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SUMMARY:Finite-temperature properties of Ba(Zr\,Ti)O3 relaxors from first 
 principles
DTSTART:20140324T131500
DTSTAMP:20260611T041449Z
UID:5cfb8ac76987689d6df5cc65ccceacbea2388bed607fe7acc7c274d6
CATEGORIES:Conferences - Seminars
DESCRIPTION:Laurent Bellaiche\, University of Arkansas\, USA\nRelaxor ferr
 oelectrics are characterized by some striking anomalous properties (see\, 
 e.g.\, Refs [1-21] and references  therein).    For  instance\,  the
 y  adopt  a  peak  in  their  ac  dielectric  response-versus-temp
 erature function while they remain macroscopically paraelectric and cubic 
 down to the lowest temperatures [1]. Furthermore\, this dielectric respons
 e deviates from the ``traditional'' Curie-Weiss law [22] for temperatures 
 lower than the so-called Burns temperature [2]. Other examples of anomalou
 s properties include the plateau observed  in  their  static\,  dc  d
 ielectric  response  at  low  temperature  [23\,24]\,  and  the  u
 nusual  temperature behavior [16] of the Edwards-Anderson parameter [25].
  Determining the origin of these intriguing effects has been a challenge t
 o scientists for more than half a century. Moreover\, many other questions
  remain opened for discussion.  Examples  of  such  questions  are: 
  what  do  the  different  critical  temperatures  usually  found 
  in relaxors  correspond  to?  Do  polar  nanoregions  really  exis
 t  in  relaxors?  If  yes\,  do  they  only  form  inside chemica
 lly-ordered regions? Is it necessary that antiferroelectricity develops in
  order for the relaxor behavior to occur? Are random fields and random str
 ains really the mechanisms responsible for relaxor behavior? If not\, what
  are these mechanisms?\nMotivated to resolve such questions and to better 
 understand relaxors\, we decided to study disordered Ba(Zr0.5Ti0.5)O3  (B
 ZT) solid solutions\, via the development and use of a first-principles-ba
 sed effective Hamiltonian. Note that BZT is also fascinating because\, in 
 addition to be a relaxor within some compositional range\, its parent comp
 ounds are rather different\, namely BaZrO3 is paraelectric while BaTiO3 is
  a typical ferroelectric.\nInterestingly\,  our ab-initio-based  calcula
 tions  not only reproduce  the anomalous  features of relaxors but also
  offer a deep microscopic insight into BZT [26\,27\,28]. Such insight allo
 ws to successfully answer the aforementioned questions\, and will be discu
 ssed in detail during this talk.\nThis work is mostly supported by ONR Gra
 nts N00014-11-1-0384\, N00014-12-1-1034 and N00014-08-1-\n0915. We also ac
 knowledge the ARO grant W911NF-12-1-0085\, NSF grant DMR-1066158\, and Dep
 artment of  Energy\,  Office  of  Basic  Energy  Sciences\,  under
   contract  ER-46612  for  discussions  with  scientists sponsored b
 y these grants. Some computations  were also made possible thanks to the 
 MRI grant 0722625 from  NSF\,  the  ONR  grant  N00014-07-1-0825  (D
 URIP)  and  a  Challenge  grant  from  the  Department  of Defense
 .\nReferences:\n[1] Cross\, L.E.\, Ferroelectrics 151\, 305 (1994).\n[2] B
 urns\, G.  and Dacol\, F.H.\, Phys. Rev. B 28\, 2527 (1983).\n[3] Smolens
 ky\, G. A. et al. Ferroelectrics and Related Materials (Gordon and Breach\
 , New York\, 1981). [4] Westphal V.\, Kleemann\, W. and Glinchuk\, M.D\, P
 hys. Rev. Lett. 68\, 847 (1992).\n[5] Tagantsev A.K. and Glazounov\, E.Z.\
 , Phys. Rev. B 57\, 18 (1998). [6] Pirc\, R. and Blinc\, R.\, Phys. Rev. B
  60\, 13470 (1999).\n[7] Jeong\, I.-K. et al. Phys. Rev. Lett. 94\, 147602
  (2005).\n[8] Bai\, Y. and Jin\, L.\, J. Phys. D: Appl. Phys. 41\, 152008 
 (2008). [9] Vogel\, H.\, Phys. Z. 22\, 645 (1921).\n[10] Fulcher\, G. S.\,
  J. Am. Ceram. Soc. 8\, 339 (1925).\n[11] Dkhil\, B. et al\, Phys. Rev. B 
 80\, 064103 (2009).\n[12] Svitelskiy\, O. et al\, Phys. Rev. B 72\, 172106
  (2005).\n[13] Tinte\, S.\, Burton\, B. P.\, Cockayne\, E. and Waghmare U.
 \, Phys. Rev. Lett. 97\, 137601 (2006). [14] Ishchuk\, V.M.\, Baumer\, V. 
 N. and  Sobolev\, V. L.\, J. Phys.: Condens. Matter 17\, L177 (2005). [15
 ] Takesue\, N\, Fujii\, Y.\, Ichihara\, M. and Chen\, H.\, Phys. Rev. Lett
 . 82\, 3709 (1999).\n[16] Blinc\, R. et al\, Phys. Rev. B 63\, 024104 (200
 0).\n[17] Vugmeister\, B. E. and Rabitz H.\, Phys. Rev. B 57\, 7581 (1998)
 .\n[18] Viehland\, D.\, Jang\, S.J.\, Cross\, L.E. and Wuttig\, M.\, J. Ap
 pl. Phys. 68\, 2916 (1990).\n[19] Colla\, E.V.\, Koroleva\, E. Y.\, Okunev
 a\, N.M. and Vakhrushev\, S.B.\, Phys. Rev. Lett. 74\, 1681 (1995). [20] G
 rinberg\, I.\, Juhas\, P.\, Davies\, P. K. and Rappe\, A. M.\, Phys. Rev. 
 Lett. 99\, 267603 (2007).\n[21] Al-Zein\, A.\, Hlinka\, J.\, Rouquette\, J
 . and Hehlen\, B.\, Phys Rev Lett. 105\, 017601 (2010). [22] Kittel\, C. I
 ntroduction to Solid State Physics 7th ed. (1996).\n[23] Kutnjak\, Z. et a
 l\, Phys. Rev. B 59\, 294 (1999).\n[24] Levstik\, A.\, Kutnjak\, Z.\, Fili
 pic\, C. and Pirc\, R.\, Phys. Rev. B 57\, 11204 (1998). [25] Edwards\, S.
  F. and Anderson\, P. W.\, J. Phys. F 5\, 965 (1975).\n[26] A. R. Akbarzad
 eh\,  S. Prosandeev\,  E. J. Walter\, A. Al-Barakaty  and L. Bellaiche\
 ,  Phys. Rev. Lett. 108\,\n257601 (2012).\n[27] S. Prosandeev\,  D. Wang
 \, A. R. Akbarzadeh\,  B. Dkhil and L. Bellaiche\,  Phys. Rev. Lett.\, 1
 10\, 207601 (2013).\n[28] S. Prosandeev\, D. Wang and L. Bellaiche\, Phys.
  Rev. Lett.\, 111\, 247602 (2013).\nBio: Professor Bellaiche earned his do
 ctorate from the University of Paris in 1994. From 1994 to 1995 he was a t
 eaching and research associate at the University of Paris\, which he left 
 to join the National Renewable Energy Laboratory in Colorado as a post-doc
 toral fellow. Before coming to the university\, he worked as a research as
 sociate at Rutgers University in New Jersey.\nHis primary research interes
 ts are to reveal the properties of ferroelectric systems at the nanoscale 
 level\, in general\, and to understand how and why they differ from the co
 rresponding bulks\, in particular. He thinks such research can lead to sma
 rt cards with higher storage\, ultrasound machines with sharper resolution
 s and sonar-listening devices that can scan greater distances.
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