Synthesis and dielectric properties of barium tantalates and niobates with complex perovskite structure

2002 ◽  
Vol 17 (12) ◽  
pp. 3182-3189 ◽  
Author(s):  
T. Kolodiazhnyi ◽  
A. Petric ◽  
A. Belous ◽  
O. V'yunov ◽  
O. Yanchevskij
Keyword(s):  
Dielectric Properties ◽  
Dielectric Loss ◽  
Point Defects ◽  
Cation Ordering ◽  
Second Phase ◽  
Extrinsic Factors ◽  
Paramagnetic Resonance ◽  
Microwave Frequencies ◽  
Disorder Phase Transition ◽  
Complex Perovskites

Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1/3B"2/3)O3, where B′ = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed. It was found that all the studied complex perovskites attained high degrees of 1:2 cation ordering at temperatures specific to each composition. A high temperature order–disorder phase transition in Ba(Zn1/3Nb2/3)O3 occurred below 1380 °C. Ba(Ni1/3Nb2/3)O3 (BNN) and Ba(Mg1/3Nb2/3)O3 (BMN) pervoskites remained 100% ordered at temperatures as high as 1500 and 1620 °C, respectively. It was found that in BMN and BNN extrinsic factors, such as the second phase (i.e., Ba3Nb5O15) and point defects, dominated the dielectric loss at microwave frequencies. Ba(Mg1/3Ta2/3)O3 (BMT) remained single phase up to 1630 °C. Above this temperature, the Ba3Ta5O15 second phase was detected. A decrease in the 1:2 cation ordering and increase of dielectric loss in BMT occurred at sintering temperatures above 1590 °C. It was also revealed by electron paramagnetic resonance that all samples studied contained a substantial amount of paramagnetic point defects. These defects contributed to extrinsic dielectric loss at microwave frequencies, thus degrading the Q factor.

Dielectric Properties of a New Ceramic System (1-x)(Mg0.95Zn0.05)2TiO4-x(Ca0.8Sr0.2)TiO3 at Microwave Frequencies

2020 ◽  
Vol 830 ◽  
pp. 37-42
Author(s):  
Shih Sheng Liu ◽  
Shiuan Ho Chang ◽  
Yuan Bin Chen
Keyword(s):  
Dielectric Properties ◽  
Microwave Dielectric Properties ◽  
Second Phase ◽  
X Ray Diffraction ◽  
Low Loss ◽  
Microwave Frequencies ◽  
Solid State Route ◽  
Microwave Dielectric ◽  
System 1 ◽  
Quality Factor Q

The microwave dielectric properties and microstructures of the (1-x)(Mg0.95Zn0.05)2TiO4-x (Ca0.8Sr0.2)TiO3 ceramics prepared using the conventional solid-state route were investigated. The structure and microstructure were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Ilmenite-structured (Mg0.95Zn0.05)TiO3 was detected as a second phase. The coexistence of the second phase, however, did not degrade the dielectric properties of the specimen because the phases were compatible. At x = 0.07, a dielectric constant (εr) of ~17.86, a quality factor (Q×f) value of ~ Q×f~133,600 Hz (at 10 GHz), and a temperature coefficient of resonant frequency (τf) of ~ –5ppm/°Cwere obtained for 0.93(Mg0.95Zn0.05)2TiO4-0.07(Ca0.8Sr0.2)TiO3 ceramic sintered at 1240°C for 4 hr. The dielectric is proposed as a candidate material for low-loss microwave and millimeter wave applications.

Multi-Component Mixture Modeling for the Dielectric Properties of Rubber Wood at Microwave Frequencies

Holzforschung ◽  
1999 ◽  
Vol 53 (6) ◽  
pp. 662-668 ◽  
Author(s):  
K.B. Khalid ◽  
M.F. Kabir ◽  
W. M. Daud ◽  
H.A.A. Sidek
Keyword(s):  
Experimental Data ◽  
Dielectric Properties ◽  
Dielectric Loss ◽  
Loss Factor ◽  
Dielectric Constants ◽  
Dielectric Loss Factor ◽  
Component Mixture ◽  
Microwave Frequencies ◽  
Conductive Loss ◽  
Rubber Wood

Summary Dielectric properties from 1 to 18 GHz of rubber wood are modeled using generalized mixture equations and also with equations proposed by Weiner, Kraszewski, Looyenga and Landou, Lichtenecker. Dielectric properties were measured with an open-ended coaxial line-sensor in three structural directions longitudinal, radial and tangential and at different moisture contents. The dielectric constants were predicted well by the Weiner model for all structural grain directions and it was found that the degree of binding decreases with increasing frequency. However, the Weiner model cannot be used for predicting the dielectric loss factor at frequencies below 3 GHz. This may be due to the high conductive loss in this frequency region. The lower value of the exponents in generalized mixture equation was found suitable for fitting the experimental data as well as the Kraszewski equation. Values predicted by Lichtenecker equations are in well agreement with the experimental data at higher microwave frequencies. The prediction of dielectric loss factor using Kraszewski, Looyenga equations were not possible at frequencies below 3 GHz since it is dominated by conductive loss. Above 3 GHz, it was well predicted by Kraszewski and Looyenga equations.

scholarly journals Complex dielectric behavior of doped polyaniline conducting polymer at microwave frequencies using time domain reflectometry

2019 ◽  
Vol 65 (6 Nov-Dec) ◽  
pp. 590 ◽  
Author(s):  
D.R. Bijwe ◽  
S.S. Yawale ◽  
A.C. Kumbharkhane ◽  
H. Peng ◽  
D.S. Yawale ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Dielectric Properties ◽  
Dielectric Loss ◽  
Conducting Polymer ◽  
Chemical Oxidation ◽  
Ammonia Solution ◽  
Dielectric Behavior ◽  
Time Domain Reflectometry ◽  
Microwave Frequencies ◽  
Absorbing Property

Nano size Tin Oxide is prepared in the laboratory from SnCl4 and ammonia solution. The polyaniline (PAni) conducting polymer is synthesized by chemical oxidation method using ammonium persulphate as oxidizing agent. The PAni-SnO2 composite was prepared by insitu method. Scanning electron microscopy (SEM) results confirm the particle size of SnO2 in the range of 30-48 nm.   Dielectric  behavior  of  nanocomposite  of  PAni-SnO2 was  studied  in the frequency range 0.01- 20 GHz at -5,0,5,10,15,20 and  25oC. The dielectric constant (real part ε׳) and dielectric loss (imaginary part ε״) have been evaluated. The relaxation time (τ, τo, and τ1) are calculated. The relaxation time was found to be of the order of ps. The dielectric properties of the solids in the form of powders may be useful in understanding the structural behavior of particles in an alternating field. These studies may also be used to formulate models for predicting the dielectric properties. The microwave absorbing property is decided from the dielectric loss of the material. It is observed that the PAni-SnO2 composite can be a good electromagnetic shielding material.

α/β Phase Transformation in Porous Reaction-Bonded Silicon Nitride Ceramics

2011 ◽  
Vol 194-196 ◽  
pp. 2225-2228
Author(s):  
Jie Xu ◽  
Jun Bo Wang ◽  
Wei Hua Cui ◽  
Xiao Lei Su ◽  
Wan Cheng Zhou
Keyword(s):  
Dielectric Constant ◽  
Phase Transformation ◽  
Dielectric Properties ◽  
Silicon Nitride ◽  
Dielectric Loss ◽  
Point Defects ◽  
Nitriding Temperature ◽  
Β Phase ◽  
Nitride Ceramics ◽  
Tan Δ

Porous reaction-bonded silicon nitride ceramics with different values of α/β ratio were obtained by setting the nitriding temperature and time. The influence of α/β phase transformation on the dielectric properties of porous silicon nitride ceramics has been investigated. The results show that the α/β transformation occurs when the nitriding temperature is higher than 1400°C . The values of α/β ratio decrease with increase of nitriding temperature and time. The dielectric constant ε′ and the dielectric loss tan δ of the samples increase because of the α/β transformation, and the change of the dielectric loss is more obvious. The increase of concentrations of point defects due to the α/β transformation leads to the significant increase of the dielectric loss.

Microstructure and Microwave Dielectric Properties of BaTi4O9 Ceramics Derived from a Sol-Gel Precursor

2011 ◽  
Vol 326 ◽  
pp. 127-130
Author(s):  
Xian Li Huang ◽  
Fu Ping Wang ◽  
Ying Song
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Dielectric Loss ◽  
Sol Gel ◽  
Microwave Dielectric Properties ◽  
Sintering Process ◽  
Temperature Coefficients ◽  
Microwave Dielectric ◽  
Ceramic Samples ◽  
Quality Factor Q

In the present work, the microstructure and microwave dielectric properties of BaTi4O9 ceramics derived from a sol-gel precursor were presented. Density measuring results demonstrated that the largest densities of ceramic sample about 96.7% could be reached by virtue of a cool iso-static press and a sintering process at at 1300 °C for 6 hours. The dielectric constant (εr), quality factor (Q×f) and the temperature coefficients (τf) of the BaTi4O9 ceramic samples were 36.65, 28000 GHz, +20.2 ppm/°C, respectively. XRD, SEM and XPS were used to characterize the microstructure of the ceramics samples. Substantial Ti3+ was proposed to be the cause of dielectric loss.

Preparation and Dielectric Properties of 1-3 La Modified PZT/IPN Piezoelectric Composites

2010 ◽  
Vol 105-106 ◽  
pp. 355-358 ◽  
Author(s):  
Z.L. Zhu ◽  
Dong Yan Tang ◽  
X.H. Zhang ◽  
Y.J. Qiao
Keyword(s):  
Heat Treatment ◽  
Dielectric Constant ◽  
Dielectric Properties ◽  
Dielectric Loss ◽  
Lead Zirconate Titanate ◽  
Polymer Network ◽  
Lead Zirconate ◽  
Interpenetrating Polymer Network ◽  
Ceramic Fibers ◽  
Piezoelectric Composites

To prevent the potential cracking of gel fibers, La modified lead zirconate titanate (PLZT) ceramic fibers with diameter within 50µm were achieved by embedding into PLZT powders during the heat treatment. Then the 1-3 PLZT fiber/interpenetrating polymer network (IPN) piezoelectric composites were prepared by casting the IPN precursors onto the well aligned ceramic fibers. The influences of the heating temperatures and La amounts on the dielectric constant, dielectric loss with frequencies and piezoelectric constant of PLZT were investigated in detail. The morphologies of fibers and composites were observed by biological microscope. And also, the dielectric constant of PLZT fibers and PLZT fiber/IPN piezoelectric composites were detected.

Dielectric Properties of Lead Alkaline-Earth Zirconate at Microwave Frequencies

1991 ◽  
Vol 30 (Part 1, No. 9B) ◽  
pp. 2343-2346 ◽  
Author(s):  
Junichi Kato ◽  
Hiroshi Kagata ◽  
Keiji Nishimoto
Keyword(s):  
Dielectric Properties ◽  
Alkaline Earth ◽  
Microwave Frequencies
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