Effects of powder preparation and sintering procedure on microstructure and dielectric properties of PLZT ceramics

PLZT ceramics belong to one of the very important groups of functional materials that make a basis for the production of a large range of electronic devices. The microstructure and properties of ceramics depend on the powder preparation and thermal processing conditions. Various techniques have been used to obtain chemically homogeneous and fine starting powders. PLZT powders have been prepared by two different production routes: by a modified Pechini method, using a polymeric precursor method (PMM) and by a partial oxalate method. A two-step sintering process, including a hot pressing, was carried out at 1100 and 1200degreesC Distinct phases obtained during the sintering process have been investigated by SEM and EDS techniques and dielectric properties such as permittivity and dielectric loss were measured in a frequency range from 1 to 20 kHz.. A significant difference in microstructure and dielectric properties, depending on powder origin and sintering procedure, has been noticed.

Effects of the postannealing atmosphere on the dielectric properties of (Ba, Sr)TiO3 capacitors: Evidence of an interfacial space charge layer

The dielectric properties of (Ba, Sr)TiO3 films were found to be remarkably sensitive to the postannealing treatment atmosphere. This study demonstrates that postannealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that postannealing in a nitrogen atmosphere produces a slight dielectric relaxation. Such dependence of the dielectric relaxation was related both to oxygen vacancies and to the presence of negatively charged oxygen, trapped at the grain boundary and/or at the electrode/dielectric film interface. (C) 2000 American Institute of Physics. [S0003-6951(00)00817-2].

Microstructure and dielectric properties of (Ba,Sr)TiO3 thin film produced by the polymeric precursor method

BaxSr1-xTiO3 (x = 0.6) (BST) thin films were successfully prepared on a Pt(111)/TiO2/SiO2/Si(100) substrate by spin coating, using the polymeric precursor method. BST films with a perovskite single phase were obtained after heat treatment at 700 degrees C. The multilayer BST thin films had a granular structure will a grain size of approximately 60 nm. A 480-nm-thick film was obtained by carrying out five cycles of the spin-coating/heating process. Scanning electron microscopy and atomic force microscopy analyses showed that the thin films had a smooth, dense, crack-free surface with low surface roughness (3.6 nm). At room temperature and at a frequency of 100 kHz, the dielectric constant and the dissipation factor were, respectively, 748 and 0.042. The high dielectric constant value was due to the high microstructural quality and chemical homogeneity of the thin films obtained by the polymeric precursor method.

Size effect on structure and dielectric properties of Nb-doped barium titanate

It is known that the dielectric properties of BaTiO3 (BT) are strongly dependent on its grain size. Coarse-grained ceramics of pure BT showed lower dielectric constant at room temperature then fine grained. Many authors considered that when the grain size is lower than 700 nm, the lattice of BT changes from tetragonal to pseudocubic, and the dielectric constant value is very low. In the doped BT this effect is more complex, because it is necessary to consider also the influence of dopants. The grain size effect on the structure and dielectric properties of niobium-doped barium titanate was investigated. Niobium-doped barium titanate was prepared from powders obtained by doping of commercial barium titanate and from organometallic complex using citrates as precursors (Pechini procedure). The crystal and microstructure of sintered niobium-doped barium titanate were determined. Dielectric constant and dissipation factor were measured. The observation confirmed that the structure and properties are strongly dependent on grain size. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Ferroelectric and dielectric properties of lanthanum-modified bismuth titanate thin films obtained by the polymeric precursor method

Lanthanum-modified bismuth titanate, Bi4-xLaxTi3O12 (BLT), thin films with a La concentration of 0.75 was grown on Pt/Ti/SiO2/Si substrates by using the polymeric precursor solution and spin-coating method. The scanning electron microscopy (SEM) showed rounded grains, which is not typical for these system. The BLT films showed well-saturated polarization-electric field curve which 2P(r) = 41.4 muC/cm(2) and V-c = 0.99 V. The capacitance dependence on the voltage is strongly nonlinear, confirming the ferroelectric properties of the film resulting from the domains switching. These properties make BLT a promising material for FERAM applications.

Dielectric properties of Na1-xLixNbO3 ceramics from powders obtained by chemical synthesis

Ultra-fine powders of Na1-xLixNbO3 (x=0; 0.06; 0.09; 0.12) were synthesized by the Polymeric Precursors Method. Such powders had their orthorhombic structures determined by X-ray diffraction and their surface area determined by BET isotherms (less than 10 m(2) g(-1)). Densification was followed by dilatometric study. The powders, calcined at 700 degrees C for 5 h, were sintered at 1290 degrees C during 2 h under ambient atmosphere with no application of extra pressure. The samples with relative densities higher than 95% were analyzed by impedance spectroscopy at room temperature, under a signal amplitude of 1 V-rms. Dielectric constants of about 180 and dielectric loss factor of about 0.03 were measured showing small dependence with frequency. The electrical properties were similar to those obtained for samples sintered by hot pressing. (C) 1999 Elsevier B.V. Limited and Techna S.r.l. All rights reserved.

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 Raman inactive above the phase transition temperature. The origin of these modes must be interpreted in terms of a local breakdown of cubic symmetry by some kind of disorder. The lack of a well-defined transition temperature suggested a diffuse-type phase transition. This result corroborate the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in the thin film. The leakage current density of the PCT24 thin film was studied at elevated temperatures, and the data were well fitted by the Schottky emission model. The Schottky barrier height of the PCT24 thin film was estimated to be 1.49 eV. (C) 2003 American Institute of Physics.

Role of oxygen vacancies in the magnetic and dielectric properties of the high-dielectric-constant system CaCu3Ti4O12: An electron-spin resonance study

We report experiments of electron spin resonance (ESR) of Cu2+ in polycrystalline samples of CaCu3Ti4O12 post-annealed in different atmospheres. After being synthesized by solid state reaction, pellets of CaCu3Ti4O12 were annealed for 24 h at 1000 degrees C under air, Ar or O-2. Our temperature dependent ESR data revealed for all samples nearly temperature independent g value (2.15(1)) and linewidth for T > T-N approximate to 25 K. However, the values of ESR linewidth are strongly affected by the oxygen content in the sample. For instance, argon post-annealed samples show a much larger linewidth than the O-2 or air post-annealed samples. We attribute this broadening to an increase of the dipolar homogeneous broadening of the Cu2+ ESR lines due to the presence of oxygen vacancies which induce an S=1/2 spin inside the TiO6 octahedra. Correlation between a systematic dependence of the ESR linewidth on the oxygen content and the high dielectric constant of these materials is addressed. Also, ESR, magnetic susceptibility, and specific heat data for a single crystal of CaCu3Ti4O12 and for polycrystals of CdCu3Ti4O12 are reported.

Effects of post-annealing on the dielectric properties of Au/BaTiO3/Pt thin film capacitors

Barium titanate thin films were prepared by the polymeric precursor method and deposited onto Pt/Ti/SiO2/Si substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR) and micro-Raman spectroscopy were used to investigate the formation of the BaTiO3 perovskite phase. Afterwards, the films were submitted to post-annealing treatments in oxygen and nitrogen atmospheres at 300 degreesC for 2 h, and had their dielectric properties measured. It was observed that the electric properties of the thin films are very sensitive to the nature of the post-annealing atmosphere. This study demonstrates that post-annealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that post-annealing in a nitrogen atmosphere produces a slight dielectric relaxation. (C) 2004 Elsevier B.V All rights reserved.

INFLUENCE OF HIGH MICROWAVE DIELECTRIC-CONSTANTS ON THE LINESHAPE OF CONDUCTION-ELECTRON SPIN-RESONANCE

Some synthetic metals show in addition to good conductivity, high microwave dielectric constants. In this work, it is shown how conduction-electron spin resonance(CESR) lineshape can be affected by these high constants. The conditions for avoiding these effects in the CESR measurements are discussed as well as a method for extracting microwave dielectric constants from CESR lines. (C) 1995 Academic Press, Inc.

Non-Ohmic and dielectric properties of a Ca2Cu2Ti4O12 polycrystalline system

An investigation was made into the non-Ohmic and dielectric properties of a Ca2Cu2Ti4O12 perovskite-type system. Compared to the traditional CaCu3Ti4O12-based composition, the imbalance between the Ca and Cu atoms caused the formation of a polycrystalline system presenting similar to 33.3 mol % of CaCu3Ti4O12 (traditional composition) and similar to 66.7 mol % of CaTiO3. As for non-Ohmic properties, the effect of this Ca and Cu atom imbalance was that a nonlinear electric behavior of similar to 1500 was obtained. This high nonlinear electrical behavior emerged in detriment to the ultrahigh dielectric property frequently reported. The high non-Ohmic property was explained by the existence of Schottky-type barriers, whose formation mechanism may be similar to that proposed for traditional metal oxide non-Ohmic devices, according to similarities discussed herein. (c) 2006 American Institute of Physics.

Dielectric properties and microstructure of SrTiO3/BaTiO3 multilayer thin films prepared by a chemical route

Multilayer thin films with perovskite structures were produced by the polymeric precursor method. SrTiO3/BaTiO3 (STO/BTO) multilayers were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the spin-coating technique and heated in air at 700 degreesC. The microstructure and crystalline phase of the multilayered thin films were examined by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), resolution-high transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and X-ray diffraction. The SrTiO3/BaTiO3 multilayer thin films consisted of grainy structures with an approximate grain size of 60 nm. The multilayered thin films showed a very clear interface between the components. The SrTiO3/BaTiO3 multilayer thin films revealed dielectric constants of approximately 527 and loss tangents of 0.03 at 100 kHz. The dielectric constant calculated for this multilayer film system is the value of the sum of each individual component of the film, i.e. The total value of the sum of each SrTiO3 (STO) and BaTiO3 (BTO) layer. The multilayer SrTiO3/BaTiO3 obtained by the polymeric precursor method, also showed a ferroelectric behavior with a remanent polarization of 2.5 muC/cm(2) and a coercive field of 30 kV/cm. The multilayer films displayed good fatigue characteristics under bipolar stressing after application of 10(10) switching cycles. (C) 2001 Published by Elsevier B.V. B.V. All rights reserved.

Non-Linear Dielectric Properties of PLMN-PT Relaxor Ferroelectrics

Recent investigations on the non-linear (NL) dielectric properties of relaxor ferroelectrics systems, not only as ceramic bodies, but also, in thin films, have showed a significant technological and scientific interest. The most common practical applications of relaxors include multilayer capacitors and actuators. In this work, non-linear dielectric properties of hot-pressed (1-x)[Pb1 -(3/2) yLayMg1/3Nb2/3O3]-xPbTiO3 (PLMN-PT) ferroelectric ceramics were investigated. The NL properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the AC electric field with variable amplitude in the frequency and temperature range of 100 Hz-1 MHz and 50-450 K, respectively. 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.

Structure, microstructure and dielectric properties of 100-x(Bi0.5Na0.5)TiO3-x[SrTiO3] composites ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microstructure, dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr0.25Ti0.75]O-3 thin films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)