| [629] | 1 | <html> |
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| 2 | <head> |
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| 3 | <title>GSAS/EXPGUI Alumina Tutorial Intro</title> |
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| 4 | </head> |
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| 5 | |
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| 6 | <style> |
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| 7 | A:link {text-decoration:none} |
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| 8 | A:vlink {text-decoration:none} |
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| 9 | </style> |
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| 10 | |
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| 11 | <BODY BGCOLOR="#FFFFFF" |
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| 12 | topmargin="0" leftmargin="0" marginwidth="0" marginheight="0" |
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| 13 | text="#000000" link="#0033ff" vlink="#0033ff" alink="#0033ff"> |
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| 14 | |
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| 15 | <? |
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| 16 | include("/var/www/include/navigation.inc"); |
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| 17 | include("/var/www/include/utility.inc"); |
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| 18 | ?> |
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| 19 | <blockquote> |
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| 20 | |
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| 21 | <TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT> |
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| 22 | </TH><TH><A Href="alumina1.html">First page in tutorial</A> |
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| 23 | </TH></TR></TABLE><BR CLEAR=ALL> |
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| 24 | |
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| 25 | <CENTER> |
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| 26 | <H1><HR noshade width="75%" size="2" align="center"> |
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| 27 | GSAS/EXPGUI Alumina example (Intro) |
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| 28 | <HR noshade width="75%" size="2" align="center"> |
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| 29 | </H1> |
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| 30 | </CENTER> |
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| 31 | <H1>What's this all about?</H1> |
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| 32 | The goal of Rietveld analysis is to fit a structural model |
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| 33 | ("crystal structure") to powder diffraction data. To do this requires |
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| 34 | determining the structural parameters [unit cell, |
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| 35 | atom positions and displacement (thermal) parameters, etc.] |
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| 36 | for all crystalline phases present, as well as a variety of |
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| 37 | instrumental and sample parameters that describe the experimental and |
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| 38 | sample conditions: scale factors, peak broadening, the background, |
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| 39 | preferred orientation, etc. |
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| 40 | In most cases Rietveld analysis is performed to determine the structural |
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| 41 | parameters, but increasingly, the method is also used to determine relative |
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| 42 | amounts of the crystallographic phases, the amount and type of peak |
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| 43 | broadening, the preferred orientation, or similar types of sample |
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| 44 | characterization. |
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| 45 | <P> |
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| 46 | This exercise provides a tutorial example of how to use the |
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| 47 | <A href="http://www.ncnr.nist.gov/xtal/software/gsas.html">GSAS</a> |
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| 48 | software package |
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| 49 | with the |
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| 50 | <A href="http://www.ncnr.nist.gov/xtal/software/expgui/expgui_intro.html">EXPGUI</A> |
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| 51 | interface to perform Rietveld analysis. The material chosen for this exercise, |
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| 52 | corundum (aka alumina, |
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| 53 | sapphire or ruby), |
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| 54 | has a simple structure, so the starting coordinates have been distorted |
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| 55 | so that there is an improvement obtained by performing the fit. |
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| 56 | Likewise, this sample exhibited virtually no sample-related broadening, |
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| 57 | so the instrumental peak profile was altered so that the peak profile |
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| 58 | terms would not agree with the data, again so that the exercise would |
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| 59 | demonstrate the sorts of steps needed for typical Rietveld refinements. |
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| 60 | The tutorial consists of 11 web pages, each has a series of related |
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| 61 | steps. There are also editorial comments, that explain a point further |
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| 62 | or explain how these steps might be applied differently in another case. |
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| 63 | <I>These comments are in specified in italic type</I>. |
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| 64 | <P> |
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| 65 | Rietveld analysis works using non-linear least-squares fitting to |
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| 66 | optimize (refine) parameters. This |
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| 67 | means that we must start with approximate values for all parameters that |
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| 68 | will be fit. We then allow the software to optimize a small subset of the |
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| 69 | parameters -- a minimal number of parameters that must be fit before any |
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| 70 | progress can be made. Slowly, additional parameters are selected to be |
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| 71 | refined, until |
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| 72 | all parameters in the model (if the data support that) are refined. |
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| 73 | Despite the simplicity of the material, this exercise |
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| 74 | demonstrates many of the procedures needed for more complex materials. |
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| 75 | <P> |
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| 76 | EXPGUI and GSAS run on Windows, Linux and IRIX (Silicon Graphics computers). |
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| 77 | The example figures show in this tutorial were generated in Unix, |
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| 78 | but virtually all GSAS and EXPGUI operation is identical between Unix and |
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| [686] | 79 | Windows. Note also that the appearance of EXPGUI changes slightly as |
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| 80 | new features are added. The screen images do not exactly match the current |
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| 81 | version of EXPGUI. |
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| [629] | 82 | <P> |
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| 83 | |
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| 84 | |
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| 85 | <H1>Getting Started</H1> |
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| 86 | |
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| 87 | To perform this tutorial on your own computer, you will need to |
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| 88 | have GSAS and EXPGUI loaded on your computer (see |
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| 89 | <a href="http://www.ncnr.nist.gov/xtal/software/expgui/expgui.html">installation links on the EXPGUI home page</a>). |
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| 90 | <a name="downloads"></a> |
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| 91 | You will also need three files that are referenced in the following |
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| 92 | web pages: |
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| 93 | <UL> |
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| 94 | <LI>The Raw data: |
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| 95 | <A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/al2o3001.gsa"> |
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| 96 | al2o3001.gsa</A> |
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| 97 | <LI>The instrument parameter file: |
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| 98 | <A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/bt1demo.ins"> |
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| 99 | bt1demo.ins</A> |
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| 100 | <LI>A CIF file with unit cell and atomic parameters: |
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| 101 | <A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/alumina.cif"> |
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| 102 | alumina.cif</A> |
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| [715] | 103 | </UL> |
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| 104 | These three files can be downloaded as a |
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| 105 | <A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/tutorial3_demo_files.zip"> |
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| 106 | single .ZIP</A> file, or accessed via anonymous ftp from site ftp.ncnr.nist.gov |
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| 107 | in directory <tt>/pub/cryst/gsas/tutorials</tt> |
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| [629] | 108 | <P> |
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| 109 | <blockquote> |
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| 110 | <B>Note:</B><I> |
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| 111 | While it is possible to have your working GSAS files |
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| [715] | 112 | (<I>i.e.</i> the .EXP file, etc.) in a separate directory from |
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| 113 | the raw data file(s), I discourage this practice, as it then |
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| [629] | 114 | becomes quite difficult to later copy or move the .EXP |
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| 115 | file from one directory or computer to another. |
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| 116 | For this reason, I suggest copying these files |
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| [715] | 117 | into the directory where you will keep your GSAS files. |
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| [629] | 118 | </I><P> |
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| 119 | </blockquote> |
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| 120 | </blockquote> |
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| 121 | |
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| 122 | <H2>Tutorial Outline</H2> |
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| 123 | <OL> |
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| 124 | <LI><A HREF="alumina1.html"> |
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| 125 | Create a GSAS Experiment File |
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| 126 | </A> |
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| 127 | <LI><A HREF="alumina2.html"> |
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| 128 | Adding a phase |
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| 129 | </A> |
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| 130 | <LI><A HREF="alumina3.html"> |
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| 131 | Specifying Powder Diffraction Data (Adding a Histogram) |
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| 132 | </A> |
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| 133 | <LI><A HREF="alumina4.html"> |
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| 134 | Changing the Background Function |
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| 135 | </A> |
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| 136 | <LI><A HREF="alumina5.html"> |
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| 137 | Initial Fitting: Refine Scale Factor and Background |
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| 138 | </A> |
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| 139 | <LI><A HREF="alumina6.html"> |
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| 140 | Plotting the Initial Fit |
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| 141 | </A> |
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| 142 | <LI><A HREF="alumina7.html"> |
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| 143 | Fitting the Unit Cell |
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| 144 | </A> |
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| 145 | <LI><A HREF="alumina8.html"> |
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| 146 | Fitting the Diffractometer Zero Correction |
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| 147 | </A> |
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| 148 | <LI><A HREF="alumina9.html"> |
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| 149 | Initial Fitting of Profile Parameters |
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| 150 | </A> |
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| 151 | <LI><A HREF="alumina10.html"> |
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| 152 | Group U<sub>iso</sub> parameters & |
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| 153 | Refine coordinates and Overall U<sub>iso</sub></A> |
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| 154 | <LI><A HREF="alumina11.html"> |
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| 155 | Finishing Up</A> |
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| 156 | </OL> |
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| 157 | |
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| 158 | <P> |
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| 159 | <H2>Sample files</H2> |
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| 160 | <UL> |
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| 161 | <LI><A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/al2o3001.gsa"> |
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| 162 | al2o3001.gsa</A> |
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| 163 | -- the alumina neutron diffraction data |
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| 164 | <LI><A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/bt1demo.ins"> |
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| 165 | bt1demo.ins</A> |
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| 166 | -- the instrument parameter file |
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| 167 | <LI><A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/alumina.cif"> |
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| 168 | alumina.cif</A> |
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| 169 | -- a CIF file with unit cell and atomic parameters: |
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| 170 | </UL> |
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| 171 | <H2>Acknowledgments</H2> |
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| 172 | <A Href="http://www.ncnr.nist.gov/programs/crystallography/software/gsas.html"> |
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| 173 | GSAS</A> |
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| 174 | is written by Allen C. Larson and <A HREF="http://www.nist.gov/cgi-bin/exit_nist.cgi?url=http://lansce.lanl.gov/lujan/staff12/vondreele.htm"> |
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| 175 | Robert B. Von Dreele</A>, MS-H805, |
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| 176 | Los Alamos National Laboratory, Los Alamos, NM 87545. Problems, questions |
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| 177 | or kudos concerning GSAS should be sent to Robert B. Von Dreele at |
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| [686] | 178 | <A HREF="MAILTO:vondreele@anl.gov">vondreele@anl.gov</A> |
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| 179 | <P>GSAS is Copyright, 1984-2003, The Regents of the University of California. |
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| [629] | 180 | The GSAS software was produced under a U.S. Government contract (W-7405-ENG-36) |
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| 181 | by the Los Alamos National Laboratory, which is operated by the University |
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| 182 | of California for the U.S. Department of Energy. The U.S. Government is |
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| 183 | licensed to use, reproduce, and distribute this software. Permission is |
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| 184 | granted to the public to copy and use this software without charge, provided |
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| 185 | that this notice and any statement of authorship are reproduced on all |
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| 186 | copies. Neither the Government nor the University makes any warranty, express |
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| 187 | or implied, or assumes any liability or responsibility for the use of this |
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| 188 | software. |
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| 189 | <P>EXPGUI is written by Brian H. Toby of the NIST Center for Neutron Research, |
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| 190 | <A HREF="MAILTO:Brian.Toby@NIST.GOV">Brian.Toby@NIST.GOV</A> |
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| 191 | |
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| 192 | <P>EXPGUI is not subject to copyright. Have fun with it. |
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| 193 | |
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| 194 | <p>Neither the U.S. Government nor any author makes any warranty, |
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| 195 | expressed or implied, or assumes any liability or responsibility |
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| 196 | for the use of this information or the software described |
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| 197 | here. Brand names cited here are used for |
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| 198 | identification purposes and do not constitute an endorsement by NIST. |
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| 199 | |
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| 200 | <P> |
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| 201 | <HR> |
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| 202 | </blockquote> |
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| 203 | <P><font size=-1><A HREF="MAILTO:crystal@NIST.gov?subject=WWW page <?=$PHP_SELF?>">Comments, corrections or questions: crystal@NIST.gov</A></font><BR> |
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| 204 | <font size=-1><? lastmod(); ?> </font> |
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| 205 | <BR>$Revision: 930 $ $Date: 2009-12-04 23:14:35 +0000 (Fri, 04 Dec 2009) $ |
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| 206 | </body> |
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| 207 | </html> |
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