Experimental and theoretical investigations on phase transitions in new ceramic oxides

Informations projet

N° de convention de subvention: INTAS-93-1707

Projet clôturé

Date de début 1 Juin 1995

Date de fin 31 Mai 1996

Financé au titre de

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

Coût total

Aucune donnée

Contribution de l’UE

€ 50 000,00

Coordonné par

Università degli Studi di Cagliari
Italy

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Résultats exploitables

Experimental and theoretical investigations on phase transitions in new ceramic oxides

This research project centres mainly on the general theme of structural, electronic and magnetic phase transitions in the new superconducting oxides of Y-Ba-Cu-O systems (123 systems). Results: -It is settled up the topotactic-like technology for the low-temperature processing of the oxygen-equalized and order-stabilized pair samples of YBCO (k-pairs) where the key variable is the oxygen ordering in the Cu(1)Ox chain. The structural, electronic, optical and NMR properties of k-pairs, have been investigated in a comparative way. The k-pair technology can be extended principally to the field of off-stoichiometry oxides where the physical properties being crucially dependent on the oxygen content are difficult to investigate in a comparative way using the conventional single-sample strategy. -The synthesis of 12zCu3O7-x samples and the investigation of the barium nonstoichiometry by structural analysis, measurements of resistivity and diamagnetic properties, the reflectivity spectra in them, have proved the idea of a superstructure generation and the formation of two-three and four-fold coordinated Cu(1) atoms with O(1) and O(4) oxygen positions. - The phase-transition-induced reconstruction of the vibrational spectra in 123 systems is investigated theoretically in the transferable shell model. The new infrared Raman optically active phonon modes are predicted. The low-frequency dielectric dispersion in the highordered phases is calculated. The Raman and infrared reflectivity experiments in k-pairs ceramic samples are performed and the influence of oxygen content and ordering on the fhonon spactra are studied.The evidences of 0II and 0III superstructures in k-pairs are established. We believe that this results open a new prospects for the superstructure characterization and for the monitoring of the oxigen ation-deoxi ge nation kinetics in YBCO. -The results are reported in 16 scientific publications and at 19 international conferences.