Difference between revisions of "Temp"

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[http://youtu.be/SIz6Ng6UzAw Axial Divergence] (i.e. low angle peak asymmetry) is modeled in GSAS profile types 3 & 4 with the Finger-Cox-Jephcoat model (see GSAS manual). The profile terms ''S/L'' & ''H/L'' describe the ''instrumental'' asymmetry.  Most users of 11-BM will not need to refine these terms.
[http://youtu.be/SIz6Ng6UzAw Axial Divergence] (i.e. low angle peak asymmetry) is modeled in GSAS profile types 3 & 4 with the Finger-Cox-Jephcoat model (see GSAS manual). The profile terms ''S/L'' & ''H/L'' describe the ''instrumental'' asymmetry.  Most users of 11-BM will not need to refine these terms.


=== Transparency=== (''trns'' profile term)  
=== Transparency===
This the ''trns'' profile term describing the x-ray penetration depth into a flat plate sample . It should *only* be used for fitting flat-plate reflection geometry (Bragg-Brentano) powder diffraction data.  Do '''*not*''' use for 11-BM data which is collected in a transmission geometry (Debye-Scherrer)


=== Displacement === (''trns'' profile term)  
=== Displacement ===
This the ''shft'' profile term describing vertical displacement of the flat plate sample . It should *only* be used for fitting flat-plate reflection geometry (Bragg-Brentano) powder diffraction data.  Do '''*not*''' use for 11-BM data which is collected in a transmission geometry (Debye-Scherrer)


=== ZERO === (''trns'' profile term)  
=== ZERO === (''trns'' profile term)  
Instead of ''trns'' or ''shft', 11-BM users may wish to refine the 2&theta zero shift "ZERO". This term is found in EXPGUI under the Histogram tab.  It describes any shift in the absolute 2theta "0" position and is measured in units of centi-degrees (100*2θ).


 
Typical values for 11-BM might be in the range +/- 0.1 (i.e. 0.001 degrees).  If used, it should be turned on near the end of the refinement.


==Suggested Profile Types & Terms for Fitting 11-BM Data==
==Suggested Profile Types & Terms for Fitting 11-BM Data==
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Many 11-BM diffraction patterns can then be well fit by refining only the LX (size), LY (strain) and  
Many 11-BM diffraction patterns can then be well fit by refining only the LX (size), LY (strain) and  


==Type 3==


Constant Wavelength X-ray GSAS Profile Type 3
==Constant Wavelength X-ray GSAS Profile Type 3==
{| class="wikitable"
{| class="wikitable"
|-
|-
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| '''S/L''' = Axial Divergence S term
| '''S/L''' = Axial Divergence S term
| '''H/L''' = Axial Divergence H term
| '''H/L''' = Axial Divergence H term
| '''trns''' = Sample 'Transparency'
| '''trns''' = Sample 'Transparency' (1)
|-
|-
| '''shft''' = Sample 'Displacement'
| '''shft''' = Sample 'Displacement' (1)
| '''stec''' = Lorentzian anisotropic strain broadening **
| '''stec''' = Lorentzian anisotropic strain broadening (2)
| '''ptec''' = Lorentzian anisotropic crystallite size broadening **
| '''ptec''' = Lorentzian anisotropic crystallite size broadening
|-
|-
| '''sfec''' = Lorentzian sublattice anisotropic broadening **
| '''sfec''' = Lorentzian sublattice anisotropic broadening (3)
| '''LXX''' = Anisotropic Lorentzian microstrain **
| '''LXX''' = Anisotropic Lorentzian microstrain (2)
| '''LYY''' = Anisotropic Lorentzian microstrain **
| '''LYY''' = Anisotropic Lorentzian microstrain (2)
|-
|-
|}
|}
NOTE 1: Do *not* use for 11-BM data, see above
NOTE 2: Better to use Profile Type #4
NOTE 3: See GSAS Manual before using




** NOTE  
** NOTE  


==Type 4==
==Constant Wavelength X-ray GSAS Profile Type 4==
 
Constant Wavelength X-ray GSAS Profile Type 4
{| class="wikitable"
{| class="wikitable"
|-
|-
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| '''GP''' = Gaussian crystallite size broadening
| '''GP''' = Gaussian crystallite size broadening
| '''LX''' = Lorentzian crystallite size broadening  
| '''LX''' = Lorentzian crystallite size broadening  
| '''ptec''' = Lorentzian anisotropic crystallite size broadening **
| '''ptec''' = Lorentzian anisotropic crystallite size broadening
|-
|-
| '''trns''' = Sample 'Transparency'
| '''trns''' = Sample 'Transparency' (1)
| '''shft''' = Sample 'Displacement'
| '''shft''' = Sample 'Displacement' (1)
| '''sfec''' = Lorentzian sublattice anisotropic broadening #
| '''sfec''' = Lorentzian sublattice anisotropic broadening #
|-
|-
| '''S/L''' = Axial Divergence S term
| '''S/L''' = Axial Divergence S term
| '''H/L''' = Axial Divergence H term
| '''H/L''' = Axial Divergence H term
| '''eta''' = mixing factor, from pure Gaussian (0) to pure Lorentzian (1)
| '''eta''' = mixing factor, from pure Gaussian (eta=0) to pure Lorentzian (eta=1)
|-
|-
| '''SXXX''' = Anisotropic microstrain broadening (Lorentzian)
| '''SXXX''' = Anisotropic microstrain broadening (Lorentzian)
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|}
|}


# stacking defects (see manual)
NOTE 1: Do *not* use for 11-BM data, see above
NOTE 2: Better to use Profile Type #4
NOTE 3: See GSAS Manual before using

Revision as of 06:10, 2 May 2012

GSAS offers 5 different Constant Wavelength (CW) X-ray profile functions. They are described in detail within the GSAS technical manual (see page 156). 11-BM users are encouraged to use either profile type 3 or type 4.

A quick reference for the various profile type 3 and 4 terms is given below. Users are strongly encouraged to read this section of the GSAS manual at least once before (or after) blindly using this guide!

Pseudo-Voigt Profile Functions

These peak profile functions are a pseudo-Voigt type, combining Gaussian (G) and Lorentzian (L) components.

The general Gaussian shape (as a function of angle θ) is described by the Cagliotti function 

Gaussian Profile ≈ U*tan2θ + V*tanθ + W + P/cos2θ

These U, V, W, and P variables match the GU, GV, GW, and GP profile terms you see below.

The Lorentzian shape is more complex (check the manual), but includes size and strain broadening terms.

Asymmetry, Zero-Shift and Related Terms

Asymmetry

Axial Divergence (i.e. low angle peak asymmetry) is modeled in GSAS profile types 3 & 4 with the Finger-Cox-Jephcoat model (see GSAS manual). The profile terms S/L & H/L describe the instrumental asymmetry. Most users of 11-BM will not need to refine these terms.

Transparency

This the trns profile term describing the x-ray penetration depth into a flat plate sample . It should *only* be used for fitting flat-plate reflection geometry (Bragg-Brentano) powder diffraction data. Do *not* use for 11-BM data which is collected in a transmission geometry (Debye-Scherrer)

Displacement

This the shft profile term describing vertical displacement of the flat plate sample . It should *only* be used for fitting flat-plate reflection geometry (Bragg-Brentano) powder diffraction data. Do *not* use for 11-BM data which is collected in a transmission geometry (Debye-Scherrer)

=== ZERO === (trns profile term) Instead of trns or shft', 11-BM users may wish to refine the 2&theta zero shift "ZERO". This term is found in EXPGUI under the Histogram tab. It describes any shift in the absolute 2theta "0" position and is measured in units of centi-degrees (100*2θ).

Typical values for 11-BM might be in the range +/- 0.1 (i.e. 0.001 degrees). If used, it should be turned on near the end of the refinement.


Suggested Profile Types & Terms for Fitting 11-BM Data

11-BM users are encouraged to the GSAS constant wavelength (CW) profile type 3 or type 4. Profile #4 is best for cases in which anisotropic terms are required.

11-BM users will not (usually!) need to change or refine the default 'G' terms given in the instrumental parameter file. For the high-resolution synchrotron powder data collected at 11-BM, the instrumental resolution is well described by Gaussian terms.

On the other hand, sample effects in 11-BM data, such as size and strain broadening are (usually!) best fit and refined using Lorentzian terms. Gaussian sample size broadening is *rarely* observed; this requires a very tight mono-disperse size distribution rarely encountered in powder samples (solid metal samples may be an exception).

Many 11-BM diffraction patterns can then be well fit by refining only the LX (size), LY (strain) and


Constant Wavelength X-ray GSAS Profile Type 3

GU = Gaussian U term GV = Gaussian V term GW = Gaussian W term
GP = Gaussian crystallite size broadening LX = Lorentzian crystallite size broadening LY = Lorentzian strain broadening
S/L = Axial Divergence S term H/L = Axial Divergence H term trns = Sample 'Transparency' (1)
shft = Sample 'Displacement' (1) stec = Lorentzian anisotropic strain broadening (2) ptec = Lorentzian anisotropic crystallite size broadening
sfec = Lorentzian sublattice anisotropic broadening (3) LXX = Anisotropic Lorentzian microstrain (2) LYY = Anisotropic Lorentzian microstrain (2)


NOTE 1: Do *not* use for 11-BM data, see above NOTE 2: Better to use Profile Type #4 NOTE 3: See GSAS Manual before using


    • NOTE

Constant Wavelength X-ray GSAS Profile Type 4

GU = Gaussian U term GV = Gaussian V term GW = Gaussian W term
GP = Gaussian crystallite size broadening LX = Lorentzian crystallite size broadening ptec = Lorentzian anisotropic crystallite size broadening
trns = Sample 'Transparency' (1) shft = Sample 'Displacement' (1) sfec = Lorentzian sublattice anisotropic broadening #
S/L = Axial Divergence S term H/L = Axial Divergence H term eta = mixing factor, from pure Gaussian (eta=0) to pure Lorentzian (eta=1)
SXXX = Anisotropic microstrain broadening (Lorentzian) SYYY = Anisotropic microstrain broadening (Lorentzian) SZZZ = Anisotropic microstrain broadening (Lorentzian)

NOTE 1: Do *not* use for 11-BM data, see above NOTE 2: Better to use Profile Type #4 NOTE 3: See GSAS Manual before using

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