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SUMMARY:Negative pressure in free standing particles and the resulting enh
 ancement of properties
DTSTART:20160530T131500
DTEND:20160530T141500
DTSTAMP:20260609T214956Z
UID:31a6c2f7380a59560816e0ff5b331878ab34258282007c7bf69b64f3
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Nava Setter\nInstitute of Materials\nEPFL\nAbstract: Str
 ain engineering has been often utilized in thin films to enhance propertie
 s. For example\, biaxially strained silicon layers\, obtained due to cryst
 alline lattice mismatch with the underlying substrate exhibit high electro
 n mobility\, which is useful in CMOS technology. Less common is strain eng
 ineering in free-standing elements / particles and it has not been used so
  far (to the best of our knowledge) to modify functional properties. We de
 monstrated recently the creation of negative pressure (tension) in free-st
 anding 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 us
 e 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 wir
 es of lead-titanate in its PX phase (2\,3). Low-density PX phase was conve
 rted 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 p
 recedes that of the inner part\, the inner part is prevented from relaxing
  during the conversion and remains stretched. The negative pressure is man
 ifested by modification of the lattice parameters of the material and by c
 avitation. 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 pr
 oduce a variety of nano- and micro-structures with enhanced properties.\nR
 eferences: 1. S. Tinte\, et al.\, Phys. Rev. B. 68\,144105 (2003). 2. J. W
 ang et al.\, Chem of Materials\, 23\, 2529 (2011). 3. J. Wang et al.\, J C
 ryst Growth 347\, 1-6 (2012). 4. J. Wang et al.\, Nature Materials\, 14\, 
 985 (2015). 5. A. Kvasov et al. (submitted).\nBiography: Prof. Nava Setter
  completed MSc in Civil Engineering in the Technion (Israel) and PhD in So
 lid State Science in Penn. State University (USA) (1980). She has been the
  director of the Ceramics Laboratory and professor of Materials Science an
 d Engineering at the EPFL since 1989.
LOCATION:Lecture Hall MX F1 http://plan.epfl.ch/?room=MXF%201
STATUS:CONFIRMED
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