Li4Mg3Ti2O9: A novel low-loss microwave dielectric ceramic for LTCC applications

Low-loss novel Li₄Mg₃Ti₂O₉ dielectric ceramics with rock-salt structure were prepared by a conventional solid-state route. The crystalline structure, chemical bond properties, infrared spectroscopy and microwave dielectric properties of the abovementioned system were initially investigated. It could be concluded from this work that the extrinsic factors such as sintering temperatures and grain sizes significantly affected the dielectric properties of Li₄Mg₃Ti₂O₉ at lower sintering temperatures, while the intrinsic factors like bond ionicity and lattice energy played a dominant role when the ceramics were densified at 1450 °C. In order to explore the origin of intrinsic characteristics, complex dielectric constants (ε^’ and ε^’’) were calculated by the infrared spectra, which indicated that the absorptions of phonon oscillation predominantly effected the polarization of the ceramics. The Li₄Mg₃Ti₂O₉ ceramics sintered at 1450 °C exhibited excellent properties of ε_r=15.97, Q·f=135,800 GHz and τ_f=−7.06 ppm/°C. In addition, certain amounts of lithium fluoride (LiF) were added to lower the sintering temperatures of matrix. The Li₄Mg₃Ti₂O₉−3 wt% LiF ceramics sintered at 900 °C possessed suitable dielectric properties of ε_r=15.17, Q·f =42,800 GHz and τ_f=−11.30 ppm/°C, which made such materials promising for low temperature co-fired ceramic applications (LTCC).     

Novel ultra-low loss and low-fired Li8MgxTi3O9+xF2 microwave dielectric ceramics for resonator antenna applications

Low temperature sintered Li₈Mg_xTi₃O_9+xF₂ microwave dielectric ceramics with x = 2−7 were developed based on a newly designed pseudo ternary phase diagram of the Li₂TiO₃–MgO–LiF system. Dense solid solution ceramics (of relative density >96 %) with cubic rock-salt structure, accompanied by a small amount of secondary phase MgO, were obtained in the temperature range of 800−925 °C. With increasing Mg²⁺ content, the value of ε_r decreased, whereas that of τ_f remained nearly constant, and the Q × f increased to a maximum at x = 5. The Li₈Mg₅Ti₃O₁₄F₂ ceramic sintered at 875 °C exhibited superior microwave dielectric properties with ε_r = 16.8, Q × f = 119,700 GHz, and τ_f = −41.6 ppm/°C. The good compatibility with Ag electrodes highlights the promising prospects of this ceramic in low-temperature co-fired ceramic technology. Furthermore, a dielectric resonator antenna fabricated based on a Li₈Mg₅Ti₃O₁₄F₂ ceramic exhibited an outstanding S₁₁ of −34.7 dB and a broad bandwidth of 360 MHz at the desired resonant frequency of 5.98 GHz.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

Phase compositions and crystal structure of Sn-deficient Ca2Sn2Al2O9 microwave dielectric ceramics with high Q×f values

The phase compositions and microwave dielectric properties of Sn-deficient Ca₂Sn₂Al₂O₉ ceramics in this study were explored. The CaSnO₃ and SnO₂ second phases existed at Ca₂Sn_2-xAl₂O_9-2x (x = 0) ceramic. Single-phase Ca₂Sn₂Al₂O₉ ceramics were obtained at 0.08 ≤ x ≤ 0.1, and the orthorhombic structure with the Pbcn space group of Ca₂Sn₂Al₂O₉ was verified. For multi-phase Ca₂Sn_2-xAl₂O_9-2x (0 ≤ x ≤ 0.06) ceramics, their microwave dielectric properties were mainly affected by second phase contents, and their Q × f values increased gradually with the rise in x. High Q × f (105,700 GHz at 12.99 GHz) was obtained by the Ca₂Sn_2-xAl₂O_9-2x (x = 0.08) ceramic with high intrinsic Q × f (175,000 GHz). The large deviation between measured Q × f values and fitted intrinsic Q × f values could be ascribed to the Sn⁴⁺ vacancies of the Sn-deficient Ca₂Sn₂Al₂O₉ ceramics. The Ca₂Sn_2-xAl₂O_9-2x (0 ≤ x ≤ 0.1) ceramics presented large negative τ_f values, and this τ_f was mainly affected by τ_ε. Meanwhile, the Ca₂Sn_2-xAl₂O_9-2x (x = 0.08) ceramic achieved optimal microwave dielectric properties (ε_r = 8.3, Q × f = 105,700 GHz at 12.99 GHz and τ_f = ?63.7 ppm/°C), indicating the good feature of this material for millimetre-wave applications.     

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.     

Enhancing the microwave dielectric performance of SrSm2Al2O7 ceramic by Sr2+ nonstoichiometry and sintering aid addition

Sr_1+xSm₂Al₂O_7+x (0 ≤ x ≤ 0.05) ceramics were prepared by a conventional solid-state reaction method. Slight Sr²⁺ nonstoichiometry dramatically enhanced the microwave dielectric performance of the ceramics. Compared with the stoichiometric material, Sr-deficient ceramics show greatly enhanced microwave dielectric properties. For x = 0.03, the ceramics exhibited good microwave dielectric properties of ε_r = 18.31, Q × f = 78,000 GHz and τ_f = 2.28 ppm/°C. ZnO and LiF sintering aids were added to the ceramic to reduce the presintering temperature and enhance the microwave dielectric properties of the ceramics. After 0.25 wt% ZnO and 0.25 wt% LiF were added, the ceramics exhibited microwave dielectric properties of ε_r = 19.40, Q × f = 81,400 GHz and τ_f = 3.27 ppm/°C.     

Effect of substituting Al3+ for Ti4+on the microwave dielectric performance of Mg2Ti1-xAl4/3xO4 (0.01 ≤ x ≤ 0.09) ceramics

In this paper, Mg₂Ti_1-xAl_4/3xO₄ ceramics (0.01 ≤ x ≤ 0.09) were synthesized through conventional solid-state ceramic route. The cubic spinel structure, microstructure and microwave properties of Mg₂Ti_1-xAl_4/3xO₄ (x = 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were investigated by X-ray diffraction, Raman spectra, infrared spectra. Rietveld refinements confirm that a spinel structure phase with space group Fd-3m is formed. The variation of the permittivity was concerned with the ionic polarizability, and the value of τ_f was influenced by the bond valence. Both Q × f values and relative density showed an identical trend. Intrinsic properties of Mg₂Ti_1-xAl_4/3xO₄ ceramics were analyzed by infrared spectra and Raman spectra. In addition, the Mg₂Ti_1-xAl_4/3xO₄ ceramic sintered at 1420 °C for 4 h possessed optimal dielectric properties (ε_r = 14.65, Q × f = 182347 GHz, τ_f = −57.7 ppm/°C) when x = 0.09.     

Co-substituted CuO–ZrO2–Nb2O5 composite ceramics with low-temperature sintering and low-loss for high-performance patch antenna

In the field of microwave dielectric ceramics for patch antennas, it has always been a thorny issue to simultaneously satisfy high dielectric constant, low sintering temperature and low dielectric loss. Here, a CCZN (x = 0.04) composite ceramic with excellent microwave dielectric properties was developed. It can be found that an appropriate amount of Co²⁺ substitution can enhance the compactness, increase the dielectric constant (ε_r), reduce the dielectric loss (tanδ) and enhance the temperature coefficient (τ_f). The composite ceramic with excellent dielectric properties (ε_r = 22.6, Q × f = 37,624 GHz, τ_f = ?64.9 ppm/°C) shows good sintering compatibility with Ag. Based on this composite ceramic, a high-performance patch antenna was designed for Beidou satellite navigation system (BDS). It presents a small size of 30 × 30*3.8 mm³ and excellent radiation performance (return loss = ?32.9 dB, VSWR = 1.047, impedance bandwidth = 60.6 MHz, radiation efficiency = 94.6% and realized gain = 7.704 dB). This work promotes the application of microwave dielectric ceramics in the field of patch antennas.     

Improved microstructure and high quality factor of Li2Ti0.9(Zn1/3Ta2/3)0.1O3 microwave ceramics with LiF additive for LTCC applications

In this study, LiF was utilized to decrease sintering temperature, improve microstructure, enhance Q×f, and regulate τ_f of Li₂Ti_0.9(Zn_1/3Ta_2/3)_0.1O₃ (abbreviated as LTZT) ceramics. A complete solid solution together with a phase transition from monoclinic to cubic rock salt structure occurred. The cell volume of LTZT ceramics decreased as the LiF content increased. Relatively dense and uniform microstructures were observed for the ceramics as the LiF content was not less than 2 wt%. The dielectric constant of LTZT ceramics initially increased and then decreased with the increasing LiF content. The FWHM of the Raman band at about 808 cm^?1 was closely related to the Q×f value. Notably, the samples with 3 wt% LiF exhibited the highest relative density of 97.4 % and satisfactory microwave dielectric properties of ε_r = 23.14 ± 0.16, Q×f = 110,090 ± 1100 GHz, and τ_f = +3.25 ± 1.45 ppm/°C when sintered at 950 °C. Good chemical compatibility with silver indicated the ceramic is a promising candidate in LTCC applications.     

Facile Synthesis of “Quench‐Free Glass” and Ceramic‐Glass Composite for LTCC Applications

The 10 mol% ZnO–2 mol% B₂O₃–8 mol% P₂O₅–80 mol% TeO₂ (ZBPT) glass was prepared by quenching as well as slowly cooling the melt. The ZBPT glass prepared by both methods show similar microwave dielectric properties. ZBPT glass has an ε_r of 22.5 (at 7 GHz), Q_u × f of 1500 GHz, and τ_f of ?100 ppm/°C. The ceramic‐glass composites of Sr₂ZnTeO₆ (SZT) and ZBPT is prepared through two convenient methods: (a) conventional way of co‐firing the ceramic with ZBPT glass powder and (b) a nonconventional facile route by co‐firing the ceramic with precursor oxide mixture of ZBPT glass at 950°C. In the former route, SZT + 5 wt% ZBPT composite sintered at 950°C showed moderately good microwave dielectric properties (ε_r = 13.4, Q_u × f = 4500 GHz and τ_f = ?52 ppm/°C). Although the SZT + 5 wt% ZBPT composite prepared through the nonconventional method also showed similar microwave dielectric properties (ε_r = 13.8, Q_u × f = 5300 GHz and τ_f = ?50 ppm/°C), the synthesis procedure is much simplified in the latter case. The composites are found to be chemically compatible with Ag. The composite containing 5 wt% ZBPT prepared through conventional and nonconventional ways shows linear coefficients of thermal expansion of 7.0 ppm/°C and 7.1 ppm/°C, respectively. Both the composites have a room‐temperature thermal conductivity of 2.1 Wm^?1 K^?1.     

Design and fabrication of a C-band patch antenna using novel low permittivity SrGa2Si2O8 microwave dielectric ceramic

A novel microwave dielectric ceramic of SrGa₂Si₂O₈ was synthesized using the traditional solid-state method. Its phase composition, microstructure, and microwave dielectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and network analyzer. XRD results indicated that the space group of the ceramic transformed from I₂/c to P₂₁/a at 700 °C. A combination of good microwave dielectric properties was obtained at 1260 °C with ε_r = 6.3, Q×f= 96,600 GHz and τ_f = −45.2 ppm/°C at 16.5 GHz. The negative τ_f can be tuned to near zero by adding 15 mol% CaTiO₃. The densification temperature can be reduced to 940 °C by adding 4 wt% LiF. Moreover, the SrGa₂Si₂O₈ ceramic had good chemical compatibility with the Ag electrode. A patch antenna was designed using the 0.85SrGa₂Si₂O₈ + 0.15CaTiO₃ + 4 wt% LiF ceramic. The antenna had a high radiation efficiency of 99.2 % and a gain of 2.988 dBi at the center frequency of 4.261 GHz. All results indicated that the SrGa₂Si₂O₈ ceramic has promising potential for applications in 5 G wireless communication technology.     

Ultra-low temperature sintered (1–x)BaV2O6-xLiF ceramics for ULTCC and 5 G millimeter-wave antenna applications

(1–x)BaV₂O₆-xLiF (x = 0.025, 0.05, 0.10, 0.15) ceramics with an ultra-low sintering temperature of 475 °C were synthesized using the standard solid-state reaction method. The ceramics demonstrated a remarkable enhancement in the quality factor (Qf), reaching a maximum value of 16,800 GHz at x = 0.10, which is 5.6 times higher than that of pure BaV₂O₆ ceramics obtained in this work. A near-zero temperature coefficient of resonant frequency (τ_f = 1.44 ppm/°C) was simultaneously achieved, together with a dielectric constant ε_r of 11.54. Additionally, the chemical compatibility between the present ceramics and the Al electrode was confirmed. Moreover, a millimeter-wave antenna with an excellent S₁₁ value of −50.3 dB, and a large bandwidth of 3.44 GHz was fabricated using the 0.9BaV₂O₆-0.1LiF ceramic as the dielectric resonator. These results highlight the potential application prospects of (1–x)BaV₂O₆-xLiF ceramics in the ultra-low temperature co-fired ceramic technology and 5 G millimeter-wave antennas.     

Microwave dielectric characterization of Ca0.6(La1-xYx)0.2667TiO3 perovskite ceramics with high positive temperature coefficient

Solid solution Ca_0.6(La_1-xY_x)_0.2667TiO₃ dielectric ceramic systems with various x values were studied, which were prepared using a solid-state reaction method. X-ray diffraction and X-ray spectroscopy analyses showed that the crystal structure of these samples was orthorhombic perovskite. The microstructures with the substitution amount of Y³⁺ and the dielectric performances of the Ca_0.6(La_1-xY_x)_0.2667TiO₃ ceramics were also explored. With x = 0.1, the Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃ ceramic could be sintered at 1350 °C, and the microwave dielectric performance was found to be strongly correlated with the sintering temperature. A maximum Qf value of 23,100 (GHz), dielectric constant (ε_r) of 111, and temperature coefficient (τ_f) of 374.6 ppm/°C were achieved for samples sintered at 1350 °C for 4 h. This dielectric ceramic possessed good potential as a τ_f compensator to obtain a near-zero τ_f mixture for high-quality substrates for use in wireless communication systems.     

A novel microwave dielectric ceramic La5Sn4O15 with medium-permittivity and low loss

A novel low-loss La₅Sn₄O₁₅ ceramic is fabricated via traditional solid-state route. The investigation mainly focused on phase composition, dielectric characteristics and crystalline from 1300 to 1400 °C. The XRD analyses confirmed the La₅Sn₄O₁₅ ceramic is consisted of cubic and hexagonal structure. The effects of relative density on the Q × f and permittivity are also investigated. The satisfactory properties (ε_r of 17.4, Q × f of 84,760 GHz and τ_f of ?19.08 ppm/°C) are obtained at optimum sintering condition (sintered at 1350 °C for 4 h), indicating La₅Sn₄O₁₅ ceramic is a promising ceramic for using in wireless applications region.     

The structure evolution and lattice energy of spinel-structured Li(Mg0.5Ti0.5)xGa5−xO8 microwave dielectric ceramics

The microwave dielectric properties of spinel-structured Li(Mg_0.5Ti_0.5)_xGa_5−xO₈ (0 ≤ x ≤ 1) ceramics were researched together with their microstructures. The X-ray diffraction and Raman spectroscopic revealed that an ordered spinel structure in 1: 3 B-site ordering with space group P4₃32 was formed in the composition range of 0 = x ≤ 0.25, and a disordered spinel with space group Fd-3m was formed in 0.5 = x ≤ 1. All the ceramics were compact with uniform grain, clear grain boundaries and high relative density (ρ_relative ≥ 95 %). With the substitution of [Mg_0.5Ti_0.5]³⁺ for Ga³⁺ increased, the dielectric constant (ε_r) increased from 10.48 to 11.28, which was related to the increased molar ionic polarizability (α_theo/V_m) and B-site bond ionicity. The temperature coefficient of the resonant frequency (τ_f) slightly increased from −66.27 ppm/°C to −61.45 ppm/°C, due to the decrease of B-site bond valence. The Q × f value firstly decreased from 125,400 GHz to 50,381 GHz and then increased to 85,360 GHz, which was affected by the intrinsic loss analyzed by lattice energy. The optimal microwave dielectric properties were obtained for LiMg_0.5Ti_0.5Ga₄O₈ ceramic (x = 1) sintered at 1260 °C with ε_r = 11.28, Q × f = 85,360 GHz and τ_f = −61.45 ppm/°C.     

Enhancement of structural and microwave properties of Zn2+ ion-substituted Li2MgSiO4 ceramics for LTCC applications

In this study, Zn²⁺-substituted Li₂MgSiO₄ ceramics (Li₂(Mg_1-xZn_x)SiO₄, x = 0.00, 0.05, 0.10, 0.15, and 0.20) were synthesized using a traditional solid-state method. A fixed amount of LiF sintering aid (1.5 wt%) was added to the ceramics for decreasing the sintering temperature and adjusting their microwave dielectric properties. X-ray diffraction (XRD) results revealed no secondary phases, and scanning electron microscopy (SEM) data suggest that the Zn²⁺ ion substitution increased the size and uniformity of the grains, thereby affecting the densification of the prepared ceramics. The maximum bulk density (2.94 g/cm³) was found in a Zn²⁺ ion-substituted ceramic with x = 0.10 at a relative density of 94.2% (compared with the XRD theoretical density). Excellent microwave dielectric properties (ε_r = 6.28, Q × f = 50400 GHz, and τ_f = ?145 ppm/°C) can also be obtained at this zirconium content. We believe that the developed ceramics are promising for use as antenna substrates or transmit/receive modules in low-temperature co-firing ceramic applications.     

Crystal structure,vibration characteristics and microwave dielectric properties of low loss MgMo1-xWxO4 solid solution ceramics

Solid-phase method was used to synthesize MgMo_1-xW_xO₄ (x = 0–0.15) ceramics. The influences of substitution Mo⁶⁺ with W⁶⁺ on crystal structure, vibration characteristics and microwave dielectric properties of MgMo_1-xW_xO₄ ceramics were comprehensively studied. X-Ray diffraction illustrated all samples exhibit single-phase monoclinic wolframite structure when x = 0–0.15, in which W⁶⁺ replaces Mo⁶⁺ sites formed solid solution. W⁶⁺ effectively improves sintering properties of the MgMoO₄, the average grain size and relative density were increased. Raman characterization reveals that suitable W⁶⁺ substitution amount leads to reduction of v₁ A_g peaks FWHM and the enhancement of specific v₃ A_g peak for Mo/WO₄ tetrahedron, which improves the ordered distribution of the crystal structure. The above combined effect results in the increased Q × f value, but has little influence of W⁶⁺ substitution on ε_r and τ_f for MgMoO₄. When x = 0.09, MgMo_0.91W_0.09O₄ ceramic sintered at 1050 °C has optimal microwave dielectric performance: ε_r = 7.21, Q×f = 90,829 GHz, τ_f = ?67 ppm/°C.     

Lattice vibrational characteristics and structure-property relationships of SrWO4- x wt.% LiF (x = 0.5–3.0) microwave dielectric ceramics

SrWO₄-x wt.% LiF (SWL, x = 0.5–3.0) ceramics were obtained by a conventional solid-state reaction at 850 °C. The effects of the LiF additive on the phase evolution and dielectric response mechanism of the SWL ceramics were comprehensively studied. The densification temperature of the SWL ceramics was successfully reduced to 850 °C by adding LiF as the sintering additive. The X-ray diffraction data indicated that the SWL ceramics were composite ceramics. The lattice vibrational properties were investigated in depth by Raman scattering and Fourier transform infrared reflectance. The intrinsic dielectric property values fitted by the four-parameter semi-quantum model agreed well with the measured dielectric property values and the theoretical values obtained from the Clausius-Mossotti & damping equations. Moreover, structure-property relationships were obtained by studying the lattice vibrational modes of the SWL ceramics. The SWL ceramic achieved the optimum dielectric property at x = 2.0, with ε_r = 9.03 and Q × f = 47,830 GHz.     

Sintering behavior,structural evolution,and dielectric properties of Li2+xMgTiO4Fx microwave dielectric ceramics

Herein, the sintering behavior, structural evolution, microstructure, and dielectric properties of Li_2+xMgTiO₄F_x (0 ≤ x ≤ 5) ceramics were investigated. At x ≤ 0.75, Li_2+xMgTiO₄F_x ceramics formed a continuous solid solution with a cubic rock salt structure. Subsequently, a composite ceramic of Li_2+xMgTiO₄F_x and LiF was formed. It was found that the maximum mass percentage of LiF required to fully form a solid solution was between 11% and 13%. The Li_2.75MgTiO₄F_0.75 exhibited the best dielectric properties: ε_r = 16.52, Q × f = 123,574 GHz, and τ_f = −18.11 ppm/°C. The substitution of F^- for O^2- resulted in a lower sintering temperature of 875 °C, which slightly suppressed the volatilization of Li, and thus optimized the dielectric properties. The decrease in lattice vibration damping behavior and the increase in electron cloud density resulted in lower dielectric losses. The reduction in molecular polarization rate led to a reduction in ε_r, and the increase in bond energy optimized τ_f. Good chemical compatibility with Ag electrode was demonstrated, indicating that Li_2+xMgTiO₄F_x ceramics have unlimited potential for LTCC applications.     

Microwave dielectric properties of Ca1.15RE0.85Al0.85Ti0.15O4 (RE=Nd,La, Y) ceramics prepared by the reaction sintering method

Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics were prepared by a reaction sintering method. The sintering behavior, phase composition, microstructure and microwave dielectric performances of ceramics were investigated. X-ray diffraction patterns illustrated that both the Ca_1.15Nd_0.85Al_0.85Ti_0.15O₄(CNAT) and Ca_1.15Y_0.85Al_0.85Ti_0.15O₄(CYAT) ceramics are single-phase structures, and the Ca_1.15La_0.85Al_0.85Ti_0.15O₄(CLAT) ceramic contain LaAlO₃ and CaO phases. The apparent morphology and elemental distribution of the ceramic samples were analyzed by using scanning electron microscope and energy dispersive spectrometer. When the sintering temperature is 1500 °C, the CNAT and CYAT ceramics have the best microwave dielectric properties with ε_r = 19.2, Q × f = 74924 GHz, τ_f = ?1.21 ppm/°C and ε_r = 17.5, Q × f = 27440 GHz, τ_f = ?5.79 ppm/°C, respectively. And the best microwave dielectric properties of ε_r = 17.5, Q × f = 22568 GHz, τ_f = ?14.69 ppm/°C were obtained for the CLAT ceramic sintered at 1525 °C. The reaction sintering method provides a low-cost, economical and straightforward method for the preparation of the Ca_1.15RE_0.85Al_0.85Ti_0.15O₄ (RE = Nd, La, Y) ceramics, which has promising potential for application.