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The PDF Databases

• Standardized data
• Comprehensive coverage
• Data are reviewed, edited and corrected prior to publication
• Each data set is evaluated for quality
• Designed for material identification and characterization

Release 2011 of the Powder Diffraction File (PDF) contains 715,953 unique material data sets. Each data set contains diffraction, crystallographic and bibliographic data, as well as experimental, instrument and sampling conditions, and select physical properties in a common standardized format. PDF databases use a Sybase^® relational database platform integrated with JAVA™ for point and click data mining, rapid searches and sorts for all materials and materials systems. All ICDD databases use an integrated editorial quality review for all data sets. This is the only crystallographic database that evaluates the quality and provides the results of the assessment to the user in the comment section of each reference. The PDF's large size and comprehensive material coverage is achieved through ICDD's historical sources of powder diffraction data, ICDD's Grant-in-Aid Program, contributions, and bibliographic searches, as well as collaborations with international crystallographic database organizations.

The database is designed and produced in several different formats in order to serve different groups of users.

PDF-2 is a collaborative product between ICDD, FIZ and NIST and is designed for inorganic materials analyses. Many common organic materials from ICDD are added to this database to facilitate rapid material identification. New for 2011—as added value to our customers, our data mining software is now integrated into PDF-2, free of charge!

PDF-4+ is an advanced database containing the data from both the PDF-2 and ICDD's collaboration with MPDS. This database has comprehensive material coverage for inorganic materials and it contains numerous additional features such as digitized patterns, molecular graphics and atomic parameters. Features to enhance the ability to do quantitative analysis have been incorporated into PDF-4+. PDF-4+ is available on CD, DVD, or accessed via the Internet using WebPDF-4+ with a USB compatible dongle.

PDF-4/Minerals is a subset of the PDF-4+ database, which includes all of the software features incorporated into PDF-4+.

PDF-4/Organics is a collaborative product between ICDD and CCDC. It is designed to identify organic and organo metallic materials and also contains a few thousand inorganic materials, primarily pharmaceutical excipients to help with formulation analyses and identification.

Printed Books and Indexes include ICDD's experimentally collected diffraction patterns and search manuals. These materials have been produced annually for 61 years and are commonly used as reference books.

Figure 1. Display of the increasing value of the Powder Diffraction File and our efforts to maintain pricing. The number of PDF-2/PDF-4+ entries are charted against our list and academic pricing over the past 20+ years. The chart tracks the list and academic pricing (right y axis) for PDF-2 (1987-2004), then PDF-4+ (2005-2011) during the history of ICDD CD products. The left axis is the number of entries during this time frame.

Value

We are pleased to announce that we will not increase our prices for the 2011 product line, the sixth consecutive year of constant database pricing! ICDD strives to maintain its pricing while increasing value by the dramatic increase in the size and technical capability in the Powder Diffraction File. Increases in entries, searches and display fields for the last six annual product releases demonstrate ICDD's commitment and dedication, as a not-for-profit organization, to bring the highest value to the scientific community (see Table 2 below).

The Powder Diffraction File

ICDD's editorial staff receives data from multiple data entry sources, shown in Table 1 below, converts the data to a common standardized powder diffraction format, and then edits and categorizes the data for the specific purposes of phase identification and quantitative phase analysis. This process, coupled with a JAVA™ interface, allows hundreds of thousands of materials to be rapidly searched and data mined. The following design features are aimed at improving our customer's ability for materials analysis.

Table 1. Powder Diffraction Data Entry Source
* MPDS entries, containing more data, replace duplicate reference patterns and citations from FIZ (01-ICSD) and NIST (03-NIST) entries in PDF-4+ and PDF-4/Minerals. PDF-4+ and PDF-4/Minerals are the only two products that contain data sources from MPDS (04-LPF).
† PDF-4/Organics is the sole product that contains data sourced from CCDC (02-CSD).
‡ While 25,233 new entries were added to the PDF-4+ database, the product increased by a net of 15,009 entries due primarily to new entries with atomic coordinate sets replacing duplicate entries without atomic coordinates.

WebPDF-4+ is equivalent to PDF-4+ accessed via the Internet.

Quality

The ICDD quality review system is applied to all data in the database from all database sources. The procedures and processes used to review and edit data in every Powder Diffraction File product are certified to be ISO 9001:2008 compliant. The quality review consists of a series of programs designed to compare measured and calculated properties with the author's stated chemistry and composition. Over one hundred different checks are performed by these automated reviews. For example, d-spacings are calculated and compared to measured values, while densities are calculated by different methods to compare with the chemical composition. The programs also compare every new entry with all existing entries in the database, which identifies similar materials, eliminates duplicates, and provides cross-references. Quality systems were independently developed for powder diffraction and single-crystal diffraction input data by teams of ICDD editors and member scientists. For single crystal data, electron densities are checked, as well as reasonable thermal vibration amplitudes. New quality systems have recently been developed to evaluate nonstandard materials, such as modulated structures (multidimensional unit cells with >3 dimensions) and noncrystalline materials (no unit cell). A commonality in all four quality systems (powder, single-crystal, modulated, noncrystalline) is the correlation between the observed diffraction characteristics and stated material and chemical properties. If a material is designated "star or S", all measured, calculated and stated properties are self consistent. Finally, after automated analytical review, the results are reviewed by ICDD editors, editorial task groups, and field experts for final confirmation of quality, structural, and subfile classifications before publication.

The quality distribution of published diffraction data over four decades contained in the PDF-4+ are shown in Figure 2. The primary quality evaluation criteria focuses on whether an accurate diffraction pattern is obtained and whether the stated chemistry matches the diffraction and other physical property data. These criteria are fundamental to the process of accurate material identification, the primary design feature of the database. The plots, as shown, demonstrate several trends. First is the historical trend of improved data quality with time and the large numbers of high-quality data produced in recent years. Second is the fact that for a specific decade there is always a distribution of quality. A prime function of ICDD's quality system is to continuously edit and correct published data. This allows us to assist the user by identifying which material data sets are the best quality, and which are poor quality, and the reasons why.

Figure 2. Reference data contained in PDF-4+ as a function of quality. The highest quality mark is displayed on the left of each graph and the lowest quality mark on the right. Each graph contains a decade of published data and reflects quality distributions after ICDD processing.

ICDD's annual product tests show that the majority of phases identified by modern analysis oftware, both ICDD's and other commercial vendors, identify Star and I quality phases in large disproportion to their share of entries. However, many of the lower quality references used in the identification processes do not have high quality equivalents so the software identifies the best candidate available. The ICDD has also reanalyzed a series of standard test samples published in the 1970s in the Methods and Practices in X-ray Diffraction. Recent results show that many of the references published in problem solutions have been replaced by newer, higher quality references resulting in higher statistical matches, such as increased Goodness of Match or Goodness of Fit. Better quality data is resulting in statistically better matches in the identification process. There were also several solid solution examples where an exact reference match exists today that would have required iterative interpretation in the past. What this means is that the database is continuously improving, adding both new materials and higher quality references. An example of our continuous database improvement is shown in Figure 3 for dolomitic materials. Studies on these materials are used to examine sedimentary and precipitation processes in geologic deposits and biogenic materials (i.e., corals and shells). With the data available in modern PDF databases, the need for extensive calibration curves for examining solid solution substitutions can be eliminated for common materials. There are hundreds of examples in our Release 2011 products.

Figure 3. Reduced cell volume versus atomic % magnesium for dolomitic materials. Each point i the graph represents a separate determination with its own diffraction pattern. In PDF databases, the diffraction pattern and card representation can be produced for any point on the graph by a left or right click of the mouse on the data point. The top graph represents the reference data published between 1930 and 1990. The bottom graph demonstrates the additional data published in the last 20 years.

The ICDD is also continuously improving the software and data mining capabilities of its databases. A versatile relational database format was adopted in 2005, which allows more data fields to be added to each entry and more fields to be displayed. Since that time, ICDD has introduced new fields, new displays, and new searches on an annual basis. These additions are summarized in Table 2, for the PDF-2 and PDF-4+ platforms. New for Release 2011 is that our data mining software is now integrated into PDF-2, free of charge! This means every PDF database will have self-contained data mining capability.

Table 2. Search options, display fields and entry counts for the last six (6) releases of database products. Searches and display fields are available with ICDD's embedded data mining software. With Release 2011, every PDF database will have self-contained data mining capability.

THE POWDER DIFFRACTION FILE SUBFILES -Targeting Your Search

Subfiles are a powerful tool in material identification. They allow users to take advantage of the expert knowledge of their fellow scientists. The Organic and Inorganic Subfiles are based on chemical definitions; while most other subfiles are based on expert opinion with editorial review. The subfiles allow users to target their search. For example, the PDF-4+ 2011 database has 316,291 data set entries. The Cement and Hydration Product subfile has 1,344 entries. Using this subfile allows the user to reduce their candidate list by 99.5%, eliminating false positives especially among isostructural polytypes, most of which are not found in cements.

A key assumption in the use of any subfile is that the subfile has comprehensive coverage. ICDD has employed numerous strategies to achieve comprehensive coverage. During a 2003–05 review, ICDD members analytically defined every subfile. We use multiple database sources and assign subfiles among these sources. We also utilize experts who annually review the subfile content. Our automated systems, described earlier, are used to search and identify subfile members using the analytical definitions and previously defined expert content. Finally, we have used our grant-in-aid program to collect data that may be missing or to replace poor quality data in the subfile. This means that new subfile materials are identified every year from the tens of thousands of new entries and the content is continually updated. The definitions and automation of this system occurred in steps between Releases 2002 and 2007. The ICDD subfiles can be used with any software system that recognizes ICDD subfile designations to improve the efficiency and accuracy of the identification process when using the ICDD database.

The ICDD subfile system is comprehensive, analytically-based, reviewed by experts, and without parallel among crystallographic and diffraction databases. This system directly leads to more accurate results.

Which Database is right for you? (PDF)

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