IntroductionThe Powder Diffraction File (PDF) has been the

primary reference for powder diffraction data sincethe Dow Chemical Company allowed their data, firstpublished by Hanawalt, Rinn and Frevel (1938), to bereprinted in a 3" x 5" card format under the auspices of the American Society for Testing and Materials(ASTM). The importance of the diffraction informa-tion was recognized by the early pioneers in the fieldwho formed a Joint Committee for Chemical Analysis by Powder Diffraction Methods co-sponsored byASTM Committee E-4, the Crystallographic Societyof America and the British-Institute of Physics. Thisreprint appeared,in 1941 as Set 1 of the PDF. Sincethis date, 38 additional sets have been published withover 51,000 diffraction patterns.

The primary information in the PDF is thecollection of d-spacings (d's) determined from theangle of diffraction and the intensities (I's), experi-mentally measured under the best possible conditionsfor a phase-pure material. These data provide a"fingerprint" of the compound because the d-spacingsare fixed by the geometry of the crystal and the inten-sities are dependent on the elements and their arrange-ment in the crystal structure. Thus, the d-I data may be used for identification of unknown materials bylocating matching d-I sets in the PDF for the d's and I's obtained from the unknown. Identification is the mostcommon use of the PDF, but the presence of consi-derable supporting information on each compoundallows further characterization of the compound un-der study. Examination of the crystal data, Millerindices, intensity values and scale factors, otherphysical property data, and even the reference pro-vides useful information to further the knowledge ofthe sample. A detailed description of the PDF may befound in Jenkins and Smith (1987).

To meet the needs of diffractionists, the PDF iscontinually being revised and updated with new andimproved information. The increased use of compu-

ters for analysis of diffraction data requires greateraccuracy of the reference information. Both improved instrumentation and more sophisticated analyses have placed more stringent requirements on how data arecollected, reviewed and presented particularly incomputer-readable form. This paper will review thehistory and present status of the PDF and examine thecurrent activities of the JCPDS-International Centrefor Diffraction Data (ICDD) with respect to futureimprovements in the PDF and related products.

The History of the PDFThe first form of publication of the PDF was as 3"

x 5" file cards formatted so that the index lines, thethree strongest and the largest d-spacing, were placedat the top edge of the card and the full d-I list and sup-porting information filled the remaining space, Fig. 1.This format was devised to use the search schemeproposed by Hanawalt and Rinn (1936). By placingthe cards in a drawer in "Hanawalt" order, the usercould thumb through the cards examining the indexlines to find a match. As the number of cards in-creased with Sets 2 (1945) and 3 (1949), the stack ofcards became quite large. The larger number ofentries made the PDF more useful because of the in-creased coverage, but it was also cumbersome to usefor identification. A book-form Search Manual wasdevised by the Editor, W. P. Davey, in 1950. Thismanual was prepared by typing one-line search en-tries with the three strongest lines, the chemicalformula and the PDF number for each compound,ordering the strips in a Termitrex holder, and photo-graphing the assembly for offset printing. With thepublication of Set 3 in 1949, the PDF containedaround 2500 entries. Set 4 (1953) and Set 5 (1955)brought the PDF up to 4500 entries and marked theend of the first era of PDF history.

In the time period 1941-1955, the PDF overcamemany of the problems of a fledgling database. Thefinancial support was initially based on contributions

3 The Rigaku Journal

The Rigaku Journal

Vol. 6/ No. 2 / 1989

CONTRIBUTED PAPERS

THE POWDER DIFFRACTION FILE: PAST, PRESENT AND FUTURE

DEANE K. SMITH AND RON JENKINS

JCPDS-International Centre for Diffraction Data, Swarthmore, PA 19081, USA

from industry and scientific societies, but by 1955 thePDF was becoming self-supporting through the salesof the File. The offices of the Joint Committee movedfrom The Pennsylvania State University to a locationin downtown State College, PA, USA for three yearsand then to ASTM headquarters in Philadelphia, PA,USA. An Associateship was established at the USNational Bureau of Standards to collect data undercontrolled and reproducible conditions. This Associ-ateship provided d-I data on common, important com-pounds to replace multiple entries in the earlier setsand greatly improved the accuracy of the PDF for thestate of the art at that time. These data were collectedon diffractometers rather than cameras. Some of theindividuals who made significant contributions to thisearly stage of the PDF were: W. P. Davey, A. S.Beward, W. L. Fink, H. W. Pickett, A. J. C. Wilsonand L. L. Wyman.

The next ten years saw regular issues of new setsof d-I data with 1000-1500 new entries each year.Several new search aids were developed includingKeysort and IBM cards, the Fink Index, the MatthewsIndex, and the Fink Graphical Index. Of thesehardcopy products, only the Fink Index has survivedthe tests of time, and it has not been prepared since1982 except for some subfiles of the PDF. In 1962, the d's, I's, formulas, and PDF numbers were first key-boarded for a computer-readable database. The pre-sence of these data in computer-readable form al-lowed the 1965 Search Manual to be computer com-posed. The availability of the d's and I's on magneticmedia spurred the development of computer-basedsearch/match schemes and the beginning of the nextera. Three important individuals during this era were

the Editors of the PDF: G. W. Brindley and J. V.Smith, and Computer Consultant: G. G. Johnson, Jr.

During the first two stages, the Joint Committeeevolved from a small group of volunteers who initi-ated the PDF to a small paid staff operating at ASTMand as Editors under the guidance of a committee ofvolunteer scientists who reviewed the progress of thisstaff and recommended policies and products. By1965, there were three committees: Finance, Techni-cal and Editorial. The membership of the Joint Com-mittee was about 30, and the meetings were simplewith each subcommittee meeting on a separate dayduring a week each Summer. Most members wereactive on all committees. A Board of Directors of 4members directed the operations: W. L. Fink, Chair-man; R. G. Simard, General Manager; A. W. Danko,Chairman, Technical Committee; and L. L. Wyman,Treasurer.

The year 1969 was a major turning point in thehistory of the PDF. For a variety of reasons, the opera-tions were moved from ASTM headquarters toanother location in Philadelphia, and the JointCommittee incorporated as a separate corporation inthe State of Pennsylvania. The name was changed tothe Joint Committee on Powder Diffraction Standards (JCPDS). In 1971, the JCPDS moved to its presentheadquarters in Swarthmore, PA. The size of the staffincreased as the production increased, and the number of volunteers also increased. The number of meetingsincreased to two each year, and the additional sub-committees required more time and concurrent ses-sions. Currently (1989), there are 10 Subcommitteesof the Technical Committee alone. The Committeesand Subcommittees are listed in Table 1. Grants-in­Aid were established to sponsor the collection of

Vol. 6 No. 2 1989 4

Fig. 1 Card image for K2Cu(SO4)2•6H2O from PDF Set 1 as issued in 1941.

new data at universities, and these projects havebecome a major source of new data.

The period 1965-1978 saw several new products,. The JCPDS sponsored an on-line search service,2dTS, as the first computer-based activity using thecomputer-readable database. Several individuals alsodeveloped programs for identifying crystalline phases using the d-I computerized information. Part of thisdevelopment was spurred by the prospect of soft-landing a diffractometer on the moon. AutomatedPowder Diffractometers (APD's) were developed bymany manufacturers who employed the PDF forphase identification as part of the supplied software.The d-I database provided the basis for the search/match procedures, but the final evaluation of theresults required consulting hard-copy forms of thePDF for the supporting information. Computer stor-age limitations were the main reason why the infor-mation in the database was usually distributed andutilized on magnetic tape. In spite of increased infor-mation density on the magnetic tape, the PDF soonexceeded the capacity of one tape. Other new products included several Subfiles, such as Minerals andMetals and Alloys, to make the PDF more amenableto identification in these specialty areas. TheseSubfiles were published in hard-copy form.

In 1978, the corporation name was changed toJCPDS-International Centre for Diffraction Data toreflect the international use of the PDF and theincreased diversity of products with the marketing ofCrystal Data. The role of the computer in futureproducts was recognized, and a project was begun tokeyboard and re-evaluate all of the data which com-

prise the PDF, including the supporting documenta-tion. This re-evaluation checked for internal consis-tency of unit cells, d-spacings, and symmetry wher-ever possible. This project was completed in 1984,and the resulting database allows computer display ofthe data-card image, so no hard-copy form is needed.The increased packing density of information on com-puter media has permitted the distribution of thisdatabase in several forms including CD-ROM's. Theincreased use of the computer-based PDF and theproblems of storage of the classic cards prompted theInternational Centre to discontinue the production ofcards in 1987, leaving books as the only hardcopyfrom published.

As of October 1989, the PDF contains 39 sets ofdata with 51,167 diffraction patterns. These patternsare divided into the categories presented in Table 2.Many patterns are classified in more than one subfile.Each individual data set contains, as a minimum, a list of the d-I pairs, the chemical formula, the mineralname if appropriate, a unique identification (PDF)number, and a reference to the original source of thedata. In addition to this information, supplementaldata may include: the crystal unit cell and symmetry,Miller indices, physical constants, experimentaldetails and other comments such as preparation tech-niques and the chemical analysis. Fig. 2 shows amodern card image which is to be compared with Fig.1 to see the changes that time and changing needshave implemented. In addition to a change in theformat, most early data sets have been replaced withmore accurate and expanded d's and I's and moredocumentation, including the crystal parameterswhere they were not known before.

In accordance with the not-for-profit classifi-cation of the corporation, the research and develop-ment activities included sponsoring programs for theimprovement of the quality of the diffraction data. Inaddition to the Associateship established at the Na-tional Bureau of Standards (now the National Insti-tute for Standards and Technology), Grants-in­Aidwere awarded to many universities for collecting newand improved data on compounds under study in theirresearch projects and for the development of compu-ter programs for analyzing diffraction data.

Structure and Operation of the InternationalCentre

As indicated above, the JCPDS-InternationalCentre consists of two parts: a permanent staff andvoluntary scientific and technical advisors. Thisstructure is somewhat parallel to ASTM, one of the

5 The Rigaku Journal

Table 1 Committees and Subcommittees of the ICDD

Board of directorsMembership CommitteeBylaws CommitteeLong-Rang Planning CommitteeFinance Committee

Budget SubcommitteeSales and MarketingGrants-in-Aid

Technical CommitteeSearch and Match Method SubcommitteeDiffraction Problems SubcommitteeData Base SubcommitteeTarget Systems SubcommitteeData Collection and Analysis SubcommitteeMinerals and Ceramics SubcommitteeMetals and Alloys SubcommitteeOrganic and Forensic SubcommitteeEducation Subcommittee

parent organizations. The headquarters are located inSwarthmore, PA where the 22 employees are respon-sible for producing and marketing the PDF. Abibliographer and several editors work under contractto locate and review the diffraction data whichcomprise the PDF. The volunteers meet twice a year to discuss the progress, to recommend new products andto consider ways to be of service to the diffractioncommunity. The corporate business in conducted atthe Annual Meeting in March of each year.

The office staff is composed of two majordepartments responsible for the PDF, the Editorial and Production Department and the Sales and MarketingDepartment, plus the supporting Com­puter Depart-ment and Accounting Department. Although theprinting of hard-copy products and the mastering ofthe CD-ROM's are done outside, most other opera-tions are done in-house. As the computer becomesmore important in the development of the PDF, moreof the operations have been undertaken by the officestaff. The General Manager is responsible for over-seeing this operation and reports to the Board of

Directors. The current General Manager is J.Messick. Previous General Managers included A. S.Beward, R. G. Simard, A. W. Danko and J. W. Caum.

The volunteers comprise 104 members of theInternational Centre. They represent industry, gover-nment and academia in about equal proportions. Also, 20% of these members are from outside the US. Themembership is structured into several special and twomajor operational committees and many subcom-mittees as listed in Table 1. The Technical Committee is responsible for recommending products, proce-dures and projects to the Board of Directors. TheFinance Committee oversees the fiscal operations,proposes the annual budget, and recommends thedisbursement of funds for projects. The Board ofDirectors, which is elected by the membership, isresponsible for setting the policies of the International Centre, for final approval of all projects, and forapproving the budget and the monitoring the use ofthe funds. In addition to direct products involving thePDF, the International Centre sponsors a Grant-in­Aid program to assist researchers in the acquisition

Vol. 6 No. 2 1989 6

Fig. 2 Card image for K2Cu(SO4)2•6H2O from PDF Set 35 as printed in the 1989 format.

of new diffraction data and in educational courses fortraining new diffractionists. The current Chairman isD. K. Smith. Previous Chairmen include W. P. Davey, H. W. Rinn, W. L. Fink, L. L. Wyman, J. D. Hanawalt, and G. J. McCarthy.

Collection and Evaluation of PDF DataSince 1965, 2,000 new patterns are added to the

PDF each year. Around 1,200 of these patterns areretrieved from the open literature, 300 are provided by regular supporters of the PDF, and 500 are providedby the Grant-in-Aid program sponsored by the ICDD.To collect the literature data, the ICDD employs afull-time bibliographer who scans through 120 jour-nals on a regular basis and around 50 other journals on an intermittent basis. This search yields 2,000 to 2,500 patterns each year including some data which isobtained by encouraging authors to supply patternswhich were implied in a paper but not published.Additional searches are contracted with computer-based abstracting services. These searches locatemore than 2,000 additional references and indicateother journals for the bibliographer to examine. Thedesired data is then extracted by the office staff andkeyboarded for evaluation. The quality of these pat-terns is highly variable because of the differingexperience of the authors in collecting reference data.

The patterns from the Grants-in-Aid projects arealso keyboarded if they are not supplied in computer-readable form from the grantee. The compoundsstudied in these projects are coordinated with theneeds of the PDF and the expertise of the grantee. Allgrant data is collected by experienced diffractionistsunder conditions which lead to accurate results, andthe samples are well characterized including thecrystal unit-cell and symmetry. These patterns areamong the best that appear in the PDF, and theirinclusion is one reason why the quality of the PDFimproves with time. The compounds studied are usu-ally part of a research project and represent materialsof considerable current interest. In 1989, the ICDDawarded over one-third of a million dollars in theGrant-in Aid program.

After the data are obtained from the source, theyare reviewed for appropriateness and quality prior totheir inclusion in the PDF. Historically, the evaluation was the responsibility of several editors who hadconsiderable experience in powder diffraction and inthe characterization of the materials involved. Earlyd-I data were replaced by newer data as the qualityimproved. The evaluation of quality, however, wassubjective until the 1960's when the d-values and

intensities were first entered into computer-readablefiles. This step allowed the d-I data to be checked forconsistency, and this checking has become morerigorous with time. The editors initially confirmed the indexing compatibility with the unit cell reported bythe author or attempted to determine an indexingsolution which would explain all the observed d-spacings.

In the early 1980's, a sophisticated data entry/review program was developed at the NationalBureau of Standards (now the National Institute ofStandards and Technology) under the nameNBS*AIDS83, Mighell et al., (1983). This programwas designed to evaluate data for both the PowderDiffraction File and for Crystal Data. A standardizedprocedure is followed which checks many aspects ofthe data as allowed by the information available. Thed-spacings are evaluated by figures-of-merit (de-Wolff, 1972 and Smith and Snyder, 1979) where unitcells were provided by the authors. These figures-of-merit are based on the average error in the observeddiffraction angle compared to the calculated valuefrom the refined unit cell and are used to assign thequality indicator for the data set. Crystallographicconditions are compared with the symmetry assign-ment provided by the author. The program alsochecks the consistency of the chemical formula bydetermining the formula weights and the density forcomparison with measured values. The summary ofthis review is provided to the PDF editors to assist intheir evalua­tion of the data. An example of AIDSinformation as stored is shown Fig. 3.

The development of NBS*AIDS83 was the major step in initiating the comprehensive review of theolder d-I data from Sets 1-32. All the data were re-evaluated, and the corrected data were entered into amaster computer-readable database. The review alsoresulted in extensive changes to many individual,older d-I data where inconsistencies were detected.Because the NBS*AIDS83 program established a

7 The Rigaku Journal

Table 2 Distribution of patterns in the PDF.

Subfile Number of Patterns

Inorganic 36936

Organic 15112

Minerals 3822

Metals and Alloys 9349

Forensic Materials 3460

Common Phases 3214

NBS Patterns 2005

consistent set of rules for pattern evaluation, one result was the adjustment of many of the quality codes,generally downgrading many "*" patterns to "i" grade.

All new data are entered into this master databasefollowing review and acceptance by the editors,maintaining it as the most current form of the PDF.Consequently, older hard-copy forms of the PDF areout-of-date. This new database in now the source forall modern PDF products. All products, including thehard-copy forms, are prepared directly from thismaster by appropriate computer formatting of thedata. The computer-readable files allow the produc-tion of search manuals directly from the master file,minimizing the errors occurring with multiple dataentry. Errors once introduced by retyping areessentially eliminated. The book products are stillbased on the 3 x 5 format used in the initial cardformat, but the image has been modified to allow more efficient use of the space. Changes such as theelimination of the three strongest lines across the topof the card image reflect the outdating of the use ofthese entries for a search system by thumbing through

the stack which was superseded when the first searchmanuals were printed.

The editing of the data is the responsibility of theEditor-in-chief, W. F. McClune, and three topicaleditors, B. Post, S. Weissmann and H. F. McMurdie,each of whom have been involved with the PDF forover 20 years. Other editors have included W. P.Davey, G. W. Brindley, J. V. Smith, A. S. Beward, L.G. Berry and M. E. Mrose. Prior to the implemen-tation of the AIDS review, a copy of the originalarticle containing the powder data was sent to theappropriate topical editor. This editor decidedwhether to continue with the review process and pre-pared a standard form with the extracted data. The of-fice staff would then type the data on a master cardand return a copy of the master to the editor for finalreview. The editor subjectively assigned one of thefive quality marks, “*”, “i”, “ “, “0”, and “C” to thedata set on the basis of experience. As the approvedpatterns accumulated in the office, they wereorganized into units of 2000 for the yearly releases ofthe PDF.

Vol. 6 No. 2 1989 8

Fig. 3 Display of the for K2Cu(SO4)2•6H2O data in the NBS*AIDS83 database format from the 1989 PDF

With the introduction of the AIDS review, theeditorial process underwent considerable revision.The potentially useful d-I data are now keyboardedinto computer-readable form, and both the data andthe AIDS output are supplied to the topical editor. The AIDS program provides the editor with sufficientinformation to make a final decision on the appropri-ateness of the new data to the PDF and to assignobjectively the quality mark, which cannot be higherthan the mark assigned by AIDS. The present criteriafor quality evaluation is given in Table 3. Once thetopical editor has approved the pattern, the Editor-in-Chief checks for similar data in the PDF and assignsthe data a position in the forthcoming PDF set. Thedata are entered into the master database when thePDF set as the data are approved.

Some patterns receive additional review by taskgroups of the International Centre. Usually, this re-view occurs when a subfile product is being prepared,such as the Metals and Alloys Subfile. The minerals,though, are now reviewed on a yearly basis even when there is no Mineral product scheduled. When it is timeto reissue the Minerals Subfile, the patterns arealready in final form. This review consists of confir-ming the nomenclature for conformity with acceptedusage and checking the presentation of the auxiliaryinformation for completeness. For minerals, the no-menclature is governed by the Commission on NewMinerals and Mineral Names of the InternationalMineralogical Association. Metals and alloys usuallyconform to the Pearson system (Villars and Calvert,1987).

The importance of the AIDS review cannot beoveremphasized. In addition to checking the items in

Table 3, it generates considerable derived information which is stored on the master database for futurereference and products. The Crystal Data cell anddeter-minative ratios, the reduced cell and its transfor-mation matrix, derived crystal parameters, lists of theten lines with the strongest intensities and the ten lines with the largest d-spacings, and the formula weightare added along with all the textual information onsource, preparation, etc., keyboarded from the origi-nal manuscript. Fig. 3 shows an example of thisinformation as recorded in the database. The original2θ data is preserved where it is provided by theauthor. All Grants-in-Aid data provide the experi-mental 2θ values. Because of round-off problems, the2θs obtained by back­calculating from reporteddevalues is not satisfactory for error analysis and thedetermi-nation of the proper figures-of-merit.

The data which now appears on a PDF image islisted in Table 4. The primary data and all the otherinformation available in the manuscript is included.Information from sources other than the principalreference are added where appropriate. The goal ofthe PDF is to provide the user with as muchinformation as possible to assist in the identificationof the compound.

Current Products of the International CentreThe Powder Diffraction File is the principal pro-

duct of the International Centre, but there are manysupportive products. Table 5 is a comprehensive listof these products. Hard-copy products are beingreplaced with computer-readable files to meet theneeds of modern instrumentation. In 1986, the Inter-national Centre published the last set in card form. Allfuture hard-copy versions of the PDF will be in bookform or as Microfiche films. Computer­readable ver-sions are available on a variety of media.

Search manuals will continue to be published inthe foreseeable future, primarily the Alphabetical andHanawalt Manuals. The Elemental and InterplanarSpacing Index (EISI) is the latest search-manual to bedeveloped which is designed to assist the electrondiffractionist by use of chemistry and d-spacings butwithout use of intensity values. It is a single-entryindex which groups the compounds by largest d-spacing and chemistry and lists the ten lines with thelargest d-spacings. The Fink Manual, also designedprimarily for electron diffraction, was last producedin 1982. Because it is a multiple-entry index, its size is too large to bind as one volume. Future editions will

9 The Rigaku Journal

Table 3 Items evaluated by NBS*AIDS83

1. Formula checking inlcuding generation of an empiricalformula.

2. Form of the chemical name and comparison with formulafor consistency.

3. Comparison of measured, calculated and estimateddenisities.

4. Validation of space group, aspect or lattice type withallowed symbols and assigned crystal system.

5. Generation of Pearson symbols for structure types.6. Refinement of d-spacings and confirmation of indexing

with extinction rules for space group.7. Calculation of the Smith-Snyder (1979) and the deWolff

(1969) figures of merit.8. Assignment of the PDF quality mark using the initial

assignment by the topical editor and the fit of the d-spacings to the refined unit cell.

9. Validation of all the editorial flags.10. Issues errors and warnings when problems are detected.

probably be coupled with computer-readable products or with subfiles where size is not a factor.

The computer-readable versions of the PDF arethe most widely distributed form of the PDF today. Atpresent there are two versions, the PDF-1 databasewith only PDF numbers, d's, I's and compound name,and the PDF-2 database with all the data present on acard image. The former version is used for search/match programs; the latter version for informationdisplay. The main media for distribution are the mag-netic tape and the CD-ROM, although some instru-ment manufacturers still use hard and floppy disks.The magnetic media are useful where the computer isprogrammed to search for matches in real time. Eitherthe medium is searched directly or the PDF is re-structured for faster implementation, and the mag-netic media is amenable to this operation.

The CD-ROM is ideal for information storage and display on personal computers. The information pack-ing density is so high on a compact disk that the fullPDF only requires around 20% of the available space.The PDF already fills a magnetic tape at the highestdensity currently available. Maximum access time on

the compact disk is about 1 second for a block of dataand less than 0.1 second for a contiguous search.Thus, the CD-ROM is less suitable for real-timesearch/match operations. When the proper index filesare prepared, it is an ideal medium for look-up anddisplay of desired information. The International

Vol. 6 No. 2 1989 10

Table 4 Documentation of PDF Data

PrimaryExperimental conditionsSample description

CompositionSourceDerived d’s and I’sReference for data

SecondaryCrystallographic data

SystemUnit CellSpac group

Density (calculated)Internal standardReference for crystal information

TertiaryMiller indicesDensity (measured)Figures-of-meritAxial ratiosCrystal Data cellIndices of refractionReference-intensity-ratioReferences for physical property data

QuarternarySynthesis or mineral localityStabilityStructure typeChemical analysis

Table 5 Products of the International Center

The Powder Diffraction File -- Inorganic and OrganicCard form (discontinued in 1987)Microfiche formBook form

Individual setsHistorical data (re-edited)NBS Associateship Pattern FileMineral FileMetals and Alloys FileCommon Phases FileForensic File

Computer-readableMagnetic tapes

PDF-1PDF-2

DisksCD-ROM

Search ManualsBook Form

Chemical AlphabeticalHanawaltFink MethodElemental and Interplanar Spacking Index

Software (provided without charge)Johnson/VandGoehner/GarbauskasToby POWDER SUITE

Educational MaterialsPDF WorkbookMineral WorkbookEducational PackageMethods and Practices ManualACS Audio Short CourseShort Courses

Crystal DataBook formIdentification File on Magnetic tapeMinerals (book form 1990)CD-ROMSoftware (provided without charge)

Mighell/HimesHarlow/Johnson

Electron Diffraction DatabaseMagnetic tapeCD-ROMSoftware (provided without charge)

Carr/JohnsonJournal

POWDER DIFFRACTION

Centre has developed programs to accompany theCD-ROM product to access information in wayssimilar to what would be done if the information werein book form. The 1989 version of the PC-PDF allowssearching on PDF number, chemistry, mineral names,and specific d-spacing combinations. Plans for thefuture include additional searches like a Hanawalt and Fink search and matching of specific key words. Truereal-time search/match programs are not being devel-oped by the International Centre because many areavailable from APD manufacturers or software de-velopers. The International Centre considers itself adatabase producer, not a software house, but it doesdistribute programs developed by others. As soon asthe PDF was available in computer-readable form inthe 1960's, several groups developed search pro-grams. Some of these older programs are still beingimproved, and many new ones are being developed by equipment manufacturers and individual entre-preneurs. The International Centre will distribute anyprogram in the public domain which will be supported by the authors. Presently, only three PDF programsfall into this category along with two for Crystal Dataand one for the Electron Diffraction Database.

The International Centre also has developedmaterials for educating both new and experienced dif-fractionists. The Education Subcommittee has beenone of most active of the subcommittees. A regularschedule of workshop-type courses is presented in theUnited States and additional courses are offered inconjunction with scientific meetings both domesticand overseas. These programs have lead to thedevelopment of workbooks which are also availablefor purchase at cost to encourage the incorporation ofpowder diffraction into courses at colleges anduniversities. Working with the American ChemicalSociety, a short course was developed for audioinstruction while following an illustrated manual. Inaddition to direct course-oriented material, theInternational Centre has assembled a Methods andPractices Manual which contains articles covering awide variety of subjects from sample preparation tothe evaluation of diffraction data. This manual iscontinually being updated as new material becomesavailable. Most of the articles are reprinted fromPOWDER DIFFRACTION. Others are prepared tofill in specific subjects in the manual. This manual isavailable to purchasers of the PDF at cost and toothers at an increased price.

In addition to the PDF, the International Centrehas been the publisher of the NBS Crystal Data since

1963. This database of crystallographic unit-cellinformation is a useful supplement to the PDF in thatit contains many more compounds than the PDF. In1989, the Crystal Data File has over 136,000 entries.This File is available both on magnetic tape and onCD-ROM. Cell matching search programs have beendeveloped by Himes and Mighell (1987) and Booleanprograms by Harlow and Johnson (personal Com-munication, 1989), which are distributed by theInternational Centre. The NBS*AIDS83 program was developed to evaluate the data for Crystal Data as well as for the PDF. The group responsible for maintaining Crystal Data is under the auspices of the Office ofStandard Reference Data at the National Institute ofStandards and Technology.

Although most new releases of Crystal Data willbe in computer-readable form, there is a project inprogress to bring all the mineral data up to date andprint this information in a form similar to the booksprinted up to 1970. Because of the limited size of themineral information, about 12,000 entries, this pro-duct is feasible. The program is being implemented by M. E. Mrose of the National Institute of Standards and Technology.

One other important product of the InternationalCentre is the publication POWDER DIFFRACTION.This journal is devoted to disseminating informationof interest to the diffractionist throughout the world. It is published 4 times each year. Articles range fromtheoretical to applied, and many new powder dif-fraction patterns are included. Appropriate articles are reprinted in the Methods and Practices Manual. Inaddition to the regular articles and data articles, theInternational Report section includes meeting reports, a computer section, and news of activities from theInternational Centre. The current editors are D. K.Smith, G. J. McCarthy, H. D. Hitchcock, B. C.O'Connor and J. W. Visser with R. Jenkins as theManaging Editor.

The Computer-Readable PDFThe first computer-readable version of the PDF

appeared in 1962 when the PDF numbers, d's, I's, andcompound formulae were distributed on magnetictape. That product is now known as PDF-1 (see Table6). Computers of that time period were memorylimited, and consequently, only the essential datawere included in this file. Magnetic tapes were thebest way to present large blocks of data to the compu-ters. The availability of these data did encourage thedevelopment of search schemes for the identificationof compounds. That stage marked the beginning of

11 The Rigaku Journal

the computer age for the International Centre. Sincethat time, computer-based products began to take amore and more important position in diffractionanalysis.

It was not until the 1980's that the next major stepwas taken. PDF-2 was introduced as soon as all thehistorical data from the older sets of the PDF werekeyboarded and checked. The contents of PDF-2 arelisted in Table 7. Essentially all the information thatappeared on a card image was now available incomputer-readable form. Search programs still usedonly the information from PDF-1; PDF-2 was used todisplay the supporting information on the computerscreen. The first version of PDF-2 was distributed onmagnetic tape, but with the availability of the CD-ROM in the middle 1980's, it too was used as amedium for the PDF. Currently, the CD-ROM is oneof the most popular media. Figure 4 illustrates the card image as presented on a PC terminal.

Future ProductsWith the availability of computer-controlled

diffractometers, it is now easy to collect and processdigitized diffraction patterns. New experiments arenow possible which analyze the peak shapes as well as the position and intensity information. Such studiesinclude structure analysis using profile fitting orwhole-pattern fitting, crystallite size and strain, andquantitative analysis. It is quite evident that the futurewill need the digitized trace in addition to the currentd-I data for complete diffraction studies. PDF-3 is

envisioned to meet these needs. The proposedcontents of PDF-3 are described in Tables 8 and 9.

There are many problems in the development of a new database such as PDF-3 which are compoundedbecause it is computer based. The major problem is todefine now what is needed 10 to 20 years in the future. The central information in this database will be thedigitized diffraction trace, but present day instru-ments will evolve into the more sophisticated instru-ments of tomorrow and perhaps change the nature ofthe data that is needed. Current instruments introduceaberrations which may be minimized, and X-raysources may become more monochromatic in thefuture. Obviously, the most desired trace to preservewould be one with the source and instrument contri-butions deconvoluted to leave the sample component. The state of the art is not quite ready for this step yet,so the alternative is to record both the instrument trace of the sample and the instrument trace of somestandard taken under the same experimental condi-tions. The International Centre is instituting a projectwith their Grant-in-Aid recipients to preserve thedigitized traces of the patterns they submit. Thepresent standard is NBS SRM640 silicon, but a studyof new possibilities has lead to the recommendationof LaB6 as a good alternative to Si. A supply of LaB6

has recently been certified by the Office of StandardReference Data of the National Institute of Scienceand Technology for profile applications. Now that

Vol. 6 No. 2 1989 12

Table 7 Contents of PDF-2

PDF # d’sCompound Name I’sCompound Formula hkl’sData Collection DocumentationCell and SymmetryZ and DensityPhysical PropertiesPreparation and PuritySources of MaterialsFigures-of-MeritI/I(cor)Data Quality MarkSubfile Code

Table 6 Contents of PDF-1

PDF # d’sCompound Name I’sCompound FormulaData Quality MarkSubfile Code

Table 8 Contents of PDF-3

PDF # Digitized traceCompound Name d’sCompound Formula I’sData Collection Documentation hkl’sDigitized Trace ParametersReference Sample TraceCell and SymmetryZ and DensityPhysical PropertiesPreparation and PuritySources of MaterialsFigures-of-MeritI/I(cor)Data Quality MarkSubfile Code

Table 9 Digitized Trace Parameters

Start Angle Finish Angle Step SizeI(2θ)

Reference intensity ratioInstrument Parameters

Standard Reference Trace

this standard is available to diffractionists, the projectof collecting digitized traces can begin in earnest.,

Other problems remain in defining the range ofthe data to be collected and the step size to be used. As with the d-I data, many of the decisions will have to be made by the diffractionist based on the nature of thesample. The range of a pattern may vary considerably. Some compounds do not produce useful diffractioninformation beyond 90°2θ or even 60°2θ in somecases. Other compounds would allow useful informa-tion to be collected beyond the range of the diffrac-tometer. Step size is more nebulous. For a referencepattern, the step size should be as small as the mostdemanding application requires. Step sizes between0.01 and 0.05°2θ seem to be in common use. Mostusers do not like to interpolate between data points, sothe 0.01°2θ step for the reference patterns seems to bethe requisite choice.

Once the database of digitized traces becomesavailable, it will be necessary to be able to transfer thetraces from instrument to instrument. Thus a standar-dized file structure is necessary, and a universal fileconversion program must be developed for eachinstrument. The International Centre is working onthis problem with the Joint Committee on Atomic andMolecular Physical Properties. A program, JCAMP-DX, is available now (McDonald and Wilks, 1988)for file conversion, and the PDF-3 will follow rulessimilar to those used in this program.

As the problems are solved, digitized traces willbe accumulated by the staff, and when there is a sig-nificant number of these data, a set of PDF-3 patternswill be issued. The development of this database willbe slow at first, but as the problems are overcome andthe applications are extended, this database shouldbecome another product of the International Centre.

In addition to PDF-3, there are several otherproducts that should appear within the next 2 years.The Metals and Alloys File is being extensivelyreviewed, and a product is on the 1990 productionschedule for this File. It is not clear whether this Filewill be printed in a hard-copy form, but it will beprepared certainly for CD-ROM display. A CrystalData for Minerals is also scheduled for 1990. Thispublication will be a hard-copy publication. A newMineral File will probably appear in 1991 or 1992.

The CD-ROM is currently the most popularcomputer media for receiving the PDF. The CrystalData File is already available on the CD-ROM and the Electron Diffraction Database will be issued beforethe end of 1989. The International Centre is currently

13 The Rigaku Journal

Fig. 4 Display of the data image for K2Cu(SO4)2•6H2O aspresented on a terminal from the CD-ROM. Five screensare requred because of the size of the data set. Positiondata may be displayed in d, θ, 2θ, Q, or sin2θ as desired.

negotiating with other database centers to put theirdatabase on CD-ROM. Some of these CD-ROMversions may appear in 1990 or soon thereafter.

Future of the International CentreThe renaissance of powder diffraction in the

1980's will continue into the next decade and probably beyond. New instrumentation will demand new pro-ducts based on diffraction data. The InternationalCentre is trying to stay ahead of these changes. Thetopic is always part of the agenda of the TechnicalCommittee whenever it meets. The Long-RangePlanning Committee tries to look ahead 5 years torecommend new directions for endeavor.

New members for ICDD are continually beingsought, and all members are encouraged to participatein as many activities as their time allows. Membership is limited only by interest. The meetings of theTechnical Committee are open to anyone wishing toattend, and as new attendees indicate interest andparticipate in the activities of the International Centre,they are invited into membership. Most meetings areheld in the Philadelphia area because of the closeproximity to headquarters, but there are usually openad-hoc sessions held at Congresses of the Interna-tional Union of Crystallography and at other technicalmeetings from time to time. Information on the nextscheduled meetings may be obtained at any time fromInternational Centre headquarters.

The International Centre is responding to thechange in its market from primarily domestic in the1960's to primarily international in the 1980's. Themarket is now about equally divided between NorthAmerica, Europe and Asia with a small but growinginfluence from Australia. About 20% of the membersof the International Centre are from outside NorthAmerica, and this number is increasing as more usersbecome aware of the activities in which they canparticipate. The Board of Directors has overseasmembers, and there are consultants from all the

technical areas of the world. Automation has certainly been one of the reasons for the rapid increase in theuse of the PDF all over the world, but technologicaldevelopments even in under-developed countries arehaving their effect. Overseas diffractionists are invi-ted to contact the International Centre to see how theycan assist in the development of projects. Individualsdo not have to be able to attend the meetings to have auseful role in the future of the PDF and relatedproducts.

ReferencesHanawalt, J. D. and Rinn, H. W. (1936) Ind. Eng. Chem.

Anal. Ed. 8, 244-250.

Hanawalt, J. D., Rinn, H. W. and Frevel, L. K. (1938) Ind.Eng. Chem. Anal. Ed. 10, 457-512.

Himes, V. L. and Mighell, A. D. (1985) in "CrystallographicDatabases", Allen et al., Eds., International Union ofCrystallography, Chester, UK. pp 144-155.

Jenkins, R. and Smith, D. K. (1987) in "CrystallographicDatabases", Allen, et al., Eds. International Union ofCrystallography, Chester, UK. pp 158-177.

McDonald, R. S. and Wilkes, P. A., Jr. (1988) Appl. Spectr.42, 151-162.

Mighell, A. D., Hubbard, C. R., Stalick, J. K. and Holomany,M. A. (1983) "NBS*AIDS83: A Manual Describing theData Format Used in NBS*AIDS83" JCPDS-Inter-national Centre for Diffraction Data, Swarthmore, PA,USA.

Smith, G. S. and Snyder, R. S. (1979) J. Appl. Cryst. 12, 60-65. Toby, B. H., Harlow, R. L. and Holomany, M. A.(1989) Powd. Diff. 4, (in press).

Villars, P. and Calvert, L. D. (1985) "Pearson's Handbook of Crystallographic Data for Intermetallic Phases", Vol. 1-3, American Society for Metals, Metals Park, OH, USA.

dewolff, P. M. (1972) J. Appl. Cryst. 5, 243.

(Received August, 1989)

Vol. 6 No. 2 1989 14