Comparative study of the disordered crystals with phase transitions, the dielectric glasses and the ferroelectric ceramics

Informazioni relative al progetto

ID dell’accordo di sovvenzione: INTAS-93-3230

Progetto chiuso

Data di avvio 1 Settembre 1994

Data di completamento 31 Dicembre 1995

Finanziato da

• International Association for the promotion of cooperation with scientists from the independent states of the former Soviet Union (INTAS), 1993-

Costo totale

Nessun dato

Contributo UE

€ 36 000,00

Coordinato da

Universidad Autónoma de Madrid
Spain

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Risultati sfruttabili

Comparative study of the disorder crystals with phase transitions, the dielectric glasses and the ferroelectric ceramics

The crystals with structural phase transitions, especially those with incommensurate (I) phases, exhibit glass-like behaviour at very low levels of disorder. The physical background of this behaviour is understood in general but a detailed study with a (semi)quantitative interpretation of the experimental data is lacking. The project will study the slow relaxation processes and the memory effects by means of X-ray and dielectric measurements in several I ferroelectrics (Rb2ZnCl4, TMAZnCl4, Sc(NH2)2, Ag2AsS3, and Sn2P2(SexS1-x)6) both in the I and in the ferroelectric phase and, for some crystals, influence of illumination on these phenomena. The existing theory of properties of disordered crystals with phase transitions will be amended taking into account the specific features of the systems in question. There will be performed low-temperature experiments on ferroelectric LiNbO3 with various concentrations of the oxygen vacancies to trace the appearance of the glass properties at high enough concentration of the vacancies. The properties probed are the heat conductivity and the dielectric constant. An experimental study of a dielectric glass, B2O3, will be performed by means of the specific heat, thermal conductivity and Brillouin scattering measurements in order to dispose of sets of the data, each for the same sample, to be able to reveal the possibilities of the soft potential model, which will explain properties of glasses in a wide temperature region. As this model resembles that of the disordered solid with phase transition it is expected that a joint discussion of the properties of the two classes of systems will be enlightening and will facilitate the understanding of the properties of ferroelectric ceramics, whose relaxation properties (for the specific case of PZT) will be studied with an emphasis to the low temperature region.