Dsl Pontes

Influence of Ca concentration on the electric, morphological, and structural properties of (Pb,Ca)TiO3 thin films

Pb1−xCaxTiO3 (0.10⩽x⩽0.40) thin films on Pt/Ti/SiO2/Si(100) substrates were prepared by the soft solution process and their characteristics were investigated as a function of the calcium content (x). The structural modifications in the films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate a decrease in lattice tetragonality with the increasing content of calcium in these films. Raman spectra exhibited characteristic features of pure PbTiO3 thin films. Variations in the phonon mode wave numbers, especially those of lower wave numbers, of Pb1−xCaxTiO3 thin films as a function of the composition corroborate the decrease in tetragonality caused by the calcium doping. As the Ca content (x) increases from 0.10 to 0.40, the dielectric constant at room temperature abnormally increased at 1 kHz from 148 to 430. Also calcium substitution decreased the remanent polarization and coercive field from 28.0 to 5.3 μC/cm2 and 124 to 58 kV/c...

Ferroelectric and optical properties of Ba0.8Sr0.2TiO3 thin film

Barium strontium titanate (Ba0.8Sr0.2TiO3) thin films have been prepared on Pt/Ti/SiO2/Si substrates using a soft solution processing. X-ray diffraction and also micro-Raman spectroscopy showed that the Ba0.8Sr0.2TiO3 thin films exhibited a tetragonal structure at room temperature. The presence of Raman active modes was clearly shown at the 299 and 725 cm−1 peaks. The tetragonal-to-cubic phase transition in the Ba0.8Sr0.2TiO3 thin films is broadened, and suppressed at about 35 °C, with a maximum dielectric constant of 948 (100 kHz). Electrical measurements for the prepared Ba0.8Sr0.2TiO3 thin films showed a remnant polarization (Pr) of 6.5 μC/cm2, a coercive field (Ec) of 41 kV/cm, and good insulating properties. The dispersion of the refractive index is interpreted in terms of a single electronic oscillator at 6.97 eV. The direct band gap energy (Eg) and the refractive index (n) are estimated to be 3.3 eV and n = 2.27–2.10, respectively.

Electrical conduction mechanism and phase transition studies using dielectric properties and Raman spectroscopy in ferroelectric Pb0.76Ca0.24TiO3 thin films

We have studied the phase transition behavior of Pb0.76Ca0.24TiO3 thin films using Raman scattering and dielectric measurement techniques. We also have studied the leakage current conduction mechanism as a function of temperature for these thin films on platinized silicon substrates. A Pb0.76Ca0.24TiO3 thin film was prepared using a soft chemical process, called the polymeric precursor method. The results showed that the dependence of the dielectric constant upon the frequency does not reveal any relaxor behavior. However, a diffuse character-type phase transition was observed upon transformation from a cubic paraelectric phase to a tetragonal ferroelectric phase. The temperature dependency of Raman scattering spectra was investigated through the ferroelectric phase transition. The soft mode showed a marked dependence on temperature and its disappearance at about 598 K. On the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature, although all optical modes should be R...

Microstructural, dielectric and ferroelectric properties of calcium-modified lead titanate thin films derived by chemical processes

Abstract Ferroelectric Pb 1− x Ca x TiO 3 ( x =0.24) thin films were formed on a Pt/Ti/SiO 2 /Si substrate by the polymeric precursor method using the dip-coating technique for their deposition. Characterization of the films by X-ray diffraction showed a perovskite single phase with a tetragonal structure after annealing at 700°C. Atomic force microscopy (AFM) analyses showed that the film had a smooth and crack-free surface with low surface roughness. In addition, the PCT thin film had a granular structure with an 80 nm grain size. The thickness of the films observed by the scanning electron microscopy (SEM) is 550 nm and there is a good adhesion between the film and substrate. For the electrical measurements metal-ferroelectric-metal of the type capacitors were obtained, where the thin films showed good dielectric and ferroelectric properties. The dielectric constant and dissipation factor at 1 kHz and measured at room temperature were found to be 457 and 0.03, respectively. The remanent polarization and coercive field for the deposited films were P r =17 μC/cm 2 and E c =75 kV/cm, respectively. Moreover, the 550-nm-thick film showed a current density in the order of 10 −8 A/cm 2 at the applied voltage of 2 V. The high values of the thin films dielectric properties are attributed to its excellent microstructural quality and the chemical homogeneity obtained by the polymeric precursor method.

Synthesis, ferroelectric and optical properties of (Pb,Ca)TiO3 thin films by soft solution processing

Calcium modified lead titanate sol was synthesized using a soft solution processing, the so-called polymeric precursor method. In soft chemistry method, soluble precursors such as lead acetate trihydrate, calcium carbonate and titanium isopropoxide, as starting materials, were mixed in aqueous solution. Pb0.7Ca0.3TiO3 thin films were deposited on platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure, dielectric and optical properties of the thin films were investigated. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 299 and 0.065, respectively, for a thin film with 230 nm thickness annealed at 600°C for 2 h. The remanent polarization (2Pr) and coercive field (Ec) were 32 μC/cm2 and 100 kV/cm, respectively. Transmission spectra were recorded and from them, refractive index, extinction coefficient, and band gap energy were calculated. Thin films exhibited good optical transmissivity, and had optical direct transitions. The present study confirms the validity of the DiDomenico model for the interband transition, with a single electronic oscillator at 6.858 eV. The optical dispersion behavior of PCT thin film was found to fit well the Sellmeir dispersion equation. The band gap energy of the thin film, annealed at 600°C, was 3.56 eV. The results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of PCT thin films.

Preparation and properties of ferroelectric Pb1 − xCaxTiO3 thin films produced by the polymeric precursor method

Pb1 − xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1 − xCaxTO3 thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10−7 A/cm2 in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 μC/cm2 and 150 kV/cm, respectively.

Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb, Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Thin films of A-site co-substituted, PbTiO3 (PTO) by Ba2+ and Ca2+, i.e., PBCT70, PBCT60, PBCT50 and PBCT40 were fabricated on Pt/Ti/SiO2/Si substrates by chemical solution deposition. Structures of the samples were investigated from the viewpoint of local-, medium- and long-range order by X-ray absorption near structure (XANES), micro-Raman and infrared spectroscopies and by X-ray diffraction (XRD). The films thickness were determined by using field-emission scanning electron microscope. The experimental results demonstrate that BaO12 clusters are the critical dominant ferroelectricity cause in PBCT thin films rather than CaO12 clusters. XRD analysis which was applied to investigate the crystal symmetry indicates the absence of long-range structural distortion for samples at higher concentrations of Ba2+ and Ca2+. However, an analysis of structural medium- and local-range order such as infrared, micro-Raman and XANES spectroscopies revealed that symmetry changes are much more prominent; i.e., local structural distortions remain. Temperature-dependent dielectric permittivity measurements confirmed a decreasing ferroelectric-to-paraelectric phase transition temperature and showed a broad phase transition with an increase in BaO12 and CaO12 clusters. In addition, the lack of long-range polar ordering for the ferroelectric dipole caused by symmetry changes decreases the remanent polarization.

Study of phase transition in (Pb,Ba)TiO3 thin films

Dielectric and Raman scattering experiments were performed on polycrystalline Pb1−xBaxTiO3 thin films (x=0.40 and 0.60) as a function of temperature. The dielectric study on single phase compositions revealed that a diffuse-type phase transition occurred upon transformation of the cubic paraelectric to the tetragonal ferroelectric phase in all thin films, which showed a broadening of the dielectric peak. Diffusivity was found to increase with increasing barium contents in the composition range under study. In addition, the temperature dependence of Raman scattering spectra was investigated through the ferroelectric phase transition. The temperature dependence of the phonon frequencies was used to characterize the phase transitions. Raman modes persisted above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by chemical disorder. The lack of a well-defined transitio...