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The thermal stability of oxynitride perovskites is very important for the fabrication of their dense ceramics. In this study, a solid solution of the oxynitride perovskite Sr1-xLaxTa1-xTixO2N was prepared via the ammonia nitridation of oxide precursors. The oxynitrides products obtained at x = 0.7 had tetragonal and triclinic perovskite-type structures, respectively. A neutron diffraction study on the oxynitride product obtained at x = 0.2 indicated that this tetragonal perovskite had a cis-type anion distribution similarly to SrTaO2N. The tetragonal perovskite released a part of nitrogen at approximately 1000 degrees C in a nitrogen atmosphere while maintaining the perovskite structure at least to 1450 degrees C. The oxynitride perovskites at x >= 0.5 gradually decomposed to a mixture of LaTiO2N, LaTiO3, La(OH)(3), La2O3, TiN and TaO above 1100 degrees C.

The perovskite-type oxynitride BaTaO2N is a promising lead-free relaxor ferroelectric material. However, this material releases a part of its nitrogen during its sintering above 1350 degrees C. Subsequent annealing of the resulting sintered BaTaO2N0.85 ceramics under an ammonia flow is necessary to recover an insulating, stoichiometric BaTaO2N ceramics. Very recently, molten BaCN2 was reported to be a useful flux for the preparation of BaTaO2N microcrystals without the loss of nitrogen. In the present work, BaTaO2N powder was sintered with a BaCN2 additive under mechanical pressure, using a spark plasma sintering system. Nitrogen loss from the BaTaO2N ceramic was avoided during liquid phase sintering at approximately 900 degrees C. The stoichiometric BaTaO2N ceramic product with a relative density of 79.8 % was an electrically insulator and it showed its relative dielectric constants, epsilon(r) in the range from 320 to 650 and a loss tans values from 0.04 to 0.19 at room temperature.

Perovskite-type oxynitride BaTaO2N has been attracting attention for its large dielectric constant, which is almost independent of the temperature by measurements on its ceramics. Its dielectric characteristics are attributed to polar nanoregions (PNRs) in the average cubic crystal structure. Polarization saturation to produce a butterfly-like piezoresponse force microscopy (PFM) signal was observed on BaTaO2N crystals in the present study. Reddish crystallites of BaTaO2N of up to 3.1 mu m in size were grown using a BaCN2 flux. Grain growth proceeded through the formation of a Ruddlesden-Popper-type oxynitride from the reaction between BaTaO2N powder and molten BaCN2. Their electrical property was studied using PFM with special care because of the small size of the crystals. They were found to be much more highly insulating than its ceramics. Ferroelectricity with complete phase inversion was observed on an oxynitride perovskite crystal for the first time. A large coercivity of 50-60 V was observed in the measurement. Such ferroelectricity is ascribed to the PNRs induced by the polar linkages between cis-type TaO4N2 octahedra.

Submicron-sized NiPS3 particles were synthesized by heating fine Ni powder ( Li4P2S6 + 2Ni), and this irreversible reaction would reduce the capacity of the cathode. The XANES spectra suggested the oxidation/reduction of Ni during discharge-charge cycles, but the change in the spectra during the cycles was considerably small if one assumed the oxidation/reduction of Ni2+/Ni-0. (C) 2018 The Ceramic Society of Japan. All rights reserved.

A new polymorph of BaCN2 was obtained via a simple nitridation reaction of BaCO3 under an NH3 flow at 900 1C. The product was analyzed via single crystal X-ray diffraction and infrared spectroscopy, and it was found to have a tetragonal I4/mcm crystal structure (space group no. 140) with a = 0.60249(4) nm and c = 0.71924(5) nm. In this structure, each Ba2+ cation is situated in the square antiprism of N atoms of NCN(2-)anionic groups. Eu2+ doped BaCN2 can be excited by irradiation of blue and green light (from 400 to 550 nm), and it generates an intense red emission peak at 660 nm with a quantum efficiency of 42% in response to 465 nm excitation at room temperature. The peak emission wavelength varies over an extremely wide range of temperature, from 640 nm at 500 K to 680 nm at 80 K, and this red-shift with decreasing temperature is attributed to a unit cell shrinkage that results in significant crystal field splitting of the 5d energy levels of the Eu2+ ions.

Translucent LiCaBO3:Ce thin plates were prepared by liquid phase sintering using LiBO2 as a sintering aid, and their fluorescent and scintillation properties were investigated to examine the possibility to use as neutron scintillator. Since the initial part of the directionally solidified specimen contained a second phase of Ca3B2O6, LiCaBO3 may melt incongruently, and simple melt growth of LiCaBO3:Ce is consequently difficult. Translucent thin plates 300 mu m in thickness were successfully fabricated from LiCaBO3:Ce sintered compacts. Although strong fluorescence with the peak wavelength of 390 nm was observed in photoluminescence measurement, scintillation light yield and detection efficiency by alpha-particle irradiation were rather poor. The diffuse reflectance spectrum of LiCaBO3:Ce revealed existence of an absorption band other than Ce3+ bands in the ultraviolet region. The band may corresponds to defect levels, which interrupt the energy transfer from the conduction band of the host to the 5d level of Ce3+ resulting in the degradation of the scintillation performance. (C) 2017 Elsevier B.V. All rights reserved.

Metal oxynitrides are generally synthesized by heating their component oxides in a flow of ammonia for longer than 20 h. In the present study, pure BaTaO2N oxynitride perovskite powder was obtained by heating a mixture of tetragonal BaCN2 and Ta2O5 in a flow of nitrogen. The BaTaO2N powder synthesized at slightly below the melting point of tetragonal BaCN2 (910 degrees C) was found to consist of coarse aggregates of 300 nm-sized particles based on scanning electron microscopy observations. In contrast, BaTaO2N powder obtained above the melting point of tetragonal BaCN2 contained highly-dispersed particles after washing with acid. This difference is attributed to the dissolution and precipitation of the surfaces of the BaTaO2N grains in the BaCN2 melt to generate grain boundary layers soluble in acid. This work represents the first report of the synthesis of a metal oxynitride using a metal carbodiimide as both the metal and nitrogen source. (C) 2020 Elsevier B.V. All rights reserved.

We report a new material, BaCN2:Eu2+ for a very sensitive optical pressure sensor, 50 times more sensitive than ruby. Photoluminescence spectra of the BaCN2:Eu2+ phosphor was measured under hydrostatic pressures from ambient pressure to 5.34 GPa at room temperature. The peak wavelength of the luminescence was drastically red-shifted at a rate of 19 nm GPa(-1), which is approximately 50 times larger than that of the ruby, most commonly used as a pressure sensor in the high-pressure experiments. This large shift of the luminescence wavelength is suitable for application in optical pressure sensors for the high-pressure experiments without a high-resolution monochromator.

Oxide ion conduction mechanism was clarified by Rietveld and MEM analysis for both RE9.33(SiO4)6O2 and Sr2RE8(SiO4)6O2 (RE = La and Nd) in high purity using neutron powder diffraction data collected at room temperature. All compounds had an apatite type structure in space group P63/m. There was neither site splitting nor interstitial site of oxide ion. RE9.33(SiO4)6O2 had cation vacancies only at 4f site. In Sr2RE8(SiO4)6O2, the 4f sites were fully occupied by strontium and rare earth with a molar ratio of 1:1. Oxide ion at hexagonal channel site had large displacement along c-axis in RE9.33(SiO4)6O2. The large displacement is induced by cooperative rotation of SiO4 tetrahedra around rare earth in 4f site through oxide ion polyhedra around another rare earth in 6h site. The displacement, enhanced by a vacancy in the 4f site, is directly related to the oxide ion conduction in RE9.33(SiO4)6O2.

Transparent and crack-free Bi12GeO20 single crystals have been grown by the pulling-down method with a continuous powder feed system. Bi-rich feed powder having a composition of 14.1mol% GeO2 is favorable to obtain stoichiometric crystals. Striation-free crystals with an increased transmittance are grown under a small temperature gradient. The shape of the solid-liquid interface during the crystal growth is nearly flat, which is advantageous to avoid core formation. Average dislocation density is estimated to be 2×104/cm2, which is comparable to that of Bi12GeO20 crystals grown by the conventional Czochralski method.

This review deals with effects of oxygen partial pressures on the crystal growth of oxides containing transition elements. Rutile (TiO_2) and chromium-doped forsterite (Cr: Mg_2SiO_4) single crystals are successfully grown by the floating zone method. Rutile single crystals are grown under a low oxygen partial pressure of about 10^3 Pa to avoid the formation of low-angle grain boundaries. Zirconium-doping is effective to grow rutile single crystals without low-angle grain boundaries and bubble inclusions at a high growth rate of 10 mm/h under a high oxygen partial pressure of 10^5 Pa. Cr^-rich Cr: Mg_2SiO_4 single crystals are grown under a high oxygen partial pressure of 1-2 10^5 Pa, which can not be realized in the conventional Czochralski method using an iridium crucible.

MgTa2O6 single crystals, which adopt trirutile structure, were successfully grown by a floating zone method, and their optical properties were invetigated. The as-grown crystals were black and opaque, but subsequent annealing in air from 1200° to 800°C rendered the crystals pale-yellow and transparent. The refractive indices for ordinary and extraordinary rays were 2.07 and 2.18 under white light, respectively, and the birefringence was 0.11. The interference figure observed with a polarizing microscope was typical one for an optically uniaxial crystal, which indicates that the crystal was optically uniform. Transmittance in the wavelength range of 500 to 2000nm was about 75%, which approximately corresponded to the theoretical value calculated from the refractive index. The absorption edge of MgTa2O6 was at 290nm.

Ceramic composites were fabricated from powder mixtures of BaTiO3 and Ni0:3Zn0:7FexO4 with different Fe contents of x ¼ 1:8, 1.9, 2.0, 2.1, and 2.2 to examine the effect of Fe content on the dielectric permittivity ("r) of the composite samples (these are referred to as Fe1.8, Fe1.9, Fe2.0, Fe2.1, and Fe2.2 composites or samples, respectively). The "r values of the composites were greatly affected by the Fe content such that a small "r value of the Fe1.8 composite sample steeply increased with increasing Fe content by about three orders of magnitude for the Fe2.1 and Fe2.2 samples. The strong Fe content dependence could be correlated with the incorporation of Ti4þ ions into the octahedral sublattices in the ferrite structure. Therefore, the markedly increasing "r values for the Fe2.1 and Fe2.2 composite samples can be attributed to the presence of Fe2þ ions synergetically created by the Ti-substitution and Fe-rich composition.

01pA05, Nd:PrVO_4 and Nd:La_xGd_VO_4 single crystals were grown by the floating zone method in order to broaden the absorption and emission bands of Nd^. Nd:La_xGd_VO_4 (X≦0.15) and Nd:PrVO_4 single crystals had no macroscopic defects, whereas cellular structures were found in a Nd:La_Gd_VO_4 crystal. The absorption band of Nd:PrVO_4 around 808nm was broader than that of Nd:GdVO_4, and intensive absorption peaks were not observed around 1.06μm and 1.3μm.

01pA06, Dy:GdVO_4 single crystals were successfully grown by the floating zone method. All the grown crystals had no macroscopic defects such as inclusions and low-angle grain boundaries. An intensive fluorescence peak was observed at 573nm, which is assigned to the radiation from ^4F_ to ^6H_. The excitation spectrum for the 573nm emission had a peak around 450nm. These results indicate Dy:GdVO_4 single crystals can be one of the candidates for LD-pumped yellow-laser materials.

19aB02, Nd: LuVO_4 single crystals were successfully grown by the floating zone method. All the grown crystals had no macroscopic defects such as inclusions and low-angle grain boundaries but contained growth striations. The effective distribution coefficient of Nd in LaVO_4 was estimated to be about 0.5. In the laser oscillation experiments, a slope efficiency of 77% was obtained for the Nd 1 at%-doped crystal by pumping with a π-polarized beam at 880nm.

26aD03, Tm:GdVO_4 single crystals were successfully grown by the floating zone method. All the grown crystals had no cracks and no inclusions for any dopant concentration. Laser oscillation was observed for the 3 at%-doped crystal at 1920nm with the pumping wavelength of 806nm. The slope efficiency was 38% with the threshold of about 400mW.

14aA2, Li_2B_4O_7 single crystals 40 mm in diameter and 100 mm long were successfully grown by the pulling-down method . Continuous Powder feeding system enabled to grow long crystals with a controlled diameter. The obtained crystals were water clear and had no macroscopjc defects such as bubbles and cracks.

801a1B6, βⅡ-Li3VO4はSakataらによって見出された比較的新しい非線形光学結晶である。Li3VO4は1152℃において一致溶融するが、冷却中に3回の相転移を経るためクラックの発生を避けることができない。今回我々はヒーター挿入型TSFZ法を採用し、最も低温の相転移点である700℃以下で育成することにより、低温相であるβⅡ-Li3VO4単結晶を直接得ることに成功した。