Browsing by Author "Liou, JW"

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Analysis of the dielectric characteristics for polycrystalline Ba(0.65)Sr(0.35)TiO(3) (I)-frequency dependence in the paraelectric state
(2000-11-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The frequency and d.c. field dependences of dielectric properties of Ba(0.65)Sr(0.35)TiO(3) (BST) with various grain sizes (0.87 mum to 5.43 mum) have been studied in the paraelectric state. The frequency response is analyzed by two approximated power laws obtained on the basis of the Cole-Cole expression. The distribution of relaxation times in BST is broader for specimens with finer grains. The d.c. field is found to affect the static permittivity epsilon (0) rather than the distribution of relaxation times. The effect of the d.c. field on the dielectric permittivity is suppressed for samples with smaller grains and transition broadening is presumed to cause this suppression. It is concluded that both the temperature dependence and the frequency response of the dielectric characteristics of Ba(0.65)Sr(0.35)TiO(3) are suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.
Analysis of the dielectric characteristics for polycrystalline Ba0.65Sr0.35TiO3 (I)-frequency dependence in the paraelectric state
(2000-11-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The frequency and d.c. field dependences of dielectric properties of Ba0.65Sr0.35TiO3 (BST) with various grain sizes (0.87 mum to 5.43 mum) have been studied in the paraelectric state. The frequency response is analyzed by two approximated power laws obtained on the basis of the Cole-Cole expression. The distribution of relaxation times in BST is broader for specimens with finer grains. The d.c. field is found to affect the static permittivity epsilon (0) rather than the distribution of relaxation times. The effect of the d.c. field on the dielectric permittivity is suppressed for samples with smaller grains and transition broadening is presumed to cause this suppression. It is concluded that both the temperature dependence and the frequency response of the dielectric characteristics of Ba0.65Sr0.35TiO3 are suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.
Analysis of the dielectric characteristics for polycrystalline Ba0.65Sr0.35TiO3 (II) - d.c. field dependence with a modified bias equation
(2000-11-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effect of direct-current (d.c.) biasing on the dielectric properties of Ba0.65Sr0.35TiO3 (BST) with various grain sizes (0.87 mum to 5.43 mum) have been studied in the paraelectric state. The leakage current of BST samples is proportional to the biasing field. Specimens with larger grains exhibit higher leakage current under biasing. The bias equation used in the literature to predict the d.c. field dependence of permittivity is modified by introducing a bias exponent parameter beta. This modified bias equation gives a better fit to the experimental results both in this study and in the literature. Similar trends of alpha (representing the distribution of relaxation times), beta, and the variance of lattice distortion with grain sizes suggests that beta is a material parameter. It is concluded that the temperature dependence, the frequency response and d.c. field effect for the dielectric characteristics of Ba0.65Sr0.35TiO3 are all suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.
DC field dependence of the dielectric characteristics of doped Ba0.65Sr0.35TiO3 with various grain sizes in the paraelectric state
(1997-07-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Different grain sizes of ferroelectric Ba0.65Sr0.35TiO3 doped with 1.0mol% MgO and 0.05mol% MnO2 were prepared to investigate the DC field dependence of dielectric characteristics. A transition broadening is observed as grain size decreases. The broadening is attributed to the variance of lattice distortion in the materials. As the grain size increases, both the maximum dielectric constant k(max) at T-c and the dielectric tunability (percentage change of dielectric constant under a DC field) increase. A phenomenological equation can be fit to the DC field dependence of the dielectric constant. The phenomenological coefficient obtained is strongly dependent on the grain size and the temperature. Above the phase transition; a ''behavior-transformation'' temperature T-b is observed. At temperatures below T-b, the dielectric loss factor that is dominated by intrinsic loss is reduced when the DC field is applied. While at temperatures above T-b; the loss factor is dominated by the conduction loss and is raised by the DC field.
DC field dependence of the dielectric characteristics of doped Ba0.65Sr0.35TiO3 with various grain sizes in the paraelectric state
(1997-07-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Different grain sizes of ferroelectric Ba0.65Sr0.35TiO3 doped with 1.0mol% MgO and 0.05mol% MnO2 were prepared to investigate the DC field dependence of dielectric characteristics. A transition broadening is observed as grain size decreases. The broadening is attributed to the variance of lattice distortion in the materials. As the grain size increases, both the maximum dielectric constant k(max) at T-c and the dielectric tunability (percentage change of dielectric constant under a DC field) increase. A phenomenological equation can be fit to the DC field dependence of the dielectric constant. The phenomenological coefficient obtained is strongly dependent on the grain size and the temperature. Above the phase transition; a ''behavior-transformation'' temperature T-b is observed. At temperatures below T-b, the dielectric loss factor that is dominated by intrinsic loss is reduced when the DC field is applied. While at temperatures above T-b; the loss factor is dominated by the conduction loss and is raised by the DC field.
Dielectric characteristics of doped Ba1-xSrxTiO3 at the paraelectric state
(1997-10-30)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Ba1-xSrxTiO3 (x=0 to 1) ferroelectric ceramics doped with 1.0 mol.% MgO and 0.05 mol.% MnO2 were prepared with a rate-controlled sintering profile. The lattice constant of this BST system decreases as the strontium molar fraction increases. This is due to the smaller Sr2+ ionic radius than that of Ba2+. The temperature dependence of the dielectric constant is measured at 10 kHz. A linear relation of the Curie temperature of the BST system to the Sr fraction for x less than or equal to 0.75 is observed. When this reaction is fitted to a modified Curie-Weiss law, two parameters, the critical exponent and the diffuseness parameter, which represent the order of transition broadening, can be calculated. From the values of these two parameters, it is suggested that the physical meanings of these two parameters are correlated to each other. The transition broadening is greatest for x = 0.5 owing to the most composition fluctuation. Dipole relaxation of the composition with x = 0.25 is observed at frequencies above 1 MHz. On the basis of Cole-Cole analysis, a low frequency relaxation due to dopants Mn4+ at below 50 kHz is observed. (C) 1997 Elsevier Science S.A.
Dielectric tunability of barium strontium titanate/silicone-rubber composite
(1998-03-30)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The dielectric tunability, which is defined as the percentage change of the permittivity under DC biasing, is over 30% for polycrystalline barium strontium titanate (BST) under a field of 5000 V cm(-1) at around the Curie peak. Various volume fractions (18%, 40%, 52%, and 64%) of BST powder are mixed with silicons rubber to obtain a multi-phase dielectric composite. The effective permittivity of the composite follows the Maxwell-Garnett relation with a shape parameter of about 14 for volume fractions below 52%. The dielectric tunabilities at 5000 V cm(-1) for the samples made with 52% and 64% powder are about 0.7% and 7.4%, respectively. The results are compared to the dielectric tunabilities obtained on the basis of series, parallel, and logarithmic models. It is suggested that the dielectric tunability is enhanced when a sample with a more continuous BST powder phase is obtained. An increase of the permittivity with a small DC field applied to the composite is attributed to the effect of polarization of the interface between the BST and silicone-rubber phases.
Effect of direct-current biasing on the dielectric properties of barium strontium titanate
(1997-12-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Ba1-xSrxTiO3 (BST, x = 0 to x = 1) ferroelectric ceramics doped with 1.0 mol% MgO and 0.05 mol% MnO2 were prepared with a rate-controlled sintering profile, As the strontium molar fraction x increased, the average grain size decreased from 14 mu m for x = 0 to 2 mu m for x = 1, Temperature dependence of the dielectric properties was measured as a function of de biasing, At 10 degrees C above the Curie temperature, the changes of dielectric constant at 5000 V/cm were 28%, 17%, 26%, and 36% for x = 0, 0.25, 0.5, and 0.75, respectively, The reduction of dielectric constant by the applied de biasing was fitted by a phenomenological equation that was based on Devonshire's theory, From this phenomenological equation, an anharmonic coefficient, which was an order parameter of the anharmonic interactions, was calculated for each composition, As the strontium molar fraction increased, these coefficients increased from 2.45 x 10(-19) cm(2).V-2 for x = 0 to 5.90 x 10(-19) cm(2).V-2 for x = 0.75, A similar trend was observed on the de field dependence of the dielectric loss, except at high field for x = 0, of which a high loss was obtained, A two-element circuit model was proposed to explain the effect of high de biasing on the dielectric loss.