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Novel CaAl 2 x B 2 O 4+3 x (x = 0.25, 0.5, 0.75, and 1) ceramics were prepared via solid-state reaction method. The investigation is concentrated on sintering behavior, phase composition and dielectric properties of CaAl 2 x B 2 O 4+3 x ceramics with various ratios of Al 2 O 3 content. The optimal sintering temperature and the content of CaAl 2 B 2 O 7 are highly related to the variation of x value. CaAl 2 x B 2 O 4+3 x ceramics possess excellent microwave dielectric properties: ε r = 5.8 ± 0.05, Q × f = 63,338 ± 2690 GHz (@13.57 GHz), and τ f =-29 ± 2 ppm/℃ when sintered at 940 ℃ for x = 0.5. Comparing the properties of CaAl 2 x B 2 O 4+3 x ceramics with reported borate ceramics, the ceramics prepared in this study with low dielectric loss and low sintering temperature have promising prospects in LTCC technology. [ABSTRACT FROM AUTHOR]

Gd2Zr3(MoO4)9 is a double trigonal molybdate crystallized in the space group R3¯c. The optimal microwave dielectric properties were achieved via solid‐state reaction at 725°C for Gd2Zr3(MoO4)9 ceramics: εr = 11.17, Q × f = 57 460 GHz, τf = −31.91 ppm/°C. The three‐dimensional framework type structure is formed by mixed MoO4 tetrahedron and ZrO6/GdO9 polyhedron. The analysis based on complex chemical bond theory shows that the Mo–O bonds account for majority contribution to controlling microwave dielectric properties. The MoO4 tetrahedron and ZrO6 octahedron stabilize the crystal structure by strong binding ability. As it was shown by Raman spectroscopy, the Raman‐active vibrations primarily originate from MoO4 tetrahedron, similarly to molybdate analogies. [ABSTRACT FROM AUTHOR]

Abstract In the present study, influences of Ta5+ substitution on Nb site on crystal structural evolution, Raman spectra and microwave dielectric properties of Zn 0.15 Nb 0.3- x Ta x Ti 0.55 O 2 (0 ≤ x ≤ 0.3) ceramics were investigated. Bond ionicity, lattice energy and octahedral distortion of Zn 0.15 Nb 0.3- x Ta x Ti 0.55 O 2 structure calculated based on chemical bond theory and Rietveld refinement analysis were used together to understand correlation between crystal structure and microwave dielectric properties. The results showed that rutile Zn 0.15 Nb 0.3- x Ta x Ti 0.55 O 2 solid solutions could be synthesized in whole composition range of x = 0–0.3. With increase of x value, cell volume and bond length are reduced, which is confirmed by blue shift of Raman vibrational peaks. Dielectric constant (ε r) is closely related to average Nb O bond ionicity. Quality factor (Q × f) values and temperature coefficient values of resonant frequency (τ f) are mainly affected by lattice energy and octahedral distortion respectively. In Zn 0.15 Nb 0.3- x Ta x Ti 0.55 O 2 ceramics, proper substitution of Ta5+ ion efficiently improves Q × f values and reduces the τ f values. Optimal microwave dielectric properties of ε r = 75.87, Q × f = 22050 GHz and τ f = 234.6 ppm/°C were obtained for Zn 0.15 Nb 0.3- x Ta x Ti 0.55 O 2 solid solutions at x = 0.2 when sintered at 1100 °C. [ABSTRACT FROM AUTHOR]

(1 − x)Zn0.9Mg0.1TiO3-xZn0.15Nb0.3Ti0.55O2 ((1 − x)ZMT-xZNT) (x = 0.100, 0.125, 0.150, 0.175, 0.200) ceramics were prepared at 900 °C by conventional mixed-oxide method. The phase content, microstructure and microwave dielectric properties had been investigated in detail. Rietveld refinement shows the coexistence of Zn0.9Mg0.1TiO3, Zn0.15Nb0.3Ti0.55O2, Zn(BO2)2 and Zn2TiO4 phases. With ZnO-B2O3-SiO2 (ZBS) glass added, the ceramics can be sintered well at 900 °C with a smaller grain size of 0.12 µm and a higher relative density (> 95%). The microwave dielectric properties are largely influenced by the phase composition according to mixture rule. A typical sample of 0.825ZMT-0.175ZNT ceramic with optimal dielectric properties (εr = 26.14, Q × ƒ = 27184 GHz, τƒ = − 3.46 ppm °C−1) was sintered at 900 °C for 4 h. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric ceramic Li9Zr3NbO13 was found and investigated. Prepared via the solid‐state reaction method, the Li9Zr3NbO13 formed as a Li2ZrO3‐type solid solution at 880‐900°C, with monoclinic structure in C2/c space group and Z = 4. Typically, the Li9Zr3NbO13 sintered at 900°C exhibited the excellent microwave dielectric properties of εr = 21.3, Q×f = 43 600 GHz (at 7.4 GHz), τf = 7.3 ppm/°C. [ABSTRACT FROM AUTHOR]

In this article, LiMgTiO + x wt% (x = 5-9) CaTiO microwave dielectric ceramics with high temperature stability were prepared by solid-state reaction. The crystal structure, microstructure, microwave dielectric properties were discussed systematically as function of x value and sintering temperature. The results show that LiMgTiO and CaTiO phases coexist and the content of CaTiO phase increases, the dielectric constant increases, quality factor and temperature coefficient of resonant frequency decreases because of the increase of CaTiO content. The LiMgTiO + 6 wt% CaTiO ceramics sintered at 1210 °C for 4 h show great properties: ε = 18.03, Q × f = 69,022 (at 7.886 GHz), τ = − 3.03 ppm/°C. [ABSTRACT FROM AUTHOR]

In this paper, the Li2/3(1− x)Sn1/3(1− x)Mg xO (LSM xO) ceramic systems were prepared by solid-state reaction using novel atmosphere-controlled sintering ( x = 0-4/7). Pure Li2SnO3 was observed for x = 0, the Li2Mg3SnO6 and Li2SnO3 coexisted for x = 1/7, and the coexistence of three kinds of phases was detected for x = 1/5 and 1/4, including Li4MgSn2O7 impurity phase. Pure Li2Mg3SnO6-like phase with cubic rock salt structure in Fm-3 m space group was obtained in the range of 1/3-4/7. All samples showed well-dense and smooth microstructures. The microwave dielectric properties highly depended on the phase composition, bond valence, FWHM of Raman spectrum, Raman shift, average grain sizes, and octahedral distortion. The LSM xO ceramics sintered at 1250°C for 5 hours possessed excellent comprehensive properties of εr = 15.43, Q×f = 80 902 GHz and τ f = +5.61 ppm/°C for x = 1/7. Typically, the LSM xO ceramics sintered at 1350°C for 5 hours showed a maximum Q × f of 168 330 GHz for x = 1/2. [ABSTRACT FROM AUTHOR]

In this paper, the compound NaNdSmTiZrO (NNSTZ x, x = 0.00, 0.01, 0.02, 0.05, 0.09, 0.14, 0.20, 0.30) ceramics were prepared by the conventional solid-state route. The main phase of all NNSTZ x samples were indexed as an orthorhombic perovskite structure. The permittivity ( ε ) and quality factor ( Q × f) were improved because of improvement of relative density and homogeneous microstructure with minor Zr substitution ( x ≤ 0.02). When x ≤ 0.14, the temperature coefficient of the resonant frequency ( τ ) could be effectively tuned to a relatively low value of 110.3 ppm/°C due to a continuous decrease of tolerance factors. A remarkable decrease of τ from 110.3 ppm/°C to −2.38 ppm/°C was obtained since a certain amount of NdTiO phase was observed with x ≥ 0.20. Typically, the NNSTZ x ( x = 0.20) ceramic sintered in air at 1450°C for 2 h exhibited good microwave dielectric properties of ε = 75.4, Q × f=6813 GHz, and τ = 67.8 ppm/°C. [ABSTRACT FROM AUTHOR]

Low-loss materials LiZnTiO (LZT) ( x = 0, 0.10, 0.17, 0.25, 1.00) were prepared by the conventional solid-state route. The effect of TiO ratio on phase composition, microstructure, and the microwave dielectric properties of LiZnTiO ceramics were investigated using x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Vector Network Analyzer. The results revealed that a two-phase system LiZnTiO-TiO was formed. The appropriate content of TiO ratio can effectively adjust the temperature coefficient of the resonant frequency ( τ) value from −14.5 to 0 ppm/ °C without obvious degradation of the microwave dielectric properties. The microwave dielectric properties of the LiZnTiO materials were characterized at microwave frequencies. Typically, the LiZnTiO ( x = 0.17) ceramic sintered at 1,160 °C for 5 h showed excellent microwave dielectric properties with ε = 28.51, Q × f = 58,511 GHz, and τ = + 2.3 ppm/ °C. [ABSTRACT FROM AUTHOR]

(1−x)ZrTiO-xZnNbO(x = 0.13-0.53) ceramics doped with 0.7 wt% MnCO were prepared by solid-state reaction and they were all sintered well in air at 1,270 °C. XRD analysis suggested there were a two-phase region for ZrTiO-TiO(x = 0.20-0.33) and a single-phase region for ZrTiO(x = 0.40-0.53) because (ZnNb) preferentially substituted Ti sites, and thereafter Zr sites. The addition of Mn, working as acceptors to receive the electrons left by the lost oxygen, raised the Q × f value dramatically. For 0.7 wt% MnCO doped (1−x)ZrTiO-xZnNbO ceramics, with the increase of x, the ε and the τ dropped from 53.4 to 41.0 and from +95 ppm/°C to −35 ppm/°C respectively, and the Q × f value increased from 26,300 GHz to 48,100 GHz. At last, 0.69ZrTiO-0.31ZnNbO+0.7 wt % MnCO ceramics showed excellent dielectric properties: ε = 45.3, Q × f = 43,300 GHz and τ = −0.5 ppm/°C. Another advantage is that the sintering atmosphere was in air, which is benefit to the commercial application. [ABSTRACT FROM AUTHOR]

The microstructure, sintering and dielectric properties of ZrO-, TiO-doped Ca-Si-B based ceramics prepared by solid-phase process were investigated, and the effects of ZrO, TiO content on these performances were analyzed. The Ca-Si-B based ceramics without additive (ZrO or TiO) showed a high sintering temperature (1,100 °C) and had the dielectric properties: dielectric constant (ε) of 8.38, dielectric loss (tanδ) of 1.51 × 10 at 1 MHz, and volume density of 2.47 g/cm. The addition of ZrO TiO was revealed to lower the sintering temperature of Ca-Si-B based ceramics to 1,000 °C and enhance the sintering and dielectric properties: ρ = 2.61 g/cm, ε = 5.85, tanδ = 1.59 × 10 (1 MHz) with ZrO addition, and ρ = 2.65 g/cm, ε = 6.12, tanδ = 6.4 × 10 (1 MHz) with TiO addition, which are superior to the pure Ca-Si-B. The results show that ZrO, TiO as nucleating agents, are conducive to the precipitation of crystals, thus decrease the sintering temperature and improve the dielectric properties of Ca-Si-B based ceramics. [ABSTRACT FROM AUTHOR]

(ZnMg)SiO powders was prepared by the sol-gel process, and the microstructure and dielectric properties of (ZnMg)SiO microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)SiO with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into ZnSiO lattice, and the solid solution limit of Mg in ZnSiO is about x = 0·1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of ZnSiO ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of ZnSiO. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (ZnMg)SiO dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: ɛ = 6·3, Q × f = 189800 GHz and τ = −63 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the LTCC composite materials containing fused silica and monoclinic zirconia ceramic particles, respectively, which based on the composite matrix composed of the barium borate glassy matrix and α-alumina ceramic particles, were prepared by traditional solid-state preparation process at a sintering temperature of 900°C. Sintering mechanism and physical properties, e.g. dielectric properties and coefficient of thermal expansion (CTE), of the LTCC composite ceramics are investigated and discussed in detail in terms of their mineral phase composition. The results indicate that a barium borate glassy phase can be easily formed from a barium borate compound, which is obtained by the chemical combination of barium hydroxide octahydrate and an aqueous solution of boric acid, at a sintering temperature of 900°C. In turn, the barium borate glassy melts can supply a liquid phase sintering aid for the fabrication of the LTCC composite ceramics with the sintering temperature of 900°C during sintering. The introduction of the α-alumina ceramic particles to the barium borate glassy matrix can improve the sintering behavior whereas the presence of fused silica or monoclinic zirconia particles in the composite ceramics is important to adjust the dielectric, thermal and mechanical properties of the LTCC composite materials. The work may be referenced for the fabrication of multi-layer LTCC structures with tailored physical properties. [Copyright &y& Elsevier]

Abstract: The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO–SiO2–B2O3 ceramic matrix composites with ZrO2 addition. The results indicated that ZrO2 addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO3 and a little SiO2 phase existed at the temperature ranging from 950°C to 1050°C. At 0.5wt% ZrO2, CaO–SiO2–B2O3 ceramic matrix composites sintered at 1000°C possess good dielectric properties: ɛ r =5.85, tan δ =1.59×10−4 (1MHz) and excellent microwave properties: ɛ r =5.52, Q · f =28,487GHz (11.11GHz). The permittivity of Zr-doped CaO–SiO2–B2O3 ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150°C. Moreover, the ZrO2-doped CaO–SiO2–B2O3 ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20Hz to 1MHz. [Copyright &y& Elsevier]

The effects of BiVO and CaTiO additives on the microwave dielectric properties of (Zn,Mg)TiO (ZMT) ceramics were investigated. BiVO as a sintering agent could effectively lower the firing temperature of ZMT ceramics below 930 °C. From XRD analysis, the secondary phase formation occurred when BiVO exceeding the solubility limit 2 wt% in ZMT matrix. SEM results indicated that due to the liquid phase sintering BiVO significantly improved the grain growth and densification. With an increase of BiVO, the dielectric constant (ε) monotonously increased, but the quality factor (Qf) gradually decreased, and also the temperature coefficient of resonant frequency (τ) dramatically linear degraded. Besides, the addition of CaTiO can adjust the τ value of this system to a near zero level. (ZnMg)TiO ceramic codoped with 1.5 wt% BiVO and 5 wt% CaTiO additives sintered at 930 °C exhibited the good microwave dielectric properties of ε = 23, Qf = 16177 GHz, τ ≈ 1.0 ppm/°C. [ABSTRACT FROM AUTHOR]

The low-fired (ZnMg)TiO3–TiO2 (ZMT–TiO2) microwave ceramics using low melting point CaO–B2O3–SiO2 as sintering aids have been developed. The influences of Mg substituted fraction on the crystal structure and microwave properties of (Zn1− xMg x)TiO3 were investigated. The result reveals that the sufficient amount of Mg ( x ≥ 0.3) could inhibit the decomposition of ZnTiO3 effectively, and form the single-phase (ZnMg)TiO3 at higher sintering temperatures. Due to the compensating effect of rutile TiO2 (τf = 450 ppm/°C), the temperature coefficient of resonant frequency (τf) for (Zn0.65Mg0.35)TiO3–0.15TiO2 with biphasic structure was adjusted to near zero value. Further, CaO–B2O3–SiO2 addition could reduce the sintering temperature from 1150 to 950 °C, and significantly improve the sinterability and microwave properties of ZMT–TiO2 ceramics, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The (Zn0.65Mg0.35)TiO3–0.15TiO2 dielectrics with 1 wt% CaO–B2O3–SiO2 sintered at 950 °C exhibited the optimal microwave properties: ε ≈ 25, Q × f ≈ 47,000 GHz, and τf ≈ ± 10 ppm/°C. [ABSTRACT FROM AUTHOR]

The low-fired (ZnMg)TiO3–TiO2 (ZMT–TiO2) microwave ceramics using low melting point CaO–B2O3–SiO2 as sintering aids have been developed. The influences of Mg substituted fraction on the crystal structure and microwave properties of (Zn1− xMg x)TiO3 were investigated. The result reveals that the sufficient amount of Mg ( x ≥ 0.3) could inhibit the decomposition of ZnTiO3 effectively, and form the single-phase (ZnMg)TiO3 at higher sintering temperatures. Due to the compensating effect of rutile TiO2 (τf = 450 ppm/°C), the temperature coefficient of resonant frequency (τf) for (Zn0.65Mg0.35)TiO3–0.15TiO2 with biphasic structure was adjusted to near zero value. Further, CaO–B2O3–SiO2 addition could reduce the sintering temperature from 1150 to 950 °C, and significantly improve the sinterability and microwave properties of ZMT–TiO2 ceramics, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The (Zn0.65Mg0.35)TiO3–0.15TiO2 dielectrics with 1 wt% CaO–B2O3–SiO2 sintered at 950 °C exhibited the optimal microwave properties: ε ≈ 25, Q × f ≈ 47,000 GHz, and τf ≈ ± 10 ppm/°C. [ABSTRACT FROM AUTHOR]

CaO–B2O3–SiO2 glass-ceramics were synthesized by sol–gel method, and the effect of Ca/Si ratio on the microstructures, electrical properties and mechanical characteristics of this ternary system was investigated. The results showed that the increase of CaO content is favorable for the crystallization of CaO–B2O3–SiO2 system and formation of the desired glass-ceramics. The bending strength of the sintered glass-ceramics increases with CaO content by increasing of crystalline phases. When the Ca/Si ratio increases, the dielectric constant ( ε r) decreases and loss (tan δ) increases gradually. The thermal expansion coefficient (TEC) enhances by increasing CaO contents due to the formation of other crystal phases with large TEC value. The glass-ceramics exhibit low dielectric constant and loss ( ε r < 4.7, tan δ < 5 × 10­4 at 1 MHz), high resistivity ( ρ > 1012 Ω · cm), as well as excellent mechanical properties ( σ ≈ 160 MPa, α ≈ 3.6 × 10−6/°C). [ABSTRACT FROM AUTHOR]

The variations of polarization and dielectric properties with the grain size of PZT films have been investigated experimentally and theoretically. It is revealed that polarization increases much more quickly with the grain size than dielectric constant does. The polarization increases as the grain size increases and is saturated when the grain size is about 60nm, whereas the dielectric constant is saturated when the grain size is about 70 nm. Because the dielectric response of ferroelectrics is affected by the domain switching and exhibits hysteresis, the contribution of domain dynamics to the dielectric properties must be considered. Varying grain size will change the domain dynamics due to the close relationship of domain width and grain size. Based on the Landau-Ginzburg (LG) model, the variations of remnant polarization and dielectric constant against grain sizes have been investigated, considering the contribution of domain motion. The calculation result is consistent with the experimental result. [ABSTRACT FROM AUTHOR]

Abstract: The BaNd2Ti4O12 (BNT) solid solution containing composite additives Ba–Zn–B (BZB) were prepared as a low-temperature co-fired ceramics (LTCC). The 20wt.% addition of BZB to BNT significantly lowered the sintering temperature from 1450°C to 900°C without secondary phase formation. The sintering properties of the low-temperature sintered BNT with additives were investigated using dilatometer, scanning electron microscopy (SEM). Liquid phase was formed in the highly doped ceramics. Energy dispersive X-ray spectrometer (EDS) results further confirmed that the material was single phase which is consistent with the X-ray diffractometer (XRD) results. The specimen doped with 20wt.% BZB sintered at 900°C for 0.5h shows excellent dielectric properties: Q×f =3234GHz, ε r =63.2 and τ f =−10.9ppm/°C. [Copyright &y& Elsevier]

Abstract: This paper demonstrates that the Clausius–Mosotti equation cannot be used for Si2N2O since the Lorenz approximation is invalid therein. Therefore a modified definition for the Lorenz electric field is suggested which can be derived from the optical dielectric constant calculated using the plane-wave pseudopotential method. In addition, other parameters of Si2N2O such as the energy band gap, density of states, elastic and optical properties are also given in this paper. Based on the new expression for local electric field, the modified Clausius–Mosotti equation is suggested, and then the dielectric constant of Si2N2O is discussed by using the additivity rule. It is found that the result of the phenomenological analysis of the dielectric constant is basically consistent with the experimental data and the first principles results, which explain the experimental observation that the dielectric constant of Si2N2O is enhanced with the increase of Li content. Also, the modified Clausius–Mosotti equation and the additivity rule are suggested to be used in predicting the dielectric behaviors of the new and complex compounds. [ABSTRACT FROM AUTHOR]

In the present work, MgAl 2-x (Mg 0 · 5 Ti 0.5) x O 4 (x = 0.02, 0.04, 0.06, 0.08, 0.10) solid solutions were synthesized via the traditional solid-state reaction route. The valence state of Ti ions, crystal structural characteristics, and microwave dielectric properties were discussed. A solid solution with spinel structure was revealed by the Rietveld refinement results. The partial substitution of (Mg 0 · 5 Ti 0.5)3+ for Al3+ lowered the sintering temperature and improved the Q × f value of MgAl 2 O 4 ceramic. The MgAl 2-x (Mg 0 · 5 Ti 0.5) x O 4 solid solutions with x = 0.06 can be well sintered at 1425 °C in an oxygen atmosphere for 8 h and exhibits excellent microwave dielectric properties with ε r = 9.1, Q × f = 98,000 GHz, τ f = −61.36 ppm/°C. The sintering temperature of MgAl 1 · 94 (Mg 0 · 5 Ti 0.5) 0.06 O 4 microwave dielectric ceramics was approximately 200 °C lower than that of conventional MgAl 2 O 4 ceramics. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric properties of (1−x)BaTi4O9–xBaZn2Ti4O11 ceramics were investigated by solid-state reaction technique for obtaining high-Q dielectric ceramics in BaO–ZnO–TiO2 system. And they were strongly determined by the chemical composition. As x was increased from 0.05 to 0.50, BaZn2Ti4O11 phase formed more and more. Therefore, the εr decreased from 37.3 to 32.8 and the Q×f values first raised from 45,300GHz to 60,600GHz (x=0.30) and then started to decline to 58,700GHz (x=0.40), and the τf values varied gradually from 12ppm/°C to −13ppm/°C. 0.7BaTi4O9–0.3BaZn2Ti4O11 ceramics sintered at 1240°C for 3h had excellent comprehensive microwave dielectric properties: εr =34.2, Q×f=60,600GHz and τf =−2ppm/°C. [Copyright &y& Elsevier]

In this study, a series of Li 5 MgABO 8 (A=Ti, Sn; B=Nb, Ta) compounds were designed and synthesized through a solid-state reaction method. The XRD patterns showed that a single phase was formed for all the samples. All the peaks were indexed based on the MgO-Like rock salt cubic structure with space group Fm-3m (225) and the peaks indicated that crystals presented different (111) orientation growths in the prepared samples. For all the specimens, the relative density values of 94% and above could be achieved when the sintering temperature exceeded 1300 °C. The ε r values of the specimens showed an increasing trend when the sintering temperatures increased. However, the Q × f values firstly increased and then decreased with the rising temperatures. The electronically-induced strains and lattice-induced strains, which were evaluated by the bond strain index (BSI) and global instability index (GII), presented same variation trends as the Q × f values when the sintering temperature increased. The lowest dielectric loss was achieved in Li 5 MgTiNbO 8 ceramics: ε r =17.55, Q × f=109,700 GHz (f=7.379 GHz), τ f =-32.5 ppm/°C, when sintered at 1290 °C for 4 h. [ABSTRACT FROM AUTHOR]

A novel low-loss and temperature stable NiSnTa 2 O 8 ceramic with trirutile structure was prepared using traditional solid-state method. The structure-performance relationships were investigated by Rietveld refinement, chemical bond theory and far-infrared spectrum. The results show that the relative densities play a dominant role in the change of dielectric constant. Theoretical dielectric constant calculated via bond theory, Clausius-Mossotti equation and fitted result of far-infrared spectrum are close to experimental value. Ta–O bonds with greatest bond ionicity and bond energy have the primary contributions to dielectric polarizabilities and dielectric loss. The optimal microwave dielectric performances of NiSnTa 2 O 8 ceramics were obtained: ε r ∼21.04, Q×f ∼31328 GHz and τ f = −2.63 ppm/°C at 1425 °C. [ABSTRACT FROM AUTHOR]

In this work, x Zn 0.5 Ti 0.5 NbO 4 -(1- x) ZrTiO 4 (0.1 ≤ x ≤ 0.5) ceramics were prepared through the traditional solid-state route. The microstructure, phase evolution and crystallographic variations were investigated in detail. An orthorhombic structure solid solution was formed with the composition of Zr 1- x Zn 0.5 x Ti 1-0.5 x Nb x O 4 (0.1 ≤ x ≤ 0.5). Variations of lattice parameters were responsible for the opposite movement of different XRD peaks as increasing x value. Chemical bond theories include that bond ionicity, bond susceptibility, lattice energy, bond energy and linear thermal expansion coefficient are correlated with dielectric properties. Temperature stable ceramics were obtained when x = 0.2 with excellent dielectric performances: Q × f = 26741 GHz, ε r = 41.93 and τ f = −2.3 ppm/oC. [ABSTRACT FROM AUTHOR]

In the work, we focused on the intrinsic dielectric behavior of Mg 2 TiO 4 spinel ceramic by P–V–L theory and infrared spectra analysis. Ti–O bonds have larger bond ionicity values, thus playing an important role in dielectric polarization. The theoretical dielectric constant was predicted by calculating the bond susceptibility of each chemical bond. Furthermore, Ti(1)–O bonds are responsible for the structural stability of Mg 2 TiO 4 ceramic. Based on classical dispersion theory, permittivity and loss corresponding to each infrared active mode were quantified, and then the crucial contribution of low-frequency modes to intrinsic dielectric properties were determined. [ABSTRACT FROM AUTHOR]

The CaMg 1- x Mn x Si 2 O 6 (x = 0–0.08)ceramics were reported here for the first time. The relationships among structural characteristics, vibrational modes and dielectric properties for the ceramics were researched based on complex chemical bond theory and Raman vibrational spectroscopy. The formation of a single phase with clinopyroxene structure when x = 0 to 0.08 was detected by X-ray diffraction. The monotonous increase of ε r is ascribed to the average bond covalency, polarizability and Raman shift. The Q × f value is influenced by total lattice energy and full width at half maximum of Raman spectra which are both connected with the intrinsic loss. The variation of τ f is related to thermal expansion coefficient and M1-site bond valence. Furthermore, the CaMg 0.98 Mn 0·02 Si 2 O 6 ceramic sintered at 1300 °C possessed optimal microwave dielectric properties of ε r = 8.01, Q × f = 83469 GHz and τ f = −45.27 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract The phase composition, microstructure, microwave dielectric properties of (Al 0.5 Nb 0.5)4+ co-substitution for Ti site in LiNb 0.6 Ti 0.5 O 3 ceramics and the low temperature sintering behaviors of Li 2 O-B 2 O 3 -SiO 2 (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li 1.075 Nb 0.625 Ti 0.45 O 3 solid solution was formed in all component. The increase of dielectric constant (ε r) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τ f value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb 0.6 Ti (0.5- x) (Al 0.5 Nb 0.5) x O 3 ceramics (x = 0.10) when sintered at 1100 ℃ for 2 h: ε r = 70.34, Q×f = 5144 GHz, τ f = 4.8 ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x = 0.10 were obtained with 1.0 wt% glass: ε r = 70.16, Q×f = 4153 GHz (at 4 GHz), τ f = -0.65 ppm/℃ when sintered at 925 ℃ for 2 h. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric ceramic Li9Zr3NbO13 was found and investigated. Prepared via the solid‐state reaction method, the Li9Zr3NbO13 formed as a Li2ZrO3‐type solid solution at 880‐900°C, with monoclinic structure in C2/c space group and Z = 4. Typically, the Li9Zr3NbO13 sintered at 900°C exhibited the excellent microwave dielectric properties of εr = 21.3, Q×f = 43 600 GHz (at 7.4 GHz), τf = 7.3 ppm/°C. [ABSTRACT FROM AUTHOR]

Low-firing (Zn 0.9 Mg 0.1 ) 1−x Co x TiO 3 (x = 0.02–0.10) (ZMC x T) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co 2 O 3 substitution on the phase composition, microstructure and microwave dielectric properties of ZMC x T ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO 3 and ZnB 2 O 4 phases at x = 0.02–0.10. (Zn 0.9 Mg 0.1 ) 1−x Co x TiO 3 ceramic with x = 0.06 (ZMC 0.06 T) obtains the best combination microwave dielectric properties of: ε r = 21.58, Q × f = 53,948 GHz, τ f = − 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B 2 O 3 -SiO 2 (ZBS) and 9 wt% TiO 2 was added into ZMC 0.06 T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: ε r = 26.03, Q × f = 34,830 GHz, τ f = − 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry. [ABSTRACT FROM AUTHOR]

A novel microwave dielectric ceramic LiNb 0.6 Ti 0.5 O 3 (LNT) with Ca substitutions LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 was synthesized by solid-state method. It was found that with Ca substitutions, the temperature coefficient of resonant frequency τ ƒ could be adjusted to zero, due to the appearance of the second phase Ca 5 Nb 4 Ti 3 O 21 . The τ ƒ of the Ca 5 Nb 4 Ti 3 O 21 phase is −144.3 ppm/°C through the simulation and numerical value calculation. Furthermore, the LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 ceramic shows a higher dielectric constant ε r and a denser microstructure. The LiNb 0.6 Ti (0.5−x) Ca 1.231x O 3 ceramic with x = 0.03 sintered at 1100 °C for 2 h shows excellent microwave dielectric properties: ε r = 76.89, Q × ƒ = 4064 GHz, τ ƒ = 0.25 ppm/°C. [ABSTRACT FROM AUTHOR]

In this paper, the influences of Al substitution and BaCu(B 2 O 5 ) (BCB2) additives on the sintering temperature, microstructures, phase structures and microwave properties were investigated in detail. The results indicated that all Al added Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x Al x O 3 (CLNTA x ) samples were crystallized as orthorhombic perovskite structure in Pnma space group. A proper amount ( x ≤ 0.03) of Al substitution for Ti was beneficial to improve the quality factors mainly due to the increase of packing fraction. But the permittivity ( ε r ) and temperature coefficient of the resonant frequency ( τ f ) deteriorated because of the decrease of B-site bond valence. The perovskite structured phase and BCB2 phase were observed in Ca 0.35 Li 0.25 Nd 0.35 Ti 0.97 Al 0.03 O 3 (CLNTA3) ceramics, when a small amount of BCB2 was added ( y ≤ 5 wt%). The sintering temperature was effectively lowered under 950 °C, and τ f was modified from 74.8 ppm/°C to 41.2 ppm/°C with the assistance of BCB2 phase and liquid phase. But excessive BCB2 contents ( y > 5 wt%) resulted in the BaNd 2 Ti 5 O 14 and unknown phase, leading to inferior dielectric properties. Therefore, 5 wt% BCB2-added CLNTA3 ceramics sintered at 950 °C for 2 h exhibited excellent comprehensive microwave dielectric properties: ε r = 109.5, Q × f = 2979 GHz and τ f = 41.2 ppm/°C. [ABSTRACT FROM AUTHOR]

Microwave dielectric properties of Li 2 Mg 3− x Ca x TiO 6 (x=0–0.18) ceramics were studied using a conventional solid-state route to find temperature stable and high Q microwave ceramics. As the calcination temperature was 500 °C, the Li 2 TiO 3 phase with monoclinic rock salt structure in C 2 /c space group started to form. When the samples were calcined from 600 °C to 900 °C, the XRD patterns exhibited a remarkable chemical reaction between the MgO and Li 2 TiO 3 phases, which eventually formed the Li 2 Mg 3 TiO 6 phase. The results indicated the Li 2 Mg 3 TiO 6 and CaTiO 3 co-existed with each other and formed a stable composite system when the calcium content was added. The SEM photographs indicated that the pores caused by the Li evaporation could be effectively reduced due to the appearance of CaTiO 3 . As x was increased from 0 to 0.18, the relative density was significantly improved due to the elimination of pores. As the Ca content increased, the dielectric constant (εr) increased from 14.8 to 20.6; the quality factor (Q×f) decreased from 148,713 GHz to 79,845 GHz, and the temperature coefficient of resonant frequency (τf) significantly increased from −42.4 to +10.8 ppm/°C due to the increased amount of CaTiO 3 . Therefore, at x=0.12, the LMC x T ceramics sintered at 1280 °C for 6 h displayed excellent comprehensive properties of εr=17.8, Q×f =102,246 GHz and τf=−0.7 ppm/°C. [ABSTRACT FROM AUTHOR]

In this work, the effects of 3ZnO-2B 2 O 3 glass on sintering temperature, phase composition, microstructure and dielectric properties of Zn 1.8 SiO 3.8 ceramics were investigated. The x-ray diffraction results showed that there no reaction between the glass and the ceramic during the sintering process. A mechanism of densification and microstructure evolution of the ceramics with glass was provided based on the x-ray, density and scanning electronic microscopy results. The study on the dielectric properties showed strong dependences of glass content and sintering temperature. At last, the compact ceramic with 20 wt% glass content, exhibited a dielectric constant of 6.5 and a low loss of 0.001, after sintering at 920 °C. [ABSTRACT FROM AUTHOR]

Abstract: The La2O3–B2O3 (LB) addition, synthesized using the traditional solid-state reaction process, was chosen as a novel sintering aid of the low temperature co-fired CaO–B2O3–SiO2 (CBS) glass–ceramic. The effects of LB on the flexural strength and microwave dielectric properties have been investigated. The LB addition promotes the crystallization of the CaSiO3 but high amount of the LB addition leads to the formation of more pores. The CBS sample with 4wt% LB addition sintered at 850°C for 15min shows good properties: flexural strength=193MPa, ɛ r =6.26 and loss=9.96×10−4 (10GHz). [Copyright &y& Elsevier]