium diboride in the presence of an inert diluent (sodium chloride). The proposed method is characterized by the simplicity of implementation, high efficiency, low cost of the product, and good perspectives for large-scale production. [ABSTRACT FROM AUTHOR]