I second all of Koray's remarks but add a comment on peak asymmetry of 00L
reflections. This asymmetry (a low-angle peak shoulder) is likely to
originate from a distinct surface layer probably common to all
ferroelectrics, and especially to BaTiO3 (Kanzig has reported it first back
in 1955). It can be discerned by grazing-incidence scans or experiments at
different x-ray energies. There were many papers on this subject; probably
the latest one that deals with this problem and anisotropic line broadening
in BaTiO3 was published a few weeks ago: Physical Review B 59 (1999)
3414-3420. A PDF reprint can be found at
http://www.boulder.nist.gov/div853/balzar/PRB03414.pdf
As for the Eui-Suk's question, a good starting point to understand the
BaTiO3 structure and other properties is the book of Jona and Shirane,
Ferroelectric Crystals, Pergamon Press.
Regards,
Davor Balzar
******************************************************
National Institute of Standards and Technology
Materials Science and Engineering Laboratory
Div. 853, 325 Broadway
Boulder, CO 80303
Tel: 303-497-3006
Fax: 303-497-5030
E-mail: [EMAIL PROTECTED]
Web: http://www.boulder.nist.gov/div853/balzar
******************************************************
University of Colorado at Boulder
Department of Physics
E-mail: [EMAIL PROTECTED]
******************************************************
-----Original Message-----
From: E. K. AKDOGAN <[EMAIL PROTECTED]>
To: RIETVELD_L Distribution List <[EMAIL PROTECTED]>
Date: Tuesday, February 23, 1999 2:52 PM
Subject: RE: Anyone has Barium Titanate related Information ?
>Eui-Suk:
>
>The main problem in the Rietveld refinement of ferroelectrics
>using laboratory x-ray data is the modeling of crystallite size
>(if you have very small particle size) and microstrain.
>In tetragonal ferroelectrics such as BaTiO3 and PbTiO3,
>microstrain seems to correlate quite well with the spontaneous
>strain associated with m3m-4mm transition. Unfortunately, (as
>expected form the point group of the system), the microstrain
>exhibits significant anisotropy and causes problems in modeling
>the peak profiles. Therefore, extraction of the intensity data
>cannot be accomplished very accurately. Especially, the (00h)
>family of reflections has an enormous peak asymmetry which is
>extremely difficult to model.
>Using GSAS you certainly can obtain fairly accurate lattice parameters
>as a function of the dopant concentration. However, obtaining accurate
>atomic positions seem to be a very long shot. To begin with, BaTiO3
>has a very low tetragonality in the undoped state. That will further
>decrease
>with increasing Zr2+ concentration. As a result, the chances of monitoring
>the changes in atomic position (which are very small) is slim to none due
>to the peak profile description problem. There is an additional
complication
>that you may need to consider. That is the problem associated with
>oxygen. Its atomic position cannot be determined very accurately with
>x-rays.
>Yet another, complication arises from the x-ray scattering cross-sections
of
>Ba2+ & Ti4+ which are very close in value.
>To make the long story short, BaTiO3 and similar ferroelectrics are not
>amenable at all for x-ray structure analysis.
>In my opinion, the best approach would be to try neutron diffraction.
>
>Regards,
>
>Koray
>
>E. Koray Akdogan, Ph.D.
>Center for Ceramic Research
>Rutgers University
>607 Taylor Road, Piscataway,
>NJ 08854-8065
>
>
>
>
>
>
>-----Original Message-----
>From: Eui-Suk Park [mailto:[EMAIL PROTECTED]]
>Sent: Monday, February 08, 1999 10:03 PM
>To: RIETVELD_L Distribution List
>Subject: Anyone has Barium Titanate related Information ?
>
>Hi, everyone?
>I am a graduate student in univ. of cincinnati.
>Recently, I knew this wonderful method and want to try structure
>refinement of Zirconia-doped-Barium-Titanate system with GSAS.
>
>I want to calculate the bond length and angle which is expected to
>change with zirconia doping
>concentration changing.
>the c/a ratio, as I observed, approached to 1.00, i.e. cubic, from
>tetragonal.
>But due to the lack of the knowledge, I faced a trouble to
>Rietveld-refinement my material.
>,so If there is anyone who did or know about this barium titanate system
>w.r.t Rietveld method,
>please let me know, then I will be so grateful.
>Thank you so much..
>
>the following is the XRD I used and will use :
>
>Title1,Philips Analytical X-Ray B.V.,/
>Title2,PC-APD, Diffraction software,/
>DiffrType PW3710
>DiffrNumber 1
>Anode Cu
>LabdaAlpha1 1.54056
>LabdaAlpha2 1.54439
>RatioAlpha21 0.50
>DivergenceSlit Fixed,1
>ReceivingSlit 0.2
>Monochromator Used,YES
>GeneratorVoltage 40
>TubeCurrent 20
>FileDateTime
>DataAngleRange 1, 120
>ScanStepSize, 0.010
>ScanType STEP
>ScanStepTime 5.00
>
>
