Synthesis and dielectric properties of tungsten-based complex perovskites

2003 ◽  
Vol 18 (11) ◽  
pp. 2600-2607 ◽  
Author(s):  
D.D. Khalyavin ◽  
Jiaping Han ◽  
A.M.R Senos ◽  
P.Q. Mantas
Keyword(s):  
Dielectric Properties ◽  
Temperature Variation ◽  
Single Phase ◽  
Low Frequency ◽  
Double Perovskites ◽  
Dielectric Measurements ◽  
Anomalous Temperature ◽  
Conventional Solid State Reaction ◽  
Thermally Activated ◽  
Second Phases

Ba2MeWO6 (Me=Mg, Ni, Zn) double perovskites were prepared by the conventional solid-state reaction in a wide temperature range. Single-phase ceramics were obtained only at low temperatures approximately 1200°C, whereas a small amount of second phases existed in the samples sintered at higher temperatures. All the compounds are characterized by the cubic perovskite structure (space group Fm3m) with a complete NaCl type ordering between B-site ions. Anomalous temperature variation of the dielectric loss tangent found in the Ba2NiWO6 perovskite is supposed to be connected with a dielectric relaxation due to electronic hopping within thermally activated Ni3+-6W(6-1/6)+/W5+-6Ni(2+1/6)+ clusters. Dielectric measurements showed that the other two perovskites—Ba2ZnWO6 and Ba2MgWO6—exhibit a positive value of the temperature coefficient of permittivity. Such temperature variation is assumed to be caused by a considerable influence of the second polar mode involving B-site ion vibrations on the low-frequency dielectric properties.

Interaction of Point Defects in Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 115-122
Author(s):  
J. H. Bilgram ◽  
H. Gränicher
Keyword(s):  
Experimental Data ◽  
Dielectric Properties ◽  
Temperature Dependence ◽  
Point Defects ◽  
Low Frequency ◽  
Defect Concentration ◽  
Dielectric Measurements ◽  
Long Time ◽  
Nmr Techniques ◽  
Bjerrum Defect

AbstractThe interaction of point detects in ice has been neglected for a long time. Experimental data obtained from dielectric measurements on HF-doped crystals stimulated a new evaluation of the possibility of an interaction between Bjerrum defects and ions. In a previous paper it has been shown that this leads us to assume the existence of aggregates of Bjerrum defects and ions. In this paper these aggregates and Bjerrum defects are used to explain the dielectric properties of ice, especially the temperature dependence of the product of the high and low frequency conductivity σ0σ∞.The interaction of Bjerrum defects and impurity molecules leads to a dependence of the concentration of frenkel pairs on Bjerrum-defect concentration. At HF concentrations above the native Bjerrum-defect concentration the formation of a Frenkel pair is enhanced. This leads to the fast out-diffusion which has been studied in highly doped crystals by means of NMR techniques.

Temperature Dependence on Dielectric Response of La0.7Ba0.3Mn0.4Ti0.6O3 Ceramic

2015 ◽  
Vol 1107 ◽  
pp. 45-52
Author(s):  
Aaliyawani Ezzerin Sinin ◽  
Walter Charles Primus ◽  
Abdul Halim Shaari ◽  
Zainal Abidin Talib ◽  
Sinin Hamdan
Keyword(s):  
Dielectric Properties ◽  
Temperature Dependence ◽  
Low Frequency ◽  
Sintered Sample ◽  
Solid State Reaction Method ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
Low Frequencies ◽  
X Ray ◽  
Lcr Meter

Ceramic sample of La0.70Ba0.30Mn0.40Ti0.60O3 oxide has been prepared by the conventional solid-state reaction method. The sintered sample was characterized by using x-ray diffraction (XRD) and low frequency LCR meter. XRD result shows that the sample has a cubic structure with the existence of impurity phase. The dielectric properties of La0.70Ba0.30Mn0.40Ti0.60O3 measured from room temperature to 200°C shows that the dielectric permittivity is temperature dependence with strong dispersion at low frequencies. A circuit model based on the universal capacitor response function is also being used to represent the dielectric properties of the sample.

DIELECTRIC PROPERTIES OF DRY, GEOLOGIC MATERIALS

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 624-645 ◽  
Author(s):  
M. Saint‐Amant ◽  
David W. Strangway
Keyword(s):  
Dielectric Properties ◽  
Loss Tangent ◽  
Relaxation Times ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Relaxation Peak ◽  
Debye Relaxation ◽  
Thermally Activated ◽  
Geologic Materials ◽  
Frequency Independent

A detailed investigation of the dielectric properties of powdered and solid dry rocks in the frequency range of 50 hz to 2 mhz has revealed the following general characteristics: 1) All dry rocks, powdered and solid, show an increase in both the dielectric constant and the loss tangent as frequency decreases and as temperature increases. This dispersion is believed to be due to polarization associated with charge buildup at grain boundaries or at grain imperfections. 2) Dry powdered rocks often show a thermally‐activated relaxation peak with a typical Debye‐relaxation character. This is due to the presence of pyroxene and biotite and may be associated with other minerals. The relaxation peak is not seen in solid rocks, where it is hidden by the low‐frequency dispersion. 3) At high frequencies, the loss tangent approaches a constant value which is frequency independent. This behavior is observed in many dielectrics and may be the result of a distribution of relaxation times.

Structure Refinement and Dielectric Properties of Bismuth-Based Pyrochlores Containing Titanium

2014 ◽  
Vol 809-810 ◽  
pp. 770-777
Author(s):  
Bing Jie Zhang ◽  
Hui Ling Du ◽  
Cen Zhao
Keyword(s):  
Dielectric Properties ◽  
Oxygen Vacancies ◽  
Single Phase ◽  
Structure Refinement ◽  
Structural Defects ◽  
Free Oxygen ◽  
Oxygen Ions ◽  
Thermally Activated ◽  
Three Samples ◽  
Xrd Patterns

Bismuth-based pyrochlore dielectrics with the formula (Bi1.5Zn0.5)(Ti1.5M0.5)O7 (M = Nb, Ta and Sb) have been synthesized to investigate the influence of M between the dielectric properties and crystal structure. The XRD patterns show that all of the three samples give single phase. The refined data by GSAS program and the bond valence theory were used to analyze the differences in dielectric properties with occupation of different ions in B site. The dielectric constant of BZTS is the smallest in the BZTM, which is due to the polarizability and the contribution of BO6octahedra which has weak correlation when Sb placed into the center of the octahedra would also result in small αε. When it comes to the moderate temperature range, oxygen vacancies migration was thermally activated as the carriers mechanism, and the different activation energies is related to the association and the disassociation of massive complex defects. The Rietveld refinement data pointed that with the respectively change of B ions, more oxygen vacancies and free oxygen ions are provided by structural defects to participate in the conduction which can lead to the σ increase gradually.

Dielectric Properties of A, B-Site Mn-Doped LaTiO3+δ

2018 ◽  
Vol 921 ◽  
pp. 78-84
Author(s):  
Yan Chen ◽  
Qi Qi Yan ◽  
Yi Min Cui
Keyword(s):  
Dielectric Properties ◽  
Dielectric Response ◽  
Low Frequency ◽  
Solid State Reaction Method ◽  
Dielectric Constants ◽  
Conventional Solid State Reaction ◽  
Dielectric Characteristics ◽  
Low Dielectric ◽  
A Site ◽  
Mn Doped

A-site Mn-doped La1-xMnxTiO3+δand B-site doped LaMnxTi1-xO3+δ(x = 0.1, 0.2) composites were synthesized by conventional solid-state reaction method. The low-frequency complex dielectric properties of the composites were investigated as functions of temperature (77 K ≤ T ≤ 360 K) and frequency (100 Hz ≤ f ≤ 1 MHz), respectively. The dielectric constants of A-site doped samples are higher than that of B-site doped samples. The loss tangents of the low doped samples are much less than that of the high doped samples. The A-site doped composites exhibit intrinsic dielectric response with a dielectric constant of ~40 in the temperature below 250 K. Interestingly, the dielectric constants of B-site doped composites always increased in the temperature range from 77 to 360 K. And it is clearly observed that extraordinarily low dielectric loss tangents appear in LaMn0.1Ti0.9O3+δ, which are much lower than that of LaMn0.2Ti0.8O3+δ. These changes indicate that the doped content can affect the intrinsic dielectric characteristics significantly.

scholarly journals Enhancement of Dielectric Properties via Crystal Structure and Microstructure Control in the (K0.5Na0.5)NbO3-SrTiO3 System

2021 ◽  
Vol 59 (7) ◽  
pp. 499-504
Author(s):  
Seong Eun Lee ◽  
Jun-Hyeong Kwon ◽  
Kyoung-Seok Moon
Keyword(s):  
Dielectric Properties ◽  
Solid Solutions ◽  
Single Phase ◽  
Sintering Temperature ◽  
Dielectric Materials ◽  
Dielectric Constants ◽  
Conventional Solid State Reaction ◽  
Cubic Structure ◽  
Two Phases ◽  
Structure And Microstructure

Solid solutions and composites of a mixture of (K0.5Na0.5)NbO3 (KNN) and SrTiO3 (ST) were respectively synthesized by different process routes using a conventional solid state reaction. All starting materials were mixed simultaneously and calcined at 800 oC for 4 h to obtain the solid solutions of KNN-ST. Meanwhile, the composites of KNN-ST were obtained by mixing the synthesized KNN and synthesized ST, respectively. KNN-ST calcined powders were sintered at 1150, 1250 and 1300 oC for 2 h. The calcined powders, in which all starting materials were mixed at once, showed a single-phase pseudo-cubic structure after sintering. On the other hand, the powders with the mixture of KNN and ST had two phases of cubic ST and orthorhombic KNN as composites. The dielectric loss values of all samples decreased as the sintering temperature increased because of increased densification. The dielectric constants of the solid solutions were increased as the sintering temperature increased, however, the dielectric constants of the composites decreased with increasing sintering temperature. It was concluded that, for enhanced dielectric properties, the dielectric materials should be synthesized as solid solutions.

Microwave Dielectric Properties of Low-Fired Nd2Ti2SiO9 Ceramics with BaCu (B2O5) Addition

2014 ◽  
Vol 941-944 ◽  
pp. 509-512
Author(s):  
Guo Hua Chen ◽  
Xiao Ling Kang ◽  
Yun Yang
Keyword(s):  
Dielectric Properties ◽  
Firing Temperature ◽  
Single Phase ◽  
Microwave Dielectric Properties ◽  
Secondary Phase ◽  
Xrd Analysis ◽  
Sintering Behavior ◽  
Reaction Route ◽  
Conventional Solid State Reaction ◽  
Microwave Dielectric

Nd2Ti2SiO9 ceramics with low-firing temperature by BaCu (B2O5) addition were prepared by the conventional solid-state reaction route and the sintering behavior, phase purity, microstructure and microwave dielectric properties were investigated. The XRD analysis results show a single phase Nd2Ti2SiO9 is formed and no secondary phase is found. Addition of BaCu (B2O5) can effectively lower the firing temperature by about 150 °C. The Nd2Ti2SiO9 ceramics with 4wt% BaCu (B2O5) sintered at 1150 °C exhibit good microwave dielectric properties with a permittivity of 28.8, a Q×f value of 16110 GHz, and a temperature coefficient of resonant frequency of-12.3 ppm /°C, which is suitable for microwave communication applications.

Interaction of Point Defects in Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 115-122 ◽  
Author(s):  
J. H. Bilgram ◽  
H. Gränicher
Keyword(s):  
Experimental Data ◽  
Dielectric Properties ◽  
Temperature Dependence ◽  
Point Defects ◽  
Low Frequency ◽  
Defect Concentration ◽  
Dielectric Measurements ◽  
Long Time ◽  
Nmr Techniques ◽  
Bjerrum Defect

Abstract The interaction of point detects in ice has been neglected for a long time. Experimental data obtained from dielectric measurements on HF-doped crystals stimulated a new evaluation of the possibility of an interaction between Bjerrum defects and ions. In a previous paper it has been shown that this leads us to assume the existence of aggregates of Bjerrum defects and ions. In this paper these aggregates and Bjerrum defects are used to explain the dielectric properties of ice, especially the temperature dependence of the product of the high and low frequency conductivity σ 0 σ ∞. The interaction of Bjerrum defects and impurity molecules leads to a dependence of the concentration of frenkel pairs on Bjerrum-defect concentration. At HF concentrations above the native Bjerrum-defect concentration the formation of a Frenkel pair is enhanced. This leads to the fast out-diffusion which has been studied in highly doped crystals by means of NMR techniques.

scholarly journals Preparation, crystal structure, and dielectric characterization of Li2W2O7 ceramic at RF and microwave frequency range

2017 ◽  
Vol 07 (01) ◽  
pp. 1720001 ◽  
Author(s):  
Jinwu Chen ◽  
Chunchun Li ◽  
Dan Wang ◽  
Huaicheng Xiang ◽  
Liang Fang
Keyword(s):  
Dielectric Properties ◽  
Single Phase ◽  
Microwave Dielectric Properties ◽  
Microwave Frequency ◽  
Solid State Reaction Method ◽  
Frequency Range ◽  
Conventional Solid State Reaction ◽  
Dielectric Characterization ◽  
Microwave Dielectric

Single phase Li2W2O7 with anorthic structure was prepared by the conventional solid-state reaction method at 550[Formula: see text]C and the anorthic structure was stable up to 660[Formula: see text]C. The dielectric properties at radio frequency (RF) and microwave frequency range were characterized. The sample sintered at 640[Formula: see text]C exhibited the optimum microwave dielectric properties with a relative permittivity of 12.2, a quality factor value of 17,700[Formula: see text]GHz (at 9.8[Formula: see text]GHz), and a temperature coefficient of the resonant frequency of [Formula: see text]232[Formula: see text]ppm/[Formula: see text]C as well as a high relative density [Formula: see text]94.1%. Chemical compatibility measurement indicated Li2W2O7 did not react with aluminum electrodes when sintered at 640[Formula: see text]C for 4[Formula: see text]h.

Raman And Fluorescence Spectra Observed in Laser Microprobe Measurements of Several Compositions in the Ln-Ba-Cu-O System

1990 ◽  
Vol 48 (2) ◽  
pp. 278-279
Author(s):  
Edgar S. Etz ◽  
Thomas D. Schroeder ◽  
Winnie Wong-Ng
Keyword(s):  
Fluorescence Spectra ◽  
Single Phase ◽  
X Ray Diffraction ◽  
Ceramic Powders ◽  
Conventional Solid State Reaction ◽  
X Ray ◽  
Raman Microprobe ◽  
Methods Of Synthesis ◽  
Compositional Homogeneity ◽  
Processing Techniques

We are investigating by Raman microprobe measurements the superconducting and related phases in the LnBa2Cu3O7-x (for x=0 to 1) system where yttrium has been replaced by several of the lanthanide (Ln = Nd,Sm,Eu,Ho,Er) elements. The aim is to relate the observed optical spectra (Raman and fluorescence) to the compositional and structural properties of these solids as part of comprehensive materials characterization. The results are correlated with the methods of synthesis, the processing techniques of these materials, and their superconducting properties. Of relevance is the substitutional chemistry of these isostructural systems, the differences in the spectra, and their microanalytical usefulness for the detection of impurity phases, and the assessment of compositional homogeneity. The Raman spectra of most of these compounds are well understood from accounts in the literature.The materials examined here are mostly ceramic powders prepared by conventional solid state reaction techniques. The bulk samples are of nominally single-phase composition as determined by x-ray diffraction.

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