R. G. Mendes

Influence of neodymium and lanthanum doping in the pyroelectric properties of strontium barium niobate (SBN) thin films

Abstract Strontium barium niobate thin films (SBN) are ferroelectric materials that can exhibit excellent pyroelectric and electro-optic properties. These properties make the SBN a very interesting material for a large variety of applications that include pyroelectric sensors. SBN thin films with a nominal composition (Sr 0.75 Ba 0.25 )Nb 2 O 6 , known as SBN75/25, doped with lanthanum or neodymium (1.0, 1.5 and 2.0 mol%) were obtained by a chemical method, in order to investigate the influence of the doping on their pyroelectric responsivity. The pyroelectric response was obtained through voltage measurements in the films, caused by the incidence of a square laser pulse applied with a different repetition rate. Structural and dielectric characterizations revealed a single polycrystalline SBN phase and a decrease of the dielectric permittivity due to the doping. The experimental results show that the additions of the dopant elements increase the pyroelectric response of the films and decrease the frequency dependence of the pyroelectric voltage responsivity R V , compared with the undoped one.

Dielectric Properties of Sr 0.75 Ba 0.25 Nb 2 O 6 Thin Films: Bias Field‚ Frequency and Temperature Dependence

Ferroelectric strontium barium niobate solid solutions had received great attention due to their excellent pyroelectric, electrooptic and photorefractive properties. Furthermore, they usually also present very interesting phase transition characteristics. In this work, polycrystalline single phase Sr 0.75 Ba 0.25 Nb 2 O 6 thin films were prepared by a hybrid chemical method and deposited on Pt/Ti/SiO 2 /Si substrates. The temperature dependence of dielectric constant was measured at different frequencies and bias field levels. The presence of two dielectric dispersion regions with relaxor characteristics was observed at distinct temperature ranges, corresponding to the ferro-paraelectric and to a structural phase transition at low temperatures, respectively. A specific dielectric dispersion region, associated with an incommensurate superstructure frequently observed in bulk samples, was not observed in this films probably due to their small grain sizes.

Investigation of nonlinear dielectric properties in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The ac and dc driving fields dependence of the dielectric permittivity for the strontium barium niobate relaxor ferroelectric thin films has been investigated. The nonlinear dielectric properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the ac and dc “bias” electric field amplitude in wide frequency 100 Hz‐10 MHz and temperature 50‐450 K intervals. The results hint the existence of a true mesoscopic dielectric relaxor response in the ferroelectric thin film, which is very similar to those observed in bulk relaxor ferroelectrics. An anomalous behavior of the NL dielectric response was observed when submitted to moderate dc electric fields levels, indicating a crossover from paraelectric to a glasslike behavior on cooling the sample toward the freezing transition. The obtained results were analyzed within the framework of the models proposed in the current literature.

Influence of the crystallization thermal treatment on the structural and electrical properties of PZT thin films

Different methods have been proposed in the literature to deposit PZT thin films. Among these, chemical based processes have been revealed as a promising preparation route due to their low cost processing and the facility for controlling the stoichiometry of complex systems. The objective of this work was to investigate the influence of the time and temperature of crystallization on the physical properties of the Pb(Zr0.53Ti0.47)O3 thin films prepared by a hybrid method. The structural and microstructural dependence on the crystallization conditions of the PZT films were investigated by X-ray diffraction and atomic force microscopy. Dielectric and ferroelectric properties were also characterized and their behaviors were related to the structural evolution of films.

Influence of Domain Switching and Domain Wall Bending on the Electrical Permittivity of PZT Thin Films

The electrical permittivity dependence on the electric bias field was investigated in Pb(Zr0.53, Ti0.47)O3 films. The results revealed the existence of two mechanisms contributing to the permittivity. The first one was related to the domain switching, which was responsible for a strong nonlinear dielectric response. The second mechanism was associated with the non-180° domain wall vibrations, which presented a reasonable linear electrical behavior with the applied field, contributing always to the permittivity independently of the poling state of the sample. The reduction of the electrical permittivity with increasing the bias field was related to the bending of non-180° domain walls.

Influence of heat treatment on crystallization of strontium barium niobate (SBN) ferroelectric thin films

Strontium barium niobate (SBN) thin films of good quality were deposited on Si and Pt/Si substrates using a polymeric resin containing metallic ions. Using x-ray diffraction, the presence of SBN phase for films annealed at 600 °C and 700 °C for 1 hour was identified on both substrates. Films were also crystallized by rapid thermal annealing (RTA) at different temperatures and for different times, presenting good crystallization. Undesired phases such as SrNb2O6 and BaNb2O6 appear in films deposited on Si and Pt/Si substrates for films crystallized using a conventional furnace. However, using RTA these phases were eliminated for films annealed at 700 °C for 60 and 120 seconds.

Mesoscopic structure evidenced by AC dielectric nonlinearities in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The AC electric field and temperature dependences of the dielectric permittivity for strontium barium niobate (Sr0.75Ba0.25Nb2O6) relaxor ferroelectric thin films have been investigated. The results indicate the existence of a true mesoscopic structure evidenced by the nonlinear dielectric response of these films, which is similar to those observed for bulk relaxor ferroelectrics. A tendency for a temperature dependent crossover from a linear to a quadratic behaviour of the dielectric nonlinearity was observed, indicating an evolution from paraelectric to glass-like behaviour on cooling the samples towards the freezing temperature transition.

Structural, Dielectric and Ferroelectric Properties of Mixed Texture PbZr0.20Ti0.80O3 Thin Films Prepared by a Chemical Method

Titanium-rich lead zirconate titanate compositions are very attractive for pyroelectric applications. Crystalline texture can result in significant thin film properties optimization. In contrast, preparation of textured films requires specific processing parameters. In this work, PbZr0.20Ti0.80O3-PZT20/80 thin films with a mixed (001)(100)/(111) texture on Pt(111)/Ti/SiO2/Si substrates were obtained through a chemical method by optimizing thermal treatment conditions. Pole figure exhibited a 6.5% texture for the (100) crystalline plane. Dielectric constant and dissipation values for textured PZT films at 100 kHz were 159 and 0.04, respectively. Remanent polarization and coercive field were 13 μC/cm2 and 119 kV/cm, respectively.

Non-linear dielectric response in the Sr(1-x)Ba(x)Nb2O6 relaxor ferroelectric thin film

In this work, the non-linear (NL) dielectric properties of the Sr 0.75 Ba 0.25 Nb 2 O 6 (SBN) ferroelectric thin film prepared by the chemical method were investigated. The NL dielectric properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the DC bias and the AC driving fields in a wide frequency (100 Hz–10 MHz) and temperature (150 K–350 K) range. An anomalous behavior of the non-linear dielectric response was observed when submitted to high electric fields levels. The obtained results were analyzed concerning one of the models for the dielectric response of relaxors ferroelectrics materials currently discussed in the literature.