The Powder Diffraction File is a database of known materials. Many elements, compounds, and alloys have more than one set of data, based on parameters such as the equipment used to calculate the data, the trace elements found, the date of the study, etc. It is unlikely that a search will produce one exact match, especially when several compounds are contained in one sample. The search approach is to match pairs of spectra with other data known about the sample (crystal structure, color, physical properties, etc.) to find close matches. Data points are not necessarily eliminated once they have been found to correspond to a particular material; some may also correspond to another material within the sample. Not all data points will be accounted for, partly because experimental error will produce high/low readings.
The 2Θ calculations, derived from the experimental data, are:
Further data points have been omitted. The strong lines are in bold.
There are two search parameters that establish the ground rules for data entry: Global Settings and Numbers. In this example, the settings should be And for the Global Operator and Range for Numeric Input:
If the Global Operator is set to Or, any record that fits even one of the criteria entered will be retrieved. If the Numeric Input is set to ESD (estimated standard deviation), the the system automtically "ranges" over that deviation. This may be either too broad or too restrictive.
Use the Search icon (or Tools/Search on the menu) to begin the search process by selecting parameters from the search screens.
NOTE: the data in this search has been deliberately expanded to show how the system works. If the data points are ranged more narrowly, the result will be only one or two choices.
The material is known to be a metal. To reduce the search time and the amount of false drops in the results, select Metals & Alloys from the Subfiles/Database Filters search screen. Note that when a selection is made from a search screen, both the selection area and the search screen title turn red. The actual selection is highlighted in blue. This feature is quite useful since often parameters are changed several times based on results returned and additional data from other sources.
The long/strong lines search options are on the Miscellaneous search screen. The old print search method was to use the three strongest or longest lines to find a (short) list of possible matches. The software is capable of adding many more, but usually three does the job. In this example, the search screen is shortened to save space. The search box indicates that any of the three lines can be entered OR each line (D1, then D2, then D3) can be specified. It's faster to not specify. After entering the first strong line range, click on the Search button at the bottom of the screen. Repeat the same process for the other two data points.
Remember that these numbers are being ranged so that everything between 2.0600000Å and 2.0800000Å will be retrieved. Again, choices are highlighted in red.
Use the Search History icon (or Tools/History) to combine search steps.
Each Search performed in Step 2 above is listed on the Search History screen. The Past Searches (top half of the screen) section shows the individual searches with the number of results ("hits") for each search. The Combined Searches (bottom half) section shows the searches to be combined. The searches can be selected one at a time or as a group. Since there were only 3 current searches needed for this answer, the "double down arrow" icon moved all of them to the Combined Results section. All three should be combined together ("anded"); click on Combined Results to see the answer list.
Search results are automatically displayed after the Combined Results operation. However, you can also use the Results icon (or Tools/Results) to display them later.
Below is the default display for search results. (The individual items in the list can be changed in the Preferences options.) In a strong or long line search, the D spacing columns are the ones to check. Each column in the results list can be sorted independently. Although beginning with the D1 column is an option, sorting the D2 is often faster because the related D1 and D3 are now close to each other. This makes it easy to see the best match.
To see the relevant PDF card(s) double click on the card number in the Results list.