V. Paunovic

Fractal Geometry and Properties of Doped BaTiO3 Ceramics

Taking into account that the complex grain structure is difficult to describe by using traditional analytical methods, in this study, in order to establish ceramic grain shapes of sintered BaTiO3, new approach on correlation between microstructure and properties of doped BaTiO3 ceramics based on fractal geometry has been developed. BaTiO3 ceramics doped with various dopants (MnCO3, Er2O3, Yb2O3) were prepared using conventional solid state procedure, and were sintered at 1350oC for four hours. The microstructure of sintered specimens was investigated by SEM-5300. Using method of fractal modeling a reconstruction of microstructure configurations, like grains shapes, or intergranular contacts has been successfully done. Furthermore, the area of grains surface was calculated using fractal correction that expresses the irregularity of grains surface through fractal dimension. The presented results, indicate that fractal method for ceramics structure analysis provides a new approach for describing, predicting and modeling the grain shape and relations between the BaTiO3-ceramic structure and dielectrical properties.

Microstructure Evolution and Dielectric Properties of Nb/Mn and Dy/Mn Doped Barium Titanate Ceramics

Nb/Mn and Dy/Mn codoped BaTiO3 specimens, prepared by conventional solid-state procedure, were investigated regarding their microstructural and dielectric properties. The powders were doped with Nb2O5 and Dy2O3 with an amount of 0.1, 0.5 and 1.0 at% of dopants ions. The MnO content of 0.05 at% Mn was the same in both types of samples. The specimens were sintered in air at 1320 and 1350 °C for two hours. Microstructural and compositional studies were done by SEM equipped with EDS. In low doped BaTiO3 the grain size is around 1-3 μm, while in ceramics with high dopant content (1.0 at%) the grain size distribution was in the range of 3-10 μm. High dielectric constant is associated with small-grained microstructure, being 5000 for Dy-doped and 6500 for Nb-doped BaTiO3 sintered at 1350 °C. The specimens with low dopant content demonstrate the Curie-Weiss behavior in a paraelectric regime. A nearly flat permittivity response with temperature was obtained for specimens with 0.5 and 1.0 at% Dy content. Loss tangents were in the range of 0.03 - 0.32.

MICROSTRUCTURE CHARACTERIZATION OF POROUS MICROALLOYED ALUMINIUM-SILICATE CERAMICS

Kaolinite and bentonite clay powders mixed with active additives, based on Mg(NO 3 ) 2 and Al(NO 3 ) 2 , sintered at high temperatures produce very porous ceramics with microcrystalline and amorphous regions and highly developed metalized surfaces (mainly with magnesium surplus). Microstructure investigations have revealed non-uniform and highly porous structure with broad distribution of grain size, specifically shaped grains and high degree of agglomeration. The ceramics samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction analysis (XRD) and IR spectroscopy analysis, prior and after treatment in “synthetic water”, i.e. in aqueous solution of arsenic-salt. Grain size distribution for untreated and treated samples was done with software SemAfore 4. It has shown great variety in size distribution of grains from clay powders to sintered samples.

Processing parameter influence on BaTiO3 ceramic fractal microstructure and dielectric characteristics

Abstract In the process of BaTiO3 ceramics consolidation, technological parameters like sintering temperature, pressing pressure and additives significantly determine the microstructure and electrical properties. Slight change of a particular sintering parameter can considerably change the microstructure as well as the electrical parameters. Structural complex grain–contact–grain is observed on Ho doped BaTiO3 ceramics, sintered from 1320 to 1380°C. The new configuration model of ceramic grain contact surfaces is presented in this paper. This model is based on Coble’s two-sphere approximation and its generalisation to ellipsoidal geometry. The integral contact surface directly influences the value of the total ceramic capacity. Fractal method is applied for intergrain contact analysis. Ceramic grains are considered to have fractal surface (as it is elsewhere in nature) and, therefore, fractal structure influences on the dielectric properties of BaTiO3 ceramics. The obtained results give better understanding of ceramic microstructure with the final aim to establish significant interrelation among processing, structural and electrical parameters.

Microstructure and Dielectric Properties of Rare-Earth Doped BaTiO3 Ceramics

The specimens of BaTiO3 doped with 0.01, 0.1 and 0.5 wt% of Er2O3 or Ho2O3 used for this investigation were prepared by the conventional solid state reaction. The specimens were sintered at 1350°C in an air atmosphere for 4 hours. The grain size and microstructure characteristics for various samples and their phase composition was carried out using a scanning electron microscope SEM equipped with EDS system. SEM analysis of Er/BaTiO3 and Ho/BaTiO3 doped ceramics showed that in samples doped with a low level of rare-earth ions, the grain size ranged from 10–60μm, while with the higher dopant concentration the abnormal grain growth is inhibited and the grain size ranged between 2–10μm. We also applied the fractal method in microstructure analysis of sintered ceramics especially as influence on dielectric properties of BaTiO3 ceramics. These fractal effects have been used for better understanding of intergranular capacitors.

Ferroelectric and Piezoelectric Nanomaterials—Basic Properties, Characterization and Applications

Electroceramics have a wide range of applications and are a subject of extensive research activities in the fields of ion-conductivity (such as batteries and sensors), electrical insulators (substrates and multilayer integrated circuit packages), semiconductors (sensors), and superconductors. Among the electroceramic materials, ferroelectric and piezoelectric nanomaterials are technically the most challenging. They are known for their unique properties, such as high dielectric constant, as well as high piezoelectric constants, and are used in multilayer capacitors or as microwave devices within wireless communication systems. In addition, perovskite ferroelectric nanomaterials show potential for applications related to solar energy conversion and the production of storage memory devices. Ferroelectric films as functional materials are being extensively explored for various microsensor and microactuator applications, some of them being suitable for biomedical engineering. The most widely investigated perovskite ferroelectric and piezoelectric nanomaterials include BaTiO3, SrTiO3, PbZrTiO3 along with suitable dopants and multiferroic oxides, and ZnO. In this review, the main concept of ferroelectricity in perovskite oxides and related nanomaterials is discussed. Fundamentals of ferroelectric nanomaterials, including size effects of ferroelectric nanomaterials properties and phase transitions are summarized. A detailed discussion on the synthesis, fabrication, nanostructure characterization of ferroelectric and piezoelectric nanomaterials such as BaTiO3, SrTiO3, and ZnO is presented. Progress in the research of ferroelectric perovskite oxide in nanometers scale is also highlighted.

Towards Electronic Materials Fractal Theory

Starting in the last two decades of 20th Century, fractal geometry and underlying analysis became a part of material sciences. From ore distribution in Earth layers to nanotechnology, from biomedical to energy applications, fractal descriptors of physicochemical properties of matter are inevitable part of scientific research and presentations. Fractal and spectral dimensions replace the usual (geometric) dimension, multifractal distributions appear instead convention statistical ones, Weierstrass functions replace standard algebraic or trigonometric polynomials. In the fractal frame of mind, description, construction or reconstruction of fairly complicated and uneven objects such as ceramic grains, ferromagnetic domains or pores labyrinth are as easy as working with ideal Euclidean objects like circles and squares. The aim of this work is to point out the most important issues where powder materials technology, like mass density, particle density, electric charge density, energy density etc., intersects with the notion of fractal dimension and power law equations and other fractal constructions and corresponding applications.

Characterization and SPICE Modeling of Passive Electronic Devices at High Frequencies

In this paper the results of characterization and modeling of passive electronic devices (capacitors and inductors) have been presented. The experimental results obtained using RF impedance analyzer have been discussed, and based on them, parameters of equivalent circuits have been determined using analytical model. Approximate functions for parasitic elements of the devices have been proposed.

The Sintering Temperature and the Ho2O3 Concentration Influence on BaTiO3-Ceramics Microstructure Fractal Nature

A new correlation between microstructure and doped BaTiO3-ceramics properties is developed based on fractal geometry. The BaTiO3-based materials structure can be controlled by using different sintering temperatures and additive concentrations. In this paper, Ho2O3-doped BaTiO3-ceramics microstructure properties have been investigated. The dopant concentration ratio is from 0.01 to 1 wt% of Ho2O3. The sintering has been done by using three different temperatures (1320, 1350, and 1380 °C). BaTiO3 microstructure and compositional studies were investigated by SEM (scanning electron microscope) equipped with EDS analysis. By using the fractal objects theory, the reconstruction of microstructure configurations such as grains contour shapes and the nature of intergranular contacts has been approximately established. Using fractal tools in studying BaTiO3-ceramics microstructure has a great significance for future components technology developments, materials function integrations, and miniaturization. The complementary statistical approach contributes to the investigation of BaTiO3-ceramic grains distribution and nature of intergrain contacts, which brings a major shift in the field of electronic components and alternative energy sources.

Electrical Characteristics of Nb Doped BaTiO3 Ceramics

The Nb doped BaTiO3 ceramics, with different Nb2O5 content, ranging from 0.5 to 2.0 at.% Nb, is investigated regarding their microstructure and electrical characteristics in this paper. The Nb/BaTiO3 ceramics is prepared by the conventional solid state reaction and sintered at 1320 °C in an air atmosphere for 2 h. As acceptor dopant Mn in concentration of 0.01 mol% is added. For low doped samples (0.5 mol% Nb), the characteristic is homogeneous and fine grained microstructure with grain size from 0.5 to 2 μm. Increasing the additive content results in the grain size increasing so that the samples doped with 2.0 mol% Nb the average grain size reaches 10 μm. The dielectric characteristic of Nb doped BaTiO3 ceramics like dielectric constant, dissipation factor and resistivity have been measured by using LCR-Meter Agilent 4284A in the frequency range 20 Hz–1 MHz and Agilent E4991A RF Impedance/Material Analyzer for high frequency measurements (1 MHz–3 GHz). Dielectric constant and tangent losses after initial large values remains nearly independent of frequency greater than 10 kHz. Dielectric measurements were carried out as a function of temperature up to 180 °C. The low doped samples (0.5Nb/BaTiO3) sintered at 1320 °C, display the high value of dielectric permittivity at room temperature, e r = 3225. A nearly flat permittivity-temperature response is obtained in specimens with 2.0 at.% additive content. The Curie–Weiss and modified Curie–Weiss law is used to clarify the influence of dopant on the dielectric properties and BaTiO3 phase transformation. All investigated samples have an electrical resistivity ρ > 106 Ωcm at room temperature. New aspect here is fractal correction, introduced as slight variation of temperature T entered from outside, due to three fractal factors α S , α P and α M being responsible for complex geometry of both morphologic and dynamic nature. This correction, naturally has impact on the Curie–Weiss low, which is stressed in this paper.