Improvement of microwave dielectric properties of the LiNb0.6Ti0.5O3 M-phase by doping with (Co1/3Nb2/3)4+

Structural evolution and microwave dielectric properties of LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ (.05≤x≤.2) ceramics have been studied in this paper. Although the doped compositions maintain the M-phase solid solutions, compositional fluctuation due to nonuniform dispersion of minor dopants could be observed as x < .05, and trace amount of Li₂TiO₃-based solid solution (Li₂TiO₃ss) secondary phase presents in the x > .05 compositions. The microwave dielectric properties could be remarkably improved by the doping of (Co_1/2Nb_1/2)⁴⁺ in comparison to the undoped counterpart. Optimized microwave dielectric properties with Q × f = ∼6500 GHz, ε_r = ∼74 and τ_f = +8.2 ppm/°C could be obtained at x = .10 after sintering at 1050°C/2 h. The sintering temperature could be further reduced to 900°C/2 h by adding .2 wt% B₂O₃ without affecting significantly its microwave dielectric properties: ε_r = 73, Q × f = 6000 GHz, τ_f = +8.5 ppm/°C. The LiNb_0.6(Ti_1-x[Co_1/3Nb_2/3]_x)_0.5O₃ ceramics obtained in this case exhibit large dielectric permittivity coupled with much improved Q × f values, near zero τ_f, and low sintering temperature simultaneously, which makes it a promising high-k microwave dielectric material for low temperature cofired ceramic applications.     

Low‐Temperature Sintering and Microwave Dielectric Properties of ZnNb2O6–TiO2 Ceramics with BaCu(B2O5) Additions

The influence of BaCu(B₂O₅) (BCB) on densification, phases, microstructure and microwave dielectric properties of ZnNb₂O₆–xTiO₂ (x = 1.70–1.90) composite ceramics have been investigated. Undoped ZnNb₂O₆–1.8TiO₂ ceramics sintered at 1200°C exhibit temperature coefficient of resonant frequency (τ_f) ~9.25 ppm/°C. When BaCu(B₂O₅) was added, the sintering temperature of the ZnNb₂O₆–1.8TiO₂ composite ceramics was effectively reduced to 950°C. The results indicated that the permittivity and Q × f were dependent on the sintering temperature and the amounts of BaCu(B₂O₅). Addition of 3.0 wt% BaCu(B₂O₅) in ZnNb₂O₆–1.8TiO₂ ceramics sintered at 950°C showed excellent dielectric properties of ε_r = 40.9, Q × f = 12,200 GHz (f = 5.015 GHz) and τ_f = +0.3 ppm/°C.     

Dielectric Properties and Low‐Temperature Sintering of the Ba0.6Sr0.4TiO3 Ceramics with B2O3/CuO Additions

The sintering behaviors and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated as a function of B₂O₃ and CuO content. The addition of both B₂O₃ and CuO reduced the sintering temperature of Ba_0.6Sr_0.4TiO₃ about 500°C. It was suggested that a liquid phase BaCu(B₂O₅) was formed and assisted the densification of Ba_0.6Sr_0.4TiO₃ ceramics. Ba_0.6Sr_0.4TiO₃ ceramics co‐doped with 3.0 mol% B₂O₃, and 2.0 mol% CuO, sintered at 950°C for 5 h, had a dense microstructure and showed good microwave dielectric properties of a moderate dielectric constant (ε = 1048), low dielectric loss (0.0090) and high tunability (42.2%) at dc electric field of 30 kV/cm.     

Influences of B2O3/CuO additions on the sintering behavior,microstructure and microwave dielectric properties of 6Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–4(Na0.5Nd0.5)TiO3 ceramics

B₂O₃ and CuO were codoped into 6Nd[(Zn_0.7Co_0.3)_0.5Ti_0.5]O₃–4(Na_0.5Nd_0.5)TiO₃ (abbreviated as 6NZCT–4NNT) ceramics as sintering aids. The influences of the sintering aids on the sintering characteristics, microstructure and microwave dielectric properties of the 6NZCT–4NNT ceramics were systematically investigated as a function of the proportion of B₂O₃ and CuO. Codoping could greatly reduce the sintering temperature from 1410 °C to 1150 °C, indicating that B₂O₃/CuO are good sintering aids for 6NZCT–4NNT ceramics. The B₂O₃/CuO sintering aids had no significant impact on the phase purity of the investigated ceramics, even though a solid solution was formed due to Cu²⁺ ion substitution. However, they had evident influences on the surface morphology and grain size. The average grain size was enlarged with increasing amounts of CuO in the B₂O₃/CuO sintering aids. Remarkable deterioration of the microwave dielectric properties for 6NZCT-4NNT ceramics was not observed when codoping an appropriate amount of B₂O₃ and CuO. The 6NZCT–4NNT ceramics codoped with 2.0 mol% B₂O₃ and 2.0 mol% CuO sintered at 1150 °C for 3 h exhibited a homogeneous microstructure and promising microwave dielectric properties: an appropriate dielectric constant (ε_r = 49.37), a high quality factor (QF = 47,295 GHz), and a near-zero temperature coefficient of resonant frequency (TCF = +0.9 ppm/^°C).     

Influence of 4ZnO–B2O3 Addition on Dielectric Properties and Microstructures of Barium Strontium Titanate

This study investigates the effect of 4ZnO–B₂O₃ on the sintering behavior, dielectric properties, and microstructures of Ba_0.6Sr_0.4TiO₃ (BST) ceramics. These ceramics were sintered in air at temperatures ranging from 900°C to 1080°C. BST ceramics with 4ZnO–B₂O₃ addition can be sintered to a theoretical density higher than 95% at 1050°C. A secondary phase (Ba₂ZnTi₅O₁₃) is produced in the BST ceramics during 4ZnO–B₂O₃ addition. Compositional analysis using TEM-EDX of the BST ceramics with 3 wt% 4ZnO–B₂O₃ revealed that the Zn ion is generally located at the triple points. This result indicates that BaO, TiO₂, and ZnO form a liquid phase that acts as a secondary phase at the lower sintering temperatures. The amount of secondary phase was observed to increase as the amount of 4ZnO–B₂O₃ additives increased. In addition, the original Ba_0.6Sr_0.4TiO₃ phase was shifted to the Ba_0.5Sr_0.5TiO₃ phase by the addition of 3 wt% 4ZnO–B₂O₃ at 1050°C. The Ba_0.6Sr_0.4TiO₃ ceramic with 2 wt% 4ZnO–B₂O₃ sintered at 1050°C in air for 2 h exhibited dielectric properties of ɛ_r=1883 and dissipation loss=0.36%. Moreover, BST with 1 wt% 4ZnO–B₂O₃ addition sintered at 1080°C exhibits dielectric properties of ɛ_r=2330, dissipation loss=0.29%, and bulk density >95% of theoretical density.     

Improved sinterability and microwave dielectric properties of [Zn0.5Ti0.5]3+-doped ZnAl2O4 spinel solid solution

Low-permittivity ZnAl_2-x(Zn_0.5Ti_0.5)_xO₄ ceramics were synthesized via conventional solid-state reaction method. A pure ZnAl₂O₄ solid-state solution with an Fd-3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn_0.5Ti_0.5]³⁺ for Al³⁺ effectively lowered the sintering temperature of the ZnAl₂O₄ ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (ε_r = 9.1, Q × f = 115,800 GHz and τ_f = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl₂O₄ ceramics.     

Sintering characteristic,microstructure and microwave dielectric properties of the borax-added Sr3(VO4)2 ceramics

Na₂B₄O₇·10H₂O (borax) doped Sr₃(VO₄)₂ ceramics for ULTCC applications were synthesized by the solid-state reaction. The influence of borax addition on the sintering characteristic, microstructure, and microwave dielectric properties of Sr₃(VO₄)₂ ceramics was investigated in detail. The result indicated that borax was an effective sintering aid for the Sr₃(VO₄)₂ system and a suitable amount of borax dramatically reduced the sintering temperature of Sr₃(VO₄)₂ ceramics from 1000 to 675 °C. Meanwhile, borax addition prevented the Q × f value from getting degenerated and improved the τ_f value of Sr₃(VO₄)₂ ceramics in the case of ultra-lower sintering temperatures. Novel Sr₃(VO₄)₂ + 1 wt% borax ceramic sintered at 675 °C with optimum properties of Q × f = 19,200 GHz, ε_r = 15.9, and τ_f = 10.9 ppm/°C was achieved in this study.     

Effects of ZnO and B2O3 on the Microstructure and Microwave Dielectric Properties of 5Li2O‐1Nb2O5‐5TiO2 Ceramics

The effects of ZnO and B₂O₃ addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li₂O‐1Nb₂O₅‐5TiO₂ (LNT) ceramics have been investigated. With addition of low‐level doping of ZnO and B₂O₃, the sintering temperature of the LNT ceramics can be lowered down to near 920°C due to the liquid phase effect. The Li₂TiO₃ss and the “M‐phase” are the two main phases, whereas other phase could be observed when co‐doping with ZnO and B₂O₃ in the ceramics. And the amount of the other phase increases with the ZnO content increasing. The addition of ZnO does not induce much degradation in the microwave dielectric properties but lowers the τ_f value to near zero. Typically, the good microwave dielectric properties of ε_r = 36.4, Q × f = 8835 GHz, τ_f = 4.4 ppm/°C could be obtained for the 1 wt% B₂O₃ and 4 wt% ZnO co‐doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as internal electrode.     

Effect of Ce3+ doping on phase and microwave dielectric properties of 0.94MgTiO3−0.06(Ca0.8Sr0.2)TiO3 ceramics

In this study, 0.94Mg_(1-3x/2)Ce_xTiO₃−0.06(Ca_0.8Sr_0.2)TiO₃ (MCe_xT−CST, 0≤x≤0.01) composite ceramics were prepared at a low temperature of 1175°C by using the 50-nm-sized powders. The effects of Ce³⁺ doping on crystalline phase, microstructure, and microwave dielectric properties of MCe_xT−CST were studied. A main ilmenite (Mg,Ce)TiO₃ phase and a minor perovskite (Ca_0.8Sr_0.2)TiO₃ phase coexist well with the appearance of impurity MgTi₂O₅ phase in MCe_xT−CST. The dielectric properties of MCe_xT−CST are affected by the molecular polarizability, the impurity phase, and the Ce³⁺ doping. The replacement of Mg²⁺ by high valence Ce³⁺ could effectively inhibit the formation of oxygen vacancy, resulting in the enhancement of Q×f. When x = 0.005, MCe_xT−CST exhibits microwave dielectric properties with a moderate ε_r of 21.5, a high Q×f of 67 000 GHz, and a near-zero τ_f of −0.74 ppm/°C. The results reveal that the Ce³⁺ substitution is a prospective approach to optimize the microwave dielectric properties of MgTiO₃-based ceramics.     

Lattice structure and microwave dielectric properties of La[Al1−x(Mg0.5Ti0.5)x]O3 (x = 0-0.2)-based ceramics

La[Al_1−x(Mg_0.5Ti_0.5)_x]O₃ (LAMT, x = 0-0.2) ceramics were synthesized by the conventional solid-state reaction method and formed a solid solution. The pure solid solutions were recorded by X-ray diffraction (XRD) in every range. Relative permittivity (ε_r) and structural stability were greatly affected because the Al³⁺ site was replaced by [Mg_0.5Ti_0.5]³⁺. The total ionic polarizability gradually increased with x, and ε_r gradually increased. The trend of τ_f is due to the change in structural stability. The variation in Q × f value increased firstly and then decreased due to the change in the symmetric stretching mode of Al/MgTi–O. The optimum microwave dielectric properties of LAMT were obtained at x of 0.1 after sintering at 1650°C for 5 hours, and ε_r = 24.9, Q × f = 79 956 GHz, and τ_f = −33 ppm/°C. The CaTiO₃ have a large positive τ_f (+800 ppm/°C), thus, the τ_f achieved near zero when CaTiO₃ and LAMT (x = 0.1) ceramics were mixed with a certain molar mass, and the optimum microwave dielectric properties of 0.65CaTiO₃–0.35LaAl_0.9(Mg_0.5Ti_0.5)_0.1O₃ were as follows: ε_r = 44.6, Q × f = 32 057 GHz, and τ_f = +2 ppm/°C.     

Effect of composite methods on the phase transition and microwave performances of ZnZrNb1.99(Sn0.5W0.5)0.01O8–TiO2 system

Tri-layer ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈–TiO₂–ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ and random distribution ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈@TiO₂ ceramics with different mass fractions of TiO₂ were initially synthesized. The effects of the laminated cofiring and the random distribution processes on the crystal structure and microwave dielectric properties of the composite ceramics were investigated. The advantages of the unique tri-layer architecture were fully demonstrated. It not only allows the effects of the chemical reactions between ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ and TiO₂ can be effectively limited to a narrow region (∼20 μm in width) within the ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈/TiO₂ interfaces, and acts as the “glues” to bond each layer well. The layers are well connected and the possibility of deterioration of Q× f values during the modification process can be greatly reduced. When compared with ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈@TiO₂ ceramics with random distribution type, the tri-layer design can produce a roughly 60% improvement in Q× f value with no noticeable loss in dielectric constant while maintaining temperature stability. After sintering at 1340°C for 6 h, ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈–TiO₂–ZnZrNb_1.99(Sn_0.5W_0.5)_0.01O₈ tri-layer ceramics exhibited excellent dielectric properties (ε_r = 30.29, Q× f = 56,880 GHz, and τ_f = −5.73 ppm/°C) with 0.05 wt% TiO₂, and the cooperative optimization of microwave dielectric properties was achieved. The current research provides a strategy for synthesizing microwave dielectric devices with high dielectric properties for applications in 5G network communications.     

Effect of excess lithium on the structure and microwave dielectric properties of LiMg0.5Ti0.5O2 ceramics

Herein, Li_1+xMg_0.5Ti_0.5O₂ (0.000 ≤ x ≤ 0.075) ceramics with excess lithium were prepared by solid-state reaction method to compensate for lithium volatilization, thus optimizing dielectric properties. The second phase Mg₂TiO₄ decreases with excess lithium content and eventually disappears at x = 0.05. Of these, Li_1.0375Mg_0.5Ti_0.5O₂ illustrates the best dielectric properties with ε_r = 16.58, Q × f = 120712 GHz (@9.18 GHz), and τ_f = −16.31 ppm/°C. From the point of view of non-intrinsic factors, excess lithium at optimum ratios slightly facilitates the sintering of the ceramics, improves densification, and increases the grain size, resulting in improved dielectric properties. For intrinsic factors, a slight increase in bond ionicity results in a slight improvement in ε_r. First-principles calculations demonstrate that suitable excess lithium increases electron cloud density in the internal space of Li/Mg/TiO₆ octahedron and increases band gap, thus optimizing the dielectric properties. The same results were obtained from the perspective of lattice vibrations. The modified Li_1.0375Mg_0.5Ti_0.5O₂ ceramics offer great potential for future microwave communication technology.     

Low‐Temperature Sintering and Microwave Dielectric Properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4–(Ca0.8Sr0.2)TiO3 Composite Ceramics

0.9(Mg_0.95Zn_0.05)₂(Ti_0.8Sn_0.2)O₄–0.1(Ca_0.8Sr_0.2)TiO₃ (MZTS–CST) ceramics were prepared by a conventional solid‐state route. The MZTS–CST ceramics sintered at 1325°C exhibited ε_r = 18.2, Q × f = 49 120 GHz (at 8.1 GHz), and τ_f = 15 ppm/°C. The effects of LiF–Fe₂O₃–V₂O₅ (LFV) addition on the sinterability, phase composition, microstructure, and microwave dielectric properties of MZTS–CST were investigated. Eutectic liquid phases 0.12CaF₂/0.28MgF₂/0.6LiF and MgV₂O₆ were developed, which lowered the sintering temperature of MZTS–CST ceramics from 1325°C to 950°C. X‐ray powder diffraction (XRPD) and energy dispersive spectroscopy (EDS) analysis revealed that MZTS and CST coexisted in the sintered ceramics. Secondary phase Ca₅Mg₄(VO₄)₆ as well as residual liquid phase affected the microwave dielectric properties of MZTS–CST composite ceramics. Typically, the MZTS–CST–5.3LFV composite ceramics sintered at 950°C showed excellent microwave dielectric properties: ε_r = 16.3, Q × f = 30 790 GHz (at 8.3 GHz), and τ_f = ?10 ppm/°C.     

Low‐Temperature Sintering Microwave Characteristics of B2O3‐doped CaLa4Ti4O15 Dielectric Ceramics

Preparation and microwave dielectric properties of B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics have been investigated. X‐ray diffraction data show that CaLa₄Ti₄O₁₅ ceramic has a trigonal structure coupled with a second phase of CaLa₄Ti₅O₁₇. The CaLa₄Ti₄O₁₅ ceramic with addition of 0.5 wt% B₂O₃, sintered at 1220°C for 4 h, exhibits microwave dielectric properties with a dielectric constant of 45.8, Q × f value of 24,000 GHz, and temperature coefficient of resonant frequency (τ_f) of ?19 ppm/^°C. B₂O₃‐doped CaLa₄Ti₄O₁₅ ceramics, which have better sintering behavior (decrease in sintering temperature ~ 330°C) and dielectric properties than pure CaLa₄Ti₄O₁₅ ceramics, are candidates for applications in microwave devices.     

Tuning of electrical properties of xBi(Zn0.5Ti0.5)O3-(1-x) (Ba0.5Sr0.5)TiO3 ceramics by composition design and bandgap engineering

Herein, the xBi(Zn_0.5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ (x = 0.05, 0.10, 0.15, 0.20) novel negative temperature coefficient (NTC) ceramic materials were fabricated by solid-state method. X-ray diffraction revealed that xBi(Zn_0·5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ successfully formed solid solution. The UV–vis diffuse spectra of the samples indicate that the band gap increases with the increasing Bi(Zn_0·5Ti_0.5)O₃ content. The resistance temperature curve showed that with the increase of Bi(Zn_0·5Ti_0.5)O₃ content, the resistivity ρ of the ceramics at 400 °C increased from 5.96 × 10⁶ to 2.67 × 10⁷ Ω cm, as well as an increase in the B_400/800 from 12374.6 to 13469.1 K. The enhanced resistivity is attributed to the increased band gap and reduced carrier pairs caused by the Bi(Zn_0.5Ti_0.5)O₃ modification. The impedance data indicates that the conduction process is activated by thermal. The ceramic samples exhibit the excellent NTC characteristics over a range of 400 °C–1000 °C. Hence, the xBi(Zn_0.5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ ceramics have the potential to become high temperature NTC ceramics that can operate in a wide temperature range.     

Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.     

Effect of MgO/La2O3 additives on sintering behavior and microwave dielectric properties of (Sr,Ca)TiO3-(Sm,Nd)AlO3 ceramics

The effect of MgO/La₂O₃ additives on phase composition, microstructures, sintering behavior, and microwave dielectric properties of 0.7(Sr_0.01Ca_0.99)TiO₃−0.3(Sm_0.75Nd_0.25)AlO₃ (7SCT-3SNA) ceramics prepared via conventional solid-state route were systematically investigated. MgO/La₂O₃ as additives showed no obvious influence on the phase composition of the 7SCT-3SNA ceramics and all the samples exhibited pure perovskite structures. The presence of MgO/La₂O₃ additives effectively reduced the sintering temperature of 7SCT-3SNA ceramics due to the formation of a liquid phase at a relatively low temperature during sintering progress. The 0.5 wt% MgO doped 7SCT-3SNA sample with 0.5 wt% of La₂O₃, sintered at 1320 °C for 4 h, was measured to show superior microwave dielectric properties, with an ε_r of 45.57, a Q×f value of 46205 GHz (at 5.5 GHz), and τ_f value of −0.32 ppm/°C, which showed dense and uniform microstructure as well as well-developed grain growth.     

High quality factor microwave dielectric ceramics in the (Mg1/3Nb2/3)O2–ZrO2–TiO2 ternary system

Novel high quality factor microwave dielectric ceramics (1?x)ZrTiO₄?x(Mg_1/3Nb_2/3)TiO₄ (0.325≤x≤0.4) and (ZrTi)_1?y(Mg_1/3Nb_2/3)_yO₄ (0.2≤y≤0.5) with the addition of 0.5 wt% MnCO₃ in the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system were prepared, using solid‐state reaction method. The relationship between the structure and microwave dielectric properties of the ceramics was studied. The XRD patterns of the sintered samples reveal the main phase belonged to α‐PbO₂‐type structure. Raman spectroscopy and infrared reflectivity (IR) spectra were employed to evaluate phonon modes of ceramics. The 0.65ZrTiO₄?0.35(Mg_1/3Nb_2/3)TiO₄?0.5 wt% MnCO₃ ceramic can be well densified at 1240°C for 2 hours and exhibits good microwave dielectric properties with a relative permittivity (ε_r) of 42.5, a quality factor (Q×f) value of 43 520 GHz (at 5.9 Ghz) and temperature coefficient of resonant frequency (τ_f) value of ?5ppm/°C. Furthermore, the (ZrTi)_0.7(Mg_1/3Nb_2/3)_0.3O₄?0.5 wt% MnCO₃ ceramic sintered at 1260°C for 2 hours possesses a ε_r of 31.8, a Q×f value of 35 640 GHz (at 6.3 GHz) and a near zero τ_f value of ?5.9 ppm/°C. The results demonstrated that the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system with excellent properties was a promising material for microwave electronic device applications.     

The influence of sintering aids for Nd(Mg0.5Ti0.5)O3 microwave dielectric ceramics properties

The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg_0.5Ti_0.5)O₃ ceramics were investigated systematically. B₂O₃, Bi₂O₃, and V₂O₅ were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg_0.5Ti_0.5)O₃ ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg_0.5Ti_0.5)O₃ microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (_r) value of 26.2, a quality factor (Q × f) value of 61,307 (at 9.63 GHz), and τ_f value of −45.5 ppm/°C. NdVO₄ secondary phase was observed at 10 mol% V₂O₅ addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg_0.5Ti_0.5)O₃ incorporated with 10 mol% B₂O₃ with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important.     

Novel Temperature Stable Li2MnO3 Dielectric Ceramics with High Q for LTCC Applications

Novel microwave dielectric ceramics in the Li₂MnO₃ system with high Q prepared through a conventional solid‐state route had been investigated. All the specimens exhibited single phase ceramics sintered in the temperature range 1140°C–1230°C. The microwave dielectric properties of Li₂MnO₃ ceramics were strongly correlated with sintering temperature and density. The best microwave dielectric properties of ε_r = 13.6, Q × f = 97 000 (GHz), and τ_f = ?5.2 ppm/°C could be obtained as sintered at 1200°C for 4 h. BaCu(B₂O₅) (BCB) could effectively lower the sintering temperature from 1200°C to 930°C and slightly induced degradation of the microwave dielectric properties. The Li₂MnO₃ ceramics doped with 2 wt% BaCu(B₂O₅) had excellent dielectric properties of ε_r = 11.9, Q × f = 80 600 (GHz), and τ_f = 0 ppm/°C. With low sintering temperature and good dielectric properties, the BCB added Li₂MnO₃ ceramics are suitable candidates for LTCC applications in wireless communication system.