2.3- Trying to identify a material knowing the cell

Knowing the cell, should we now record the complete data for a structure determination or has the compound been already characterized ?

The exact formulation of the compound is not always known at this stage.

Divide the volume by nearly 20 and you will not be far from obtaining the number of anions if your material is an oxyde or a fluoride.

Estimate Z, the number of formula units per cell.

Measure the density.

Thermal analysis (DSC, TGA) is something to do absolutely.

Explore now all the databanks, not only the PDF-2.

WARNING : You will have to examine
the 3 or 4 recent years bibliography by using :

the Current Contents,
the Chemical Abstract
or the other (commercially) available databanks
(PASCAL... see INIST). Do not neglect the more than 16000 indexed periodical in the Uncover database to which you can access too by Telnet (URL database.carl.org).

Last but not least, most of the scientific revues have placed their content together with a summary in a catalog of references searchable by keyword.
See Acta Crystallographica and all the IUCr journals, for instance,
indexed since 1983.

If all attempts for identification failed, an ab initio structure determination from powder data is not always the best thing to do :

If you have sufficiently large single crystal, turn in the four-circle diffractometer direction (avoid wasting time with isostructural compounds unless you have good reasons).

If really you have only a powder : have you tried all the possible means for synthesis available to you which could enlarge the crystal size ? If yes, we continue (but see the alternative).