The atomic resolution chemical structure of defects in multiferroic oxides

多铁材料有可能对大众市场消费电子产品的数据存储做出颠覆性的改变。原则上，多铁体可以在保持永久磁化的同时保持永久电极化，两者之间存在强耦合。这使得存储器设计人员可以产生位阵列，其中数字数据可以使用电场(这很容易并且占用很小的空间)来存储，并使用磁传感器(这是非常敏感的)来读取。使用这种技术，数字信息可以以更高的密度存储，因此iPad、iPod和智能手机等手持设备可以以更大的内存和速度运行。铋铁氧体(BiFeO3)是少数几种有望在室温下实现磁电耦合的材料之一，因为它同时具有永久磁化和极化。不幸的是，磁有序是非常复杂的，只有微弱的铁磁响应。此外，高电导率确保了介电和铁电性能无法优化。尽管存在这些问题，谢菲尔德的Reaney教授的研究小组通过使用适当的等价A位(Nd3+)和异价B位(Ti4+)取代基在增强铁磁响应和降低电导率方面取得了重大进展。然而，我们的初步结果表明，由于掺杂机制，在晶体结构中出现了许多不寻常的特征，如果要进一步改善性能，需要了解这些特征。因此，该提议的目的是通过在达累斯伯里科学创新园区的SuperSTEM设施中以非常高的分辨率观察陶瓷，从原子尺度上了解BiFeO_3的掺杂机制。这将使我们能够用原子分辨率来研究缺陷的结构和化学，并使我们能够更好地了解哪些掺杂剂在改变BiFeO_3的结构和性能方面最有效。这一结果将使谢菲尔德大学的CI能够改进陶瓷配方和工艺参数，从而提高磁性和电学性能，从而导致下一代存储设备的开发。

Multiferroic materials have the potential to make a disruptive change to data storage in mass market consumer electronics. In principle, a multiferroic may hold a permanent magnetisation at the same time as a permanent electrical polarisation, with the two strongly coupled. This allows memory designers to produce arrays of bits in which digital data may be stored using an electric field (which is easy and takes little space), and read using a magnetic sensor (which is fantastically sensitive). Using such technology, digital information may be stored at much greater densities and thus hand held devices such as iPads, iPods and smartphones could operate with great memory and speed.Bismuth ferrite (BiFeO3) is one of the few materials that promises to deliver magnetoelectric coupling at room temperature since it has both a permanent magnetisation and polarisation. Unfortunately, the magnetic ordering is very complex with only a weak ferromagnetic response. Moreover, the high conductivity ensures that the dielectric and ferroelectric properties cannot be optimised. Despite these problems, Prof. Reaney's research group at Sheffield have made significant advances by the use of the appropriate isovalent A-site (Nd3+) and aliovalent B-site (Ti4+) substituents in enhancing the ferromagnetic response and decreasing conductivity. Our initial results, however, show that there are many unusual features in the crystal structure which arise due to the doping mechanism which need to be understood if the properties are to be further improved.The aim of the proposal therefore is to understand the doping mechanism in BiFeO3 on the the atomic scale, by examining ceramics at very high resolution in the scanning transmission electron microscope at the SuperSTEM facility, at the Daresbury Science and Innovation Campus. This will allow us to study the structure and chemistry of defects with atomic resolution and allow us to better understand which dopants are most effective in modifying the structure and properties of BiFeO3. The results will enable the CI at the University of Sheffield to improve ceramic formulations and processing parameters and thus enhance the magnetic and electrical properties, leading to the development of next generation memory storage devices.