Microwave Dielectric Characteristics Research Articles

Structure evolution and microwave dielectric characteristics of Hf1−xSnxO2 ceramics

AbstractHigh Q (Hf1−xSnx)O2 ceramics were prepared via a standard solid‐state reaction route, and the microwave dielectric characteristics were investigated systematically together with the structure evolution. With increasing x, the structure changed from HfO2 (monoclinic in space group P21/c, x = 0 and 0.03) to Hf0.77Sn0.23O2 (orthorhombic in space group Pbcn, x = 0.23), while the two‐phase structure: HfO2 major phase and Hf0.77Sn0.23O2 secondary phase, was determined for x = 0.05–0.21, and Hf0.77Sn0.23O2 major phase combined with SnO2 tetragonal secondary phase in space group P42/mnm was confirmed for x = 0.30–0.40. The Qf value was significantly increased from 24,500 to 167,650 GHz by Sn‐substitution, and the best combination of microwave dielectric characteristics was obtained in Hf0.77Sn0.23O2 ceramics: εr = 17.2, Qf = 167 650 GHz at 9.6 GHz and 230 710 GHz at 26.1 GHz, and τf = −52.6 ppm/°C. The dielectric loss was deeply linked with the structure stability and lattice‐distortion. Also, the phase composition, the bond strength, as well as the degree of covalency, had a tight connection with dielectric loss. The present ceramics were expected to be the promising candidates as low‐εr microwave dielectric ceramics.

The effect of ionic redistributions on the microwave dielectric response of cytosol water upon glucose uptake.

The sensitivity of cytosol water's microwave dielectric (MD) response to D-glucose uptake in Red Blood Cells (RBCs) allows the detailed study of cellular mechanisms as a function of controlled exposures to glucose and other related analytes like electrolytes. However, the underlying mechanism behind the sensitivity to glucose exposure remains a topic of debate. In this research, we utilize MDS within the frequency range of 0.5-40 GHz to explore how ionic redistributions within the cell impact the microwave dielectric characteristics associated with D-glucose uptake in RBC suspensions. Specifically, we compare glucose uptake in RBCs exposed to the physiological concentration of Ca2+ vs. Ca-free conditions. We also investigate the potential involvement of Na+/K+ redistribution in glucose-mediated dielectric response by studying RBCs treated with a specific Na+/K+ pump inhibitor, ouabain. We present some insights into the MD response of cytosol water when exposed to Ca2+ in the absence of D-glucose. The findings from this study confirm that ion-induced alterations in bound/bulk water balance do not affect the MD response of cytosol water during glucose uptake.

Microstructure, bonding characteristics, far-infrared spectra and microwave dielectric properties of co-substituted Ce2[(Zr1-x(Zn1/3Sb2/3)x]3(MoO4)9 ceramics

In this contribution, Ce2[(Zr1-x(Zn1/3Sb2/3)x]3(MoO4)9 (CZ1−x(ZS)x) (0 ≤ x ≤ 0.1) ceramics were fabricated using the solid-state reaction method, and the phase composition of the synthesized ceramics was analyzed via XRD and Rietveld refinement. The outcomes revealed that the ceramics, characterized by different x values, constituted a solitary phase with an R-3C space group, and the cell volume demonstrated a decrease with an increase in x value. The examination of the ceramics microwave dielectric characteristics using P–V−L theory reveals that the fi(Ce–O(6)) bond was found to be related to εr, while Q × f was influenced by the average grain size and Uave.(Mo–O), and Eave.(Mo–O) and αave.(Mo–O) were related to the τf value. The optimal properties were achieved at 750 °C (x = 0.02), resulting in εr = 10.08, Q × f = 100,954 GHz, τf = −12.46 ppm/°C. The infrared reflection spectrum analysis revealed that the primary polarization contribution was due to the dielectric response of intrinsic phonons. Additionally, the effects of three different complex ions (Zn1/2Sb2/3)4+, (Zn1/2Ta2/3)4+, and (Zn1/2Nb2/3)4+ doping on the properties of Ce2Zr3(MoO4)9 ceramics were investigated using SEM, packing fraction, and chemical bond analysis. The results showed that (Zn1/2Sb2/3)4+ doping was effective in improving the grain size and apparent density of Ce2Zr3(MoO4)9 ceramics, and the high packing fraction and U(Mo–O) were found to be the primary intrinsic factors for the optimal properties.

Effect of raw material pretreatment and ionic radius on the preparation and microwave dielectric properties of Re2TiO5 ceramics

The present study focuses on the synthesis and characterization of rare-earth titanates, specifically Re2TiO5 (ReLa, Nd, Sm), with a particular emphasis on their microwave dielectric properties. The factors influencing the synthesis of La2TiO5 compound through the traditional solid-state method were thoroughly investigated, with a significant finding being the notable impact of moisture absorption in La2O3. The impact of variations in rare-earth cation radii on the structure and dielectric properties was systematically analyzed. Re2TiO5 (ReLa, Nd, Sm) ceramics crystallized into an orthorhombic structure with space group Pnam, which was confirmed through Rietveld refinement. The resulting materials demonstrated exceptional microwave dielectric properties characterized by a low permittivity range of 13.72–17.39, high-quality factors ranging from 8331 to 17,795 GHz, and a significantly reduced temperature coefficient of resonance frequency (−33.2∼-12.6 ppm/°C). The correlation between microwave dielectric properties and structural characteristics (including ionic polarizability, packing fraction, and bond valence) was investigated. The exceptional potential of these rare-earth titanates lies in their ability to meet the stringent requirements for low signal transmission delay in wireless communication systems, owing to their advantageous low permittivity within the microwave frequency spectrum.

Effects of F− substitution on crystal structure, band characteristics and microwave dielectric properties of Li3Mg2NbO6 ceramics for high frequency applications

The structure–performance mechanism is essential to achieve comprehensive characteristics for advanced communication system. In the present work, F− ions were adopted to fabricated Li3Mg2NbO6-x/2Fx ceramics at a nitrogen atmosphere to modify dielectric characteristics. Correlation between bond characteristics, crystal structure and enhanced microwave dielectric characteristics was investigated through vibration analysis, P–V-L theory, Rietveld refinement, and First-principle calculations. Raman analysis and Rietveld refinement show that F− substitution led to a single phase. First-principle calculations indicates a high energy gap of 3.676 eV and p orbit contributed to Fermi energy. F− substitution led to the increase of Nb O bond ionicity and lattice energy, accounting for the variation in Q×f value and dielectric constant. The τf value was related to the expansion coefficient of the Li–O bond. Remarkably, the samples (x = 0.08) exhibited comprehensive dielectric characteristics with εr = 15.9, Q×f = 143,000 GHz and near-zero τf = −2.1 ppm/°C, proving an effective strategy for collaborative regulation. Based on structure simulation, 5G filter with ultra-low loss and high-suppression was designed through introducing transmission zeros from cross coupling. More specifically, a dielectric filter exhibited an interpolation loss of 0.2 dB at 3.3–3.6 GHz and high attenuations of 15 dB for 20 MHz outside the passband, verifying the feasibility for 5G applications.

Sintering behavior, crystal structure, and microwave dielectric properties of a novel NaY9Si6O26 ceramic

AbstractThis study investigates NaY9Si6O26 ceramics prepared through the solid‐phase method, focusing on their microwave dielectric properties and crystallographic characteristics. X‐ray diffraction analysis reveals a hexagonal crystal structure for NaY9Si6O26 ceramics within the P63/m (176) space group. Rietveld refinement analysis precisely determines the lattice constants as a = b = 9.3423 Å, c = 6.7524 Å, and a unit cell volume of V = 510.3877 Å3. Additionally, Raman spectroscopy unveils a noteworthy correlation between the quality factor and the full width at half maximum of the A1g(O) mode at 878 cm−1. The structural attributes, including lattice fringes and diffraction patterns of hexagonal NaY9Si6O26 ceramics, are elucidated through transmission electron microscopy. Of significance are the microwave dielectric properties of NaY9Si6O26 ceramics sintered at 1465°C, revealing a relative permittivity (εr) of 10.42, an impressive Q × f product of 33 766 GHz (at f = 11.14 GHz), and a temperature coefficient of resonant frequency (τf) of −28.7 ppm/°C. This comprehensive investigation contributes to the understanding of both the structural and microwave dielectric characteristics of NaY9Si6O26 ceramics, with potential applications in advanced electronic devices.

Effect of cation occupancy on crystal structure and microwave dielectric characteristics of spinel-structured (1-x)Zn2TiO4-xli2MgTi3O8 ceramics

Excellent spinel microwave dielectric ceramics (1-x)Zn2TiO4-xLi2MgTi3O8 (ZTLMTx, x = 1/3 and 2/3) were prepared at relatively low densification temperatures of 1100 °C and 1080 °C, respectively. A disordered cubic phase with space group Fd-3m was formed at x = 1/3, whereas an ordered cubic phase with space group P4332 was formed at x = 2/3. The ceramics at x = 1/3 and 2/3 exhibited promising microwave dielectric properties of ɛr = 18.27 and 22.96, Q × f = 91,877 GHz and 75,186 GHz, and τf = −42.3 ppm/°C and −21.05 ppm/°C, respectively. The large deviation between the experimental ԑr and theoretical εth of 1/3 and 2/3 ceramics were 18.3 % and 57 %, respectively, due to the underestimation of the ionic polarizability of Ti4+. The difference in their ɛr, Q × f, and τf were discussed by the structure, FWHM of A1g, lattice energy and bond energy in detail.

Ilmenite-type structure and pervoskite structure mix-phase ceramics at microwave frequency

ABSTRACT The impact of CuB2O4 additive used as a sintering aid on the microstructures and microwave dielectric characteristics of mixed phase (Mg0.95Zn0.05)Co0.05TiO3-Ca0.6(La0.9Y0.1)0.2667TiO3 ceramics was investigated. CuB2O4 additives can effectively lower the densification temperature of (Mg0.95Zn0.05)Co0.05TiO3-Ca0.6(La0.9Y0.1)0.2667TiO3 from 1450°C to the range of 1050°C ~ 1175°C. Doping CuB2O4 (0.25 ~ 2 wt%) in 0.875(Mg0.95Zn0.05)Co0.05TiO3-0.125Ca0.6(La0.9Y0.1)0.2667TiO3 ceramics can substantially enhance their microwave dielectric properties and density. With the addition of 1% and 0.25% CuB2O4, Q × f values of 43,000 GHz and 7700 GHz were obtained at 1050–1175°C, respectively. Different additions of CuB2O4 have a significant effect on the Q × f value. Temperature coefficient of resonant frequency of 0.875(Mg0.95Zn0.05)Co0.05TiO3-0.125Ca0.6(La0.9Y0.1)0.2667TiO3 (0.875MZCT–0.125CLYT) varied from 16 to 30.9 ppm/°C when adding different CuB2O4 (0.25 ~ 2 wt%).

High Dk and ultra-high thermal conductivity ST/μBN/polyolefin composites for microwave applications

In this work, we examined the structure, microwave dielectric, thermal and mechanical characteristics of composites containing SrTiO3/xμBN/polyolefin (with x at 0, 6, 8, 10 and 12 weight percent). SrTiO3 (ST) and micro boron nitride (μBN) powders were fabricated with 1,2-PB/EPDM/SBS (1,2-PB, EPDM and SBS are abbreviations of 1,2-polybutadienes, ethylene-propylene-dicyclopentadiene and styrene-butadiene-styrene triblock copolymer, respectively) by hot-press process after modified by Vinyltrimethoxysilane (VTMS) and 3-aminopropyltriethoxysilane (KH550), respectively. The ball mill and surface modification procedure enhanced the dispersion of the boron nitride in the solution and promoted compatibility between ceramic particles and polyolefin matrix. The incorporation of BN created more effective boron transfer pathways with ST particles, significantly improving the thermal conductivity of the composite. However, as μBN content increased, more ceramic agglomerates and pores were introduced, deteriorating dielectric, thermal and mechanical properties of the samples. The particle size test and XPS were conducted to determine the effect of surface modification on the dispersion and surface properties of ceramics. Cross-plane thermal conductivity, TGA and stress-strain curves were used to evaluate the thermal and mechanical properties of the composites. In all, a composite with high-Dk and high thermal conductivity was obtained when x = 10 wt.%: Dk = 17.4, Df = 0.0071 and λ = 1.784 W/(m*k), which is promising for microwave applications.

Structure and microwave dielectric properties of Al3+-doped (Zn1/6Ba1/6Ca1/6Sr1/6La1/3)TiO3 high-entropy ceramics system

In this study, based on the highly disordered multi-component system with high-entropy and traditional perovskite with high dielectric constant, a series of the Al3+-doped high-entropy perovskite (Zn1/6Ba1/6Ca1/6Sr1/6La1/3)Ti1-xAlxO3 (0 ≤ x ≤ 0.1) ceramics was designed and synthesized by using a solid state reaction method to explore the effects of different doping amounts on microwave dielectric characteristics together with the microstructures. The single-phase structure in space group Pm-3m was determined in the sintering temperature range of 1325 °C–1400 °C and both had high dielectric constant (from 74.46 to 93.44). With the increase of Al doping amount, the variation trend of dielectric constant was closely related to the density and ionic polarizability. The Q × f value of doped samples was higher than that of undoped samples, which was mainly due to the interaction of oxygen vacancy content and grain size. Due to the high-entropy effect resulting in [Ti-O6] octahedral torsion, the τf value was greatly reduced compared with traditional perovskite, which exhibited outstanding microwave dielectric properties (εr = 74.46, Q × f = 4108 GHz at 4.31 GHz, and τf = +184 ppm/°C). The present work provided an effective approach to improve the properties of microwave dielectric ceramics.

Structure, composition, microwave dielectric properties and improved ultra-low temperature sintering characteristics of Lyonsite structural Li2Mg2Mo3O12 ceramic

(1-x)Li2Mg2Mo3O12-xTiO2 (x = 0.1–0.5) composite ceramics are prepared by solid-state sintering process. And the structure, composition, microwave dielectric properties and ultra-low temperature sintering characteristics are studied. The result of two-phase (Li2Mg2Mo3O12 and TiO2) coexistence is definitely identified through XRD, mapping and Raman analysis along different regions. Furthermore, as the sintering temperature increases, the enhanced degree of densification plays a positive role in determining microwave dielectric properties. Sintering additives are used to lower sintering temperature of 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramics, where 1 wt% H3BO3 is applied to reduce the temperature from 750 °C to 700 °C and maintain excellent microwave dielectric characteristics. The cooling mechanism of sintering aids are also thoroughly studied. In all, 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramic with 1 wt% H3BO3 sintered at 700 °C displays excellent microwave dielectric properties (εr∼11.27, Q × f ∼43056 GHz, τf ∼ -3 ppm/°C). It can be served as a pioneering candidate in applications of ULTCC (ultra-low temperature co-fired ceramic).

Improvement of τf in HfTiO4 microwave dielectric ceramics with Zr‐ and Sn‐substitution

Abstract(Hf1‐xZrx)TiO4 and (Hf1‐xSnx)TiO4 ceramics were prepared through a standard solid‐state reaction route, and the microwave dielectric characteristics were determined together with the microstructures. The single‐phase solid solution in space group Pbcn was obtained in (Hf1‐xZrx)TiO4, while the two‐phase structure with (HfTiO4(s.s.) major phase in space group Pbcn and Sn0.3Ti0.7O2 secondary phase in space group P42/mnm) was determined in (Hf1‐xSnx)TiO4. The temperature coefficient of resonant frequency τf could be significantly improved to near‐zero in both systems, and the best combination of microwave dielectric characteristic was achieved at x = 0.5 in (Hf1‐xZrx)TiO4: εr = 39.0, Qf = 43,150 GHz at 5.3 GHz and τf = 3 ppm/°C, and at x = 0.225 in (Hf1‐xSnx)TiO4: εr = 37.2, Qf = 52,600 GHz at 5.5 GHz and τf = ‐6 ppm/°C. In the solid solutions, the obvious improvement of τf could be deeply linked with the degree of covalency and the restoring forces of structure. While, the intermediate near‐zero τf is achieved by mixing the phases with opposite τf in multiphase materials. The present work provided an effective way to modify the temperature coefficient of resonant frequency in microwave dielectric ceramics.

Low‐k dielectric materials derived from ZSM‐5 zeolite

AbstractLow‐k dielectric materials were prepared by sintering ZSM‐5 zeolite powder compacts at temperatures ranged 1200–1300°C, and the microwave dielectric characteristics were investigated together with the structure evolution during sintering. It was failed to obtain ZSM‐5 ceramics by high temperature sintering because the densification could never occur below the tolerable temperature and the ordered porous structure completely collapsed above the tolerable temperature. The structure changed from ZSM‐5 zeolite to SiO2‐Al2O3 glass at 1240°C, and finally to SiO2‐based cristobalite ceramics above 1275°C. A low dielectric constant (2.63‐2.78) combined with low dielectric loss (< 0.0005 at 18 GHz) and small temperature coefficient of resonant frequency (varied from ‐18.6 to ‐8.1 ppm/°C) was achieved in the present materials, and the value of dielectric loss was the lowest one achieved so far in the dielectric materials with a dielectric constant lower than 3. With the structure evolution from ZSM‐5 zeolite to SiO2‐Al2O3 glass and finally to SiO2‐based cristobalite ceramics, the dielectric constant increased from 2.27 to 2.78, while the Qf value indicated a complicated variation tendency, and the higher Qf values were achieved in the amorphous and crystalline states, while significant drop was determined in the partial amorphous state. It should be a great challenge to prepare dense zeolite ceramics without collapse of ordered porous structure, and then the ultra‐low dielectric constant materials with high Q could be expected.

Rattling and compressed cations resulting in distinct microwave dielectric characteristics of SrPrBO4 (B = Ga, Al) with K2NiF4 structure

In this work, tetragonal K2NiF4 structured SrPrBO4 (B = Ga, Al) ceramics with I4/mmm space group were synthesized via the conventional solid-phase method. High relative density (>95 %) and excellent microwave dielectric properties of εr = 18.15, Q×f = 36,643 GHz, τf = −20.20 ppm/°C for SrPrAlO4, and εr = 22.02, Q×f = 27,475 GHz, τf = +19.11 ppm/°C for SrPrGaO4 were obtained when sintered at 1500 °C and 1375 °C, respectively. Analyses of the bond valences show that the εr and τf values are closely related to the rattling and compressing effects of the A-site cation. The strong compressed effect of Sr2+ in SrPrAlO4 leads to its εr value less than the εr(C-M); while, the strong rattling effect of Pr3+ in SrPrGaO4 leads to its εr value higher than the εr(C-M), and thus to a positive τf. The Al/Ga–O bonds play a crucial role in the influence of the dielectric loss according to the P–V–L chemical bonding theory analysis. The Edc of SrPrAlO4 (0.99 eV) and SrPrGaO4 (0.52 eV) indicates that the formation mechanisms of oxygen vacancies in both ceramics are different.

Structure evolution and adjustment of τf in (Ba, Sr)HfO3 and (Sr, Ca)HfO3 microwave dielectric ceramics

AbstractThe crystal structure evaluation of Ba1−xSrxHfO3 and Sr1−yCayHfO3 ceramics with varying composition was determined together with its influence on microwave dielectric characteristics. The variation mechanism of temperature coefficient of resonant frequency (τf) was discussed in details, and the strong correlation between τf and bond valence sum (BVS) and tolerance factor (t) was interpreted from the view point of energy. With increasing Sr‐content, the stable phase of Ba1−xSrxHfO3 at room temperature changed from Pmm (x ≤ 0.25) to I4/mcm (0.35 ≤ x ≤ 0.40), then to Imma (0.50 ≤x < 0.75) and finally to Pnma (0.75 ≤ x ≤ 1.0). The peak temperature of dielectric constant changed due to the structure transition, resulting in that τf rapidly declined at first, reached near zero, then slowly decreased, and finally rapidly decreased. Sr1−yCayHfO3 (0 ≤ y ≤ 1.0) belonged to space group Pnma. As the bond lengths and bond angles between B‐atom and O‐atom became more and more changeable (or BVS became smaller), the crystal could store more input heat energy through bond vibrational energy, and consequently τf became closer to zero with increasing Ca‐content, which was consistent with the physical meaning of the rattling effect on τf. With decreasing t, the dominant mechanisms responsible for tuning τf changed from (i) phase transition and (ii) dilution of ion polarizability to (iii) rattling effect. One could investigate what were the dominant mechanisms tuning τf and hopefully predict its trend with the help of τf–t graph. These findings provided a new idea for developing solid solution ceramics with excellent temperature stability.

Phase Structure, Bond Features, and Microwave Dielectric Characteristics of Ruddlesden-Popper Type Sr2TiO4 Ceramics.

This work studied the phase constitution, bond characteristics, and microwave dielectric performances of Sr2TiO4 ceramics. Based on XRD and Rietveld refinement analysis, pure tetragonal Ruddlesden-Popper type Sr2TiO4 ceramic is synthesized at 1425~1525 °C. Meanwhile, the microstructure is dense and without porosity, indicating its high sinterability and densification. Great microwave dielectric performances can be obtained, namely an εr value of 39.41, and a Q × f value of 93,120 GHz, when sintered at 1475 °C. Under ideal sintering conditions, the extrinsic factors are minimized and can be ignored. Thus, the intrinsic factors are considered crucial in determining microwave dielectric performances. Based on the P-V-L complex chemical bond theory calculation, the largest bond ionicity, and proportions to the bond susceptibility from Sr-O bonds suggest that Sr-O bonds mainly determine the dielectric polarizability. However, the Ti-O bonds show lattice energy about three times larger than Sr-O bonds, emphasizing that the structural stability of Sr2TiO4 ceramics is dominated by Ti-O bonds, and the Ti-O bonds are vital in determining the intrinsic dielectric loss. The thermal expansion coefficient value of the Sr2TiO4 structure is also mainly decided by Ti-O bonds.

Microwave dielectric properties and relaxation characteristics of Ba0.5Sr0.5TiO3 –Bi2MoO6 composite ceramics

The (1-x) Ba0.5Sr0.5TiO3-xBi2MoO6 (x = 10, 20, 30, and 40 wt%) composite ceramics were successfully synthesized through a conventional solid-phase reaction method, and the influence of A- and B- site co-doping on the dielectric properties of the BST composite ceramics was comprehensively investigated. Bi3+ ions acted as donors to replace Ba2+ and Mo6+ replaced Ti4+, producing a (BiBa∙ + MoTi∙∙)-VBa″ dipole to achieve electrovalent equilibrium. In addition, the liquid phase inhibited the growth of grains and promoted densification of the composite ceramics. The degree of B-site order was analyzed using Raman spectroscopy. With an increase in the amount of Bi2MoO6 composite, the dielectric permittivity peak broadened, the Curie temperature gradually decreased, and the tunability of the composite ceramics declined gradually. The dielectric properties of the composite ceramics benefitted from the inclusion of Bi2MoO6 and its composite effects. At the composition of x = 30 wt%, the composite ceramics exhibited excellent comprehensive properties with ε = 457 (RT), T = 14% (at 30 kV/cm), and Q = 780 (at 1148 MHz).

Effects of (Li0.5Nb0.5)3+ co-substitution on microwave dielectric characteristics of MgAl2O4 ceramics

Effects of (Li0.5Nb0.5)3+ co-substitution on microwave dielectric characteristics of MgAl2O4 ceramics

Influences of substituting of (Ni1/3Nb2/3)4+for Ti4+on the phase compositions, microstructures, and dielectric properties of Li2Zn[Ti1−x(Ni1/3Nb2/3)x]3O8(0 ≤x≤ 0.3) microwave ceramics

Complex ions substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics. In this work, Li₂Zn[Ti_1-<em>x</em>(Ni_1/3Nb_2/3)<em>_x</em>]₃O₈ (LZTNN<em>x</em>, 0 ≤ <em>x</em> ≤ 0.3) ceramics were designed based on complex ions substitution strategy, following the substitution rule of radius and valence to investigate the relationships between phase composition (containing oxygen vacancies and Ti³⁺ ions), microstructure, and microwave dielectric characteristics of LZTNN<em>x</em> ceramics. The samples maintained a single Li₂ZnTi₃O₈ solid solution phase as <em>x</em> ≤ 0.2 whereas the <em>x</em> = 0.3 sample produced a secondary phase with LiNbO₃ structure. The appropriate amount of (Ni_1/3Nb_2/3)⁴⁺ substitution could slightly improve the densification of LZTNN<em>x</em> ceramics due to the formation of Li₂ZnTi₃O₈ solid solution accompanied by a decrease in average grain size. The presence of a new <em>A</em>_1g Raman active band at about 848 cm^-1 indicated that the local symmetry changed, affecting the atomic interactions of LZTNN<em>x</em> ceramics. The variation in dielectric constant (ε<em>_r</em>) was closely related to molar volume ionic polarizability, and the temperature coefficient of resonant frequency (τ<em>_f</em>) was related to the bond valence of Ti. The increase in density, the absences of Ti³⁺ ions and oxygen vacancies, and the reduction in damping behavior were responsible for decreased dielectric loss. The LZTNN0.2 ceramic sintered at 1120 ^oC exhibited favorable microwave dielectric properties: ε<em>_r</em> = 22.13, quality factor (<em>Q</em>×<em>f)</em> = 97350 GHz, and τ<em>_f</em> = −18.6 ppm/^oC, which might be a promising candidate for wireless communication applications in highly selective electronics.

Structure, far-infrared spectroscopy, microwave dielectric properties, and improved low-temperature sintering characteristics of tri-rutile Mg 0.5Ti 0.5TaO 4 ceramics

In this study, tri-rutile type Mg_0.5Ti_0.5TaO₄ ceramics were synthesized, where the structure–property relationship, especially the structural configuration and intrinsic dielectric origin of Mg_0.5Ti_0.5TaO₄ ceramics, and the low-firing characteristics were studied. It is found that the tri-rutile structural type is unambiguously identified through the Rietveld refinement analysis, the selected area electron diffraction (SAED), and the high-resolution transmission electron microscopy (HRTEM) along the [110] zone axis. With the increase in sintering temperature, the densification and uniformity of crystal growth play important roles in regulating the microwave dielectric properties of Mg_0.5Ti_0.5TaO₄ ceramics. Intrinsically, theoretical dielectric properties calculated by the far-infrared reflective spectra approached the experimental values, indicating the importance of structural features to dielectric properties. Furthermore, a glass additive with high matching relevance with ceramics has been developed to decrease the high sintering temperature of Mg_0.5Ti_0.5TaO₄ ceramics, where 2–4 wt% Li₂O–MgO–ZnO–B₂O₃–SiO₂ (LMZBS) glass frit was adopted to reduce the suitable temperature from 1275 to 1050 ℃ without significantly deteriorating the microwave dielectric characteristics. Specifically, Mg_0.5Ti_0.5TaO₄ ceramics containing 2 wt% glass addition sintered at 1050 ℃ for 4 h possess excellent microwave dielectric properties: dielectric constant (<i>ε</i>_r) = 44.3, quality factor multiplied by resonant frequency (<i>Q</i>×<i>f</i>) = 23,820 GHz (<i>f</i> = 6.2 GHz), and the temperature coefficient of resonant frequency (<i>τ</i>_<i>f</i>) = 123.2 ppm/℃.