Dielectric Properties of Compounds Exhibiting C*α Phase and Theoretical Analysis of the Results

1995 ◽  
Vol 263 (1) ◽  
pp. 207-216 ◽  
Author(s):  
M. Čepič ◽  
G. Heppke ◽  
J. M. Hollidt ◽  
D. Lötzsch ◽  
D. Moro ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Theoretical Analysis ◽  
Α Phase

EFFECT OF PARTICLE ROTATION ON THE ELECTRORHEOLOGICAL (ER) EFFECTS IN SOME ER SUSPENSIONS

2005 ◽  
Vol 19 (07n09) ◽  
pp. 1222-1228 ◽  
Author(s):  
K. NEGITA ◽  
Y. MISONO ◽  
J. SHINAGAWA ◽  
Y. INAMASU
Keyword(s):  
Relaxation Time ◽  
Dielectric Properties ◽  
Dielectric Permittivity ◽  
Theoretical Analysis ◽  
Interfacial Polarization ◽  
Resonance Peak ◽  
The Other ◽  
Particle Rotation ◽  
The Difference ◽  
High Electric Field Strength

The electrorheological (ER) and dielectric properties were measured simultaneously on carbon and BaTiO 3 suspensions to investigate the relationships between the ER effect and the dielectric permittivities at high electric field strength. In the carbon suspension, frequency dependence of the ER effect and the 1st order dielectric permittivity shows a relaxation type of spectra, while in the 3rd order dielectric permittivity a resonance type of spectrum due to shear-induced particle rotation is observed. On the other hand, in BaTiO 3 suspension, a resonance type of spectrum is observed in each spectrum of the ER effect, 1st order and 3rd order dielectric permittivities. These resonance spectra are also attributed to the shear-induced particle rotation. From a theoretical analysis, it is indicated that the magnitude of the relaxation time of the interfacial polarization is responsible for the difference in the type of the spectra. It is also suggested that the shear-induced particle rotation would be a general property of the ER suspension since the resonance peak in the 3rd order dielectric permittivity, which is caused by the particle rotation, is observed in most of ER suspensions.

Structural Characterization for Ceramic Pyrochlores of Bi-Zn-Nb-O

2018 ◽  
Vol 912 ◽  
pp. 16-20 ◽  
Author(s):  
Francisco Werley Cipriano Farias ◽  
Antonio Sidnel Gomes Alves ◽  
Yuri Mikael dos Santos Alves ◽  
Francisca Maria Martins Pereira ◽  
Maria das Dores Bandeira Barroso ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
X Ray Diffraction ◽  
Orthorhombic Crystal ◽  
Ceramic Method ◽  
X Ray ◽  
Low Dielectric ◽  
Α Phase ◽  
Refinement Method ◽  
Tan Δ ◽  
High Dielectric

Ceramic pyrochlores, the basis of Bi2O3-ZnO-Nb2O5 (BZN), have dielectric properties of great interest, such a high dielectric constant (ε), a low dielectric loss tangent (tan δ) and a low coefficient of capacitance with temperature (TCC). The system has two main phases, Bi1,5ZnNb1,5O7 (α) and Bi2Zn0,67Nb1,33O7 (β) with cubic and orthorhombic crystal structures, and very different dielectric properties. The purpose of this article was to synthesize chemically homogeneous ceramic pyrochlores BZN-α and BZN-β, using the ceramic method in obtaining nanopowders and their characterizations by scanning electron microscopy (SEM), X-Ray Diffraction (XRD), and the Rietveld refinement method of the structures. The powders were weighed in stoichiometric proportions and calcined at 700 °C/2h, they were sintered at 900, 950 and 1000 °C/2h. A pure BZN-α phase was obtained, while the BZN-β has remained in phases as Bi5Nb3O15 and BiNbO4.

Dielectric Relaxation and Microwave Dielectric Properties of Bi2O3–ZnO–Ta2O5 Ceramics

2002 ◽  
Vol 17 (6) ◽  
pp. 1502-1506 ◽  
Author(s):  
Hyuk-Joon Youn ◽  
Clive Randall ◽  
Ang Chen ◽  
Tom Shrout ◽  
Michael T. Lanagan
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Low Frequency ◽  
Microwave Dielectric Properties ◽  
Β Phase ◽  
Microwave Dielectric ◽  
Α Phase ◽  
Frequency Independent ◽  
Temperature Relaxation ◽  
Two Phases

The permittivity of two primary phases within the Bi2O3–ZnO–Ta2O5 system was measured from 100 Hz to approximately 8.7 GHz. A cubic pyrochlore (Bi3/2Zn1/2)(Zn1/2Ta3/2)O7 phase (a phase) exhibited a dielectric constant of 71 at low frequency which decreased to 64 at approximately 10 GHz. A lower symmetry zirconolite Bi2(Zn1/3Ta2/3)2O7 phase (β phase) was also measured and had a frequency independent dielectric constant of 60. The temperature dependence of the capacitance (τC), measured from −55 to 120 °C, was 78 ppm/°C for the β phase and nonlinear for the α phase having no unique slope. The primary difference in dielectric properties between these two phases was a low-temperature relaxation of the α phase, which is modeled as a basic Debye-type relaxation.

Experimental evidence of soft mode in the smectic C*α phase of chiral ferroelectric liquid crystals

Soft Matter ◽  
2014 ◽  
Vol 10 (42) ◽  
pp. 8548-8557 ◽  
Author(s):  
Jerzy Hoffmann ◽  
Kamila Nowicka ◽  
Wojciech Kuczyński ◽  
Natalia Bielejewska
Keyword(s):  
Liquid Crystals ◽  
Dielectric Properties ◽  
Experimental Evidence ◽  
Soft Mode ◽  
Relaxation Spectrum ◽  
Smectic Liquid Crystals ◽  
Frequency Range ◽  
Ferroelectric Liquid Crystals ◽  
Smectic C ◽  
Α Phase

Dielectric properties of chiral smectic liquid crystals characterised by the occurrence of the C*α phase were investigated in the frequency range 10 Hz–1 MHz. In the range of existence of this phase the observed relaxation spectrum is composed of two kinds of mode, and not of a single one, as commonly thought.

Microtomy of spherical Al2O3 powders

1983 ◽  
Vol 41 ◽  
pp. 74-75
Author(s):  
E.J. Jenkins ◽  
D.S. Tucker ◽  
J.J. Hren
Keyword(s):  
Thin Film ◽  
Size Range ◽  
Particle Aggregation ◽  
Ion Milling ◽  
Thin Sections ◽  
Α Phase ◽  
Convenient Means ◽  
Van Der Waals Attraction ◽  
Negative Feature ◽  
Film Substrate

The size range of mineral and ceramic particles of one to a few microns is awkward to prepare for examination by TEM. Electrons can be transmitted through smaller particles directly and larger particles can be thinned by crushing and dispersion onto a substrate or by embedding in a film followed by ion milling. Attempts at dispersion onto a thin film substrate often result in particle aggregation by van der Waals attraction. In the present work we studied 1-10 μm diameter Al2O3 spheres which were transformed from the amprphous state to the stable α phase.After the appropriate heat treatment, the spherical powders were embedded in as high a density as practicable in a hard EPON, and then microtomed into thin sections. There are several advantages to this method. Obviously, this is a rapid and convenient means to study the microstructure of serial slices. EDS, ELS, and diffraction studies are also considerably more informative. Furthermore, confidence in sampling reliability is considerably enhanced. The major negative feature is some distortion of the microstructure inherent to the microtoming operation; however, this appears to have been surprisingly small. The details of the method and some typical results follow.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

High-resolution EM investigation about effect of stress on formation of ω-phase crystals in β-tttanium alloys

1996 ◽  
Vol 54 ◽  
pp. 1006-1007
Author(s):  
E. Sukedai ◽  
M. Shimoda ◽  
A. Fujita ◽  
H. Nishizawa ◽  
H. Hashimoto
Keyword(s):  
High Resolution ◽  
Titanium Alloys ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Zone Refining ◽  
Ω Phase ◽  
Α Phase ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Bcc Structure

ω-phase particles formed in β-titanium alloys (bcc structure) act important roles to their mechanical properties such as ductility and hardness. About the ductility, fine ω-phase particles in β–titanium alloys improve the ductility, because ω-phase crystals becomes nucleation sites of α-phase and it is well known that (β+α) duplex alloys have higher ductility. In the present study, the formation sites and the formation mechanism of ω-phase crystals due to external stress and aging are investigated using the conventional and high resolution electron microscopy.A β-titanium alloy (Til5Mo5Zr) was supplied by Kobe Steel Co., and a single crystal was prepared by a zone refining method. Plates with {110} surface were cut from the crystal and were pressured hydrostatically, and stressed by rolling and tensile testing. Specimens for aging with tensile stress were also prepared from Ti20Mo polycrystals. TEM specimens from these specimens were prepared by a twin-jet electron-polishing machine. A JEM 4000EX electron microscope operated at 400k V was used for taking dark field and HREM images.

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