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Colossal Permittivity: Novel Developments
In recent years, researchers have been investigating materials with Colossal Permittivity; the research was focused mainly on the optimization of the three features described above, that is CP and, at the same time, low dielectric loss and temperature stability.
Researchers of the Australian National University have obtained very good results in this field, with their findings published in Nature Materials on the 30th of June 2013.
The material they developed is titanium dioxide (TiO2) in its rutile form, doped with a mixture of indium (In) and niobium (Nb).
Combination of Indium and Niobium
Professor Yun Liu, leading scientist of this study, explains to Decoded Science:
“We tested the properties of TiO2 with various dopants. We saw the use of indium alone did not cause an increase in the permittivity. Using indium and niobium at the same time, however, really lead to colossal permittivity; we measured values as high as 6×10+4. This corresponded to a (indium + niobium) concentration of 10 % mol.
We think that the key to these results is the different oxidation state of the dopant elements we use, in respect to titanium oxidation state, and their ability to accept or donate electrons. Indeed the titanium is in the form Ti4+, while the indium in In3+ (electron acceptor) and the niobium in Nb5+ (electron donor).”
Colossal Permittivity: Excellent Performance
As already said, the materials showed CP; at the same time, however, the dielectric loss was low for a material with such high permittivity (< 0.05).
Both the CP and the dielectric loss were almost independent of the temperature, for values between approximately -200 and +170 oC. Moreover, these properties also showed virtually no change with the applied frequency in the range between 100 Hz and 1 MHz.
According to Professor Liu “the independence of both CP and dielectric loss makes these materials strikingly superior to the CP ones developed until now.”
Improving High-Energy-Density Storage
Professor Liu commented on the importance of these results.
“We think we achieved something important; we made a material with excellent properties, which could be really used for high-energy-density storage. We finally overcome the difficulties experienced in this field.
Our compound is a TiO2-based material; TiO2, due to its numerous applications, is already industrially produced on a large scale. Therefore, it is possible in principle to produce also our material on a larger scale.
Moreover, the same principle we applied here could potentially be used for other materials with different applications; the properties of ferroelectric materials, for instance, could also be improved in the same way.”
Hu, W. et al. Electron-pinned defect-dipoles for high-performance colossal permittivity materials. (2013) Nature Materials, doi:10.1038/nmat3691. Accessed July 5, 2013.
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