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MgO ceramics have good microwave dielectric properties, but the high sintering temperatures limit its application. The effects of TiO 2 additive on the phase composition and microwave dielectric properties of MgO ceramics with 4mol%LiF were investigated by solid state reaction method. TiO 2 and MgO form Mg 2 TiO 4 in a magnesium-rich environment with 4mol%LiF at about 900 °C, which as a solid solution or second phase had a huge impact on MgO ceramic with 4mol % LiF. When the content of TiO 2 less than 2mol %, Mg 2 TiO 4 as a solid solution in MgO ceramics, which made the grain of MgO larger. When the content of TiO 2 more than 2mol %, Mg 2 TiO 4 as a second phase in MgO ceramics, which made the microwave dielectric properties of MgO ceramics bad. Typically, the MgO-4mol%LiF-0.5mol%TiO 2 ceramic sintered at 1075 °C for 6 h acquired the best dielectric properties: ε r = 9.7, Qf = 617,000 GHz and τ f = −59.49 ppm/°C. [ABSTRACT FROM AUTHOR]

A low temperature co-fired ceramic (LTCC) material of Li2ZnTi3O8-TiO2 (L2ZT3-TiO2) doped with BaO-B2O3-ZnO (BBZ) glass were prepared by conventional solid-state method. The effects of BBZ glass on the phase composition, microstructure, and microwave dielectric properties were investigated. The results indicated that BBZ glass as a sintering aid could effectively reduce the sintering temperature of L2ZT3-TiO2 ceramic below 950 °C. The XRD patterns indicated that L2ZT3-TiO2 ceramic consisted of Li2ZnTi3O8 and TiO2 phases. BBZ glass addition did not change the phase composition. In addition, the SEM demonstrated that BBZ glass could significantly improve the grain growth and densification. The sintering mechanism was analyzed through the wetting behavior and the activation energy (Ea). When added 2.5 wt% BBZ glass, the average activation energy reduced from 492.38 ± 139.03 to 370.69 ± 20.98 kJ/mol, which indicated that the BBZ glass not only effective lowered the sintering temperature but also promoted the sintering process. The L2ZT3-TiO2 ceramic with 2.5 wt% BBZ sintered at 925 °C for 4 h had excellent microwave dielectric properties of εr = 26.3, Q × f = 36,554 GHz and τf = − 4.16 ppm/°C. In addition, the good chemical compatibility of this material with Ag electrode could make it as a potential candidate for LTCC technology. [ABSTRACT FROM AUTHOR]

Abstract: Four MgO‐Ta2O5 ceramics with the MgO/Ta2O5 mole ratio x = 1, 2, 3, and 4 were prepared by traditional solid‐state reaction method, and the influence of x on the phase composition, microstructure, and dielectric properties (the dielectric constant εr, the temperature coefficient of resonant frequency τf and the quality factor Qf) of the materials was investigated using XRD, SEM, etc. The results indicated that the ceramics were composed of two crystalline phases MgTa2O6 and Mg4Ta2O9 in the composition range studied, and that the dielectric properties ln ε, 1/Qf, and τf changed proportionally to the fraction of main crystal phases, which meet perfectly with the mixing model proposed in this study. It is obvious that the proportion of the two crystal phases could be precisely controlled by x, and thereby, the dielectric properties can be conveniently and precisely tailored. Our research provided a new microwave dielectric ceramic with the composition of 2MgO‐Ta2O5, which has an ultrahigh Qf value (211 000 GHz), low dielectric constant εr (19.9), and near zero temperature coefficient of resonant frequency τf (8 ppm/°C). [ABSTRACT FROM AUTHOR]

A low temperature co-fired ceramic (LTCC) was fabricated at 910 °C /2 h from the powder mixture of Li2Zn3Ti4O12, TiO2 and a B2O3-La2O3-MgO-TiO2 glass (BLMT), and the influence of TiO2 on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT-(80 − x)Li2Zn3Ti4O12-xTiO2 (x = 0, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li2Zn3Ti4O12, TiO2, LaBO3 and LaMgB5O10 phase. And LaBO3, LaMgB5O10 and a small amounts of TiO2 were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of x = 0 wt% was about 41,500 GHz and the ones maintained stable at a high level of 49,000-51,000 GHz for other samples. The composite with x = 9 wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000 GHz and temperature coefficient of resonant frequency of − 0.33 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the microstructure and microwave dielectric properties of translucent polycrystalline alumina (PCA) with different amounts of La2O3 (co-doped with 500ppm MgO) were investigated. Compared with those doped only with 500ppm MgO, the translucent PCA co-doped with 500ppm La2O3 exhibited a higher Q×f value, which might be caused by the significantly larger ionic radius of La3+. As the La2O3 content was further increased, the presence of an increasing amount of impurities (LaAl11O18) would deteriorate the Q×f value significantly. [Copyright &y& Elsevier]

Abstract: Ba4Nd9.33Ti18O54·x wt%Al2O3 (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al2O3 on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al2O3 additive gave rise to a second phase BaAl2Ti5O14 (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al2O3 additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180GHz and decreased the τ f value from 53.4 to 11.2ppm/°C. A BNT-A ceramic with excellent dielectric properties: ε r =70.2, Q×f=12,180GHz, τ f =20ppm/°C was obtained with 2.0wt% Al2O3 added after sintering at 1320°C for 4h. [Copyright &y& Elsevier]

Abstract: Glasses with molar composition of (100-x)B2O3-x[0.5 BaO–0.5 ZnO], x=40, 50, 60, 70 were prepared from the melts of ZnO, BaCO3 and H3BO3 mixture. The structure and thermal behavior were characterized by IR and Raman spectroscopy, DSC and Dilatometer. The investigation shows that the transition of the structural unit [BO4] (BIV) to [BO3] (BIII) happens when BaO and ZnO content x increases in the borate glass, resulting in fewer BIII–O–BIV bonds and more BIII–O–BIII bonds. At the same time, the diborate groups, which are found to be the predominant structural group of the glass with high B2O3 content, gradually changes into ring-type metaborate, pyro- and orthoborate groups. With increasing ZnO and BaO content x, the glass transition temperature (T g) and the softening point (T f) decreases, while linear expansion coefficient (α) increases, that comes from the weakening of the glass network. [Copyright &y& Elsevier]

Porous Si 3 N 4 ceramics were fabricated via pressureless sintering employing ternary lithium oxides (LiScO 2 , LiYO 2 , LiYbO 2) derived from various Re 2 O 3 as sintering additives under nitrogen atmosphere at the temperature of 1400–1700 °C. The study studied how sintering temperatures andternary lithium oxide additives affect the phase, microstructure, and material properties of Si 3 N 4. The results show that as the amount of sintering aids increases, the bulk density of samples increases. At the same time, the apparent porosity diminishes, leading to enhancements in flexure strength and dielectric constant. The Si 3 N 4 -based porous ceramic sample containing 5 wt% LiYbO 2 sintered at 1600 °C exhibits a volumetric weight of 1.828 g/cm3, an apparent porosity of 35.14 %, an average flexure strength of 114.8 MPa, a dielectric constant of 3.95, a loss tangent of 5.457 × 10−3, and a low thermal conductivity of 8.241, offering insights into the preparation of radome materials. [ABSTRACT FROM AUTHOR]

In this work, a novel anti-reduction mechanism was put up by substituting (Mg 1/3 Ta 2/3)4+ complex ion for Ti4+ ion in Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 (0 ≤ x ≤ 0.1) ceramics. The influence of (Mg 1/3 Ta 2/3)4+ complex ion on the sintering behavior, crystal structure, anti-reduction mechanism and microwave dielectric properties of Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics was investigated. The results indicated that Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics maintained a typical single-phase tungsten bronze structure. After doping, the ceramic exhibited dense structure and typical columnar grains. Raman spectroscopy and XPS analysis confirmed the reduction of oxygen vacancies and obtained a 7.86 % decrease of Ti3+ ions. Due to the anti-reduction of Ti4+ ions, Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 ceramics possessed an improvement in microwave dielectric properties. In Ba 4.2 Sm 9.2 Ti 18-x (Mg 1/3 Ta 2/3) x O 54 (0 ≤ x ≤ 0.1) ceramics, the Ba 4.2 Sm 9.2 Ti 17·95 (Mg 1/3 Ta 2/3) 0.05 O 54 (x = 0.05) ceramic sintered at 1350 °C for 4 h showed the best integrated microwave dielectric properties with ε r = 79.62, Q f = 10,450 GHz and τ f = −10.66 ppm/°C. [ABSTRACT FROM AUTHOR]

In this study, Ba(Mg 1/3 Ta 2/3)O 3 (BMT) ceramics added with different amounts of CaO–B 2 O 3 –ZnO (CBZ) glass were prepared through the solid-state sintering route. The sintering behavior, microstructure, phase composition and dielectric properties of the BMT ceramics added with CBZ glass were investigated. The addition of CBZ glass decreased the sintering temperature of BMT ceramics by over 300 °C, resulting in a highly dense microstructure without interacting with the main BMT phase. The lower sintering temperature led to small ceramic grains and caused a decrease in the Q × f value. Prolonging the sintering time improved the ordering degree of cations on the B-site in BMT ceramic, leading to an enhancement in the Q × f value. The BMT ceramic added with 0.4 wt% CBZ glass exhibited excellent microwave dielectric properties: ε r = 24.19, Q × f = 115,100 GHz, τ f = 9.84 ppm/°C, after sintering at 1400 °C for 12 h. [ABSTRACT FROM AUTHOR]

In this paper, thermal stable Y 3 MgAl 3 SibO 12 -TiO 2 microwave composite ceramics were firstly fabricated by the high temperature solid phase reaction method. The influence of the sintering temperature, microstructure on microwave dielectric properties of Y 3 MgAl 3 SiO 12 by doping TiO 2 were investigated in detailed. TiO 2 addition reduced the ceramic sintering temperature and improved the distribution of grain size. The negative temperature coefficient of resonant frequency (τ f = −32 ppm/°C) of Y 3 MgAl 3 SiO 12 was adjusted to near zero value. 0.8Y 3 MgAl 3 SiO 12 -0.2TiO 2 ceramic sintered at 1475 °C for 6 h achieved the optimized microwave dielectric properties: ε r = 12.2, Q × f = 21,050 GHz, τ f = +5.2 ppm/°C, which indicated that 0.8Y 3 MgAl 3 SiO 12 -0.2TiO 2 is a potential candidate for dielectric patch antenna and substrate. [ABSTRACT FROM AUTHOR]

Abstract β-eucryptite (β-LiAlSiO 4) ceramic has been fabricated via a novel solid state reaction method by taking hydroxides LiOH∙H 2 O, Al(OH) 3 and SiO 2 as reactants. The changes of mass, heat and evolution of crystal phases during the reaction process, as well as the reaction sequences, sintering characteristic, micro-morphology and thermal expansion property of the β-LiAlSiO 4 ceramic have been fully studied. The results show that a highly reactive intermediate phase γ-Al 2 O 3 forms after heating Al(OH) 3 over 550℃. γ-Al 2 O 3 preferentially reacts with dehydrated LiOH to form LiAlO 2 , which further reacts with SiO 2 to produce β-LiAlSiO 4 at 700℃. Single-phase β-LiAlSiO 4 powders can be obtained at a low temperature of 950℃. The β-LiAlSiO 4 ceramic sintered at 1200℃ for 1 h shows dense and less cracked microstructure with zero coefficient of thermal expansion α=-0.5 × 10-6/K, which is expected to be a promising material in laser gyroscope and telescope fields. [ABSTRACT FROM AUTHOR]

0.9(Zn 0.9 Mg 0.1 )TiO 3 -0.1TiO 2 (ZMT-TiO 2 ) ceramics doped with BaO-B 2 O 3 -ZnO(BBZ) glass were prepared by conventional solid-state routes. The effects of BBZ glass on the phase evolution, microstructure, sintering mechanism and microwave dielectric properties have been investigated. The BBZ glass as a sintering agent can effectively reduce the sintering temperature of ZMT-TiO 2 ceramic below 1000 °C. The XRD patterns indicate that the ZMT-TiO 2 ceramic consisted of ZnTiO 3 , Zn 2 TiO 4 and TiO 2 phases. Added BBZ glass inhibit the decomposition of the ZnTiO 3 into Zn 2 TiO 4 and TiO 2 . In addition, SEM results showed that BBZ significantly improved the grain growth and densification, this is due to the fact that the BBZ glass liquid sintering mechanism. The sintering mechanism was analyzed through the wetting behavior and the activation energy(Ea). When added 3 wt% BBZ glass, the activation energy reduced from 614.79 KJ/mol to 417.49 KJ/mol. This result indicate that the BBZ glass can promote the sintering process. Typically, the ZMT-TiO 2 ceramic with 3 wt% BBZ sintered at 950 °C for 4 h has shown excellent microwave dielectric properties of ε r = 24.46, Q × f = 47500 GHz and τ f = -14.68 ppm/°C. [ABSTRACT FROM AUTHOR]

A series of novel low temperature co-fired ceramics were fabricated in x BLMT-(100-x) Li 2 Zn 3 Ti 4 O 12 (2.5 ≤ x ≤ 80 wt%) composites sintered at 900 °C. The sintering mechanism, phase composition, microstructure and dielectric properties of the composites were investigated. The results showed that the sintering mechanism of composites with <20 wt% BLMT glass could be attributed to non-reactive liquid-phase sintering and LaBO 3 phase was crystallized from glass beside Li 2 Zn 3 Ti 4 O 12 phase, while composites with ≥20 wt% glass were controlled by the coexistence of viscous sintering and reactive liquid-phase sintering, BLMT glass crystallized forming LaBO 3 , MgLaB 5 O 10 and a small amount of rutile phase, nevertheless, more rutile phase was formed by reacting between glass and ceramic. As BLMT glass was increased, LaBO 3 , MgLaB 5 O 10 and rutile phase gradually dominated the material and Li 2 Zn 3 Ti 4 O 12 phase decreased. Meanwhile, the dielectric constant (ε r ) and quality factor (Q × f) demonstrated gradually decrease, whereas the temperature coefficient of resonant frequency (τ f ) presented a trend of fall first then rise. Typically, the composite with 60 wt% glass displayed excellent dielectric properties with ε r = 14, Q × f = 23,000 GHz, and τ f = −3.56 ppm/°C. The corresponding fitting equations of ε r , Q × f and τ f on the BLMT glass content were obtained by the Origin software, which indicated that the dielectric properties of BLMT/Li 2 Zn 3 Ti 4 O 12 composites could be precisely adjusted by adding the suitable content of glass. Therefore, the sintering process, phase composition and dielectric properties of BLMT/Li 2 Zn 3 Ti 4 O 12 composites can be controlled by varying the content of Li 2 Zn 3 Ti 4 O 12 ceramic and B 2 O 3 -La 2 O 3 -MgO-TiO 2 glass. [ABSTRACT FROM AUTHOR]