Preparation, characterization and microwave dielectric properties of Ba(B 1/2Nb1/2)O3 [B = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb and In] ceramics (original) (raw)
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Low-loss dielectric ceramics based on Ba(B0 1/2Ta1/2)O3 (B0 5La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In) complex perovskites have been prepared by the solid-state ceramic route. The dielectric properties (er, Qu, and tf) of the ceramics have been measured in the frequency range 4–6 GHz by the resonance method. The resonators have a relatively high dielectric constant and high quality factor. Most of the compounds have a low coefficient of temperature variation of the resonant frequencies. The microwave dielectric properties have been improved by the addition of dopants and by solid solution formation. The solid solution Ba[(Y1xPrx)1/2Ta1/2]O3 has x50.15, with er533.2, Quf551,500 GHz, and tf 0. The microwave dielectric properties of Ba(B0 1/2Ta1/2)O3 ceramics are found to depend on the tolerance factor (t), ionic radius, and ionization energy.
The Sr(B0 0.5Ta0.5)O3 ceramics where B0 5La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, and Yb have been prepared by the conventional solid-state ceramic route and their microwave dielectric properties have been investigated. The structure and microstructure of the ceramics have been characterized by X-ray diffraction and scanning electron microscope techniques. The relative permittiviy (er) varies linearly with B0-site ionic radii, except for La, and the temperature coefficient of resonant frequency (sf) varies linearly with the tolerance factor. The Sr(B0 0.5Ta0.5)O3 ceramics have er in the range 25.9–32, Quf54500–54 300 GHz, and sf579 to 42 ppm/1C. A slight deviation from stoichiometry affects the dielectric properties of these double perovskites. Partial substitution of Ba for Sr could tune the dielectric properties. Addition of rutile (TiO2) lowered the sintering temperature and improved the dielectric properties of Sr(B0 0.5Ta0.5)O3 ceramics.
Microwave dielectric properties of double perovskite ceramics Ba2Zn1−xCaxWO6(x=0−0.4)
Ceramics International, 2015
The structural, vibrational and microwave dielectric properties of double perovskite ceramics 2 1 6 Ba Zn Ca WO (x 0 0.4) x x − = − were investigated. The samples were sintered at different temperatures in the range 1300 1400 °C for 4 h. The grown samples were characterized by means of X ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersive X ray spectroscopy analysis. Microwave dielectric properties of the samples were measured using the 01į TE resonance mode of the cylindrical pellets. The relative permittivity (r ε), calculated using Clausius Mossotti equation is found to be comparable with the experimental results. Our analysis shows that the tolerance factor () t as well as the temperature coefficient of resonant frequency () f τ of these perovskites decreases with the increase in Ca content. The value of f τ is zero for the samples with 0.3 x = and 0.4.
Microwave dielectric resonators based on Ba[( Bi,Dl)1/2 Nb1/2]O3 (D= Y, Pr, Sm, Gd, Dy, Er)
Dielectric resonator ceramics with composition formula Ba[(D~.:Bi,,)Nb,,]O,, where D3+= Y, Pr, Sm, Gd, Dy and Er, were prepared by the conventional ceramic preparation route. The dielectric properties at microwave frequencies were measured using a resonance method. The ceramics showed the dielectric constant (E,) above 40 and Q Xf> 1.5 X IO”. The temperature coefficient of resonant frequency (or) varied from - 27 to + 15 ppm K- ‘_ The dielectric properties and low processing temperatures make these materials suitable for practical applications.
Ba(Tb12Nb12)O3: A new ceramic microwave dielectric resonator
Materials Letters, 1997
has been prepared and characterized in the microwave frequency region. 1 wt% CeO, is used as additive to reduce the sintering temperature. The sintered samples were characterized by XRD, SEM and Raman spectroscopic methods. Microwave DR properties such as Ed, Q factor and temperature-coefficient of resonant frequency (~~1 have been measured using a HP 8510 B Network Analyzer. Cylindrical DRs of Ba(Tb,,,Nb,,:!)O, showed high E, (-371, high Q (-3,200) and low 7f (-10 ppm/"C) at 4 GHz and hence are useful for practical applications. 0 1997 Elsevier Science B.V.
Journal of Materials Science, 2005
Tetragonal-structured Mg 2 YVO 6 ceramics were prepared by conventional solid-state method, and their physical and microwave dielectric properties were investigated for the first time. The forming of Mg 2 YVO 6 main phase was confirmed by XRD diffraction pattern. XPS and Raman spectrum were recorded to clarify the chemical states of elements and vibration and rotation modes of the specimen, respectively. In addition, the relationships between sintering temperature, packing fraction, and microwave dielectric properties in Mg 2 YVO 6 ceramics were also studied. The new microwave dielectric material Mg 2 YVO 6 ceramics sintered at 1290°C for 4 h has a dielectric constant (e r
Microwave Dielectric Properties of Hexagonal 12R-Ba3LaNb3O12 Ceramics
Journal of the American Ceramic Society, 2006
The dielectric properties of dense ceramics of the n 5 0 member of a newly identified homologous series Ba 31n LaNb 3 Ti n O 1213n , where n 5 0, 1, and 2, are reported. Single-phase powders can be obtained from the mixed-oxide route at 13501C and dense ceramics (497% of the theoretical X-ray density) with uniform microstructures (3-5 lm) can be obtained by sintering in air at 15001C. The ceramics are excellent dc insulators with a band gap 42.6 eV that resonate at microwave frequencies with a relative permittivity, e r B44, a quality factor, Q Â f r , of B9000 at f r B5.5 GHz and a temperature coefficient of resonant frequency, TC f ,BÀ100 ppm/K.
Journal of Applied Physics, 2007
Ceramics of 0.35Ba͑Ni 1/3 Nb 2/3 ͒O 3-0.65Ba͑Zn 1/3 Nb 2/3 ͒O 3 were prepared by the mixed oxide route. The effect of the cooling rate ͑2°C-240°C/h͒ after sintering on the microwave dielectric properties of the ceramics was examined. While the extrinsic factors, such as porosity and secondary phases, markedly influence the dielectric properties in the low-frequency regime, they have minimal effect on these properties in the high-frequency regime. The mechanisms involved in modifying the high-frequency dielectric properties of the materials were investigated by Fourier transform infrared and Raman spectroscopy, in conjunction with the Rietveld analysis of x-ray diffraction ͑XRD͒ spectra. A reduction in the cooling rate after sintering results in an increase in the high-frequency Q ϫ f ͑product of dielectric Q value and measurement frequency͒ from 42 to 58 THz in the high-frequency regime ͑ϳ1.5 THz͒. Such behavior correlates very well with the increase in the B-site occupancy by Nb ͑deduced from the Rietveld analyses of XRD spectra͒ and the increase in the coherency of the lattice vibration ͑deduced from the reduction in the full-width-athalf-maximum of the A 1g ͑O͒ Raman mode͒. In contrast, the cooling rate after sintering has very limited effect on the relative permittivity ͑varying from 40.8 to 41.9 at 1.5 THz͒, which is in accord with the phenomenon that the cell volume and the Raman shift of A 1g ͑O͒ Raman mode are essentially independent of the cooling rate.
Journal of Applied Physics
Dielectric spectroscopy in the submillimeter, millimeter, microwave, and radio frequency range has been performed between 300 and 600 K (for some cases below 300 K) on nine Ba(131nB';n)03 complex perovskite ceramic compounds. The real part of the permittivity d decreases linearly with the increasing tolerance factor t< 1 approaching unity. It is insektive to imperfections in the ceramic, such as impurities, vacancies, etc., and entirely determined by polar lattice vibrations. Its temperature dependence is influenced by the presence of a structural phase transition observed in six of the investigated compounds. It is shown that the imaginary part of the permittivity 8 in the submillimeter range is mainly of intrinsic origin. The e"(f) dependences were fitted applying a microscopic theory using polar-phonon parameters that have been determined in the phonon resonance region by infrared reflection spectroscopy (Part I). The theory allows the extrapolation of minimum intrinsic loss due to polar-p]honon contributions down to the microwave region. The difference between the extrapolated and measured loss at 10 ,GHz is due to-other intrinsic and extrinsic contributions gaining importance at lower frequencies. The submillimeter measurements reveal a systematic loss decrease .with the tolerance factor approaching .unity (optimal packing), suggesting the ionic size to-be of importance for intrinsic loss. A fourth power dependence of loss on permittivity has been found which compares well with the theoretically expected dependence. The contribution of two-phonon difference absorption processes due to the nonpolar soft branch influences the microwave loss as evidenced in particular by P(T) measurements. In the case of Ndand Gd-con@ining compounds losses related to the paramagnetic subsystem are believed to be the origin of increasing Ioss-with decreasing temperature at 10 GHz. 0 1995 American Institute of Physics. II