Temperature Coefficient Of Resonant Frequency Research Articles

Phase evolution and microware dielectric properties of high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics

In this study, high-entropy spinel-type (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics were synthesized by solid-state reaction method. The raw materials gradually formed spinel aluminates from 700 to 1400 °C and finally formed high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics after calcination at 1400 °C for 4 h. The high-configuration entropy and low average atomic-size difference were beneficial to form single-phase high-entropy ceramics. Partial lattice distortion occurred within the high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics structure, and its grain size gradually increased with increasing sintering temperature. The high-entropy (Mg0.2Co0.2Ni0.2Li0.4Zn0.2)Al2O4 ceramics exhibited good microwave dielectric properties when sintered at 1550 °C for 4 h: dielectric constant (εr) = 7.4, quality factor (Qf) = 58,200 GHz, and temperature coefficient of resonance frequency (τf) = –64 ppm/°C. The εr values were mainly affected by the dielectric polarizability. The Qf values were highly related to the relative density and covalency of A-site bond, whereas the τf values closely depended on the bond strength of A-site.

KNN-Based Lead-Free Piezoelectric Ceramics with High Qm and Enhanced d33 via a Donor-Acceptor Codoping Strategy.

The wide application of KNN-based lead-free piezoelectric ceramics is constrained by the contradictory relationship between its mechanical quality factor and piezoelectric constant. From an application point of view, searching for chemical composition with enhanced piezoelectric constant (d33) and mechanical quality factor (Qm) is one of the key points of KNN-based ceramics. In this work, KNN-based ceramics with enhanced d33 and high Qm values were obtained by the solid solution method via a donor-acceptor codoping strategy. The donor dopant Ho3+ enhanced d33 values by refining the domain size, while the acceptor dopant (Cu1/3Nb2/3)4+ improved Qm by the formation of defect dipoles. The composition (KNN-5Ho-4CN) exhibits optimal integrated performances, of which d33, Qm, and TC values are 120 pC/N, 850, and 392 °C, respectively. Moreover, the temperature coefficient of resonant frequency (TCF = -429 ppm/K) indicates that KNN-5Ho-4CN ceramic has good temperature stability. This work provides a new insight for developing KNN-based ceramics with enhanced d33 and high Qm.

Novel (1-x)MgCu2Nb2O8 − xTiO2 composite ceramics with high Q×f and near-zero τ f

For the MCu2Nb2O8 (M=Ca, Mg, Zn or Ni) composite ceramics, it is still a difficult problem to achieve both high Q×f valule and near-zero temperature coefficient of resonant frequency (τ f ). In this paper, the (1-x)MgCu2Nb2O8 − xTiO2 (0 ≤ x ≤ 0.28) ceramics were fabricated by the two-step sintering (TSS) technique. Results of x-ray diffraction (XRD) and Raman spectroscopy proved that the ceramic samples were composite phases of MgNb2O6, CuO and TiO2. The chemical compositions and valences of Mg, Cu, Nb, O and Ti were investigated by x-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) showed that proper TiO2 addition could promote growth of grains and increase the average grain size. Appropriate TiO2 content and enhanced densification contributed to the 0.84MgCu2Nb2O8 − 0.16TiO2 ceramics sintered at 935 °C with ε r = 18.75, Q×f = 34,398 GHz (f 0 = 7.8 GHz), and τ f = −0.56 ppm/°C, exhibiting potential applications in Low Temperature Co-fired Ceramic (LTCC) devices.

Novel ultralow-permittivity BaMg2Al6Si9O30-based microwave dielectric ceramics with self near-zero temperature coefficient of resonant frequency and thermal expansion

Novel BaMg2Al6Si9O30-based ceramics were prepared using the traditional solid-phase reaction method, and this paper presents the fabrication procedure, crystal structure, microstructure, microwave dielectric properties and temperature coefficient of thermal expansion of BaMg2Al6Si9O30-based ceramics. BaMg2Al6Si9O30-based ceramics were found to possess a hexagonal crystal structure with the P6/mcc space group. The BaAl2Si2O8 and BaMg2Al6Si9O30 phases coexisted in BaMg2Al6Si9O30 ceramic given that raw MgO material reacted easily with water vapour in the air, and the BaMg2Al6Si9O30 single-phase ceramic could be synthesized with calcined raw MgO material. The BaMg2Al6Si9O30 single-phase ceramic exhibited ultralow εr (5.68 at 14.05 GHz), moderate Q×f value (28534 GHz at 14.05 GHz), a self near-zero τf value (7.35 ppm/°C), a near-zero average temperature coefficient of thermal expansion (+1.89 ppm/°C) at 30 °C1000 °C and a rare negative temperature coefficient of thermal expansion (9.43 ppm/°C) at 655 °C710 °C. The rare near-zero and negative thermal expansions of the BaMg2Al6Si9O30 single-phase ceramic were mainly related to the strong Si/Al-O bonds with high relative covalency and 2 coordinate O(1) allowing longitudinal vibrations.

A high-performance, temperature-stable Mg1.99Ga0.01Si0.99Al0.01O4-CaTiO3 microwave dielectric ceramic and its 5 G/6 G waveguide filter

New ultra-low loss, temperature-stable composite ceramics, (1-x) Mg1.99Ga0.01Si0.99Al0.01O4-xCaTiO3, have been developed with a view to expanding the portfolio of low-cost, MW dielectrics available for 5 G/6 G telecommunications, currently dominated by 95 wt%MgTiO3-5 wt%CaTiO3, (Mg,Ca)TiO3 (relative permittivity, εr ∼ 21, quality factor, Q×f ∼ 56,000 GHz and temperature coefficient of resonant frequency, τf ∼ 0 ppm/°C). Compared with (Mg,Ca)TiO3, 89 wt%Mg1.99Ga0.01Si0.99Al0.01O4-11 wt%CaTiO3 ceramics are also temperature stable (τf = −2.72 ppm/°C) but have lower εr (∼8.55) and a higher Q×f (∼ 72,900 GHz @ 12 GHz and 80,900 GHz @ 26 GHz), better suited to the higher frequencies earmarked for 6 G millimeter-wave (mm-wave) applications. To demonstrate its potential for 5 G/6 G telecommunications, a waveguide filter with novel negative coupling structure was fabricated based on simulated results. The filter had low insertion loss (0.43 dB) at the center frequency (4.8 GHz) and high selectivity with a roll-off rate of 576/375 dB/GHz. The S-parameters matched well at 25 °C and 85 °C, demonstrating that the filter had excellent temperature stability and was therefore suitable for future 5 G/6 G microwave and mm-wave communication devices.

Electroceramic based on Ca3-xBaxZrSi2O9 solid solutions for microwave and radiofrequency application

The structural and dielectric characterization of the Ca3ZrSi2O9 (CZS) ceramic compound and the Ca3-xBaxZrSi2O9 (BaCZS) solid solution were investigated for their application in radiofrequency (RF) and microwave (MW) antenna devices. All of the samples were synthesized using the solid-state route. The structural characterization of the samples was performed by X-ray powder diffraction pattern. Infrared and Raman spectroscopy were used to correlate the absorption bands of the main chemical bonds in the materials. Scanning electron microscopy was used to examine the surface and microstructure of the samples. Dielectric properties at MW and RF ranges were analyzed using the Hakki-Coleman and Silva-Fernandes-Sombra methods. The CZS electrocemaric showed a dielectric relative permittivity (ε’) of 10.96, a dielectric loss (tan δ) of 8.28 × 10−4 at 10.20 GHz, and a resonant frequency temperature coefficient (τf) of −44.30 ppm °C−1. The influence of Ba ions on the CZS phase was evaluated using molar ratio variations (x = 0.15, 0.30, and 0.45), denotated as Ca2.85Ba0.15ZrSi2O9, (0.15BaCZS), Ca2.70Ba0.30ZrSi2O9, (0.30BaCZS), and Ca2.55Ba0.45ZrSi2O9 (0.45BaCZS), respectively. Among these samples, 0.45BaCZS showed a τƒ of approximately zero (−5.78 ppm °C−1), demonstrating an improvement in the material with the addition of Ba. Preliminary tests at MW and RF showed that the permittivity values and dielectric losses varied accordingly with the increase in the proportion of barium, as well as τƒ. For the dielectric resonator antenna (DRA) tests, the samples operated below −10 dB, between 6.57 and 7.7 GHz, behaving like materials used in microwaves devices for C-Band applications.

Exploration of MgTiO3-CaTiO3 Ceramic-Based Dielectric Resonator Antenna for Sub-6 GHz 5G Communication Application

There has been extensive research on microwave dielectric materials considering their applications in 5G communication technologies. In this work, the microwave dielectric performances of 0.95MgTiO3−0.05CaTiO3 (MCT) ceramic for sub-6 GHz frequency 5G application have been reported. The solid-state reaction technique was used to develop the MCT ceramic. The structural as well as dielectric properties of MCT were systematically examined. X-ray diffraction (XRD) was used to examine the crystalline phase of the MCT sample. The microwave dielectric properties, including relative permittivity, temperature coefficient of resonant frequency, and quality factor of MCT were measured. Using MCT ceramic as the resonator, a dielectric resonator antenna (DRA) has been simulated using HFSS software, which realizes that the S11 curve is in good accordance and that efficiency is high at 5.22 GHz. The extraordinary performances indicate that MCT ceramic is a potential candidate for 5G application.

Novel high-entropy microwave dielectric ceramics Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 with excellent temperature stability and mechanical properties

Novel high-entropy Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 ceramics with a layered perovskite structure have been prepared via the standard solid-state reaction method. The design of high-entropy improves the bond valence and subsequently optimizes the large negative temperature coefficient of resonant frequency (τf = −32 ppm/°C) of the simple SrLaAlO4 ceramics. Excellent temperature stability (τf = −6 ppm/°C) together with a relative permittivity (εr) of 18.6 and a quality factor (Qf = 14,509 GHz) are obtained in Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 ceramics sintered at 1475 °C. It indicates that the present ceramics have great application prospects in passive microwave components such as resonators and filters. Meanwhile, significant improvements in compressive strength and strain are achieved, which are 1040 MPa and 15.7% for Sr(La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO4 compared to 583 MPa and 12% in SrLaAlO4. The enhanced mechanical properties originate from the dislocation strengthening mechanism as the intertwining of interlayer lattices is revealed from the high-resolution transmission electronic micrographs.

Microwave Dielectric Properties of Li3TiO3F Oxyfluorides Ceramics

Using a solid-state reaction strategy, nominal Li3TiO3F oxyfluorides ceramics were fabricated, and its sintering behavior, microstructure, phase assemblages, as well as microwave dielectric performances were all investigated. The main phase of Li3TiO3F with cubic structures accompanied with small amounts of the LiF or Li2TiO3 secondary phase was identified by XRD analysis. SEM analysis showed that a uniform and dense microstructure was obtained for 750 °C-sintered samples. The dielectric constant (εr) and quality factor (Q × f) were found to be strongly correlated with porosity and grain size distribution, whereas the temperature coefficient of resonance frequency (τf) was mainly dominated by the phase assemblages. In particular, the 750 °C-sintered Li3TiO3F samples exhibited good microwave dielectric performances: εr = 18, Q × f = 57,300 GHz (under 9.2 GHz), τf = −43.0 ppm/°C.

Crystal structure and microwave dielectric properties of temperature stable (CoxZn1–x)TiNb2O8 ceramics

Abstract(CoxZn1–x)TiNb2O8 (x = 0.2–0.8) microwave dielectric ceramics were synthesized via the conventional solid‐state reaction route, and the correlation of microwave dielectric properties on the crystal structure was discussed. Crystal structures of ceramic samples were systematically investigated by X‐ray powder diffraction. Moreover, composition‐induced phase transitions were confirmed via the following sequence: for x ≤ 0.2, single‐phase orthorhombic ixiolite (ZnTiNb2O8) was formed, whereas for 0.3 ≤ x<0.8, ixiolite and rutile coexisted. When x ≥ 0.8, only single‐phase rutile was detected. For the (CoxZn1–x)TiNb2O8 ceramics, the microwave dielectric properties were changed with the crystal structural transitions: the dielectric constant (εr) and the temperature coefficient of resonant frequency (τf) increased upon increasing the Co2+, but the quality factor (Q) decreased. A near‐zero τf = +1.6 ppm/°C was obtained in the Co0.38Zn0.62TiNb2O8 ceramics with εr = 40.7 and high Q × f = 16 790 GHz. These research outcomes are expected to have great significance for developing microwave dielectric ceramics in practical applications.

Novel temperature stable (Na0.5Y0.5)MoO4 microwave dielectric ceramics with TiO2 addition

Novel scheelite-structured (Na0.5Y0.5)MoO4 ceramic materials featuring high quality factor (Q׃) values (>80000 GHz) were sintered at the temperatures ranging from 900 to 1100 °C. The sintering characteristics, crystalline structure, and microwave dielectric properties of the (Na0.5Y0.5)MoO4 ceramic samples were investigated systematically. The optimal properties of εr = 11.5, Q׃ =88673 GHz, and τf = -56.49 ppm/°C were achieved in the specimen sintered at 1050 °C. Moreover, TiO2 was employed to modify the large negative temperature coefficient of resonance frequency (τf) of (Na0.5Y0.5)MoO4. In the ceramic samples of 1-x(Na0.5Y0.5)MoO4-xTiO2, a near-zero τf of 0.68 ppm/°C with εr = 15.2 and Q׃=49047 GHz was achieved at x = 0.25 sintered at 975 °C.

Entropy regulation in LaNbO4-based fergusonite to implement high-temperature phase transition and promising dielectric properties

High-entropy effect is a novel design strategy to optimize properties and explore novel materials. In this work, (La_1/5Nd_1/5Sm_1/5Ho_1/5Y_1/5)NbO₄ (5RNO) high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature (S.T.) range of 1210–1290 ℃ via a solid-phase reaction route, and medium-entropy (La_1/3Nd_1/3Sm_1/3)NbO₄ and (La_1/4Nd_1/4Sm_1/4Ho_1/4)NbO₄ (3RNO and 4RNO) ceramics were compared. The effects of the entropy (<i>S</i>) on crystal structure, phase transition, and dielectric performance were evaluated. The entropy increase yields a significant increase in a phase transition temperature (from monoclinic fergusonite to tetragonal scheelite structure). Optimal microwave dielectric properties were achieved in the high-entropy ceramics (5RNO) at the sintering temperature of 1270 ℃ for 4 h with a relative density of 98.2% and microwave dielectric properties of dielectric permittirity (<i>ε</i>_r) = 19.48, quality factor (<i>Q</i>×<i>f</i>) = 47,770 GHz, and resonant frequency temperature coefficient (<i>τ</i>_f) = –13.50 ppm/℃. This work opens an avenue for the exploration of novel microwave dielectric material and property optimization via entropy engineering.

Effect of Co and Sr substitution on the microwave dielectric properties of CaMg0.9Li0.2Si2O6-based ceramics for LTCC application

In this work, two low-temperature co-fired silicate ceramics (CaMg0.9-xLi0.2CoxSi2O6, x = 0.15–0.75, CMLCS; CaMg0.9-yLi0.2SrySi2O6, y = 0, 0.05, 0.1–0.5, CMLSS) were synthesized via solid-state reaction method with 0.5 wt%LBSCA glass addition. CMLCS and CMLSS were densely sintered at 925 °C, and had good chemical compatibility with silver. Optimal microwave dielectric properties (εr = 6.71, Q×f = 30124 GHz, and τf = −79.06 ppm/°C) and (εr = 6.78, Q×f = 32530 GHz, and τf = −52.99 ppm/°C) were obtained for CMLC0.15S and CMLS0.05S respectively. With increase in Co and Sr substitution, XRD and Raman spectra showed that second phases were produced, and densification process of CaMgSi2O6-based ceramics was promoted. Dielectric constant was influenced by relative density, Raman shift and second phase. The parameter Q×f was affected by the FWHM of Raman peaks as well as extrinsic factors that affected the temperature coefficient of resonant frequency. Therefore, the results suggested the potential of these two ceramics as candidates for LTCC application.

Structure characteristics and microwave dielectric properties of novel Re2Ce6O15 (Re[dbnd]Y, Sm, Nd, La) ceramics

Based on the cubic fluorite structure, novel ceramic series with Re2Ce6O15 (ReY, Sm, Nd, La) formula had been designed and prepared successfully using solid-state reaction method. The new Re2Ce6O15 (ReY, Sm, Nd, La) ceramics all presented a single phase indexed as CeO2-type structure, belonged to Fm-3m space. The formation mechanism and lattice constant of the crystal structure had been investigated using Rietveld structural refine method. The microstructure of the Re2Ce6O15 (ReY, Sm, Nd, La) ceramics had been evaluated by pores, grain size and its distribution. The dielectric constant had been corrected for the exclusion of pores and depended on the ionic polarizability. The quality factors of the Re2Ce6O15 (ReY, Sm, Nd, La) ceramics had been investigated by packing fraction related to the phonon vibration. The temperature coefficient of resonance frequency had been analyzed using the bond valence theory. The Re2Ce6O15 (ReY, Sm, Nd, La) ceramics exhibited excellent microwave dielectric properties with medium dielectric constant, high quality factors and stable resonant frequency temperature coefficient.

Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System.

Microwave dielectric ceramics with permittivity (εr) ∼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V5+ ions (rV = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (rNb = 0.48 Å with CN = 4) in the Nd(Nb1-xVx)O4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition (TF-S) to 400 °C for x = 0.2. The thermal expansion coefficient (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of εr at TF-S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd(Nb0.8V0.2)O4 (εr ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at TF-S is thus demonstrated that may also be extended to other fergusonite systems.

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.

Effects of chemical ordering and homogeneity on microwave dielectric properties of LaGaO3-SrTiO3 compounds

(1-x)LaGaO3-xSrTiO3 (x = 0–0.6) microwave dielectric ceramics were synthesized by using conventional solid-state reaction method and sintered at 1450 °C with different sintering conditions. The variations of microstructure, relative density, and phase formation were observed by different composition and sintering conditions. The microwave properties, such as permittivity/dielectric constant (εr), quality factor (Qf), and temperature coefficient of resonant frequency (TCF, τf) at a high frequency were investigated in terms of lattice distortion, chemical ordering, and chemical homogeneity according to the composition and equilibrium sintering conditions. A maximum Qf ∼64,900 GHz was observed at x = 0, and the best τf ∼ 0 ppm/°C was obtained at x = 0.4. Consequently, it was found that the permittivity is related mainly to the lattice distortion, whereas the quality factor is primarily affected by chemical ordering and chemical homogeneity of the microstructure-induced composition.

Co‐optimization of microwave dielectric properties in Ba(Mg1/3Ta2/3)O3 complex perovskite ceramics through ordered domain engineering

AbstractIt is an important subject to improve the temperature coefficient of resonant frequency (τf) and thermal conductivity (κ) of microwave dielectric ceramics without reducing the Qf value. Ordered domain engineering was applied to realize the previous objectives in Ba(Mg1/3Ta2/3)O3 ceramics. With the increasing ordering degree from 0.835 to 0.897, the optimized Qf value was obtained. Meanwhile, near zero τf from 11.9 to 5.6 ppm °C−1 was achieved, together with increased κ from 5.5 to 7.6 W m−1 K−1, and enhanced dielectric strength from 801 to 921 kV cm−1. The noticeable ordered domain structure with large ordered domains (∼100 nm) and low‐energy domain boundaries was revealed in Ba(Mg1/3Ta2/3)O3. The consequent weakened phonon scattering rises the thermal conductivity. The increased bond covalency and oxygen distortion in ceramics with higher ordering degree were suggested as a cause of enlarged bandgap, which enhanced the dielectric strength. The reduced τf is dominated by the less “rattling” space of the cations in the ordered state by inducing more positive τε. The reduced τf, optimized thermal conductivity, and Qf value in the present work indicate that the ordered domain engineering could open up a new direction for the optimization of microwave dielectric ceramics.

Fabrication of High Radiation Efficiency Dielectric Resonator Antenna Array Using Temperature Stable 0.8Zn2SiO4‐0.2TiO2 Microwave Dielectric Ceramic

AbstractArray antenna is of great significance in realizing the Sub‐6 GHz fifth‐generation (5G) mobile communication systems, however, its utilization in the base station systems implementation is limited due to high power consumption. In this paper, a high radiation efficiency 4 × 4 cylindrical dielectric resonator antenna (CDRA) array fabricated using the temperature stable 0.8Zn2SiO4‐0.2TiO2 composite ceramic is proposed. TiO2‐doped Zn2SiO4 composite ceramics are synthesized by the conventional solid‐state method. Notably, 0.8Zn2SiO4‐0.2TiO2 composite ceramic sintered at 1250 °C demonstrates excellent microwave dielectric properties with dielectric constant (εr ≈ 8.24), high‐quality factor (Q × f ≈ 35 000@8.08GHz), and the temperature coefficient of resonant frequency (TCF ≈ +4.6 ppm °C−1). Moreover, the composite ceramic CDRA array is designed by exciting fundamental HE11δ mode using the aperture coupling microstrip feeding network. The fabricated composite ceramic based 4 × 4 CDRA array has enhanced measured radiation efficiency of up to 87%, high gain of 17.85 dBi and is a promising candidate for utilization in Sub‐6 GHz 5G Base Station communications systems.

Phase transitions and microwave dielectric behaviors of the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4 ceramics

AbstractMicrowave dielectric ceramics with intrinsic low sintering temperatures are potential candidates for low temperature co‐fired ceramics technology. In the present work, the (Li0.5Y0.5)MoO4 ceramic with tetragonal scheelite structures was selected to improve microwave dielectric properties of BiVO4 ceramics. As proved by X‐ray diffraction (XRD) results, scheelite structured solid‐solution ceramics were formed with x value ≤0.1 in the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4. In situ XRD results further confirmed that the addition of (Li0.5Y0.5)MoO4 also lowered transition temperature from distorted monoclinic to tetragonal scheelite structure. When x value increased further, zircon phase was detected by XRD. Room and high‐temperature Raman spectra also supported the XRD results. Differences of thermal expansion coefficients of both monoclinic and tetragonal scheelite phases lead to an abnormality at phase transition temperature. Good microwave dielectric properties with permittivity above 70 and Qf (Q = quality factor = 1/dielectric loss and f = frequency) value above 8000 GHz were obtained in the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4 solid‐solution ceramics with x value ≤0.1 sintered below 800°C. However, permittivity peak values at phase transition temperatures lead to large positive or negative temperature coefficient of resonant frequency, and this needs to be modified via composite technologies in the future.