Effect of nickel on microwave dielectric properties of Ba(Mg1/3Ta2/3)O3

The dielectric and physical properties of the complex perovskite Ba(Mg_1/3Ta_2/3)O₃ system in which magnesium was substituted for nickel from 0.03–0.67 mol%, were investigated in the temperature range 20–110C, and the frequency range 10.5–14.5 GHz. As the nickel content was increased, the dielectric constant, the degree of ordering, and the unloaded Q decreased. The temperature dependence of the dielectric constant and the temperature coefficient of resonant frequency of the specimens annealed at 1500C for 20 h were found to be greater than those of the specimens sintered at 1650C for 2 h. These results are due to the increase in the density, the increase in grain size, and the lattice distortion.     

Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

Improved microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramic with Ba2+ substitution

The microwave dielectric properties of La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics contained La₂Sn₂O₇. An apparent density of 6.54 g/cm³, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg_0.43Ba_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Preparation,microstructural development and dielectric properties of Pb(Mg1/3Nb2/3)O3-Pb(TixZr1−x)O3 multilayer ceramic capacitors

Multilayer ceramic capacitors based on PMN-PZT solid solutions have been prepared using a 70 % Ag-30% Pd alloy as internal electrode. Some interaction of the electrode-dielectric with Ag⁺ diffusion into the dielectric was observed. The Ag⁺ diffusion influenced the normal microstructural development present in the PMN-PZT ceramics. In spite of this, the dielectric behaviour of a five active layers capacitor sintered at 1050 °C for 2 h in air showed a capacitance of 120 nF, an effective dielectric constant maximum of ~200 000 and dielectric losses of about 3% near room temperature and 1 kHz.     

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

Effect of preparation methods on microstructures and microwave dielectric properties of Ba(Mg_1/3Nb_2/3)O₃ ceramics was investigated. Ba(Mg_1/3Nb_2/3)O₃(BMN) ceramics were prepared by the conventional mixed oxides method and the molten salt synthesis method. It was shown that the single-phase of BMN was obtained at 900 °C in the molten salt synthesis method. No single-phase BMN was obtained in the conventional mixed oxides method, although the calcining temperature was increased up to 1400 °C. BMN powders prepared by the molten salt synthesis method had better sinterability than that prepared by the conventional mixed oxides method. Because of the very different nature of the powders, different microstructures were observed. The molten salt synthesis method ceramics have a higher B-site ordering parameter (S) and larger grain size than that of the conventional mixed oxides ceramics at same sintering temperature. The variation of Qf, ε _r and τ _f were also explained based on the difference in microstructures.     

Influence of V2O5 additions to Ba(Mg1/3Ta2/3)O3 ceramics on sintering behavior and microwave dielectric properties

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg_1/3Ta_2/3)O₃ exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V₂O₅ (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg_1/3Ta_2/3)O₃ ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V₂O₅ addition. The detected second phase Ta₂O₅ was mainly the result of V⁵⁺ substitution in the ceramics. Dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V₂O₅ addition due to the increase in B-site ordering. The ε_r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τ_f value of 7.2 ppm/°C were obtained for Ba(Mg_1/3Ta_2/3)O₃ ceramics with 0.25 wt.% V₂O₅ addition sintered at 1500 °C for 3 h.     

Effect of B2O3 additive on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

Journal of Materials Science: Materials in Electronics - This paper reported a research of the sinterability, microstructures, and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 (BMT) ceramics...     

Sintering characteristic,crystal structure and microwave dielectric properties of a novel thermally stable ultra-low-firing Na2BiMg2V3O12 ceramic

A novel ultra low-firing microwave dielectric ceramic with the composition of Na₂BiMg₂V₃O₁₂ was fabricated by a solid state reaction method. The phase structure, sintering behavior and microwave dielectric properties of ceramics were investigated. The ceramic can be well densified at 660 °C for 4 h. X-ray diffraction data show that Na₂BiMg₂V₃O₁₂ has a cubic garnet structure with lattice parameters of a = 12.4929 Å, V = 1,949.80 Å³, Z = 8 and ρ = 4.42 g/cm³. The microwave dielectric properties are strongly related to the density and morphology of the samples. The ceramic sintered 660 °C exhibits good microwave dielectric properties with ε_r = 23.2, Q × f = 3,700 GHz and τ _f  = 8.2 ppm/°C. These results indicate that Na₂BiMg₂V₃O₁₂ ceramic is a candidate for low temperature co-fired ceramics devices, such as chip multi-layer LC filter, microstrip bandpass filter, multilayer antenna.     

Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

The process and nature of structural ordering and the factors that influence them have been investigated in the microwave dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy. The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

Processing, sintering characteristics and dielectric properties of barium-substituted Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solution

Solid solutions in the lead-based relaxor system Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ were modified by minor substitutions of Ba in the Pb-site of the perovskite lattice. The modified compositions were calcined at 830 °C for 3 h to yield fine-grained, single-phase perovskite materials. A small amount of excess MgO(0.05 wt %), which mostly served as a sintering aid, was added to the calcined batches and the resulting mixtures were sintered at temperatures between 1150 and 1250 °C for periods ranging from 3 to 5 h. The substitutions of BaO for PbO in the perovskite solid solution lattice caused a progressive lowering of the Curie point with increasing BaO content. On average, the Curie point decreased by about 10 °C for each mole of BaO substituted for PbO. Among the various Ba-substituted solid solutions studied, the one with a nominal composition Pb_0.99Ba_0.01[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ which has a Curie point located near 28 °C, exhibited excellent dielectric properties. On sintering at 1250 °C for 3 h, this composition yielded a density near 96% of the theoretical density. The peak dielectric constant of the composition at 1 KHz was slightly higher than 22000, and the corresponding tan δ value was 1.5% with a specific resistivity of 2.5 × 10¹² Ω cm^-1. This revised version was published online in November 2006 with corrections to the Cover Date.     

New dielectric materials of xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 ceramic system at microwave frequency

The crystal structures and the microwave dielectric properties of the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ perovskite ceramic system have been investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. SrTiO₃ has dielectric properties of dielectric constant ε_r ∼ 205, Q × f value ∼ 4200 GHz and a large positive τ_f value ∼ 1700 ppm/°C. Ca(Mg_1/3Nb_2/3)O₃ possesses high dielectric constant (ε_r ∼ 28), high quality factor (Q × f value ∼ 58,000 at 7 GHz) and negative τ_f value (− 48 ppm/°C). As the x value varies from 0.2 to 0.8, the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ system has the dielectric properties as follows: 40 < ε_r < 123, 4600 < Q × f < 33,400 and − 23 < τ_f < 600. A new microwave dielectric material, 0.3SrTiO₃–0.7Ca(Mg_1/3Nb_2/3)O₃, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε_r ∼ 46, a Q × f value ∼ 29,300 GHz (at 6.8 GHz) and a τ_f value ∼− 2 ppm/°C. A near-zero τ_f value can be achieved by adjusting the x value of xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ ceramics.     

Effect of lithium salts addition on sintering temperature, cationic ordering and dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramic

The effect of different lithium salts (LiF, Li₂CO₃, LiNO₃) addition on sintering temperature, cationic ordering and dielectric properties of Ba(Mg_1/3Ta_2/3)O₃ ceramic has been investigated. This perovskite was synthesised by solid state reaction from BaCO₃, MgO and Ta₂O₅. It was shown that, by addition of LiNO₃, the sintering temperature was decreased to 1300°C (versus 1550°C–1600°C for the pure Ba(Mg_1/3Ta_2/3)O₃ ceramic) without altering dielectric properties at 1 MHz. A cationic ordering was also observed. Sintering with co-fired nickel electrodes in Ar/H₂ atmosphere was also successfully performed for Multi Layer Ceramic Capacitors applications.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.