International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.7, pp. 314-316

Section 3.7.4. Inorganic Crystal Structure Database (ICSD)

J. A. Kaduka,b,c*

aDepartment of Chemistry, Illinois Institute of Technology, 3101 South Dearborn Street, Chicago, IL 60616, USA,bDepartment of Physics, North Central College, 131 South Loomis Street, Naperville, IL 60540, USA, and cPoly Crystallography Inc., 423 East Chicago Avenue, Naperville, IL 60540, USA
Correspondence e-mail: kaduk@polycrystallography.com

3.7.4. Inorganic Crystal Structure Database (ICSD)

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The Inorganic Crystal Structure Database (ICSD; https://icsd.fiz-karlsruhe.de ; Bergerhoff & Brown, 1987[link]; Belsky et al., 2002[link]; Hellenbrandt, 2004[link]) strives to contain an exhaustive collection of inorganic crystal structures published since 1913, including their atomic coordinates. It is a joint project between FIZ Karlsruhe and NIST. The database is accessed through the online WebICSD or the locally-installed program FINDIT. Typical interatomic distances in inorganic compounds derived from the ICSD have been collected in Chapter 9.4[link] of International Tables for Crystallography Volume C (Bergerhoff & Brandenburg, 1999[link]). Applications of the ICSD have been discussed by Kaduk (2002[link]), Behrens & Luksch (2006[link]) and Allmann & Hinek (2007[link]).

The ICSD began as an inorganic crystal structure database of published structures with atomic coordinates. The scope was gradually extended to include intermetallic compounds. Since 2003, FIZ Karlsruhe has started to fill in the gaps, and the aim is for the ICSD to include all published intermetallic compounds. Originally the ICSD did not contain structures with C—H or C—C bonds. After 2003, this rule was modified so that new entries should not contain both C—H and C—C bonds; compounds containing tetramethylammmonium and oxalate ions are now included.

The ICSD contains fully determined structures with atomic coordinates. Coordinates of light atoms (such as H atoms) or extra-framework species (such as in zeolites) may be missing. Structures described as isotypic to other structures, but without determination of the atomic coordinates, are included using the coordinates from the corresponding structure-type prototype. Such entries get a special remark/comment: `Cell and Type only determined by the author(s). Coordinates estimated by the editor in analogy to isotypic compounds.' Currently there are more than 26 000 entries with derived coordinates. At present, the ICSD contains more than 187 000 entries, including 2033 crystal structures of elements, 34 785 records for binary compounds, 68 730 records for ternary compounds and 68 083 records for quaternary and quintenary compounds. About 149 000 entries have been assigned a structure type; there are currently 9093 structure prototypes.

Most of the structures contained in the ICSD are from published journal articles, although private communications are also accepted. The entries are tested for formal errors, plausibility and logical consistency. The data are stored as published; the authors' settings of space groups are considered to be valuable information which should not be changed. Only some `exotic' space groups are transformed. In addition, for each entry in the ICSD the structure is standardized using the program STRUCTURE TIDY by Gelato & Parthé (1987[link]). The published cell, standardized cell and reduced cell are all searchable. Since 2003, FIZ Kalrsruhe has been assigning structure-type classifications (Allmann & Hinek, 2007[link]). In the future, this feature will enable easier searches for compounds that are closely related in structure.

3.7.4.1. General features of the ICSD

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The chemical name is given in English following IUPAC rules, with the oxidation state in roman numerals. The formula upon which the name is based is calculated from all atoms with defined coordinates. Phase (polymorph) designations are given after a hyphen. Mineral names and group names are given for all entries that correspond to minerals. Details of the origin are given after a hyphen. The formula is coded as a structural formula, which provides the opportunity to search for typical structure units (such as SiO4). Such searches can be useful, but can easily miss structurally similar compounds, and should be used with caution.

The title of the publication is given in English, French or German. There can be several citations, but an author list is only given for the first reference. I have encountered truncated author lists. Authors' surnames can vary when the original publication uses a non-roman alphabet. In some cases, the first and last names of Chinese authors may be interchanged.

The Hermann–Mauguin space-group symbol is given according to the conventions of International Tables for Crystallography Volume A . If different origin choices are available, those space groups with the origin at a centre of symmetry (origin choice 2) are characterized by an additional `z', while an additional `s' is used for special origins (origin choice 1). Thus, the space group for magnetite may be reported as Fd-3mz or Fd-3ms, depending on which origin the authors used. Since all contemporary Rietveld programs use origin choice 2, care must be taken when importing coordinates.

Along with the fractional coordinates, atom identifiers are reported. These are principally running numbers and may differ from those reported by the authors. The oxidation state is given with a sign. When importing coordinates into a Rietveld program these oxidation states can influence which scattering factors are used, and so should be examined by the user. Both site multiplicities and Wyckoff positions are generated for all atoms.

The ICSD archives displacement coefficients (both isotropic and aniostropic) according to what the authors reported. Isotropic displacement coefficients can be given as either B or U values and anisotropic coefficients can be given as β, B or U values (or, in rare cases, using other conventions). Displacement coefficients imported into a Rietveld program should always be checked, as it is common for the program to interpret B as U and vice versa. Such wrong displacement coefficients can make Rietveld refinements hard to perform. There are a number of standard remarks and standard test codes; these text fields can be useful for limiting the universe of the search (such as for neutron-diffraction structures).

3.7.4.2. Features particularly useful for powder crystallography

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A field which is particularly useful for identifying structural analogues is the ANX formula. This formula is generated according to the following rules:

  • (i) H+ is not taken into account, even if coordinates are available.

  • (ii) The coordinates of all sites of all other atoms must be determined.

  • (iii) Different atom types on the same positions (for example, in solid solutions) are treated as a single atom type.

  • (iv) An exception: if cations and anions occupy the same site they will not be treated as one atom type.

  • (v) All sites occupied by the same atom type are combined, unless the oxidation state is different. Thus, Fe2+(Fe3+)2O4 yields AB2X4, while (Fe2.667+)3O4 yields A3X4.

  • (vi) For each atom type, the multiplicities are multiplied by the site-occupancy factors and the products are added. The sums are rounded and divided by the greatest common divisor.

  • (vii) If the rounded sum equals zero, all sums are multiplied by a common factor so that the smallest sum equals unity, so no element will be omitted.

  • (viii) Cations are assigned the symbols A–M, neutral atoms are assigned N–R and anions are assigned X, Y, Z and S–W.

  • (ix) The symbols are sorted alphabetically and the characters are assigned according to ascending indices: AB2X4, not A2BX4.

  • (x) All ANX symbols with more than four cation symbols, three neutral atom symbols or three anion symbols are deleted.

The utility of these symbols is illustrated by the fact that the three garnets Mg3Al2(SiO4)3, Ca3(Al1.34Fe0.66)Si3O12 and (Mg2.7Fe0.3)(Al1.7Cr0.3)Si3O12 all yield ANX = A2B3C3X12.

Reduced-cell searches [see International Tables for Crystallography Volume A, Section 3.1.3[link] (de Wolff, 2016[link])] are particularly easy to carry out in the `Cell' section of Advanced Searches. Once a unit cell has been determined by indexing the powder pattern, it is always worth carrying out a reduced-cell search to identify potential isostructural compounds using lattice-matching techniques. It is often wise to first carry out such a search using relatively narrow tolerances (say, 1% on the lattice parameters) and then carry out additional searches using larger tolerances. Systematic searches of the subcells and supercells of a given unit cell, as could be carried out using the NBS*LATTICE program with the NIST Crystal Data Identification File (Mighell & Himes, 1986[link]; Mighell, 2003[link]), are not yet implemented.

Under the `Crystal Chemistry' section it is possible to search for crystal structures that contain bonds between particular atom types in a distance range. Such searches are particularly valuable in assessing the chemical reasonableness of crystal structures, such as the study by Sidey (2013[link]) on the shortest BIII—O bonds.

Because the ICDD Powder Diffraction File `01' entries contain the ICSD collection code in the comments, searching for the collection code of a hit in a search/match is particularly easy in the `DB Information' section. In this way, the relevant ICSD entry can be located without any ambiguity and the best structure for the problem at hand can be used to start the Rietveld refinement.

References

Allmann, R. & Hinek, R. (2007). The introduction of structure types into the Inorganic Crystal Structure Database ICSD. Acta Cryst. A63, 412–417.Google Scholar
Behrens, H. & Luksch, P. (2006). A bibliometric study in crystallography. Acta Cryst. B62, 993–1001.Google Scholar
Belsky, A., Hellenbrandt, M., Karen, V. L. & Luksch, P. (2002). New developments in the Inorganic Crystal Structure Database (ICSD): accessibility in support of materials research and design. Acta Cryst. B58, 364–369.Google Scholar
Bergerhoff, G. & Brandenburg, K. (1999). Typical interatomic distances: inorganic compounds. International Tables for Crystallography, Vol. C, edited by E. Prince, pp. 770–781. Dordrecht: Kluwer Academic Publishers.Google Scholar
Bergerhoff, G. & Brown, I. D. (1987). Crystallographic Databases, edited by F. H. Allen, G. Bergerhoff & R. Sievers. Chester: International Union of Crystallography.Google Scholar
Gelato, L. M. & Parthé, E. (1987). STRUCTURE TIDY – a computer program to standardize crystal structure data. J. Appl. Cryst. 20, 139–143.Google Scholar
Hellenbrandt, M. (2004). The Inorganic Crystal Structure Database (ICSD) – present and future. Crystallogr. Rev. 10, 17–22.Google Scholar
Kaduk, J. A. (2002). Use of the Inorganic Crystal Structure Database as a problem solving tool. Acta Cryst. B58, 370–379.Google Scholar
Mighell, A. D. (2003). The normalized reduced form and cell mathematical tools for lattice analysis – symmetry and similarity. J. Res. Natl Inst. Stand. Technol. 108, 447–452.Google Scholar
Mighell, A. D. & Himes, V. L. (1986). Compound identification and characterization using lattice-formula matching techniques. Acta Cryst. A42, 101–105.Google Scholar
Sidey, V. (2013). On the shortest BIII—O bonds. Acta Cryst. B69, 86–89.Google Scholar
Wolff, P. M. de (2016). International Tables for Crystallography, Vol. A, 6th ed., edited by M. I. Aroyo, pp. 709–714. Chichester: Wiley.Google Scholar








































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