Eui-Suk:
As Davor mentioned, surface layers are an additional "handicap"
in modelling the line profiles and suggest you take a look at
his paper....it's a very good one.
I would like to remind you one more thing...the peak asymmetry
associated with the (00h) reflections has traditionally been
attributed to 90 degree domain (twin) phenomena although
those "suggested" models are quite speculative. In my own studies
on mesoscopic BT & PT powders (they're ~ monodomain) I have still
seen peak asymmetry. Since the (00h) family is the polar direction
in tetragonal ferroelectrics, if one can come up with a model to describe
the line profiles properly that would be big step forward in furthering
the understanding on the so-called "coherence length" in ferroelectrics.
Though it is not 100% related to Rietveld refinement, I thought you might
want to consider this as well...
Regards,
Koray
E. Koray Akdogan, Ph.D.
Center for Ceramic Research
Rutgers University
Piscataway, NJ 08854-8065
-----Original Message-----
From: Davor Balzar [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, February 24, 1999 11:54 AM
To: RIETVELD_L Distribution List
Subject: Re: Anyone has Barium Titanate related Information ?
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
>
>
