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
