Negative pressure in free standing particles and the resulting enhancement of properties
Event details
| Date | 30.05.2016 |
| Hour | 13:15 › 14:15 |
| Speaker |
Prof. Nava Setter Institute of Materials EPFL |
| Location | |
| Category | Conferences - Seminars |
Abstract: Strain engineering has been often utilized in thin films to enhance properties. For example, biaxially strained silicon layers, obtained due to crystalline lattice mismatch with the underlying substrate exhibit high electron mobility, which is useful in CMOS technology. Less common is strain engineering in free-standing elements / particles and it has not been used so far (to the best of our knowledge) to modify functional properties. We demonstrated recently the creation of negative pressure (tension) in free-standing ferroelectric particles. The pressure proved to sustain for several years. The material, as predicted a decade ago from first principles (1) shows strongly enhanced properties. To obtain the negative pressure we use materials that undergo a solid-solid phase transformation in which the density of the final phase is higher than that of the initial phase, in parallel exploiting conditions during the transformation that prevent the transformed structure from relaxation: We prepared hydrothermally nano wires of lead-titanate in its PX phase (2,3). Low-density PX phase was converted to high-density ferroelectric perovskite phase by heating in air (see figure). This conversion requires catalytic oxygen, which diffuses from the surface into the particle. Because the conversion of the outer shell precedes that of the inner part, the inner part is prevented from relaxing during the conversion and remains stretched. The negative pressure is manifested by modification of the lattice parameters of the material and by cavitation. The properties, Curie temperature and spontaneous polarization are enhanced dramatically (4). The piezoelectric activity is enhanced too (5). The process may work on a large range of materials to potentially produce a variety of nano- and micro-structures with enhanced properties.
References: 1. S. Tinte, et al., Phys. Rev. B. 68,144105 (2003). 2. J. Wang et al., Chem of Materials, 23, 2529 (2011). 3. J. Wang et al., J Cryst Growth 347, 1-6 (2012). 4. J. Wang et al., Nature Materials, 14, 985 (2015). 5. A. Kvasov et al. (submitted).
Biography: Prof. Nava Setter completed MSc in Civil Engineering in the Technion (Israel) and PhD in Solid State Science in Penn. State University (USA) (1980). She has been the director of the Ceramics Laboratory and professor of Materials Science and Engineering at the EPFL since 1989.
References: 1. S. Tinte, et al., Phys. Rev. B. 68,144105 (2003). 2. J. Wang et al., Chem of Materials, 23, 2529 (2011). 3. J. Wang et al., J Cryst Growth 347, 1-6 (2012). 4. J. Wang et al., Nature Materials, 14, 985 (2015). 5. A. Kvasov et al. (submitted).
Biography: Prof. Nava Setter completed MSc in Civil Engineering in the Technion (Israel) and PhD in Solid State Science in Penn. State University (USA) (1980). She has been the director of the Ceramics Laboratory and professor of Materials Science and Engineering at the EPFL since 1989.
Practical information
- Expert
- Free
- This event is internal
Organizer
- Prof. Fabien Sorin
Laboratory of Photonic Materials and Fibre Devices
Contact
- Prof. Fabien Sorin
Laboratory of Photonic Materials and Fibre Devices