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Inorganic Phase Equilibrium Data


Compile and evaluate phase equilibrium data for NIST Standard Reference Database 31 (Phase Equilibria Diagrams); disseminate the data in a readily accessible and searchable format in partnership with the American Ceramic Society

Technical One Pagers Drafts



Every deliberate effort to develop a new material or to improve processing begins with chemical composition and the conditions (temperature, pressure) under which pure compounds and their mixtures are stable (an equilibrium phase diagram).  In the absence of such information, materials scientists must resort to trial-and-error approaches or conduct studies themselves to obtain the data. For commercially important materials, phase equilibrium diagrams provide critical starting information to devise processing schemes that optimize the properties needed for specific applications, and to facilitate quality-assurance efforts.  For the exploration and design of new materials, including computational studies, the diagrams provide fundamental information on the occurrence and chemical composition of existing compounds as well as their thermodynamic properties.  

This critically evaluated database contains more than 32,000 maps of the equilibrium chemical and structural behaviors exhibited by a wide range of non‐organic material‐types including:  Oxides and mixed systems with oxides; chalcogenides (sulfides, selenides, tellurides); pnictides (N, P, As, Sb, Bi); actinides (U, Pu, Th) and actinide‐surrogates (Ce); oxy‐cation systems (e.g. molybdates, vanadates); semiconductors (Si, Ge, Sn); group-3 systems (B, Al, Ga, In, Tl); and salts, including mixed systems with salts.  The data are pertinent for materials used across a broad spectrum of technologies in applications such as optoelectronics, thermal‐barrier coatings, sensors, energy converters, nuclear‐waste reprocessing, nuclear‐reactor technology, photovoltaics, pigments, fuel cells, catalysts, thermoelectrics, capacitors, transducers, thermoluminescents, molten‐salt batteries, photovoltaics, electrolytic refining, and semiconductor manufacturing.


Published from 1964 to 1992 as the reference-series Phase Diagrams for Ceramists ("Blue Books"), SRD 31 is the result of a long-standing collaboration between NIST and The American Ceramic Society to develop and maintain a state-of-the-art database of evaluated phase equilibria data for industrial and academic customers.  NIST (then NBS) staff played key roles in establishing the project as a data-driven extension of existing core expertise in phase equilibrium science, thermodynamics, crystallography, and diffraction methods for the identification and characterization of crystalline materials.  In 1992 the title was changed to the more general Phase Equilibria Diagrams to emphasize that the data are useful to the broader inorganic materials community.  Since 2005 the database has been disseminated only electronically; each updated version is a comprehensive collection of all content previously published in any format, plus new content consisting of 600-800 new phase diagrams annually. 

SRD31 Numbers 2023

SRD 31 is produced by the NIST data center using a custom, web-based Content Management System (CMS) running under Ubuntu Linux using the Ruby programming language.  The system uses an Nginx web-server, SQLite database, the Route scheduling system, and an object relational mapper for the GUI.  Commentary data is entered using the LaTeX document preparation system; phase diagrams are entered as interactive digital files after digitization using custom software developed by NIST staff.  The data-center process begins with bimonthly searches of the most recently published literature using a systematic set of keywords.  Papers with new diagrams deemed suitable for the collection are then sent to scientists with expertise in phase-equilibria science – and foreign-language translation as necessary – who write critical summaries of each study and diagram according to guidelines provided by NIST; the American Ceramic Society assists in recruiting these subject-matter experts via their print media.  New diagrams are digitized at NIST, paired with the commentary text, and entered in the database as new Figures, which are reviewed and edited in multiple passes by NIST editors prior to final publication.  Each step of this process is entered, tracked, and completed within the CMS.


Annual sales of SRD 31 total $100-$200 K.  The current international base of approximately 370 customers includes major universities and materials developers working across industry, government, and academia.



NIST SRD 31 can be purchased as a stand-alone PC product (at NIST Standard Reference Database 31) or as an online subscription-based version (at  Both products use the same browser-based search interface, which includes expandable detailed help icons at each user‐input location.  Phase diagrams can be viewed and manipulated interactively; capabilities include zoom, rotate, curve-follow, mol/wt % cursor-readout, lever rule, and overlay.  The diagram display-window includes a Help file detailing each function.  Users can perform keyword-searches of the critical evaluations of all PED Figures, allowing them to associate material systems with any potential applications mentioned in the evaluation.  All PED Figures can be viewed or printed as complete .pdf files (commentary plus diagrams) which are similar in quality to those in the previously published books. 

NIST staff and Associates with computers having NIST IP addresses (Gaithersburg and Boulder) can access SRD31 online free of charge at

A Demonstration Version of SRD 31 can be downloaded at NIST Standard Reference Database 31 and provides several useful features at no cost.  This version allows the user to experience the complete functionality of the product, including all functions of the diagram-display software, but with limited content.  Also included is a comprehensive Cumulative Index for the entire database, which can be searched and sorted by chemical system to reveal what materials are covered in all 32,000 diagrams. 

In addition, the Help menu provides a downloadable .pdf file of the classic tutorial General Discussion of Phase Diagrams, by F.P. Hall et al. (containing a glossary of phase-equilibrium terminology and thermodynamic definitions), background information for using the database (sections Common Tasks, FAQ, Chemical System Designation Rules), and a detailed history of this project and its publications. 

The PED Editor, custom software developed by NIST staff, is also available for free download at NIST Standard Reference Database 31.  This program can be used to digitize phase diagrams or to extract data from phase diagrams or other two‐dimensional scientific drawings.  The PED Editor is a Java program which uses the iText open‐source PDF file generation library, Batik open‐source SVG file generation library, Jackson open‐source JSON file generation library, and the JAMA Java Matrix package.

Related Publications

Phase Equilibria Diagrams, NIST Standard Reference Database 31, v.5.1, NIST and The American Ceramic Society, Westerville, OH, ©2023.

Crystal chemistry and phase equilibria of the CaO-½Ho2O3-CoOz system at 885 °C in air, W. Wong-Ng , W. Laws, Q. Huang, J. Hou, S.H. Lapidus, L. Ribaud, J.A. Kaduk; Solid State Sciences 107 (2020) 106348

Crystal chemistry and phase equilibria of the CaO-½Dy2O3-CoOz system at 885 °C in air, W. Wong-Ng, W. Laws, J.A. Kaduk, Solid State Sciences 88 (2019) 57–62

Phase equilibria and crystal chemistry of the CaO-½Gd2O3-CoOz system at 885 °C in air, W. Wong-Ng a, *, W. Laws a, S.H. Lapidus b, L. Ribaud b, J.A. Kaduk; Solid State Sciences 72 (2017) 47-54

Crystal chemistry and phase equilibria of the CaO-½Eu2O3-CoOz system at 885 °C, W. Wong-Ng, W. Laws, J.A. Kaduk, Solid State Sciences 58 (2016) 105-110

Experimental Determination of Phase Equilibria Diagrams in Ceramic Systems, R.S. Roth and T.A. Vanderah, in Solid State Ionics, The Science And Technology Of Ions In Motion, pp. 3-18, edited by B.V.R. Chowdari et al., World Scientific Publishing Co., 2004.

Major Accomplishments

SRD31 Logo

Version 5 of Standard Reference Database 31 introduces a custom JavaScript viewer for interactive display of the diagrams – the SRD31 software is now a self-contained application, no longer requiring the installation and use of Java.  As confirmed by customer feedback since the initial release in 2022, the new viewer simplifies and significantly enhances the user experience while preserving all previously available analytical capabilities.

The second release in this new series, Version 5.1, is now available to the public.  Together with the first release of Version 5.0 in 2022, the series-5 versions add 318 new entries with 1305 new phase diagrams, including phase information for 244 chemical systems not previously covered by the database.

The new content in Version 5.1 reflects the explosion of research on the fundamental properties of materials needed to enable the transition to energy technologies that do not depend on fossil fuels.  New chemical systems and diagrams in v.5.1 are dominated by results from studies to develop low-cost, highly abundant, chemically stable materials for energy applications and include:  complex salt systems for advanced nuclear reactors (fuels, coolants), concentrated solar power (heat-transfer/storage), batteries, and fuel-cells; mixed oxide/non-oxide systems for electrodes (batteries, fuel-cells, photovoltaics); chalcogenide systems for electronic-ionic conductors (batteries, sensors); and semiconductor systems for solar-photovoltaics.  New diagrams added here also reflect increased research on the recycling/recovery of critical metals including rare earths, Sc, and key transition metals, as well as an uptick in studies of systems for ultra-lightweight structural materials for aerospace applications.

Created October 24, 2008, Updated April 12, 2023