Method for Calculation of Dielectric Properties of Modulated Semiconducting Structures

1995 ◽  
Vol 417 ◽  
Author(s):  
V. Yu. Mirovitskii ◽  
O. Yu. Mashtakov
Keyword(s):  
Dielectric Properties ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Landau Theory ◽  
Point Of View ◽  
Dielectric Constants ◽  
Initial Structure ◽  
Numerical Estimation ◽  
Spatial Correlations ◽  
Phenomenological Landau Theory

AbstractA new method for calculation the effects of composition modulation upon the dielectric properties of semiconductors is proposed. Specific consideration is carried out for ultrathin [001] oriented (AIIICV)m(BIIICV)n superlattices (SL). These SL are formally considered to result from complete A(B) atoms orderiig over a-sublattice in a hypothetical initial structure –bulk mixed crystal (AxB1−x)C with zincblende lattice and x = m/(m + n). From this point of view a variation in dielectric constants tensor (DCT) induced by the ordering can be calculated nearly in a spirit of the phenomenological Landau theory of second-order phase transitions. It is shown that the changes in spatial dispersion of the DCT are expressed through the coefficients at invariants in the expansion of SL thermodynamic potential in a power series of the order parameter components. The way is described for numerical estimation of the thermodynamic potential coefficients from microscopic model of the initial alloy which take account of spatial correlations in A(B) atoms distribution.

Elastic Modulus of the (GaA.s)m(A.l A.s)n Superlattices

1992 ◽  
Vol 291 ◽  
Author(s):  
Vadim Yu. Mirovitskii
Keyword(s):  
Elastic Modulus ◽  
Order Parameter ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Landau Theory ◽  
Point Of View ◽  
The Other ◽  
Symmetry Properties ◽  
Phenomenological Landau Theory ◽  
Elastic Modulus Tensor

ABSTRACTThe ultrathin (GaAs)m (AlAs)n superlattices ( SL ) grown along [001] are formally considered as a result, of ordering-type phase transition from an initial hypothetical mixed crystal (Gax Al1-x)As with x = m/(m+n) . From this point of view changes of elastic modulus tensor (EMT) induced by ordering can he calculated nearly in a spirit of phenomenological Landau theory of second-order phase transitions. It .is shown that a change of EMT component. S66 is completely determined by symmetry properties of two translational (Dzyaloshinskji) invariants of m+n power .in the expansion of SL thermodynamic potential in a power series .in order parameter components. The changes of the other EMT components depend on the second power of order parameter .The expressions are found out to connect. EMT of a definite ordered phase (SL - family with m+n = 3) with that, of the initial one.

Calculation of the (GaAs)m(AlAs)n Superlattice Piezoelectric Constants

1994 ◽  
Vol 356 ◽  
Author(s):  
Vadim. Yu. Mirovitskii
Keyword(s):  
Phase Transitions ◽  
Order Parameter ◽  
Thermodynamic Potential ◽  
Mixed Crystal ◽  
Piezoelectric Properties ◽  
Phenomenological Theory ◽  
Initial Structure ◽  
Spatial Correlations ◽  
Specific Calculations ◽  
Piezoelectric Constants

AbstractA new method for calculation of superlattice (SL) piezoelectric properties is proposed. It is used for derivation of the piezoelectric constants of ultrathin [001] oriented (GaAs)m(AlAs)n SL. These SL are formally considered to result from complete ordering Ga (Al) atoms over a-positions of a hypothetical initial structure of a bulk mixed crystal of (GaxAl1-x)As with x=m/(m+n). This viewpoint allows us to develop a method which is close to the Landau phenomenological theory of second- order phase transitions and which is intended for calculation of the SL crystal-lophysical constants. It is shown that a nontrivial term has much significance in changing one of the piezoelectric constants, γz,xy, when the initial structure is transformed into a SL. This term is composed of coefficients at three translational invariants (Dzyaloshinskii invariants) in the expansion of the thermodynamic potential of the “ordering” system in a power series of the order parameter components. The values of these coefficients must be obtained from microscopic calculations which take account of spatial correlations in Ga(Al) atomic distribution. Specific calculations are carried out for a SL with m+n=3.

scholarly journals Dielectric Properties of Wood-Polymer Composites: Effects of Frequency, Fiber Nature, Proportion, and Chemical Composition

2021 ◽  
Vol 5 (6) ◽  
pp. 141
Author(s):  
Imen Elloumi ◽  
Ahmed Koubaa ◽  
Wassim Kharrat ◽  
Chedly Bradai ◽  
Ahmed Elloumi
Keyword(s):  
Dielectric Properties ◽  
Polymer Composites ◽  
Wide Frequency Range ◽  
Dielectric Constants ◽  
Cellulose Content ◽  
Wood Fibers ◽  
Low Frequencies ◽  
Wood Polymer ◽  
Wood Polymer Composites ◽  
New Applications

The characterization of the dielectric properties of wood–polymer composites (WPCs) is essential to understand their interaction with electromagnetic fields and evaluate their potential use for new applications. Thus, dielectric spectroscopy monitored the evolution of the dielectric properties of WPCs over a wide frequency range of 1 MHz to 1 GHz. WPCs were prepared using mixtures of different proportions (40%, 50%, and 60%) of wood and bark fibers from various species, high-density polyethylene, and maleated polyethylene (3%) by a two-step process, extrusion and compression molding. Results indicated that wood fibers modify the resistivity of polyethylene at low frequencies but have no effect at microwave frequencies. Increasing the fiber content increases the composites’ dielectric properties. The fibers’ cellulose content explains the variation in the dielectric properties of composites reinforced with fibers from different wood species. Indeed, composites with high cellulose content show higher dielectric constants.

Crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 tungsten–bronze glass–ceramics

2001 ◽  
Vol 16 (7) ◽  
pp. 2057-2063 ◽  
Author(s):  
Jiin-Jyh Shyu ◽  
Hsin-Wei Peng
Keyword(s):  
Heat Treatment ◽  
Dielectric Properties ◽  
Tungsten Bronze ◽  
Glass Ceramics ◽  
Dielectric Behavior ◽  
Dendritic Morphology ◽  
Dielectric Constants ◽  
Two Stage ◽  
Tetragonal Tungsten Bronze ◽  
Stage Heat Treatment

The crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 glass–ceramics were investigated. One- and two-stage heat-treatment methods were used to convert the parent glass to glass–ceramics. Strontium barium niobate (SBN) with a tetragonal tungsten-bronze structure formed as the major crystalline phase. When the crystallizing temperature/time was increased, the secondary crystalline BaGe2O5 phase coexisted with SBN. BaGe2O5 formed as a surface layer grown from the surface into the interior of the sample. The dendritic morphology of SBN crystals was examined. The glass–ceramics crystallized by two-stage heat treatment have higher dielectric constants than those crystallized by one-stage heat treatment. The highest dielectric constant that was obtained in the present glass–ceramics was 320. The glass–ceramics showed relaxor-type dielectric behavior.

Epitaxial Growth and Anisotropic Dielectric Properties of La-Doped Bi4Ti3O12 Thin Films

2007 ◽  
Vol 124-126 ◽  
pp. 177-180
Author(s):  
Jang Sik Lee ◽  
Q.X. Jia
Keyword(s):  
Thin Films ◽  
Dielectric Constant ◽  
Dielectric Properties ◽  
Bottom Electrode ◽  
Dielectric Constants ◽  
The Other ◽  
Field Range ◽  
Anisotropic Dielectric ◽  
Dielectric Nonlinearity ◽  
La Doped

To investigate the anisotropic dielectric properties of layer-structured bismuth-based ferroelectrics along different crystal directions, we fabricate devices along different crystal orientations using highly c-axis oriented Bi3.25La0.75Ti3O12 (BLT) thin films on (001) LaAlO3 (LAO) substrates. Experimental results have shown that the dielectric properties of the BLT films are highly anisotropic along different crystal directions. The dielectric constants (1MHz at 300 K) are 358 and 160 along [100] and [110], respectively. Dielectric nonlinearity is also detected along these crystal directions. On the other hand, a much smaller dielectric constant and no detectable dielectric nonlinearity in a field range of 0-200 kV/cm are observed for films along [001] when c-axis oriented SRO is used as the bottom electrode.

A study of the dielectric properties of PZT and PT ceramics depending on the lattice distortion

2005 ◽  
Vol 83 (5) ◽  
pp. 527-540 ◽  
Author(s):  
Duan -Ming Zhang ◽  
Xiang -Yun Han ◽  
Zhi -Hua Li ◽  
Zhi -Cheng Zhong ◽  
Wen -Sheng Yan ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Lattice Distortion ◽  
Volume Fraction ◽  
Structural Phase ◽  
Rhombohedral Phase ◽  
Point Of View ◽  
Distribution Model ◽  
Coexistence Region ◽  
Pzt Ceramics ◽  
Lattice Distortions

Depending on the lattice distortion, the dielectric properties of PZT and PT ceramics are studied from a structural phase transition point of view. The study involves a more profound physical process than the study of the relation between the dielectric properties and composition x. Two equations connecting the dielectric properties and the lattice distortions are established in the tetragonal and rhombohedral phase regions. In particular, the relation between the dielectric properties and the lattice distortion is investigated in the phase coexistence region of PZT ceramics using a phase statistical distribution model, and we determine the fitting value of the volume fraction of the tetragonal phase VT to composition x in the equation. All the fitting results indicate that our results are very consistent with the related experimental data for PZT and PT ceramics.PACS Nos.: 64.70.–p, 77.22.–d, 77.84.–s

Technique for Measuring the Dielectric Properties of Minerals as a Function of Temperature and Density at Microwave Heating Frequencies

1990 ◽  
Vol 189 ◽  
Author(s):  
Johanna B. Salsman
Keyword(s):  
Dielectric Properties ◽  
Microwave Heating ◽  
Research Effort ◽  
Coaxial Line ◽  
Dielectric Constants ◽  
Dielectric Constant And Loss ◽  
Electrical Conductivities ◽  
Natural Density ◽  
The Common ◽  
Method Of Measurement

ABSTRACTAs part of the research effort on investigating the effects of microwave energy absorption on the chemical and physical properties of minerals and ores, the Bureau of Mines, Tuscaloosa Research Center has developed a technique of measuring the dielectric constant and loss tangent of minerals at the common microwave heating frequencies. The objective was to establish a reliable data base to aid in predicting the effects of microwave heating on minerals.In this phase of microwave research, the Bureau measured the dielectric properties of powdered minerals with medium to high electrical conductivities (a ≥ 0.02 Mho/m) in the frequency range of 300 MHz to 3 GHz using an open-ended coaxial line probe connected to an HP 8753A network analyzer. Since the minerals were prepared as powders, techniques were used to relate the measured dielectric properties of the powdered minerals to the dielectric properties of the mineral at Its theoretical or natural density. Also, these measurements were performed as a function of temperature, from 25° to 325° C.The measured values of the dielectric constants and loss tangents using this method were accurate within ±5 percent. This report describes the method of measurement and discusses the results of the Bureau's investigations into dielectric properties of minerals.

A facile method for the preparation of aliphatic main-chain benzoxazine copolymers with high-frequency low dielectric constants

2018 ◽  
Vol 9 (21) ◽  
pp. 2913-2925 ◽  
Author(s):  
Ming Zeng ◽  
Jiangbing Chen ◽  
Qingyu Xu ◽  
Yiwan Huang ◽  
Zijian Feng ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
High Frequency ◽  
Main Chain ◽  
Polymerization Kinetics ◽  
Dielectric Constants ◽  
Low Dielectric

The effects of the reaction solvent on the preparation, polymerization kinetics, and high-frequency dielectric properties of aliphatic main-chain benzoxazine copolymers were investigated.

Radiothermal radiation method for aqueous solutions

2021 ◽  
Author(s):  
L.A. Morozova ◽  
S.V. Savel’ev
Keyword(s):  
Dielectric Properties ◽  
Alkali Metal ◽  
Thermal Radiation ◽  
Aqueous Solutions ◽  
Physical Properties ◽  
Dielectric Constants ◽  
Water Molecules ◽  
Absorption Coefficients ◽  
Basic Substance ◽  
High Dilutions

For the first time, an ultra-high-sensitivity method for measuring radio-thermal radiation was developed and used in practice in order to establish the difference in the physical properties of aqueous solutions of substances in the millimeter region of the spectrum. The method is used to study the dynamics of the dielectric properties of aqueous solutions depending on the composition of the base substance and its concentration. The dynamics of dielectric properties establishes a one-to-one correspondence between the number and concentration of ions of the dissolved basic substance contained in water and the number of water molecules involved in cooperative interaction, which gives a consistent microscopic picture of ion-water cooperative interactions in the studied aqueous solutions of K2SO4 and Cs2SO4. The density of water molecules perturbed by the ions of the base substance contained in the hydration shell at normal concentrations is proportional to the number of ions, while the transition to weaker solutions leads to the creation of multilayer hydration shells. This means that the number of perturbed water molecules, depending on the number of ions, increases according to a law different from linear. In accordance with the experimental data, the values of the absorption coefficients of aqueous solutions were determined in a wide range of concentrations for alkali metal sulfates. It is noted that alkali metal sulfates have physical properties that generalize the dynamics of dielectric constants depending on the concentration of the base substance. A monotonic increase in the values of the absorption coefficients of solutions with a decrease in the concentration of basic substances in the region of high dilutions was established with individual dynamics for each basic substance, reflecting the total hydration changes in salt solutions. Research has shown that the proposed method for measuring radio-thermal radiation fixes a significant difference in the values of the dielectric constants of aqueous solutions at high dilutions from their values for water.

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