Defects versus grain size effects on the ferromagnetism of ZrO2 nanocrystals clarified by positron annihilation
Defects versus grain size effects on the ferromagnetism of ZrO2 nanocrystals clarified by positron annihilation
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DOI：
10.1063/1.4790156
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发表时间：
2013-01
影响因子：
4
通讯作者：
D. D. Wang-D.;N. Qi;M. Jiang;Zhongwei Chen
中科院分区：
文献类型：
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作者：
D. D. Wang-D.;N. Qi;M. Jiang;Zhongwei Chen
未掺杂的ZrO2纳米晶在100 ~ 1300℃的露天温度下退火。采用x射线衍射和透射电子显微镜对其结构变化和晶粒生长进行了研究。两种方法均表明，在900℃退火后，ZrO2晶粒尺寸有微小的增大。正电子湮灭测量结果显示，极有可能存在于晶界区域的空位缺陷高度集中。500℃以上的热退火会使这些缺陷恢复，1200℃退火后，大部分缺陷被去除。在100°C和500°C退火后，观察到样品的室温铁磁性。在700℃退火后，纳米晶的磁化强度变得非常弱，在1000℃退火后几乎消失。结果表明，ZrO2纳米晶体的本征铁磁性主要与界面缺陷有关，而与晶粒尺寸效应无关。
Undoped ZrO2 nanocrystals were annealed in open air from 100 °C to 1300 °C. X-ray diffraction and transmission electron microscope were used to study the structure change and grain growth. Both the methods reveal that the ZrO2 grain size has very slight increase after annealing up to 900 °C. Positron annihilation measurements reveal a high concentration of vacancy defects which most probably exist in the grain boundary region. Thermal annealing above 500 °C causes recovery of these defects, and after annealing at 1200 °C, most of them are removed. Room temperature ferromagnetism is observed for the sample annealed at 100 °C and 500 °C. The magnetization becomes very weak after the nanocrystals are annealed at 700 °C, and it almost disappears at 1000 °C. It is clear that the intrinsic ferromagnetism in our ZrO2 nanocrystals is mostly related with the interfacial defects instead of grain size effects.