稀土掺杂氮化铝稀磁半导体纳米颗粒的高压相变研究

利用金刚石对顶砧和原位角散高压同步辐射X射线衍射技术,对电弧法制备的、稀土元素钪和钇掺杂的氮化铝(AlN)纳米颗粒进行了最高压力分别为51.29 GPa和33.80 GPa的高压相变研究.实验结果表明:钪和钇掺杂的AlN分别在压力为20.09 GPa和19.70 GPa时发生由六方纤锌矿结构向立方岩盐矿结构的转变,在压力分别为28.12 GPa和28.60 GPa时完全转变为立方岩盐矿结构;卸压后,岩盐矿结构保留下来,相变过程不可逆.通过对比研究我们发现,相同制备条件、相同形貌和尺寸的两个样品的相变点较之AlN纳米线均有所降低,高于AlN纳米晶,接近于AlN体材料,相变开始到结束的时间间隔缩短.对比两个实验结果,掺杂具有大离子半径的钇的样品相变点低于掺杂离子半径较小的钪的样品.结合原位角散高压X射线衍射研究结果,我们认为掺杂引起相变点降低是由于掺杂后引入的杂质离子及其诱导产生的铝空位导致AlN晶格结构畸变进而降低了掺杂AlN晶体结构的稳定性.

Research on High Pressure Phase Transitions of Rare-earth Doped AlN Diluted Magnetic Semiconductor Nanoparticles

In situ X-ray diffraction studies of rare-earth metals Sc-and Y-doped AlN nanoparticles were carried out using angle dispersive synchrotron radiation technique in a diamond anvil cell up to approximately 51. 29 and 33. 80 GPa,respectively. The samples were synthesized using plasma assisted arc discharge methods and the morphology and size of the two samples were nearly the same. Pressure induced wurtzite-to-rocksalt phase transitions start at 20. 09 and 19. 7 GPa and complete at 28. 12 and 28. 6 GPa,showing lower phase-transition pressures compared with AlN nanowires while higher than that of AlN nanocrystals and close to bulk AlN. The pressure intervals of the two coexisting phase in AlN： Sc and AlN： Y nanoparticles shortened greatly during the phase transformation process. The critical pressure of the initial phase transition for AlN： Y nanoparticles is lower than that of AlN： Sc nanoparticles. After decompression,the rocksalt phase preserved revealing irreversible phase transitions. The effects of volume expansion,volume collapse,and crystal defects on phase transition have been discussed. The distinct high pressure behaviors can be explained in terms of the doping induced Al vacancy defects along with substitute ions sit at the cation sites,which lead to the distortion of the crystal structure that reduce the structural stability of the doped AlN nanoparticles.