Microwave Dielectric Properties Of Er Research Articles

Sintering behavior, lattice vibrational characteristics and dielectric properties of B-site ion substituted BaWO4 ceramics for LTCC applications

The influences of Mo6+ substitution at the B-site of scheelite structure on the sintering character, microstructures, lattice vibrational characteristics, and dielectric properties of BaW1-xMoxO4 (x = 0.10-0.30) ceramics were studied in detail in this paper. The sintering temperature of BaW1-xMoxO4 ceramics was effectively reduced to less than 950oC through forming a scheelite solid solution. The densification and the quality factor (Q×f) of BaW1-xMoxO4 ceramics were also enhanced compared with pure BaWO4 ceramic. Raman spectroscopy confirmed that the dielectric constant (εr) was highly correlated with molecular polarizability, and the Q×f was strongly dependent on the symmetric stretching bond of [WO4] tetrahedron. Oxygen bond valence was one of crucial parameters for modulating the temperature coefficient of resonant frequency (τf). Interestingly, the BaW0.75Mo0.25O4 ceramic sintered at 910oC exhibited favorable microwave dielectric properties of εr = 9.44, Q×f = 46,820GHz (@12.5GHz), and τf = −69.2 ppm/oC. Meanwhile, the BaW0.75Mo0.25O4 ceramic had stupendous dielectric properties in low-frequency band: εr = 17.5 and dielectric loss (tanδ) = 2.2×10-4 (@10MHz). In addition, there was good chemical compatibility between BaW0.75Mo0.25O4 ceramic and silver electrodes. These findings evidence that BaW1-xMoxO4 ceramics are competitive candidates in LTCC technology.

Novel single-phase Li2SiO3 microwave dielectric ceramic with low permittivity

Novel low-permittivity lithium metasilicate (Li2SiO3) ceramics were synthesized to explore the relationships between crystal structure parameters and dielectric properties. X-ray diffraction and Rietveld refinement indicated that the Li2SiO3 ceramics formed a single orthorhombic structure with a Cmc21 space group. Optimal microwave dielectric properties of εr = 6.20 ± 0.02, Q×f = 30,550 ± 250 GHz (f0 = 15.5 GHz), and τf = −40.95 ± 0.56 ppm/℃ were achieved through sintering at 1025 ℃. Raman spectroscopy analysis showed that the values of εr and Q×f were negatively correlated with the Raman shift and full width at half maximum of the strongest peak at 982 cm−1, respectively. Meanwhile, the Phillips–Vechten–Levine theory revealed that the εr values and the Q×f values were closely related to the average bond ionicity and the lattice energy of the Si-O bonds, respectively. Moreover, the increase in τf values depended on the increase in oxygen bond valence and the distortion of the [LiO4] tetrahedron. These results on the Li2SiO3 ceramics could provide some theoretical information for developing high-performance microwave dielectric ceramics.

A series of Ba12M0.5Zr0.5Nb9O36 (M=Ni, Mg, Co, and Zn) microwave dielectric ceramics with hexagonal perovskite structure

A series of hexagonal perovskite Ba12M0.5Zr0.5Nb9O36 (M = Ni, Mg, Co, Zn) ceramics were prepared by solid-state reaction method. XRD and Rietveld refinement results showed that all ceramic samples belong to the hexagonal perovskite structure with R-3m space group. With different B-site ion substitution, variation of permittivity (εr) can be ascribed to the average ion polarizability. Ceramics with highest relative density exhibit maximum quality factor (Q×f) values. Among all samples, the optimal microwave dielectric properties of εr = 35.2, Q×f = 57,985 GHz, and τf = 26.4 ppm/°C for Ba12Mg0.5Zr0.5Nb9O36 were obtained, which indicated that Ba12Mg0.5Zr0.5Nb9O36 ceramic is a candidate material for microwave communication applications.

Low permittivity germanate LaAlGe2O7 ceramics: Synthesis, sintering behavior, spectral characteristics and microwave dielectric properties

Novel low permittivity LaAlGe2O7 ceramics was prepared by a solid-state reaction method, and the relationship between microstructure and microwave properties was revealed. XRD and Rietveld refinement confirmed that the crystal structure of LaAlGe2O7 is monoclinic P21/c space group. Raman spectroscopy reflects the trend of internal structural order and phonon-damping behavior of LaAlGe2O7 ceramics. The ceramic sintered at 1250 °C exhibited the best surface morphology and optimum microwave dielectric properties of εr = 9.22, Q × f = 33417 GHz, τf = −71.68 ppm/°C. The lattice energy and packing fraction are used to explain the change of Q × f value. The relationship between phonon damping behavior and microwave dielectric properties was revealed. The temperature stability was studied by bond valence. The LaAlGe2O7 ceramics is a strong candidate for the substrate material of millimeter wave communication.

Chemical bond features and microwave dielectric properties of olivine-type LiMSiO4 (M = Ho, In) ceramics

Orthorhombic olivine-structured LiMSiO4 (M = Ho, In) ceramics were synthesised using the solid-state reaction. Promising microwave dielectric properties of εr = 10.04, τf = 23.3 ppm/°C and a high-quality factor (Q × f) of 11,415 GHz for LiHoSiO4 were obtained at 1050 °C, and εr = 7.78, τf = −46.8 ppm/°C and Q × f = 23,390 GHz for LiInSiO4 were achieved at 1140 °C. According to the bond valence result, Ho3+ presented a slightly compressed state but Li+ and Si4+ exhibited a strong rattling state in LiHoSiO4, which led to higher εr than the εtheo. The integrated effect of rattling cations (Li+ and In3+) and a compressed cation (Si4+) in LiInSiO4 resulted in a small positive deviation Δεr. The larger packing fraction of LiInSiO4 contributed to a higher Q × f than LiHoSiO4. The Si–O bond in both ceramics played a leading role in influencing the Q × f according to the Phillips−Van Vechten−Levine chemical bond theory.

Investigating the ultralow dielectric loss of spinel-like and modified orthorhombic perovskite ceramic structures for microwave applications

ABSTRACT This study prepared ultralow electron-loss perovskites with spinel-like structures via a solid-state reaction. The (Mg0.95Co0.05)2(Ti0.95Sn0.05)O4 (MCTS) ceramic exhibited approximate values for ultrahigh quality factor, permittivity, and negative temperature coefficient (τf) of 310,000 GHz, 14.25, and −48.1 ppm/oC, respectively. To bring the τf closer to zero, a trace amount of (Ca0.95Sr0.05)(Ti0.97Sn0.03)O3 (CSTS) perovskite was added to MCTS during ceramic manufacturing. CSTS exhibited a permittivity of 92 and a large positive τf value of 810 ppm/°C. A 0.92MCTS–0.08CSTS hybrid ceramic sintered at 1325°C achieved remarkable microwave dielectric properties of εr ~18.42, Q×f ~ 237,000 GHz and τf ~3.72 ppm/°C. This mixed ceramic has significant potential for applications in manufacturing microwave devices.

A novel spinel-type Mg3Ga2SnO8 microwave dielectric ceramic with low εr and low loss

This research used the co-substitution strategy to prepare novel spinel-type Mg3Ga2SnO8 ceramics sintered at 1430–1510 °C. Rietveld refinement and SEM showed that the Mg3Ga2SnO8 ceramic had a cubic spinel structure with a space group of Fd3¯m(227), where Mg1 and Mg2/Ga1/Sn1 occupy the tetrahedron and octahedron, respectively. The relative density exhibited a considerable influence on the εr of Mg3Ga2SnO8 ceramics. In addition, the Q×f of the ceramics was closely related to the packing fraction and FWHM. Infrared reflection spectra were used to investigate the intrinsic dielectric characteristics of the ceramics. The P−V−L theory indicated that Sn−O and Ga−O bonds contribute substantially to the εr and Q×f, respectively. The Mg3Ga2SnO8 ceramics had the optimum microwave dielectric properties of εr = 9.3, Q×f = 189,052 GHz, and τf = −34.25 ppm/°C when sintered at 1470 °C. Therefore, Mg3Ga2SnO8 ceramics exhibit a wide range of possible applications in the field of microwave media.

A novel dielectric ceramic Na0·48La0·52MoO4 with excellent thermal stability for LTCC applications

This article reports the fabrication of a novel molybdate compound, Na0·48La0·52MoO4 (NLM), through the solid-state reaction method. The structural characterization and dielectric properties of NLM were conducted via powder X-ray diffraction, SEM, laser Raman spectroscopy, and vector network analysis. The research results indicate that the sintering temperature directly affects the firing process and microwave dielectric properties. NLM ceramics sintered at 920 °C demonstrate excellent microwave dielectric properties of εr = 8.86, Q × f = 61,378 GHz (at 13.5 GHz) and τf = −10.8 ppm/°C. Furthermore, NLM ceramics exhibit favorable chemical compatibility with Ag. These findings underscore the significant potential of NLM ceramics for utilization in LTCC applications.

Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity (εr) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics, as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr4+ and Hf4+ substituted Ba4Sm9.33Ti18O54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency (τf) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm2Ti2O7 second phase with a large positive τf. Optimal microwave dielectric properties of εr = 81.3, Q × f = 10,800 GHz, and τf = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies (VO∙∙). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr4+ and Hf4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.

AY2Al4GeO12 (A = Ca, Mg) ceramics: Phase composition, microstructure, lattice vibration, bond characteristics, and microwave dielectric properties

In this work, cubic garnet-type AY2Al4GeO12 (A = Ca, Mg) ceramics were synthesized by a solid-state reaction method. XRD detected that CYAG was a single-phase, and the secondary phase existed in the MYAG. SEM, density, and dielectric properties results indicate that the optimum sintering temperature of CYAG and MYAG ceramics is 1550 °C, the CYAG and MYAG ceramics exhibited the best microwave dielectric properties of εr = 8.94, Q×f = 93805 GHz, τf = −48 ppm/°C and εr = 7.06, Q×f = 30549 GHz, τf = −26.55 ppm/°C, respectively. Rietveld refinement, Raman and XPS confirmed that the significant difference in dielectric properties is related to the secondary phase, structural disorder and oxygen vacancy. The relationship between the Q×f and lattice vibration are discussed. τf is explained by oxygen bond valence. The influence of bond characteristics on dielectric properties was analyzed. The reported microwave ceramics are expected to be used as substrate materials in the millimeter wave band.

Crystal structures, Raman spectra, chemical bonds, and microwave dielectric properties of novel low-εr CaASbWO8 (A = Gd, La) ceramics with opposite temperature coefficients

In this work, two novel CaASbWO8 (A = Gd, La; named CGSWO and CLSWO) microwave dielectric ceramics were synthesized by a classical solid-state method. Remarkably, the outstanding microwave dielectric properties (εr = 12.97, Q×f = 45,034 GHz, and τf = −16.29 ppm/°C) were achieved for CGSWO ceramics sintered at 1440 °C, and CLSWO ceramics sintered at 1300 °C possessed the excellent microwave dielectric properties of εr = 9.89, Q×f = 61,326 GHz, and τf = 0.55 ppm/°C. Bond valence, ionic polarizability, Raman spectroscopy and Phillips–Vechten–Levine (P-V-L) theory were used to study the internal lattice vibration and chemical bonds in detail, and the dielectric properties were explored from the internal factors. In comparison to the εr, the εtheo of CGSWO was found to be consistently underestimated, whereas CLSWO exhibited a contrasting pattern. This discrepancy was primarily attributed to the rattling and compressed effects of A-site cation. According to the analysis of P-V-L theory, W-O bond played an important role in regulating the Q×f value. Moreover, the τf values of CGSWO and CLSWO ceramics were opposite, which provided an opportunity to manufacture microwave ceramic devices with good temperature stability.

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.

Sintering characteristic, phase structure, micromorphology, and microwave dielectric properties of novel BaSrSm4O8 ceramic

A novel microwave dielectric ceramic composed of BaSrSm4O8 was prepared using a solid-state reaction method. XRD and Rietveld refinement indicated that the ceramic was a BaSrSm4O8 pure phase with a CaFe2O4 structure and space group of Pnma. As the sintering temperature increased, the density of the samples increased, reached a maximum, and then decreased. The grain boundaries of the BaSrSm4O8 samples at the optimum temperature were clear, the grain size was uniform, the elements were evenly distributed, and no enrichment was observed. The quality factor of the BaSrSm4O8 ceramics showed a significant negative correlation with the Raman half peak (FWHM). BaSrSm4O8 ceramic sintered at 1475 °C exhibited the best microwave dielectric properties of εr = 10.77, Q×f = 54183 GHz, and τf = −30.69 ppm/°C.

Bond characteristics, microstructure, and microwave dielectric properties of Bi2O3–ZnO–B2O3 glass-ceramics with Li2O substitution

The effect of Li2O substitution on the sintering behavior, lattice structure, microstructure, and microwave dielectric properties of ZnO–B2O3–Bi2O3 glass-ceramics was studied by various amounts of Li2O to substitute ZnO. The substitution of Li2O decreases the glass network connectivity and thus decreases the sintering temperature of the glass. In the sintered glass-ceramics, the substitution of 0.2 mol% Li2O leads to the most significant lattice activation resulting in the glass-ceramic exhibiting the smallest cell volume of Zn3B2O6 crystal and the microstructure with fine and uniform grains. The P–V-L theory is innovatively applied to glass-ceramic materials to characterize the variation in bond characteristics caused by lattice activation and it indicates that the 0.2 mol% Li2O substitution decreases the Zn–O bond ionicity and increases the lattice energy of the B–O bond, in the Zn3B2O6 crystalline phase. The refinement of microstructure and the optimization of bond characteristics improve the microwave dielectric properties of glass-ceramics. The glass-ceramic with 0.2 mol% Li2O substitution sintered at 620 °C for 5 h exhibits excellent microwave dielectric properties of εr ∼5.05, Q×f ∼15,383 GHz, τf ∼ −6 ppm/°C and good chemical compatibility with Ag or Al electrodes, which is a favorable candidate for application in ULTCC substrate materials.

Crystal structure, bond characterization and lattice energy of B-site 1:3 ordering inverse spinel Li1.25Ga0.25Ti1.5O4 ceramic

In this work, inverse spinel structured Li1.25Ga0.25Ti1.5O4 ceramics with a space group of P4332 were synthesized by a solid-state reaction method. XRD, SAED, HRTEM, and Raman spectra analysis demonstrated that the Li1.25Ga0.25Ti1.5O4 ceramic was formed a A-site 1:3 disordered and B-site 1:3 ordered spinel structured. A high relative density (98.7%) with excellent microwave dielectric properties of εr = 23.8, Q×f = 93,800 GHz, and τf = –21.9 ppm/oC were obtained in 1110 °C for 4 h. Bond valence analysis demonstrated that the average cations of Li1.25Ga0.25Ti1.5O4 were in the rattling state, and the polarizability of Ti4+ was underestimated. The P–V-L chemical bond theory and lattice energy analysis results indicated that B–O bonds were the main factor to affect the εr and Q × f, and the under-bonding Ti4+and Ga3+ has a significant effect on the τf. All the results show that the Li1.25Ga0.25Ti1.5O4 ceramic might be a potential candidate for 5 G communication technology.

Effects of (Li0.5Nd0.5)2+ on the phase evolution, Raman spectra and microwave dielectric properties in CaO–Nd2O3–TiO2 ceramic

The rapid advancement of mobile communications technology is imposing greater demands on electronic components. Microwave dielectric ceramics with a high dielectric constant (ϵr ) are crucial for the miniaturization and integration of microwave devices. Herein, The perovskite-structured (Ca0.61Nd0.26)1−x (Li0.5Nd0.5) x TiO3 (0 ⩽ x ⩽ 0.8) microwave dielectric ceramics with high ϵr value were prepared by solid-state reaction method. The results demonstrated that the ϵr value reached its peak at x = 0.6, which was influenced by the bond valence at B-sites. The τ f and Q× f values decreased with increasing x value. Doping (Li0.5Nd0.5)2+ at A-sites led to an increase in the full width at half maximum of Raman peaks, indicating higher internal loss. A high dielectric constant and temperature-stable (Ca0.61Nd0.26)0.27(Li0.5Nd0.5)0.73TiO3 ceramic can be sintered with good microwave dielectric properties of ϵr = 129.4, Q× f= 2,787 GHz, and τ f = +1.9 ppm/°C.

A TiSnNbTaGa2O12 high-entropy microwave dielectric ceramic with rutile structure and near-zero τf

TiSnNbTaGa2O12 (TSNTGO) high–entropy dielectric ceramic was successful synthesized using the solid-state reaction method. X–ray diffraction (XRD), Rietveld refinement and transmission electron microscopy (TEM) were used to verify that all samples have rutile structure of P42–mnm space group. The analysis of Raman spectra proved that the εr exhibited a contrary changing trend as that of Raman shift near 822 cm−1, and the same similar relationship occurred between Q×f values and full width at half maximum (FWHM). The exploration of complex chemical bonding theory (P–V–L theory) for TSNTGO ceramics suggested that the bond ionicity played a dominant role in εr, while Q×f and τf were primarily determined by lattice energy and bond energy, respectively. Notably, the TSNTGO ceramics sintered at 1275 ℃ demonstrated optimal microwave dielectric properties of εr = 33.62 ± 0.03, Q×f = 51,832 ± 1000 GHz (f0 = 6.4 GHz), and τf = –0.38 ± 0.16 ppm/℃.

Structural features of glass-free Al2Mo3O12 ceramic with excellent microwave dielectric properties

The Al2Mo3O12 ceramic with monoclinic type is prepared at the sintering temperature as low as 750 °C, which exhibits excellent microwave dielectric properties of εr = 4.99, Q × f = 49,579 GHz (f = 14.8 GHz), and τf = −26 ppm/°C. The relationship between structure and characteristics is analyzed through the P–V–L chemical bond theory in depth, and the dielectric properties are investigated in combination with far-infrared spectroscopy. Results show that it is Mo–O bond that is responsible mainly for bond ionicity and dielectric polarizability, and structural stability as well. Based on the far-infrared reflectivity spectra and complicated dielectric function analysis, the calculated and measured results are in relative agreement using the classical damped oscillation mode, indicating that the mode at 80.23 cm−1 is dominant for the contribution to dielectric properties. This study gives an insight into the structural characteristic and provides a guide to further improve the microwave dielectric performance of Al2Mo3O12 ceramic.

Investigation on the bond characteristics and microwave dielectric properties of rock salt-structured Li2Mg0.5nTiO3+0.5n (n = 1–8) ceramics based on the complex chemical bond theory

Cubic rock salt structured ceramics are of great interest due to their outstanding microwave dielectric properties. Complex chemical bond theory and polarization theory combined with XRD refinement as well as XPS were employed to reveal the mechanisms of the compositional effect on the microwave dielectric properties of Li2Mg0.5nTiO3+0.5n ceramics with a rock salt structure. It was demonstrated that when n = 1, the microwave dielectric properties exhibit a biphasic structure. However, as n increased to 2 and higher levels, the specimens were consisted of a single cubic rock salt phase. εr of single-phased samples decreased with an increase in the n value, which was due to the decreases in both the bond ionicity and polarizability of unit cell. Meanwhile, as lattice energy increased, the formation of oxygen vacancies was effectively suppressed, and anharmonic lattice vibrations were weakened, leading to an increase in Q×f. Moreover, τf showed a negative shift due to an increase in the aL,ave of the chemical bond and an decrease in the bond energy. The optimal microwave dielectric properties of εr= 17.3, Q×f= 81,000 GHz, and τf = −7.7 ppm/℃ were achieved in the component with n = 1 when sintered at 1350 °C for 4 h.

Phase Compositions and Microwave Dielectric Properties of Na1+xSrB5O9+0.5x Ceramics

Microwave dielectric ceramics composed of Na1+xSrB5O9+0.5x (0 ≤ x ≤ 0.125) were synthesized via a traditional solid-state reaction approach. The effects of non-stoichiometric Na on the crystal structures, phase compositions, chemical bond characteristics, and microwave dielectric properties of the Na1+xSrB5O9+0.5x ceramics were systematically studied. All Na1+xSrB5O9+0.5x ceramics sintered at optimum temperatures consisted of a NaSrB5O9 solid-solution phase and a SrB2O4 phase. Appropriate excess Na could suppress the generation of the SrB2O4 phase, and the lowest content of the SrB2O4 phase was achieved at x = 0.075. The εr values of the Na1+xSrB5O9+0.5x ceramics were primarily affected by the relative density and molecular polarization. The Q × f values showed a positive correlation with the lattice energy. The τf value was correlated to the SrB2O4 phase content, bond valence, and bond energy. Typically, the Na1.075SrB5O9.0375 ceramic sintered at 825 °C possessed good microwave dielectric properties of εr = 5.61, Q × f = 31, 937 GHz, and τf = −3.09 ppm/°C, which are suitable for high-frequency, low-temperature co-fired ceramics (LTCCs) substrate applications.