Temperature Coefficient Of Resonant Frequency Research Articles

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.

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/℃.

High-Q×f value and temperature stable MgZrTa2O8 ceramics by Li heterovalent substitution

The Mg1-xLixZrTa2O8-x/2 (x = 0–0.07) ceramics were fabricated to investigate the effects of Li+ heterovalent substitution for Mg2+. The site occupancy and existence of the Li+ were examined based on Vienna Ab-initio Simulation Package (VASP) and X-ray photoelectron spectroscopy (XPS), respectively. Single phase solid solution with wolframite structure was identified in the whole region. Li+ substitution reduced the densification temperature from 1475 °C to 1400 °C. Notably, the Q×f exhibited an obvious increase by up to 74 % from 41,844 GHz at x = 0–72,782 GHz at x = 0.05. The Q×f for x < 0.01 was largely dependent on the intrinsic loss originating from packing fraction, while as 0.01 ≤ x ≤ 0.05, it was dominated by extrinsic factors, especially the oxygen vacancy concentration. The corresponding dielectric constant εr decreased in term of ionic polarizability. The variations of resonant frequency temperature coefficient τf were explained from the views of [TaO6] oxygen octahedral distortion and bond energy. A near-zero τf was obtained for x = 0.05 composition, accompanied by εr = 11.97, Q×f= 72,782 GH at 1450 °C. Li substitution was effective and inexpensive for MgZrTa2O8 ceramic to realize dielectric properties enhancement and densification temperature optimization simultaneously.

Research Progress of Ba(Zn1/3Nb2/3)O3 Microwave Dielectric Ceramics: A Review

Ba(Zn1/3Nb2/3)O3 (BZN) microwave dielectric ceramics have attracted great attention due to their high-quality factor (Q), near-zero temperature coefficient of resonant frequency (τf), and suitable dielectric constant (εr), making them promising materials for application in microwave devices. Due to their superior dielectric properties, composite perovskite ceramics are widely used in the field of microwave communication, base stations, navigation, radar, etc. This article summarized the latest research progress of BZN ceramics and discusses the main preparation methods and performance modifications. Furthermore, the problems faced by BZN ceramics and solutions to improve their performance, as well as their potential applications, are analyzed. This article provides a reference for the design and preparation of BZN ceramics.

Dielectric and microwave properties of ceramics of the Bi-Ti-O system

Dielectric and microwave properties of ceramics based on binary systems Bi2Ti2O7-TiO2 and Bi2Ti4O11-TiO2 were studied. In order to obtain dielectric materials with high stability of temperature coefficient of resonance frequency, high values of dielectric permittivity and quality factor modification of ceramics by chemical elements with different valence and ionic radii was performed. It is established, that on the basis of Bi2Ti4O11-TiO2 system, it is possible to receive microwave materials for manufacturing of resonators. It is shown that the introduction of different valence ions in the Bi2Ti2O7-TiO2 system allows to change its basic dielectric parameters in given limits and directed to choose the optimal composition of ceramics for the development of materials that can be used, for example, when creating storage capacitors.

High-performance 0.9Al2O3-0.1TiO2 microwave dielectric ceramics prepared by digital light processing

In this work, the 0.9Al 2 O 3 -0.1TiO 2 ceramic sample with good microwave dielectric properties and complex structures can be well fabricated by digital light processing (DLP). A relationship between dispersant content and rheological behavior of 0.9Al 2 O 3 -0.1TiO 2 slurry was explored. When dispersant content was 3.0 wt%, 0.9Al 2 O 3 -0.1TiO 2 slurry with high solid loading (50 vol%) and low viscosity (2.9 Pa s) could be obtained. 0.9Al 2 O 3 -0.1TiO 2 ceramic parts with high accuracy were fabricated successfully by adding 3.0 wt% photoinitiator under 600 mJ/cm 2 exposure energy. With the increase of sintering temperature from 1400 °C to 1600 °C, relative density, dielectric constant ( ε r ), and quality factor ( Q × f ) of 0.9Al 2 O 3 -0.1TiO 2 ceramic sample increased first and then decreased, and all reached the maximum value at 1550 °C due to the uniformity and densification of microstructures. The temperature coefficient of resonant frequency ( τ f ) value showed an almost monotonous increase, changing from negative to positive, and near-zero τ f value at 1550 °C. In addition, 0.9Al 2 O 3 -0.1TiO 2 ceramic samples sintered at 1550 °C fabricated by DLP method presented much better microwave dielectric properties: ε r = 11.30 ± 0.02, Q × f = 35,345 ± 143 GHz (@∼12 GHz), τ f = 2.16 ± 0.21 ppm/°C than that of by dry pressing method: ε r = 11.16 ± 0.11, Q × f = 30,195 ± 257 GHz (@∼12 GHz), τ f = 4.45 ± 0.13 ppm/°C, especially the Q × f value achieved a 17% increase. Accordingly, DLP technique, which has advantages of producing relatively high properties and complex geometry of microwave dielectric ceramics as well as without extra high-cost mold, greatly satisfies application requirements.

The effect of (Mg1/3Ta2/3)4+ on the structure, Raman vibration, Terahertz time domain spectroscopy and dielectric properties for the Li2TiO3 ceramic

The ceramics of Li2Ti1-x(Mg1/3Ta2/3)xO3 (x = 0.00–0.30) (LTMTx) were fabricated via the solid-phase method. The changes in crystal structure of LTMTx ceramics were confirmed by the X-ray diffraction (XRD). The microstructure of LTMTx ceramics was observed by the scanning electron microscope (SEM). The evolution of crystal structure and vibration for chemical bonds of LTMTx ceramics were studied by Raman spectra. The improvement on quality factors (Q × f values) was related to the weakening of asymmetric vibration in Li–O–Li bond. Based on the THz time domain spectrum (THz-TDS), the polarization mechanism and dielectric properties in THz frequency band were discussed. The satisfactory quality factor (80,005 GHz) was acquired in LTMT0.15 ceramic, and the best resonant frequency temperature coefficient (τf) value (0 ppm/°C) was achieved at x = 0.25, which firmly improved the application potential of LTMTx ceramics.

Crystal structure and microwave dielectric properties of Li-modified BaSi2O5 ceramics

Ba1-xLixSi2O5-x/2 (x = 0–0.5) ceramics were prepared by solid-state reaction method. The occupation tendency of Li+ was well explained based on First-principle calculation and unit cell volume changes. Li+ non-equivalent substitution for Ba2+ considerably reduced the sintering temperature to 975 °C, in comparison with 1225 °C for pure BaSi2O5. Single phase solid solution with orthorhombic structure was observed with x = 0–0.1. Nevertheless, trace amounts of unexpected secondary phases Li2Si2O5 and SiO2 were detected for higher Li-containing samples. Notably, the Q×f significantly enhanced up to 58.16% from 16,134 GHz (x = 0) to 25,518 GHz (x = 0.01), which predominantly depended on the structural characteristics, such as packing fraction and bond covalence. Increase x from 0 to 0.5 led to the reduction of dielectric constant εr from 7.11 to 5.95. The resonant frequency temperature coefficient τf was directly dominated by oxygen bond valence (VO), rather than VBa and VSi. Ba0.99Li0.01Si2O4.995 ceramic sintered at 1050 °C for 4 h exhibited a high Q×f value of 25,518 GHz, and the εr and τf values were 6.94 and −29.46 ppm/°C, respectively.

Crystal structure, chemical bond characteristics, infrared reflection spectrum, and microwave dielectric properties of Nd 2(Zr 1− x Ti x ) 3(MoO 4) 9 ceramics

Microwave dielectric ceramics (MWDCs) with low dielectric constant and low dielectric loss are desired in contemporary society, where the communication frequency is developing to high frequency (sub-6G). Herein, Nd₂(Zr_1−<i>x</i>Ti_<i>x</i>)₃(MoO₄)₉ (NZ_1−<i>x</i>T_<i>x</i>M, <i>x</i> = 0.02–0.10) ceramics were prepared through a solid-phase process. According to X-ray diffraction (XRD) patterns, the ceramics could form a pure crystal structure with the <i>R</i><inline-formula> <math display="inline" id="MA1"><mover accent="true"><mn>3</mn><mo>¯</mo></mover></math></inline-formula><i>c</i> (167) space group. The internal parameters affecting the properties of the ceramics were calculated and analyzed by employing Clausius–Mossotti relationship, Shannon’s rule, and Phillips–van Vechten–Levine (P–V–L) theory. Furthermore, theoretical dielectric loss of the ceramics was measured and analyzed by a Fourier transform infrared (IR) radiation spectrometer. Notably, when <i>x</i> = 0.08 and sintered at 700 ℃, optimal microwave dielectric properties of the ceramics were obtained, including a dielectric constant (<i>ε</i>_r) = 10.94, <i>Q</i>·<i>f</i> = 82,525 GHz (at 9.62 GHz), and near-zero resonant frequency temperature coefficient (<i>τ</i>_<i>f</i>) = −12.99 ppm/℃. This study not only obtained an MWDC with excellent properties but also deeply analyzed the effects of Ti⁴⁺ on the microwave dielectric properties and chemical bond characteristics of Nd₂Zr₃(MoO₄)₉ (NZM), which laid a solid foundation for the development of rare-earth molybdate MWDC system.

Low-loss and temperature stable (1-x)Ba3P2O8-xMg2B2O5 composite ceramics with low sintering temperature

In this study, the Ba3P2O8 and Mg2B2O5 were fabricated by the solid-state reaction method separately, and the (1-x)Ba3P2O8-xMg2B2O5 (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba3P2O8-xMg2B2O5 composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE01δ mode dielectric resonator method, respectively. The results revealed that the Mg2B2O5 phase and Ba3P2O8 phase could coexist well in the (1-x)Ba3P2O8-xMg2B2O5 composite ceramics without formation of any new phases. The abnormal grain growth of Ba3P2O8 grains was inhibited by the addition of Mg2B2O5. In addition, through composition of Ba3P2O8 and Mg2B2O5, the temperature coefficient of resonant frequency (τf) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba3P2O8-0.2Mg2B2O5 composite ceramic was achieved at a sintering temperature of 920 °C, τf = −1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity εr = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba3P2O8-0.2Mg2B2O5 composite ceramic is a candidate LTCC material with wide application prospects.

Improvement microwave dielectric properties of Ba2MgWO6 ceramics by substituting Mg2+ with Zn2+

The microwave dielectric properties of Ba2Mg1– x Zn x WO6 ceramics were examined with a view to their exploitation for mobile communication. The Ba2Mg1– x Zn x WO6 ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of the Ba2Mg1– x Zn x WO6 ceramics revealed that Ba2MgWO6 is the main crystalline phase, which is accompanied by small amounts of BaWO4 and Ba2WO5 as secondary phases. A maximum density of 6.72 g/cm3 was obtained for Ba2Mg0.95Zn0.05WO6 ceramic, sintered at 1650 °C for 4 h. Dielectric constant () of 17.9, quality factor (Q f) of 157,000 GHz, and temperature coefficient of resonant frequency () of −35 ppm/°C were obtained for Ba2Mg0.95Zn0.05WO6 ceramics that were sintered at 1650 °C for 4 h.

Phase compositions and microwave dielectric characteristics of xMg2B2O5-(1-x)Ba3V2O8 (0.5 ≤x ≤ 0.7) ceramics

Herein, xMg2B2O5-(1-x)Ba3V2O8 (0.5 ≤x ≤ 0.7) microwave dielectric composite ceramics were prepared via the solid-state reaction method at a relatively low sintering temperature (around 940–1020 °C). The phase compositions, microstructure, and elemental compositions of the ceramics were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS), respectively. According to the results, both Mg2B2O5 and Ba3V2O8 phases coexisted after sintering in the temperature range of 940–1020 °C. The growth of Ba3V2O8 grains was inhibited by the increase in amount of Mg2B2O5 inclusions. Moreover, mixing these two phases in a proper ratio did not only reduce the sintering temperature, but also improved the temperature coefficient of resonant frequency (τf) and Q×f value (Q is quality factor=1/ dielectric loss, f=resonant frequency) of the xMg2B2O5-(1-x)Ba3V2O8 microwave dielectric ceramics. In particular, the optimal microwave dielectric properties (εr = 10.1, Q×f = 48,050 GHz, τf = −3 ppm/°C) were reached after 2 h of sintering at 960 °C for the ceramic with x = 0.7.

Electrical Properties of Sr3Mo1–xWxO6‐Based Solid Solution

Herein, a study on the suitability of the Sr3Mo1–xWxO6 (0.1 ≤ x ≤ 0.9) solid‐solution system for radio frequency and microwave (MW) applications is reported. The ceramic powders are synthesized via solid‐state reaction at 1423 K for 6 h. X‐ray diffraction and scanning electron microscopy are performed to confirm the double‐perovskite‐type structure and investigate the surface morphology, respectively. Electrical characterization of the system as a function of temperature is performed using impedance spectroscopy. The equivalent circuit with two parallel association resistor‐constant phase elements (R‐CPEs), connected in series, associated with grain and grain boundary effects is used to adjust the electric response of the solid solutions. Sr3Mo0.9W0.1O6 solid solution exhibit a resonant frequency temperature coefficient (τf) value close to zero (8.5 ppm K−1), showing great potential for MW applications.

Band gap engineering and microwave dielectric properties evolution of mixed (Sr, La, Ce) TiMgO3 titanate–aluminate system

A mixed perovskite titanate-aluminate [(1-x)(Sr0.6La0.2Ce0.2Ti0.8Mg0.2O3)-xNdAlO3 for x = 0.1 to 0.4] solid solution was successfully synthesized. X-ray diffraction patterns (XRD) and Rietveld refinement results indicated a stable perovskite phase with a cubic structure, in which Nd3+ occupies the A-site randomly while Al3+ occupies the B-site. No additional reflection spots (superlattice reflections) were detected in the HRTEM pattern (see SAED), confirming the cubic symmetry. All samples showed small Urbach tails, mainly due to compositional disorder. Microstructural analysis based on atomic force microscopy (AFM) showed no traces of impurity phases. For x = 0.4, excellent microwave dielectric properties (MWD) are obtained with a quality factor (Q × f) of 37,131 GHz at f = 5.2801 GHz, relative permittivity (εr) of 43, and temperature coefficient of resonant frequency (τf) of +1.3 ppm/°C. Variations in εr, Q × f values, and τf may be related to changes in relative density (ρrel), ion polarizability, optical band gap, and tolerance factor, respectively.

Crystal structure and microwave dielectric characteristics of ixiolite ceramics with molybdenum ion modification and tri-layered structure

The ZnTi1−xMoxNb2O8 (0.000 ≤ x ≤ 0.060) microwave dielectric ceramics were prepared through traditional solid-state reaction. Mo4+ substitution for Ti4+ can markedly improve the microwave dielectric characteristics of ZnTiNb2O8 system. In the microstructures investigation, a suitable degree of Mo4+ substitution was shown to be useful for creating uniform grain size and minimizing dielectric loss. Raman spectroscopy and complex chemical bond theory analyses demonstrate that the bond ionicity of NbO bond is the intrinsic component influencing the εr value. The lattice energy of NbO bond, bond valence of Cation-O bond, and the FWHM of Raman spectra were the primary determinants of Q×f value. The τf value is mostly determined by variations in NbO bond energy and the bond valence of Cation-O bond. When x = 0.010, ZnTi0.990Mo0.010Nb2O8 ceramics exhibit excellent microwave dielectric characteristics: εr = 33.91, Q×f = 64,136 GHz, and τf = − 50.57 ppm/°C. Furthermore, in order to improve the temperature coefficient of resonant frequency (τf values close to zero) for the ZnTi0.990Mo0.010Nb2O8 ceramics, the TiO2 and laminated co-firing technique were used to adjust the comprehensive microwave dielectric characteristics of the ZnTiNb2O8 system. When the mass fraction of the TiO2 layer reaches 0.03 wt% after sintering at 1150 °C, the tri-layer structural ZTMN-0.03TO-ZTMN ceramics obtain outstanding microwave dielectric characteristics: εr = 41.52, Q×f = 50,827 GHz, and τf = − 2.59 ppm/°C, and these characteristics make them potential for usage in 5G communications.

Effect of A-site modification on structural and microwave dielectric properties of calcium titanate

This article presents studies on characteristics properties of CaTiO3, Ca0.8Sr0.2TiO3, and Ca0.6La0.8/3TiO3 ceramics. These ceramics were synthesized using the solid-state reaction process. Structural examination revealed that the grown ceramics have an orthorhombic structure with the Pbnm space group. The random distribution of particle size was shown through morphological investigation. Apparent density of developed ceramics was determined using the Archimedes technique and found to be ˂ 90%. The microwave dielectric properties of grown ceramics are compared on the basis of ionic polarizability. It is observed that partial replacement of Ca-ions by Sr-ions provides a high permittivity value (er = 168.93), higher quality factor Q × f = 9,330 GHz), and enhanced positive temperature coefficient of resonant frequency (tf = 908.17). However, the substitution of Ca-ions by La-ions offers a low permittivity value (113.35), higher quality factor (16,730 GHz), and decreased temperature coefficient of resonant frequency (229.49 ppm/°C). These materials can be used with the ceramics possessing a negative temperature coefficient of resonant frequency to balance its tf- value nearly to zero.

Effect of Co substitution on the structural, dielectric and reflection properties of MgTiO3 solid solutions

Cobalt-substituted magnesium titanate solid solutions with a chemical composition of Cox Mg1-x TiO3, where x = 0.00, 0.025, 0.05, 0.075, 0.10, were synthesized and characterized for their structural, dielectric and reflection properties. The formation of single-phase MgTiO3 was revealed by X-ray diffraction (XRD). A low porosity and tightly packed grains were observed with scanning electron microscopy (SEM). Raman spectroscopy confirmed the presence of the desired modes. The dielectric properties showed that the composition of Cox Mg1-x TiO3 with x = 0.05 possessed a relatively good combination of a relative permittivity (ɛr ) of 16.90, loss tangent (tan δ) of 1.7 × 10 −3, and temperature coefficient of resonant frequency (τf) of -41.32 ppm/°C at 100 kHz. The electromagnetic reflection analysis indicated that this composition could be proposed as a substrate material for antennas, filters and microwave reflectors in the studied frequency range.

Temperature stable dielectric properties of Mg2TiO4–MgTiO3–CaTiO3 Ceramics Over a Wide Temperature range

The zero resonant frequency temperature coefficient (τf) of microwave dielectric ceramics (MWDCs) at high and low temperature have attracted great attention in the development of microwave communication equipment. In this work, the Mg2TiO4–MgTiO3–CaTiO3 (MMC) ceramics with meeting the application requirements of 5G communication were prepared by traditional solid-phase sintering after investigating the relationship among phase compositions of xMg2TiO4-(0.931-x)MgTiO3-0.069CaTiO3 and 0.34Mg2TiO4-0.591MgTiO3-yCaTiO3, sintering process, and dielectric properties in detail. The results show that the dielectric properties of MMC ceramics are strongly affected by the phase relative contents of MgTiO3, Mg2TiO4 and CaTiO3. For instance, MMC ceramics with approximate τf = 0 is contributed by mutual compensation of Mg2TiO4 and MgTiO3, in which the Mg2TiO4 phase plays an important role in decreasing the τf value; and the increase of CaTiO3 will greatly increase the εr value for MMC ceramics, while has a negative effect in the Q × f value. After three-phase regulation, the 0.32Mg2TiO4-0.611MgTiO3-0.069CaTiO3 microwave dielectric ceramic has a better dielectric temperature stability, associated with dielectric properties of εr = 19.7, Q × f = 55,400 GHz (at 8.43 GHz), τf- = 4.5 ppm/°C (−40 °C–25 °C), and τf+ = −5.1 ppm/°C (25 °C–90 °C).

MgTiO3–Ca1−xSm2x/3TiO3 (x = 0.2–0.5) microwave dielectric composites with greatly improved temperature stability

AbstractMgTiO3–CaTiO3 composite is one of the most important commercial microwave dielectric ceramics. However, the significant nonlinear change in resonant frequency with temperature and the temperature dependence of its temperature coefficient of resonant frequency (τf) severely deteriorate the temperature stability of MgTiO3–CaTiO3 composite. In this study, the Ca2+ in CaTiO3 was partially substituted with Sm3+ to prepare a series of (1 − y)MgTiO3–yCa1−xSm2x/3TiO3 (x = 0.2–0.5) composites that was subsequently characterized. With increasing x from 0 to 0.5, the y value for obtaining the near‐zero average τf between 20 and 80°C increases from 0.07 to 0.23; the dielectric constant of the composite correspondingly increases from 21.5 to 27.1, whereas the Qf value first increases and then decreases. Notably, (1 − y)MgTiO3–yCa1−xSm2x/3TiO3 composites with greatly improved temperature stability are realized, and the nonlinearity of the change in resonant frequency with temperature and the rate of change of τf with temperature are reduced by 48%–73%, relative to those of 0.93MgTiO3–0.07CaTiO3 composite. These results are attributed to the significantly reduced temperature dependence of τf for the constituent phase of Ca1−xSm2x/3TiO3. This study sheds light on the development of temperature‐stable microwave dielectric composites featuring constituent phases with τf of opposite signs.