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Journal ArticleDOI

Far-IR reflectance study on B-site disordered Ba (Zn1/3Ta2/3)O3 dielectric resonator

TL;DR: In this paper, a far-IR reflectance spectrum of a disordered Ba(Zn1/3Ta2/3)O3 dielectric resonator has been studied with the Generalized Oscillator model.
About: This article is published in Materials Research Bulletin.The article was published on 2000-06-01. It has received 11 citations till now. The article focuses on the topics: Dielectric resonator & Dielectric.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1 3 B" 2 / 3 )O 3, where B' = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed.
Abstract: Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1 3 B" 2 / 3 )O 3 , where B' = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed. It was found that allthe 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(Zn 1 / 3 Nb 2 / 3 )O 3 occurred below 1380 °C. Ba(Ni 1 / 3 Nb 2 / 3 )O 3 (BNN) and Ba(Mg 1 / 3 Nb 2 / 3 )O 3 (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., Ba 3 Nb 5 O 1 5 ) and point defects, dominated the dielectric loss at microwave frequencies. Ba(Mg 1 / 3 Ta 2 / 3 )O 3 (BMT) remained single phase up to 1630 °C. Above this temperature, the Ba 3 Ta 5 O 1 5 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.

50 citations

Journal ArticleDOI
TL;DR: In this article, the symmetry of perovskite ceramics is characterized by x-ray diffraction, far-infrared reflectance, Raman spectroscopy, and microwave dielectric properties.
Abstract: La(Mg0.5Ti(0.5−x)Snx)O3 perovskite ceramics with composition (x=0.0−0.5) are prepared by the solid state reaction method. The ceramics are characterized by x-ray diffraction, far-infrared reflectance, Raman spectroscopy, and microwave dielectric properties. The symmetry of ceramics is monoclinic with P21/n space group. Intrinsic dielectric constant and loss are estimated by fitting reflectance to the four-parameter semiquantum model. Transverse optic phonon mode strengths and average phonon damping are calculated. The modes corresponding to B-site ordering are identified in Raman spectra and the A1g mode of La(MgTi)0.5O3 is analyzed by assuming two merging modes. The variation of long-range order is correlated with full width half maximum of the A1g mode. Microwave measurements are carried out in the frequency range of 8–10 GHz. The dielectric constant (e′) is found to gradually decrease from 28.4 to 19.7 with an increase in tin concentration, whereas the temperature coefficient of resonant frequency (τf)...

48 citations

Journal ArticleDOI
01 Mar 2019
TL;DR: In this article, lattice dynamics and phonon characteristics of complex perovskite microwave dielectric ceramics (MWDCs) are summarized and presented in detail to introduce remarkable progress in this field and make a guide for the design of novel advanced MWDCs.
Abstract: Complex perovskite microwave dielectric ceramics (MWDCs) of A ( B 1 / 3 ′ B 2 / 3 ′ ′ ) O 3 -type (A = Ba, Sr,…; B′ = Mg, Zn,…; B″ = Nb, Ta), which exhibit excellent dielectric properties, have currently been widely used in microwave and millimetre wave devices. Vibrational spectra, including both Raman and far-infrared (FIR) spectra, are powerful tools to investigate the atomic thermal vibrational properties of MWDCs and reveal the intrinsic origin of dielectric properties. In this review, lattice dynamics and phonon characteristics of the A ( B 1 / 3 ′ B 2 / 3 ′ ′ ) O 3 -type MWDCs are summarised and presented in detail to introduce remarkable progress in this field and make a guide for the design of novel advanced MWDCs. The atomic sites and the corresponding modes in Raman and FIR spectra are identified and illuminated. The effects of the processing conditions and the ordered superstructures in the nanoscale region on vibrational modes are summarised systemically. Intrinsic properties can be extrapolated from the fitting results of FIR spectroscopy, which were also discussed based on the Kramers–Kronig relations, Lorentz three-parameter classical model and four-parameter semi-quantum model. The correlations between vibrational modes (phonons), crystal structures, and dielectric properties are created, which can help to build the mathematical models so as to understand the structure–property relationship of MWDCs better.

21 citations

Journal ArticleDOI
TL;DR: In this article, the effects of CuO and TiO2 additives on the microstructure and microwave dielectric properties of Al2O3 ceramics were investigated.
Abstract: The effects of CuO and TiO2 additives on the microstructure and microwave dielectric properties of Al2O3 ceramics were investigated. Al2O3 ceramics with CuO and TiO2 additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti4Cu2O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO2 content, due to the formation of the second phase Ti4Cu2O. However, the varying behaviors of the dielectric constant (ɛr) and temperature coefficients (τf) were associated with phase constitutions, as a result of the change of CuO and TiO2content. The τf can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO2. The specimens with 0.5 wt.% CuO and 7 wt.% TiO2 sintered at 1,360 °C for 4 h showed ɛr of 11.8, Qf value of 30,000 GHz, and τf of −7 ppm/°C.

15 citations

Journal ArticleDOI
TL;DR: In this article, the structural and electrical properties of LiPO3 glass over a wide range of frequencies (10 Hz - 2 MHz) and temperatures (290 K -627 K) were studied at different frequencies.
Abstract: This paper reports on the structural and electrical properties of LiPO3 glass over a wide range of frequencies (10 Hz - 2 MHz) and temperatures (290 K -627 K). The temperature dependence of a.c. conductivity is studied at different frequencies. The d.c. conductivity is due to the hopping of lithium ions. A theoretical model and mathematical fit of conductivity measurements are used for characterization of the ionic hopping motion connected with the mobility of conducting Li+ ions. The acoustic attenuation spectroscopy can be useful technique for the study of relaxation processes in ion conducting glasses too. Raman experiments showed the rings and chains configuration at the medium range.

10 citations

References
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Journal ArticleDOI
TL;DR: In this article, a novel technique for the measurement of dielectric and magnetic properties of a homogeneous isotropic medium in the range of approximately 3 to 100 kmc is described.
Abstract: A novel technique for the measurement of dielectric and magnetic properties of a homogeneous isotropic medium in the range of approximately 3 to 100 kmc is described. An accuracy of /l.chemc/ 1 per cent is possible in the determination of permittivity or permeability in those cases where the loss tangent is sulliciently small. The measuring structure is a resonator made up of a right circular cyndrical dielectric rod placed between two parallel conducting plates. For measurement of permittivity two or more resonant TE/sub onl/ mode frequencies are determined whereas for the measurement of permeability two or more resonant TM/sub onl/ mode frequencies are determined. The dielectric or magnetic properties are computed from the resonance frequencies, structure dimensions, and unloaded Q. Since the loss tangent is inversely proportional to the unloaded Q of the structure, the precision to which Q is measured determines the accuracy of the loss tangent.

2,648 citations

Journal ArticleDOI
TL;DR: In this article, a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies was proposed and experimental results of the temperature dependence of the relative dielectrics constant of nonmagnetic materials with /spl epsilon/sub r/, varying from 4 to 60, and also loss tangent measurements at room temperature.
Abstract: Theory and experimental results are presented to show the possibility of using a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies. Results of the temperature dependence of the relative dielectric constant of nonmagnetic materials with /spl epsilon//sub r/, varying from 4 to 60 are presented and also loss tangent measurements at room temperature. The complex permittivity and permeability of a number of garnet materials has also been measured with 4/spl pi//spl gamma/M/sub s/ / /spl omega/ varying from 0.25 to 0.8. The measured real part of the permeability is in good agreement with the theoretical predictions of Schlomann and the imaginary part of the permeability agrees with measurements by Green et al. on similar materials.

1,247 citations

Journal ArticleDOI
TL;DR: In this article, the dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated.
Abstract: The dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.

549 citations

Journal ArticleDOI
TL;DR: In this article, the authors show that the loss of ZnO explains the improved microwave loss quality for Ba(Zn /SUB 1/3/Ta/SUB 2/3 )O3 ceramics which have been sintered at high temperatures or longer times.
Abstract: Loss of ZnO explains the improved microwave loss quality (Q) for Ba(Zn /SUB 1/3/ Ta /SUB 2/3/ )O3 ceramics which have been sintered at high temperatures or longer times. Ordering of Zn and Ta is complete in 60 h at 1400C, but crystallographic distortion and Q continue to increase up to 120 h. As ZnO volatilizes from the sample, Ba replaces Zn on the B sites and permits additional crystallographic distortion; meanwhile, barium tantalate phases also appear. Crystallographic compositional data are presented to confirm this interpretation.

284 citations

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to find a correlation between ionic parameters of ceramic materials and their complex permittivity at microwave frequencies, using the Fourier transform infrared reflectivity spectra in the 30-4000 cm−1 range.
Abstract: An attempt has been undertaken to find a correlation between ionic parameters of ceramic materials and their complex permittivity at microwave frequencies Ten Ba(B1/2’B1/2‘)O3 complex perovskite compounds (B’=Y3+, In3+, Nd3+, Gd3+; B‘=Nb5+, Ta5+ and B’=Mg2+, Cd2+, B‘=W6+) are compared in order to study the effect of ionic radii, mass, and valence state on dielectric properties Fourier transform infrared reflectivity spectra in the 30–4000 cm−1 range were measured and evaluated by means of Kramers–Kronig analysis and classical oscillator fit The data were extrapolated below the measured frequency range to estimate the intrinsic microwave losses The correlations between loss, permittivity, ionic size, mass, and effective charge and polar‐phonon mode parameters were investigated Ionic size was revealed to be the most important parameter, determining the tolerance factor of the structure packing and through this controlling the phonon frequencies and dampings as well as the extrapolated low‐frequency int

148 citations