P. Marchet

New heavy metal oxide glasses: investigations within the TeO2–Nb2O5–Bi2O3 system

The TeO2–Nb2O5–Bi2O3 system was investigated by differential scanning calorimetry and temperature programmed X-ray diffraction. A large glass-forming domain was evidenced and the complex structural evolution with temperature of these glasses was followed. The glass transition and crystallisation temperatures and the nature of crystalline phases formed were determined. Moreover, this study confirmed the existence of the metastable γ-TeO2 polymorph and of a new crystalline compound, BiNbTe2O8.

In situ growth of YBaCuO superconducting thin films by excimer laser ablation: influence of deposition and cooling parameters

In situ YBaCuO thin films are deposited on MgO single-crystal by pulsed laser ablation using an excimer laser (KrF, 248 nm). Deposition and cooling conditions are investigated in order to obtain c-oriented samples. The influence of substrate temperature and oxygen pressure during both deposition and post-deposition processes on the structural (orientation, lattice parameters) and electrical (resistivity at 300 K, critical temperature, transition width) film properties is analyzed. These studies lead to reproducible high quality c-oriented thin films which exhibit a critical temperature of 90 K, a superconducting transition width less than 1 K and a good behavior in the normal state.

Characterization of the KrF laser-induced plasma plume created above a BiSrCaCuO target

The laser‐induced plasma plume created above a BiSrCaCuO superconducting target by a KrF laser beam (248 nm) is investigated by time‐resolved spectroscopy. The influence of the oxygen partial pressure on the ejection velocities of the ablated species and on the relaxation of atomic and molecular excited species is particularly studied.

Characterization of the KrF laser-induced plasma plume created above an YBaCuO superconducting target and preparation of superconducting thin films

Abstract The laser-induced plasma plume created above an YBaCuO superconducting target irradiated by a KrF laser beam (248 nm) is investigated by time-resolved spectroscopy. High-resolution spectra are obtained and ejection velocities of ablated species are deduced as a function of the ambient oxygen pressure. Preliminary results on the preparation of YBa2Cu3O7−x thin films on 〈100〉 SrTiO3 substrates, by the excimer laser ablation of a stoichiometric 1 : 2 : 3 target, are presented.

Unexpected behaviour of IR reflectivity of a YBa2Cu3O7-δ oriented film

a-b plant oriented YBa2Cu307 ,7 films have been obtained by laser ablation. Electrical and structural characterization is presented as well as temperature dependent (4 K up to room temperature) optical reflectance spectra recorded between 50 cm-1 and 22 000 cm-1. Extra absorptions at low frequencies and low temperatures are analysed and their connection with a possible superconducting gap is discussed. It is emphasized that the overall conducting behaviour in the normal state is well described by a single Drude-like modified term.

Glass formation study in the Bi2O3-TeO2-WO3 system

Summary Glass formation regions in the Bi 2 O 3 -TeO 2 -WO 3 system have been determined at 650 °C, 700 °C and 800 °C. Physical characteristics of some vitreous samples have been measured.

Epitaxial ferroelectric PZT and BST thin films by pulsed UV laser deposition

Abstract Ferroelectric PbZr0.52Ti0.48O3 (PZT) and Ba0.65Sr0.35TiO3 (BST) thin films are prepared by laser ablation of sintered ceramic targets. The influence of the substrate temperature during deposition on the composition and the crystallographic structure is investigated for different substrates, in order to achieve an oriented or epitaxial growth.

Analysis of infrared-visible-near-ultraviolet reflectivity of conducting and superconducting oxides

Abstract We analyse infrared-visible-near-ultraviolet spectra of oxide materials in the semiconducting or metallic phase. We show that the response of laser-ablated YBa 2 Cu 3 O 7 film can be fitted by a modified Drude term without mid-infrared absorptions. Mid-infrared and visible absorptions are discussed for textured YBaCuO, BaBiO 3 and Pr 2 NiO 4+δ as well as indication of their polaronic origin.

Pulsed laser deposition of YBa2Cu3O7−x superconducting thin films: correlation between preparation conditions and structural and electrical properties

Abstract YBa 2 Cu 3 O 7−x thin films were obtained on MgO single crystals using pulsed laser deposition with a KrF excimer laser (248 nm) operated at 10 Hz with a laser fluence of 3 J/cm 2 . Substrate temperature was monitored at 790°C with an halogen lamp and oxygen pressure was maintained at 0.3 mbar. Structural parameters were systematically investigated by X-ray diffraction. Electrical properties were characterized using a dc four probes method (25 to 300 K). In order to understand parameters which may lead to epitaxial thin films with high superconducting properties (i.e. transition temperature as high as 90 K, low transition width and critical current density of about 10 5 to 10 6 A/cm 2 ), the role of cooling process was studied for purely c-axis oriented films using different cooling gases (oxygen or argon) and different cooling pressures. The effects of cooling process were checked by systematic study of cell parameters, rocking curves, critical temperature and transition width. Optimum cooling pressure led to thin films with a transition width of about 0.5 K and critical current density of about 10 6 A/cm 2 at 80 K.

The Bi2WO6-TeO2 pseudo binary system

Summary The phase diagram of the Bi 2 WO 6 -TeO 2 pseudo-binary system has been established from 60 to 100 TeO 2 mol %, using DSC and XRD experiments. Three fixed temperature events were found: one eutectic and two peritectics. The new compounds Bi 2 Te 2 WO 10 and Bi 2 Te 5 WO 16 were identified and characterized by X-ray diffraction.