635 research outputs found
Crystal structure of Eu-doped magnetoplumbite-type lanthanum aluminum oxynitride with emission site splitting
No full textEu-doped lanthanum aluminum oxynitride (LaAl12(O,N)19) with magnetoplumbite structure was prepared by nitridation of the oxide precursor obtained from aluminum glycine gel and subsequent post-annealing. Eu-doped lanthanum aluminum oxynitride exhibited blue light emission at 440 nm with a shoulder at 464 nm under excitation at 254 nm. Isostructural Eu-doped calcium aluminum oxide (CaAl12O19) exhibited a single emission peak at 415 nm. Structural refinement using neutron powder diffraction indicated that the lanthanum site occupied partially by Eu^[2+] splits into 2d and 6h sites in the aluminum oxynitride. The longer emission and the shoulder peak in the former aluminum oxynitride were observed in relation to the increasing covalency as well as crystal field splitting around doped Eu^[2+] induced by site splitting involved with the two kinds of anions
Ammonolysis of HTiNbO5-n-Propylamine Intercalation Compound
No full textThe ammonolysis reaction to form (Ti,Nb)N was enhanced by the use of HTiNbO5 (n-propyl amine) intercalation compound as a starting material and compared with that for a simple mixture of TiO2 and Nb2O5. The ammonolysis product formed at 1200℃ was a superconductor (Tc = 15K) with a rock-salt type crystal structure having many structural defects along the stacking direction of the intercalation compound
Synthesis, thermal stability, and oxygen intake/release characteristics of YBa(Co1−xAlx)4O7+δ
No full textThe YBaCo4O7+d (Y-114) phase has recently attracted interests as a potential oxygen storagematerial due to its oxygen intake/release capability at 200–400 8C. Nevertheless, thermal instability of Y-114 has been an obstacle for future applications, since this compound immediately starts to decompose when the sample is heated at 700–800 8C in oxygen-rich atmosphere. Here we demonstrate that Al-for-Co substitution in Y-114 drastically enhances the thermal stability. Substituting only 10 at.% of aluminum for cobalt in Y-114 essentially suppresses the decomposition reaction seen at 700–800 8C, while well retaining its remarkable oxygen intake/release capability at 200–400 8C. It is also revealed that the addition of aluminum effectively reduces the particle size. The Al-substituted Y-114 products exhibit superior oxygen intake/release response to the Al-free products upon switching the atmosphere between O2 and N2
High pressure densification and dielectric properties of perovskite-type oxynitride SrTaO2N
No full textPerovskite-type SrTaO2N was densified using a belt-type high pressure apparatus at 2.5-7.7 GPa with and without sample heating. The relative density of the samples treated at 2.5 GPa was 64% and was increased to 75% in those treated at 7.7 GPa without sample heating. The color of the compact changed from orange to brown with densification and the crystals were fractured to nanometer size grains. The density was increased up to 86% with heating above 800 degrees C at 7.7 GPa and the sample color changed to black, accompanied by electrically conductive nature. The permittivity of compacts that were densified to a relative density of around 75% with heating at 600 degrees C and without sample heating were 200 and 90 at 100 Hz, respectively
Synthesis of perovskite-type oxynitrides SrNb(O,N)(3) and CaTa(O,N)(3) using carbon nitride
No full textThe synthesis of oxynitride perovskites based on the use of gaseous ammonia as the nitrogen source requires high reaction temperatures and long durations. In the resent work, reduction and nitridation reactions using carbon nitride (C3N4) were employed to prepare SrNbO2N and CaTaO2N from their oxide precursors, without the use of ammonia. The phase evolution behaviors and the reaction mechanisms were investigated by acquiring thermogravimetric and X-ray diffraction data. The formation of metal cyanamide as an intermediate was found to be vital to realizing low-temperature synthesis of these compounds. Scanning electron microscopy observations also indicated that the particle sizes of the oxynitrides prepared using C3N4 were smaller than those obtained by ammonolysis reactions, due to the low formation temperature of 800 degrees C associated with the present C3N4 process
Synthesis, structure and properties of new functional oxynitride ceramics
No full textNovel metal oxynitrtides have been prepared by nitridation of amorphous metal oxide precursors obtained through citrate route. Their crystal structure, especially in O/N distribution and local bonding characteristics has been analyzed by using neutron diffraction, X-ray absorption and transmission electron microscopy, to investigate their electric and optical properties. In dielectric SrTaO2N, crystal structure refinement suggested the short range O/N ordering and local tilting of cis-TaO4N2 octahedra, resulting in its unusual large permittivity. Its dense ceramics were sintered with SrCO3 additive and exhibited superior dielectric constant above 1 x 10(4) at room temperature. New biphasic wurtzite and zinc-blende structure of gallium oxynitride nanowire was observed by using transmission electron microscopy. As-grown long gallium oxynitride nanowire exhibited a characteristic broad UV emission at 4.3 eV in its cathodoluminescene spectrum. New oxynitride phosphor having magnetoplumbite structure, LaAl12(O,N)(19):Eu showed photoluminescence emission peak splitting due to Eu2+ site splitting to two crystallographic sites induced by the two kinds of anions in its crystal structure
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