Dielectric permittivity and loss of CaCu3Ti4O12 (CCTO) substrates for microwave devices and antennas

The solid state procedure was used to produce bulk ceramics of CCTO (CaCu3Ti4O12). The samples of the CCTO ceramic were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. The infrared and Raman scattering spectroscopy confirm the formation of the CCTO phase as seen by X-ray diffraction analysis. For one experimental procedure one uses an organic binder in the process of shaping the samples. In the second procedure the samples were prepared without the presence of the organic phase. For the second situation, we had higher dielectric constant (epsilon(r) = 7370) with high loss (D = 0.2) at 1 KHz. For the first procedure one has the lower dielectric constant (epsilon(r) = 1530) and lower loss (D = 0.11) at 1 KHz. Simple rectangular antenna prototypes were also designed on substrate samples (C1, C2, P1 and P2). For the antennas (with P2, C1 and C2 as substrates), the bandwidth (BW) is 90 MHz (around 3%). The antenna with P1 substrate presented a surprisingly high BW of 270 MHz that corresponds to a 10% bandwidth. In the microwave range one observes that higher values of the Er in the range of 3 GHz antennas is also presented by the P1 sample (epsilon(r) = 41.6), and the lowest one was presented by P2 (epsilon(r) = 33.7). Sample P1 also presents the highest value for the loss (Q(-1)) which is around 0.1 compared to the other samples which is around 0.03. Therefore, these measurements confirm the potential use for small high dielectric planar antennas. These materials are also attractive for capacitor applications and certainly for microelectronics, and microwave devices (e.g., cell mobile phones), where the miniaturization of the devices is crucial. (C) 2004 Kluwer Academic Publishers.151065766

Microstrip antenna on a high dielectric constant substrate: BaTiO3 (BTO)-CaCu3Ti4O12(CCTO) composite screen-printed thick films

The performance of microstrip antennas using composite thick films of (BTOBaTiO3) and CCTO (CaCu3Ti4O12) as a substrate were studied. The dielectric permittivity and loss of (BTO)(x)-(CCTO)(1-x) thick films with x = 0, 0.2, 0.5, 0.8, 0.9, and 1 were examined. These films were prepared in two-layer geometry using the screen-printing technique on Al2O3 substrates. Mechanical alloying followed by the solid-state procedure was successfully employed to produce powders of CCTO (CaCu3Ti4O12) used in the films. We also studied the films dielectric permittivity (K) and loss (D) in the medium-frequency (MF) range (100 Hz to 1 MHz). The performance of a planar microstrip antenna that uses the (BTO)(x):(CCTO)(1-x) thick films as a substrate of high K was also examined in the microwave range of frequencies. From the analysis of the antenna operation of the samples, one can conclude that the higher values of K in the range of 2.5-3.3 GHz antennas is presented by the BTO substrates. For the BTO film, the K value is similar to 66 (2.6 GHz) and decreases to 34 for the CCTO film (3 GHz). For the BTO and CCTO films, the antenna bandwidths (BW) are similar to 50% and similar to 38%, respectively. The higher bandwidth presented by the BTO compared to the CCTO is certainly associated with the higher loss presented by the BTO phase, which is a ferroelectric phase. Therefore, these measurements confirm the potential use of such materials for small microwave planar antennas, where the miniaturization of the devices is crucial.35101848185

Microstructural and electrical properties of PbTIO3 screen-printed thick films

In this article we will study the structural and electrical properties of PbTiO3 (PTO) screen-printed thick films. These properties can change with synthetic routes employed for synthesis of PTO. The ceramic powder has been synthesized by mechanical alloying and solid state route. This material crystallizes in the tetragonal system, with space group P4mm and unit cell dimensions a = b = 3.904, c = 4.152 angstrom, and Z = 1. From our results, it was observed that PTO obtained by mechanical alloying provides smaller crystallite size. The Rietveld refinement showed that the samples synthesized by mechanical alloying and solid state route crystallize in the tetragonal system but with different cell parameters. The Raman shifts of these films agree with modes from literature. However, some displacements happen, because the morphology and structural characteristics of the thick films are different, compared to single crystal and thin film. The photomicrographs of the PTO thick films showed that the choice of synthetic routes obtained samples with different microstructures.191097398

Microstructure and magneto-dielectric properties of ferrimagnetic composite GdIG(X):YIG(1-X) at radio and microwave frequencies

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The gadolinium iron garnet (GdIG, Gd3Fe5O12) and yttrium iron garnet (YIG, Y3Fe5O12), and their GdIG(X):YIG(1-X) composites, were obtained by a new solid-state procedure. The microstructure of the samples was studied by X-ray powder diffraction and Rietveld refinement, Vickers microhardness and scanning electron microscopy. The density and microhardness behavior were studied as a function of the lattice parameters for the composite samples. In the present work, the magnetic and dielectric properties of the GdlG(X):YIG(1-X) composite at radio and microwave frequencies were also studied. The magnetic permeability and dielectric permittivity and loss properties for the composite GdIG(X):YIG(1-X) showed good potential for use in components, when one is looking for moderate epsilon(r)' and mu(r)' materials with low loss in the radio-frequency and microwave range. (C) 2009 Elsevier Ltd. All rights reserved.705804810Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FUNCAP (Brazilian agencies)CELESTICAUS Air Force Office of Scientific Research (AFOSR) [FA9550-08-1-0210]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)US Air Force Office of Scientific Research (AFOSR) [FA9550-08-1-0210

Synthesis, structure and vibrational properties of GdIG(X):YIG(1-X) ferrimagnetic ceramic composite

Y3Fe5O12 (YIG) crystal has many attractive characteristics, such as low dielectric loss, narrow resonance linewidth in microwave region and also possesses a good saturated magnetization value. Composite technology in general sets out to combine materials in such a way that the properties of the composite are the optimum for a particular application. The different materials work together to give a composite of unique properties. In this work, we present the preparation procedure (obtaining) of the GdIG(x):YIG(1-X) ferrimagnetic ceramic matrix composite by mechanical alloying and calcinations. Besides that, we study its properties by X-ray powder diffraction, infrared, Micro-Raman, Fe-57 Mossbauer spectroscopy and hysteresis loop measurements. (c) 2008 Elsevier Ltd. All rights reserved.70120220