Full structural data
Full structural data are in Inorganic Crystallographic Data Base (ICSD), CRYSTMET and Cambridge Crystallographic Database (CCD, organic). The University of Cambridge has free access to these databases. Data can be downloaded from https://www.psds.ac.uk/ as Crystallographic Information Files (.CIF), which contain the unit cell parameters, space group, atomic coordinates, reference, etc., and can be used to calculate diffraction data, make atomic drawings and more. There are multiple entries for most phases so the user must choose the best set of data to use.
Diffraction databases
For phase identification lists of d-spacings & relative intensities are required, which are found in diffraction databases.
International Centre for Diffraction Data Database (ICDD previously JCPDS) http://icdd.com/ is a historic database started in 1940s. Originally all the data were experimental. Some of these data from NBS & NIST in ~1950-1970 are the best available. More recently data calculated from ICSD and NIST (another metal & alloys database) have been included. The experimental data are checked & have a quality mark. Data that have been superseded remain in the database but are marked as deleted (beware - do not use them). Experimental data are usually unique but there are multiple entries for calculated data. The user has to make their own judgement on calculated data (i.e., could be from say single crystal data collected in ~1930!).
Crystallographic Open Database (COD) is a newer free database http://www.crystallography.net/. COD currently has ~300,000 sets of data for inorganic, metals, metal-organics & organics (bio-polymers are excluded) both experimental & calculated from ICSD and various journals. As a self-depositing free database the user must make their own judgement as to data reliability. In some areas, COD maybe more up to date than our ICDD but its weakness is the lack of the older high quality powder data from NIST & NBS on standard materials.
Current laboratory setup
Because of licences & payment ICDD 2021 has recently been set up on one alaysis PC. ICDD is interfaced to both HS+ & EVA on this PC & the ICDD software ‘SIeve’ as an alternative to HS+ or EVA for Search Identify/Match. Other PCs have HS+ running with older versions of ICDD (2003 is fine for most work). EVA and HS+ can be made to run with COD. COD is okay for phase identification but lacks the excellent experimental powder data from 1950-1970 that are in ICDD & might be needed say for accurate cell parameters.
Polymers
Unfortunately none of the databases above have much information on polymers, probably because the data are considered to be ‘poor quality’. The original references are given in various books or can be obtained by searching (often old ~1950s). From these a CIF can be made & the diffraction data calculated (e.g. in HighScore+). Note that depending on heat & processing conditions, the same polymer could be amorphous, semi-crystalline, well crystalline, unoriented or oriented.