Researchers at Rice University (US), University of Arkansas (US), College of William and Mary in Virginia Fayetteville (US), South Federal University (RU), and Umm Al-Qura University, Saudi Arabia, have determined important information about the nanoscale properties of materials called relaxors, which can be used in electronic devices to change temperature or shape. The discoveries may help maximize efficient use of relaxors to create better medical ultrasound, sensors and heart implants.

The researchers performed calculations on a certain type of relaxor, barium zirconium titanium oxide, Ba(Zr,Ti)O3. They found that the relaxor stopped being polarized at higher temperatures. Meanwhile, the material developed nanoregions with the same polarities at lower temperatures. They also showed that this happens because of competition between opposite effects, such as differences in the way titanium ions and zirconium ions want to move or stay in non-polar positions. Another struggle between opposites involves ferroelectric interactions at short distances versus antiferroelectric interactions at larger distances between the titanium atoms. At low temperatures, the changes in position of titanium atoms are parallel to each other within small polar nanoregions. At higher temperatures, the changes in position of titanium atoms are mostly random, which make the polarity disappear.

The researchers also resolved a long-standing controversy about the role of these random polar nanoregions in relaxors. Using their model, they could switch off and on the random fields and examine their effect on the properties of the material. They found that, contrary to what scientists thought previously, turning off random fields did not affect the relaxor’s behavior at different temperatures.

A. R. Akbarzadeh, S. Prosandeev, Eric J. Walter, A. Al-Barakaty, and L. Bellaiche: Finite-Temperature Properties of Ba(Zr,Ti)O3 Relaxors from First Principles, In: Physical Review Letters, Vol. 108, Issue 25, Article 257601 [5 pages], DOI:10.1103/PhysRevLett.108.257601: http://dx.doi.org/10.1103/PhysRevLett.108.257601

Researcher at NSF Nanoscale Science and Engineering Center for High-rate Nanomanufacturing, Department of Mechanical and Industrial Engineering, Northeastern University in Boston, USA, report a simple, bottom-up/top-down approach for integrating drastically different nanoscale building blocks to form a heterogeneous complementary inverter circuit based on layered molybdenum disulfide and carbon nanotube (CNT) bundles. The fabricated CNT/MoS2 inverter is composed of n-type molybdenum disulfide (MOS2) and p-type CNT transistors, with a high voltage gain of 1.3. The CNT channels are fabricated using directed assembly while the layered molybdenum disulfide channels are fabricated by mechanical exfoliation. © IOP Publishing

Jun Huang, Sivasubramanian Somu and Ahmed Busnaina: A molybdenum disulfide/carbon nanotube heteroge- neous complementary inverter, In: Nanotechnology, Volume 23, Number 33, August 24, 2012, Article 335203, DOI:10.1088/0957-4484/23/33/335203: http://dx.doi.org/10.1088/0957-4484/23/33/335203