Lu Daling, Kondo Junko Nomura, Hara Michikazu, Takata Tsuyoshi, Domen Kazunari
Materials Analysis Suzukake-dai Center, Technical Department.
Chemical Resources Laboratory.
Microscopy (Oxf). 2014 Aug;63(4):313-24. doi: 10.1093/jmicro/dfu019. Epub 2014 Jun 19.
Tantalum oxynitrides with various nitrogen contents were synthesized from Ta2O5 powder by nitridation under a flow of ammonia at 1123 K for various durations. X-ray powder diffraction, transmission electron microscopy, Ultraviolet-visible spectroscopy, energy-dispersive spectroscopy, elemental analysis and photocatalytic reaction were performed to investigate these samples. Selected-area electron diffraction analysis of the mixed crystalline phases of powder samples revealed that each particle had only one crystalline phase. This indicates that entire particles underwent a rapid structural transformation once their nitrogen content reached a critical value. We discovered a new intermediate crystalline phase of tantalum oxynitride, TaO(a > 1)N(b <1), appeared before the generation of the β-TaON phase. The crystal structure of TaO(a > 1)N(b <1) is suggested to be monoclinic, with unit cell parameters of a = 5.1 Å, b = 35.6 Å, c = 5.4 Å and β = 93.5°. The ratio of nitrogen to oxygen in the samples increased with increasing nitridation duration. The increasing rate is different in the different nitridation stage due to the different structure of the samples. Nitrogen entered the samples quickly during the initial 5 h of nitridation, and a monoclinic β-TaON phase was formed. A mesoporous structure emerged in the nitrided particles during the phase transition, greatly increasing the surface area of the samples. The more the nitrogen entered one sample, the darker the color of it due to the narrower the band gap. H2 and O2 evolved by water splitting from the nitrided samples irradiated with visible light. Change in the evolution rate of H2 and O2 had a relation with the structure of the samples.
在1123K的氨气气流中，通过氮化不同时间，由Ta2O5粉末合成了具有不同氮含量的氮氧化钽。通过X射线粉末衍射、透射电子显微镜、紫外可见光谱、能量色散光谱、元素分析和光催化反应对这些样品进行了研究。粉末样品混合晶相的选区电子衍射分析表明，每个颗粒只有一个晶相。这表明一旦颗粒的氮含量达到临界值，整个颗粒就会经历快速的结构转变。我们发现，在β-TaON相生成之前，出现了一种新的氮氧化钽中间晶相TaO(a > 1)N(b <1)。TaO(a > 1)N(b <1)的晶体结构被认为是单斜晶系，晶胞参数为a = 5.1 Å，b = 35.6 Å，c = 5.4 Å，β = 93.5°。样品中氮与氧的比例随着氮化时间的增加而增加。由于样品结构不同，在不同的氮化阶段增加速率不同。在氮化的最初5小时内，氮迅速进入样品，并形成了单斜β-TaON相。在相变过程中，氮化颗粒中出现了介孔结构，大大增加了样品的表面积。氮进入样品越多，由于带隙越窄，其颜色越深。氮化样品在可见光照射下通过水分解产生H2和O2。H2和O2的析出速率变化与样品结构有关。
