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SUMMARY:Negative pressure in free standing particles and the resulting enh
 ancement of properties
DTSTART:20160530T131500
DTEND:20160530T141500
DTSTAMP:20261002T033111Z
UID:7ced1feaa1919ed82c40c35b541d19cb16e4276e02c5f5962f5aa5f9
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Nava Setter\, Ceramics Laboratory - EPFL (flyer)\nStrain
  engineering has been often utilized in thin films to enhance properties. 
 For example\, biaxially strained silicon layers\, obtained due to crystall
 ine lattice mismatch with the\nunderlying substrate exhibit high electron 
 mobility\, which is useful in CMOS technology. Less common is strain engin
 eering in free-standing elements / particles and it has not been used so f
 ar (to the best of our knowledge) to modify functional properties.\nWe dem
 onstrated recently the creation of negative pressure (tension) in free-sta
 nding 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.\nTo obtain the negative pressure we us
 e materials that undergo a solid-solid phase transformation in which the d
 ensity of the final phase is higher than that of the initial phase\, in pa
 rallel exploiting conditions during the transformation that prevent the tr
 ansformed structure from relaxation: We prepared hydrothermally nano wires
  of lead-titanate in its PX phase (2\,3). Low-density PX phase was convert
 ed to high-density ferroelectric perovskite phase by heating in air (see f
 igure). This conversion requires catalytic oxygen\, which diffuses from th
 e surface into the particle. Because the conversion of the outer shell pre
 cedes that of the inner part\, the inner part is prevented from relaxing d
 uring the conversion and remains stretched.\nThe negative pressure is mani
 fested by modification of the lattice parameters of the material and by ca
 vitation. 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 pro
 duce a variety of nano- and micro-structures with enhanced properties.\nRe
 ferences: 1. S. Tinte\, et al.\, Phys. Rev. B. 68\,144105 (2003). 2. J. Wa
 ng et al.\, Chem of Materials\, 23\, 2529 (2011). 3. J. Wang et al.\, J Cr
 yst Growth 347\, 1-6 (2012). 4. J. Wang et al.\, Nature Materials\, 14\, 9
 85 (2015). 5. A. Kvasov et al. (submitted).\nBio: Nava Setter completed MS
 c in Civil Engineering in the Technion (Israel) and PhD in Solid State Sci
 ence 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.
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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