Effect of Sm substitution on microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd_(1?x)Sm_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd_(1?x)Sm_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.87 g/cm³, a dielectric constant (ε _r ) of 19.2, a quality factor (Q × f) of 104,300 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?57 ppm/°C were obtained for Nd_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Influence of B2O3 on microstructure and microwave dielectric properties of 0.4Nd0.96Yb0.04(Mg0.5Sn0.5)O3–0.6Ca0.8Sr0.2TiO3 ceramic system

The effect of B₂O₃ on the microstructure and microwave dielectric properties of the 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their use in microwave devices. A B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system was prepared by the conventional solid-state method. The X-ray diffraction patterns of the B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system did not significantly vary with sintering temperature. A 1.25 wt% B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system that was sintered at 1,525 °C for 4 h had a dielectric constant of 38.0, a quality factor (Q × f) of 68,600 GHz, and a temperature coefficient of resonant frequency of 2 ppm/°C.     

Improved microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics with Ni2+ substituting

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5?xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant ( $ \varepsilon_{r} $ ) of 19.3 and a quality factor (Q × f) of 93,400 GHz and a temperature coefficient of resonant frequency ( $ \tau_{f} $ ) of ?66 ppm/ °C were obtained for Nd(Mg_0.43Ni_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

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.     

Measurement of dielectric properties of high-absorption materials at microwave frequencies

A method is proposed for measuring the dielectric constant ε′ and dielectric loss ε″ of high-absorption dielectric materials by measuring the reflection of electromagnetic radiation with the aid of an adjustable quarter-wave matching plate of nonabsorbing material close to the dielectric surface. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 45–47, May, 1999.     

Enhancing the microwave dielectric properties of Nd (Mg0.5Sn0.5)O3 ceramics by substituting Nd3+ with Ca2+

The microwave dielectric properties of Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were examined to evaluate their exploitation for mobile communication. Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with the sintering temperature. Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h had the following properties: a density of 6.86 g/cm³, a dielectric constant (ε_r) of 19.3, a quality factor (Q × f) of 99,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65 ppm/°C.     

Influence of Ba2+ substitution on the microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.91 g/cm³, a dielectric constant (ε _r ) of 19.14, a quality factor (Q × f) of 97,500 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65.4 ppm/°C were obtained for Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics that were sintered at 1,600 °C for 4 h.     

Microstructure and dielectric properties of CBS glass-doped Sr0.5Ba0.5Nb2O6 ceramic system

40CaO–20B₂O₃–40SiO₂ (abbreviate as CBS) glass-doped Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO₃. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric constant of the samples at the Curie temperature (T _c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase are found to obviously increase with increase in CBS glass doping level.     

Sintering and microwave dielectric properties of LTCC-zinc titanate multilayers

The effects of ZnO–B₂O₃–SiO₂ (ZBS) on the sintering behavior and microwave dielectric properties of ZnO–TiO₂ system were investigated as a function of ZBS content and sintering temperature. Densities of the specimens were enhanced with an increase of ZBS up to 2 wt.% and then decreased. X-ray diffractometry analyses results indicated that the phase stability region of the hexagonal ZnTiO₃ extended to lower temperatures as the amount of ZBS increased. The dielectric properties of ZnO–TiO₂ system with ZBS are strongly dependent on the sintering conditions, especially near the phase decomposition temperature. The sintering temperature of the specimens could be reduced to 900 °C without the degradation of the microwave dielectric properties. From 900 °C, the temperature compensation characteristics occurred as the phase composition changed from ZnTiO₃ to two phases: Zn₂TiO₄ and rutile. The dielectric constant (ɛ_r) increased and Q×f value decreased due to the phase decomposition. The ɛ_r value of 27, Q×f value of 19,396 (at 6 GHz) and τ_f value of 2 ppm/°C were obtained for ZnO–TiO₂ ceramics with 2.0 wt.% ZBS sintered at 900 °C for 3 h. The low-temperature sintering ceramics powders were suitable for the tape casting process. Also, the material is compatible with Ag electrodes and, therefore, is suitable for LTCC application.     

Structure,phase composition,and microwave dielectric properties of Ba16SnNb12O48 ceramic

Journal of Materials Science - The Ba16SnNb12O48 ceramics are prepared using a solid-state reaction method. The relationship between microstructure and dielectric properties are investigated. XRD...     

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.     

Sintering behaviors,microstructures and dielectric properties of CaO-B2O3-SiO2 glass ceramic for LTCC application with various network modifiers content

CaO-B₂O₃-SiO₂ (CBS) glass ceramic with various glass network modifiers were synthesized to develop a kind of material sintered at low temperature for multi-layer ceramic substrates. The influence of double alkali metal oxides (Na₂O and K₂O) on sintering characteristics, microstructures and dielectric properties of CBS glass ceramic were investigated. XRD analysis showed that the major crystalline phase was β-CaSiO₃ and CaB₂O₄, and the strength of the peak increased with the addition of network modifiers. DSC curve revealed that the process of crystallization and softening were obviously affected. SEM photographs exhibited that the microstructures were composed of amorphous phases, pores and crystalline phases. FTIR showed that the additives changed the continuity of CBS glass structure. An appropriate amount of Na₂O and K₂O additives could significantly improve the sintering characteristics and dielectric properties. CBS samples with 1.5 wt% (Na₂O?+?K₂O) sintered at 850 °C for 15 min presented the best performances with the bulk density of 2.53 g/cm³, ε_r?=?5.94 and tanδ?=?1.22?×?10^?3 at 10 GHz.

     

Formation and microwave dielectric properties of Sr(Ga0.5Ta0.5)O3-based complex perovskites

The Sr(Ga0.5Ta0.5)O3-based perovskites with O2- and/or Sr2+ vacancies were formed by changing the A-site and/or B-site cation ratios. The Sr-deficient perovskites with a limited composition of Sr0.86(Ga0.36Ta0.64)O3 could be obtained, whereas oxygen vacancies were hardly created. The B′-site Ga3+ cation could be replaced with large Sc3+, In3+, Y3+, Nd3+ and La3+. The crystal symmetry of the complex perovskites changed from cubic (B′=Ga3+, Sc3+, In3+) to tetragonal (B′=La3+) through rhombohedral (B′=Y3+, Nd3+). The dielectric permittivities of these ceramics indicated no distinct dependence on the B′-site cation species. The temperature coefficient of permittivity might be associated with the symmetry change of the perovskite phases. Higher microwave Qf values, >Qf=38 000 GHz, were obtained for our complex perovskite ceramics, except with B′=La3+. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sintering, microstructure and microwave dielectric properties of rare earth orthophosphates, RePO4 (Re = La, Ce, Nd, Sm, Tb, Dy, Y, Yb)

Various rare earth orthophosphates, such as monazite and xenotime RePO₄ (Re = La, Ce, Nd, Sm, Tb, Dy, Y, Yb) were prepared by a conventional solid-state reaction method. The crystal structure and microstructure of the sintered ceramics were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The dielectric properties were measured in the microwave region using a network analyzer. It was found that the monazite RePO₄ could be sintered near 1400 °C, although the xenotime RePO₄, which had a smaller Re³⁺ ionic radius, could be sintered above 1600 °C. The permittivity (?_r) of the monazite structures was higher than that of the xenotime structures. This difference was explained by the differences in ionic polarizability and bond strength. Both monazite and xenotime rare earth orthophosphates, however, exhibited a high quality factor (Q × f), where Q = 1/tan δ and f is the measuring frequency, of greater than 60,000 GHz. The temperature coefficient of resonant frequency (τ_f) was a negative value, ranging between −17 and −56 ppm/°C.     

New lithium bismuth phosphate ceramic: crystal structure,microstructure, microwave dielectric properties and co-firing compatibility with aluminum electrode

A new type of lithium bismuth phosphate 3Li₂O–Bi₂O₃–6P₂O₅ (3L1B6P) microwave dielectric ceramics were prepared via a conventional solid-state route. Crystal structure, microstructure, microwave dielectric properties and aluminum electrode co-firing compatibility of the 3L1B6P ceramics were investigated. The 3L1B6P ceramics mainly consists of a new phase similar to the NdLiP₄O₁₂ with monoclinic structure [C2/C(15)]. The 3L1B6P ceramics are composed of BiLiP₄O₁₂ grains of?~?10 μm in length and?~?2 μm in width and BiPO₄ grains of?~?1 μm in size. The 3L1B6P ceramic sintered at 625 °C shrinkage and the corresponding microwave dielectric properties are dielectric constant ε_r?=?6.8, Q?×?f?=?16,900 GHz and negative temperature coefficient of resonant frequency TCF?=???71 ppm/°C. More importantly, the 3L1B6P ceramic with ultra-low sintering temperature (625 °C) can be co-fired with aluminum electrode, which illustrates it can be applied for the ultra-low temperature co-fired ceramic (ULTCC) application.

     

Electrical properties of films at microwave frequencies

A technique suitable for the measurement of electrical properties of films/sheets at microwave frequencies has been described. Groups of materials are identified for which the absence of any kind of electrodes in these microwave measurements can be utilised with advantage. Results are presented for a variety of materials such as metal films, superionic conductors, semiconductors and insulating polymers.     

Study of dielectric and electrical properties of mortar in the early hydration period at microwave frequencies

The dielectric constant, , and electrical conductivity, , of mortars with various sand-cement ratios,s/c, were measured for the first 30 h hydration using microwave techniques in the frequency range 8.2–12.4 GHz. The and of the mortars were found to increase linearly with increasing water-solid ratiow/(s + c), but decrease with increasings/c. It was found that as long as thes/c values were the same, the rate of changes in and of the mortars were the same. It appears that thes/c is the key factor controlling the rates of changes in dielectric and electrical parameters of cement hydration in mortar. The relationship between compressive strength and dielectric and electrical properties of mortars was also discussed.