Judit G. Lisoni

Water incorporation in BaTiO3 films grown under hydrothermal conditions

The influence of temperature on water incorporation into barium titanate films grown hydrothermally was investigated. The films were prepared using titanium foils that were immersed in 0.5 M barium hydroxide aqueous solutions for 4 h. Working temperatures were 100, 150 and 215°C. The samples were characterized by X-ray diffraction, Auger electron spectroscopy, forward recoil spectrometry and thermal desorption spectrometry. The latter showed that water was incorporated mainly in the molecular form and that this was favored at lower temperatures, leading to a slightly larger unit cell as has been observed in hydrothermal powders. Films grown at lower temperatures exhibited stronger XRD reflections.

Ultrasound as a probe of dislocation density in aluminum

Abstract Dislocations are at the heart of the plastic behavior of crystalline materials yet it is notoriously difficult to perform quantitative, non-intrusive measurements of their single or collective properties. Dislocation density is a critical variable that determines dislocation mobility, strength and ductility. On the one hand, individual dislocations can be probed in detail with transmission electron microscopy. On the other hand, their collective properties must be simulated numerically. Here we show that ultrasound technology can be used to measure dislocation density. This development rests on theory—a generalization of the Granato–Lucke theory for the interaction of elastic waves with dislocations—and resonant ultrasound spectroscopy (RUS) measurements. The chosen material is aluminum, to which different dislocation contents were induced through annealing and cold-rolling processes. The dislocation densities obtained with RUS compare favorably with those inferred from X-ray diffraction, using the modified Williamson–Hall method.

Hydrothermal growth of BaTiO3 on TiO2 single crystals

Abstract The hydrothermal growth of polycrystalline BaTiO 3 deposits on the surface of TiO 2 rutile single crystals has been studied with respect to the following parameters: (a) small quantities of Sr (1.0 and 0.04 at.%) in the Ba(OH) 2 aqueous solution and (b) crystallographic surface of TiO 2 . For this purpose, the substrates were immersed in hydrothermal baths at temperatures between 100 and 200 °C for 4 h. It was found that the deposits grown with the high purity Ba(OH) 2 reagent (Sr∼0.04 at.%) exhibited grains with a pronounced crystal habit of octahedral shape with well-defined {1xa01xa01} faces. The grains grew at temperatures as low as 100 °C. The strontium rich Ba(OH) 2 solution (Sr∼1.0 at.%) led to grains of spherical shapes, which appeared only at temperatures of 150 °C and above. The use of single crystal substrates with different orientations strongly influences the growth of the BaTiO 3 layer: the same treatment to deposit BaTiO 3 on the (0xa00xa01) TiO 2 face did not produce BaTiO 3 on the (1xa01xa00) surfaces. This result can be interpreted in term of the stability of the single crystal surfaces and the related dissolution of TiO 2 . The samples were characterized by means of XRD, RBS, EDX, XPS, SEM (secondary and backscattered electrons), WDS, TEM and AFM.

Tetragonal BaTiO3 thin films hydrothermally grown on TiO2 single crystals

Abstract Tetragonal BaTiO 3 films were prepared on single crystal TiO 2 substrates by the hydrothermal method. The films were grown in 0.5 M Ba(OH) 2 aqueous solutions at 150°C and 200°C during 4 h. X-ray diffraction analysis demonstrated the presence of polycrystalline BaTiO 3 in its tetragonal phase, in contrast to hydrothermally grown BaTiO 3 on metallic substrates, which usually results in the cubic phase under similar conditions. Rutherford backscattering measurements in the channeling mode showed that the barium ions did not occupy lattice positions and that there is not a sharp film–substrate interface. The diffusion range of the moving species — either Ti or Ba — was about 1 μ m, and the diffusion coefficient at 150°C was estimated to be about 10 −16 m 2 s −1 .

Epitaxial BaTiO 3 Thin Films on Different Substrates for Optical Waveguide Applications

In the process of developing thin film electro-optical waveguides we investigated the influence of different substrates on the optical and structural properties of epitaxial BaTiO 3 thin films. These films are grown by on-axis pulsed laser deposition (PLD) on MgO(100), MgAl 2 O 4 (100), SrTiO 3 (100) and MgO buffered A1 2 O 3 (1 1 02) substrates. The waveguide losses and the refractive indices were measured with a prism coupling setup. The optical data are correlated to the results of Rutherford backscattering spectrometry/ion channeling (RBS/C). X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). BaTiO 3 films on MgO(100) substrates show planar waveguide losses of 3 dB/cm and ridge waveguide losses of 5 dB/cm at a wavelength of 633 nm.

Controlled Nucleation and Growth in the Hydrothermal-Electrochemical Formation of BaTiO3 Films

The influence of controlled potential conditions on the structure and phases of BaTiO 3 films grown on titanium by the hydrothermal-electrochemical method was studied. The experiments were conducted using a three electrode high pressure electrochemical cell in a 0.2 M Ba(OH) 2 electrolyte at 150 °C. The spontaneous initial nucleation linked to pure hydrothermal BaTiO 3 formation was inhibited by cathodically protecting the titanium electrode since its immersion in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. The growth of tetragonal BaTiO 3 was achieved combining the initial inhibition of the pure hydrothermal growth, followed by nucleation under controlled potentiostatic conditions.