Databases of crystals with structural phase transitions

Václav Janovec¹, Pawel E. Tomaszewski², Milan Čmelík¹, Lubor Machonský¹,

Zdeněk Kluiber³

¹Technical University of Liberec,  Hálkova 6, 461 17 Liberec

²Institute of Low Temperature and Structural Research, PAN, 50-950 Wroclav, Poland

³University of Hradec Králové, Faculty of Education, Rokitanského 62, 500 03 Hradec Králové

janovec@fzu.cz

Crystals with structural phase transitions (SPT´s) exhibit unusual physical properties that are utilized in many technical applications (e.g. anisotropic ceramics, memories, sensors, transducers) and in other fields (e.g. earth sciences). Though basic structural data on SPT´s can be found in existing structural databases (ICSD, CSD) special features and advanced theoretical background of SPT´s call for a specialized database.

The most comprehensive listing of non-metallic crystals with SPT´s is available in Tomaszewski´s database of structural phase transitions [1,2]. This is a printed table in which each row (record) is related to one chemical formula of a crystal and columns (fields) give transition temperatures as well as the main available structural data of corresponding phases in between two neighbouring transitions. In updated version [2] about 4 300 crystals are recorded with more than 6 300 phase transitions and about 10 000 crystal phases observed at normal pressure. This presentation provides useful information about the appearance of SPT´s in crystals but does not allow an efficient search.

This drawback can be partially removed if the records are arranged according to the symmetry changes at the SPT. Such tables have been created from the updated Tomaszewski´s database [2]. In the first step only crystals which exhibit just a single SPT associated with a dissymetrization (reduction of the space group symmetry) have been included. To increase the reliability of data only those SPT´s have been taken into account for which structures of both phases are commensurate and are recorded in the Inorganic Crystal Structure Database (ICSD). These restrictions drastically reduce the number of considered crystals (only 20% of crystal phases that appear in [2] have a structure solved and recorded in ICSD!). A table formed from these selected data constitutes a simple Ferroic Phase Transition Database which can provide answers to useful simple queries and from which some statistical conclusions can already be deduced [3].

Present effort concentrates on creation of computerized relational databases of SPT´s. This approach makes use of recent advances in database techniques and can utilize the extensive theoretical knowledge on SPT´s (see, e.g. [4]).

1. P. Tomaszewski, Structural phase transitions in crystals. I. Database. II. Statistical analysis. Phase Transitions, 38, (1992), 127.

2. P. Tomaszewski, Golden Book of Phase Transitions, Phase transitions database PTDB, manuscript, 2002.

3. V. Janovec, P. Tomaszewski, L. Richterová, Z. Kluiber, Inverse database of phase transitions in crystals with a single phase transition. Ferroelectrics, 301, (2004), 169.

4. International Tables for Crystallography, vol. D, edited by A. Authier (Dordrecht: Kluwer Academic Publishers), 2003, Part 3: Structural phase transitions.

Acknowledgement
This work has been partially supported by the grant 202/07/1289 of the Grant Agency of the Czech Republic.