Paula M. Vilarinho

Performances presented by zinc oxide thin films deposited by spray pyrolysis

Abstract The effect of doping and annealing atmosphere on the performances of zinc oxide thin films prepared by spray pyrolysis have been studied. The results show that the way doping influences the electrical and structural properties depends also on the characteristics of the doping element. Annealing the as-deposited films in an inert atmosphere leads to a substantial reduction in the resistivity of the films deposited and to an increase on the degree of film’s crystallinity.

Dependence of the Structural and Dielectric Properties of Ba1-xSrxTiO3 Ceramic Solid Solutions on Raw Material Processing

Abstract The structures and dielectric properties of Ba1-xSrxTiO3 ceramic solid solutions in the whole x range and their dependence on the material processing are investigated. A short time pre-calcination milling–mixing of the precursor powders causes compositional inhomogeneity and thus a diffuse phase transition. For long milling–mixing time, the diffuse phase transition is observed only in the SrTiO3 rich compositions (x>0·8).

Thickness effect on the dielectric, ferroelectric, and piezoelectric properties of ferroelectric lead zirconate titanate thin films

Lead zirconate titanate (PbZr0.52Ti0.48O3−PZT) thin films with different thicknesses were deposited on Pt(111)/Ti/SiO2/Si substrates by a sol-gel method. Single perovskite phase with (111)-texture was obtained in the thinnest films, whereas with the increase in thickness the films changed to a highly (100)-oriented state. An increase in the mean grain size as the film thickness increased was also observed. Dielectric, ferroelectric, and piezoelectric properties were analyzed as a function of the film thickness and explained based on film orientation, grain size, domain structure, domain wall motion, and nonswitching interface layers. Both serial and parallel capacitor models were used to analyze the influence of the nonswitching interface layer in the dielectric properties and the effect of substrate clamping in the microscopic piezoelectric response as the film thickness decreased. The scanning force microscopy technique was used to study the effect of thickness on the microscopic piezoresponse. Signific...

Domain populations in lead zirconate titanate thin films of different compositions via piezoresponse force microscopy

Pb (ZrxTi1−x)O3 (PZT) thin films with (111) texture were deposited onto commercially available Pt/Ti/SiO2/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then used to analyse the evolution of domain populations as a function of the Zr content x. Domain structures of virgin films, local piezoelectric properties of individual grains and piezoelectric histograms were studied in films with different compositions (x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In films with low Zr content mainly single-domain grains were observed. As the Zr content increased, a larger fraction of polydomain grains was found. The local piezoelectric response measured inside sufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70 (x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieved due to the (111) texture and influence of the dielectric constant. In tetragonal films with their lower dielectric constants the electric field seen by a ferroelectric is higher as compared to other compositions, giving rise to an apparent increase of the effective piezoelectric response measured by PFM. The analysis of the domain images indicated that sol–gel derived PZT films are slightly self-polarized near the free surface. With increasing Zr/Ti ratio, the variation of domain populations resulted in reversing the sign of the average piezoelectric response at x≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition and can be used as a signature of complex domain structures in ferroelectric thin films.

Dielectric properties of Ba(Ti1−yYy)O3 ceramics

Temperature and frequency dependence of the real (e′) and imaginary (e″) parts of the dielectric permittivity of Ba(Ti1−yYy)O3 (0.028⩽y⩽0.258) ceramic samples were studied in the temperature range 12–500 K at 102, 103, and 104, and 105 Hz. The permittivity peaks are rounded and frequency dispersive when y>0.028. The maximum of the rounded peak (em′) decreases with an increase in the yttrium concentration. The temperature corresponding to the permittivity maximum is linearly shifted to lower temperatures at a rate of 29 K per molar percent of yttrium when y⩽0.122, but it remains constant when y⩾0.122. The solid solubility limit of 0.122 is confirmed. Typical relaxor behavior was observed and characterized with empirical parameters in Ba(Ti1−yYy)O3 solid solutions.

INFLUENCE OF THE DOPING AND ANNEALING ATMOSPHERE ON ZINC OXIDE THIN FILMS DEPOSITED BY SPRAY PYROLYSIS

Abstract Undoped and doped (indium and aluminium) zinc oxide (ZnO) thin films have been prepared by spray pyrolysis, and the effect of the doping and annealing atmosphere on the electrical, optical and structural properties of the produced films has been investigated. The deposited films have a high resistivity. Annealing the films in an argon atmosphere or under vacuum leads to a substantial reduction of the electrical resistivity of the films and to an increase on the degree of cristallinity of the deposited material. The most pronounced changes were observed in the films annealed in Argon. The results also indicate that doping highly influences the electrical and structural properties of the films, which is more pronounced in the films doped with Indium.

Analysis of the composition-induced transition from relaxor to ferroelectric state in PbFe2/3W1/3O3–PbTiO3 solid solutions

The low-field dielectric response of the relaxor-ferroelectric (1−x)PbFe2/3W1/3O3–xPbTiO3 ceramics with various x, was investigated. The permittivity data were analyzed with empirical laws that describe the diffuse phase transitions in relaxors. A change of the character of the phase transition was found with increasing x, from a total diffuse, characteristic of relaxors, to a sharp one, typical of ferroelectrics. The deviations from the Curie–Weiss law of the dielectric constant data in the paraelectric phase were used to calculate a local order parameter within a modified-Landau theory for relaxors. The nonzero values of the local order parameter far above the Curie region indicate the thermal stability of the polar nanoregions in the relaxor state. The temperature dependence of the local order parameter clearly shows the evolution of the system from a short range ordered to a long range ordered ferroelectric, with increasing the PbTiO3 addition.The low-field dielectric response of the relaxor-ferroelectric (1−x)PbFe2/3W1/3O3–xPbTiO3 ceramics with various x, was investigated. The permittivity data were analyzed with empirical laws that describe the diffuse phase transitions in relaxors. A change of the character of the phase transition was found with increasing x, from a total diffuse, characteristic of relaxors, to a sharp one, typical of ferroelectrics. The deviations from the Curie–Weiss law of the dielectric constant data in the paraelectric phase were used to calculate a local order parameter within a modified-Landau theory for relaxors. The nonzero values of the local order parameter far above the Curie region indicate the thermal stability of the polar nanoregions in the relaxor state. The temperature dependence of the local order parameter clearly shows the evolution of the system from a short range ordered to a long range ordered ferroelectric, with increasing the PbTiO3 addition.

Dielectric properties of bismuth doped Ba1-xSrxTiO3 ceramics

Abstract The dielectric properties of bismuth (5 at.%) doped Ba 1− x Sr x TiO 3 ( x =0, 0.2, 0.4, 0.6 and 0.8) ceramics are investigated. Bi doping significantly decreases the dielectric permittivity maximum of ferroelectric–paraelectric phase transition of Ba 1− x Sr x TiO 3 solid solutions and shifts the ferroelectric–paraelectric phase transition temperature to lower temperatures for the x =0, 0.2, 0.4 and 0.6 compositions but to higher temperature for the x =0.8 composition. Bi doped BaTiO 3 still exhibits normal ferroelectric characteristic while a relaxor behavior was observed in Bi doped Ba 1− x Sr x TiO 3 and the degree of the diffuseness and the relaxation increases as x increases. A random electric field is suggested to be responsible for the relaxor behavior observations.

Dielectric properties of Bi doped SrTiO3 ceramics in the temperature range 500–800 K

The (Sr1−1.5xBix)TiO3 (0.0133⩽x⩽0.133) ceramic system reveals several sets of dielectric permittivity peaks in different temperature ranges. Dielectric permittivity and dielectric loss peaks were detected in the temperature range 500–800 K and in the present article the dielectric polarization behavior is presented and discussed. The activation energy of the dielectric relaxation is in the range of 0.99–1.12 eV. It is suggested that the permittivity peaks are related to the movement of oxygen ions or oxygen vacancies.

Polar behavior in Mn-doped SrTiO3 ceramics

Polar behavior was found in Sr1−xMnxTiO3(x=0.005–0.02) ceramic system. Radio-frequency dielectric measurements showed a diffuse maximum at 25–65 K shifting to higher temperatures with increasing measurement frequency and amount of Mn. The observation of hysteretic behavior in the P versus E curves shows the existence of a polar state at low temperatures. The hysteresis response slowly degenerates into just nonlinearity as the temperature increases. The observed relaxor-type dielectric behavior is attributed to the formation of electric dipoles and corresponding random fields due to the off-center position of Mn2+ ion at the Sr site of highly polarizable SrTiO3 lattice.