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Microwave Ceramics (microwave + ceramics)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

The Effect of Dopants on the Dielectric Properties of Ba(B,1/2Ta1/2)O3 (B,=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In) Microwave Ceramics

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2009
Lamrat Abdul Khalam
Low-loss dielectric ceramics based on Ba(B,1/2Ta1/2)O3 (B,=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In) complex perovskites have been prepared by the solid-state ceramic route. The dielectric properties (,r, Qu, and ,f) of the ceramics have been measured in the frequency range 4,6 GHz by the resonance method. The resonators have a relatively high dielectric constant and high quality factor. Most of the compounds have a low coefficient of temperature variation of the resonant frequencies. The microwave dielectric properties have been improved by the addition of dopants and by solid solution formation. The solid solution Ba[(Y1,xPrx)1/2Ta1/2]O3 has x=0.15, with ,r=33.2, Qu×f=51,500 GHz, and ,f,0. The microwave dielectric properties of Ba(B,1/2Ta1/2)O3 ceramics are found to depend on the tolerance factor (t), ionic radius, and ionization energy. [source]

Structure Sequence in the CaTiO3,LaAlO3 Microwave Ceramics,Revised

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006
Dmitry D. Khalyavin
The composition-induced crystal structure transformations in the (1,x)CaTiO3,xLaAlO3 microwave ceramics were studied by X-ray powder diffraction. Increasing LaAlO3 content results in two-phase transitions: Pnma,Imma (0.4[source]

Synthesis of Ba(Mg1/3Ta2/3)O3 Microwave Ceramics through a Sol,Gel Route Using Acetate Salts

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2004
Chien-Cheng Tsai
A sol,gel process to unsophisticatedly synthesize Ba(Mg1/3Ta2/3)O3 (BMT) ceramics at low cost has been developed in the present work. This process involves the reaction of TaCl5 with acetates of Ba and Mg in the presence of citric acid. Pure BMT polycrystalline powders can be obtained by calcining the synthesized products at 1000°C. The BMT powders were found to have a primary particle size as small as 100 nm. BMT ceramics with favorable structural characteristics can be obtained from sintering of the sol,gel BMT at temperatures much lower than that for the conventional solid-state BMT. Sintering the sol,gel BMT in pellet form at 1300°C resulted in an ordering parameter of 0.72 for the pellet, and a relative density of >95% was achieved with sintering at 1500°C. The grain size of the sintered sol,gel BMT was large and uniform in comparison with the products from the solid-state method. Using the sol,gel route, sintering at temperatures as low as 1400°C gave ceramics with acceptable microwave dielectric properties (a dielectric constant of 16 and Qf factor of 14 400 GHz), while higher temperatures (>1600°C) are needed for the solid-state route to give similar properties. [source]

Low-Fire Processing (Ca1,xNd2x/3)TiO3 Microwave Ceramics

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003
Chih-Hung Wei
Effects of 3ZnO·2B2O3 (3Z2B) glass addition on densification and microwave properties of (Ca1,xNd2x/3)TiO3(CNT-X) have been investigated. With the 3Z2B glass content greater than 20 vol%, the densification temperature can be greatly reduced from 1400°C for pure CNT-X to 850°,900°C for CNT-X + 3Z2B microwave ceramics. The above result is attributed to a chemical reaction taking place at the interface of 3Z2B/CNT-X during firing. The Ca in CNT-X dissolves into 3Z2B, forming a new glass of CaO-ZnO-B2O3 at 870°,880°C which enhances the densification kinetics of 3Z2B + CNT-X microwave ceramics. For the samples with 20,40 vol% 3Z2B, the resulting 3Z2B + CNT-X microwave ceramics have a dielectric constant (k) of 30,60 and a quality factor (Q) of 200,550 at 1,10 GHz, and a temperature coefficient of resonant frequency of 20,60 ppm/K in the temperature range of 20°,80°C. [source]

Influence of Copper(II) Oxide Additions to Zinc Niobate Microwave Ceramics on Sintering Temperature and Dielectric Properties

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001
Dong-Wan Kim
The effect of CuO additions on the firing temperature of ZnNb2O6 ceramics was investigated using dilatometry, transmission electron microscopy, and X-ray diffractometry. A 5 wt% CuO addition to ZnNb2O6 ceramics significantly lowered the firing temperature from 1150° to ,900°C. The presence of a CuO-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu2)Nb2O8. In particular, the low-fired ZnNb2O6 ceramics had good microwave dielectric characteristics,Q×f= 59 500, ,r= 22.1, ,f=,66 ppm/oC. These properties were correlated with the formation of a second phase, (ZnCu2)Nb2O8. [source]