Search

This study delves into the microwave dielectric properties of Li2Y9(SiO4)6O2F ceramics, synthesized using the conventional solid-state method. By employing x-ray diffraction analysis and meticulous data refinement across various temperatures, we unequivocally confirm the hexagonal crystal structure of Li2Y9(SiO4)6O2F ceramics. The refined lattice parameters, observed at a sintering temperature of 1275°C, exhibit a = b = 9.33318 Å, c = 6.71725 Å, with a corresponding unit cell volume of V = 506.73529 Å3. In-depth scrutiny of the microstructure of the ceramics' grains using scanning electron microscopy (SEM) reveals an optimal relative density of 96.2%. Subsequently, the study explores the impact of porosity, packing fraction, relative density, and Si-O bond valence (VSi-O) on the microwave dielectric properties of Li2Y9(SiO4)6O2F ceramics. Notably, the Li2Y9(SiO4)6O2F ceramic sintered at 1275°C demonstrates superior performance metrics, boasting an εr value of 14.28, a Q × f product of 16,760 GHz (at f = 9.4 GHz), and a temperature coefficient of frequency (τf) at 3.14 ppm/°C. This comprehensive investigation contributes valuable insights into optimizing the microwave dielectric characteristics of Li2Y9(SiO4)6O2F ceramics for potential applications in advanced electronic devices. [ABSTRACT FROM AUTHOR]

In this work, a silicate ceramic, CaY2Al4SiO12 (CYASO), with a low dielectric constant and low loss was prepared using traditional solid-state methods. X-ray diffraction (XRD) refinement analysis shows that the CYASO material crystallized into a phase with an Ia-3d space group and an impurity peak. The orthogonal cubic structure of the CYASO ceramic was confirmed through transmission electron microscopy (TEM), and the structure exhibited an orderly layered arrangement. The internal microstructure was characterized using scanning electron microscopy (SEM), which showed that the sample's relative density reached 97.8%. We discuss the correlation between the full width at half maximum (FWHM) of the Raman matrix corresponding to the vibration mode of the symmetric bending mode of AlO4 at the Raman shift of 855 cm−1 and the Q × f value. Additionally, the analysis focused on the various factors that influence the dielectric constant, including density, secondary phase, and porosity changes. The ceramics exhibited remarkable microwave dielectric properties (εr = 8.7, Q × f = 34,700 GHz, τf = −35 ppm/°C) when calcined at 1425°C. CYASO ceramic shows great capacity as a microwave dielectric material. [ABSTRACT FROM AUTHOR]

The rapidly developing field of wireless communication technology requires advanced microwave dielectric ceramic materials. Here, spinel-structured MgGa2O4 and ZnGa2O4 ceramics were prepared using a reaction sintering method. The effect of sintering temperature was investigated with respect to the crystal structure, microstructure, and microwave dielectric properties of MgGa2O4 and ZnGa2O4 ceramics. Rietveld refinement analysis and quality factor (Q×f) values suggested that the occupancy sites and percentage of cations in MgGa2O4 would affect the microwave dielectric properties. Microstructure analysis indicated that abnormal grain growth at higher sintering temperatures would degrade the microwave dielectric properties of ZnGa2O4 ceramics. MgGa2O4 ceramics sintered at 1610°C exhibited promising microwave dielectric properties, i.e., εr = 9.4, Q×f = 167,500 GHz, and τf = −63 ppm/°C, while ZnGa2O4 ceramics sintered at 1550°C possessed a higher εr and a lower Q×f value of 10.5 and 126,900 GHz, respectively, and τf = −60 ppm/°C. The τf values of MgGa2O4 and ZnGa2O4 ceramics were tuned to near-zero levels by adding 8 mol.% CaTiO3. These results indicate that MgGa2O4 and ZnGa2O4 ceramics produced by reaction sintering show promise for applications in the field of 5G communication. [ABSTRACT FROM AUTHOR]

Monoclinic Sm 2 O 3 ceramics were prepared using the conventional solid-state sintering method. The influences of sintering temperature on structure, morphology, and performance of Sm 2 O 3 ceramics were studied systematically. The excellent microwave dielectric properties (ε r = 21.95, Q × f = 47,000 GHz, and τ f = +30.15 ppm/°C) were achieved in Sm 2 O 3 ceramic sintered at 1550 °C for 4 h. Interestingly, varying degrees of cracking were observed after the sintered samples were placed for a short time, with the extent depending on the sintering temperatures. The reasons for cracking were analyzed through chemical bond characteristics and microstructure. The analysis of bond valence and microstructure revealed that Sm 2 O 3 ceramics sintered at higher temperatures exhibited larger bond strain index, global instability index, and interplanar spacings. These results suggest that the cracking of Sm 2 O 3 ceramics originates from inner stress resulting from structural variations caused by variations in sintering temperatures. The effect of MgO addition on microwave dielectric properties and stability of Sm 2 O 3 ceramics was also investigated. Phase identification and elemental distribution indicated that MgO existed as a secondary phase. The Sm 2 O 3 ceramic with 20 wt% MgO addition exhibited optimal microwave dielectric properties: ε r = 17.72, Q × f = 61,100 GHz, and τ f = +2.4 ppm/°C. Importantly, cracking was not observed when MgO addition amounts were 5 wt% or higher. The attractive microwave dielectric properties and favorable stability confirm the possibility of the 5G applications for Sm 2 O 3 /MgO composite ceramics. [ABSTRACT FROM AUTHOR]

The structural characteristics and microwave dielectric properties of SrBi2TeO7 ceramics intended for low-temperature co-fired ceramic (LTCC) applications were investigated. Comprehensive analyses were conducted using x-ray diffraction, structural refinement, transmission electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. The findings demonstrated that SrBi2TeO7 ceramics possess a pure cubic structure. Scanning electron microscopy characterizes the grain microstructure, revealing a relative density of 95.5% for SrBi2TeO7 ceramic. Optimal microwave dielectric properties were achieved for SrBi2TeO7 ceramics calcined at 765°C, displaying a relative permittivity (εr) of 24.96, a Q × f value of 25,898 GHz (f = 6.6 GHz), and a temperature coefficient of resonant frequency (τf) of –80.7 ppm/°C. The combination of low sintering temperature and minimal dielectric loss renders these ceramics advantageous for utilization in LTCC materials. [ABSTRACT FROM AUTHOR]

This study presents the dielectric properties of Ba2Zr2Si3O12 ceramics, synthesized using the solid state method. The cubic crystal structure of Ba2Zr2Si3O12 ceramics was conclusively verified through the analysis of XRD patterns and subsequent structural refinement. Refined lattice parameters of a = b = c = 10.23178 Å were found, with a corresponding unit cell volume of V = 1071.159026 Å3. The grain microstructure of the ceramics was characterized using SEM, which showed density of 97.6% for the Ba2Zr2Si3O12 ceramic. The Si-O bond valences (VSi-O) were found to be closely related to the τf of the Ba2Zr2Si3O12 ceramics. The microwave dielectric properties of the Ba2Zr2Si3O12 ceramics sintered at 1490°C were ascertained to be εr = 15.08, Q × f = 14885 GHz (f = 9.9 GHz), and τf = −78.6 ppm/°C. [ABSTRACT FROM AUTHOR]

The Y2.97Re0.03Al5O12 ceramics have been prepared with Y3+ ions substituted by rare-earth ions (Re = La, Sm, Gd, Er, Yb). We have analyzed the phase composition, crystal structure, surface micromorphology, and microwave dielectric properties of the Y2.97Re0.03Al5O12 ceramics. The results of x-ray diffraction and Rietveld refinement show that with a doping amount of x = 0.03, a stable Y3Al5O12 phase can be formed, while the crystal structure is slightly changed. Samples of each component illustrate different characteristics of grain boundaries that influence the microwave dielectric properties. Based on the Phillips–Van Vechten–Levine (P-V-L) theory, the ionicity, lattice energy, and bond energy of Y2.97Re0.03Al5O12 ceramics have been calculated to characterize the relative dielectric constant, quality factor, and temperature coefficient, respectively. Among all the samples, La3+ ions substitution significantly improves the quality factor of the YAG ceramics. Optimal microwave dielectric properties (εr = 10.73, Q × f = 178102 GHz, τf = − 35.18 ppm/°C) of Y2.97La0.03Al5O12 ceramics were prepared at 1700 °C for 9 h. [ABSTRACT FROM AUTHOR]

In this article, the strategy of co-doping Mn2+ ions with W6+ ions is used to improve the comprehensive dielectric performances of TiO2 ceramics. According to the analysis of XRD results, a pure TiO2 phase with a rutile structure can be found throughout the whole substitution range (0 ≤ x ≤ 0.02). Based on the refinement method, it is noted that the tetragonality firstly increase for 0 ≤ x ≤ 0.005, and then decreases for x > 0.005. A slight blue shift is observed for the A1g mode, whereas the Eg mode shows a red shift. The permittivity is highly dependent on the relative density, fc of Ti/(Mn0.5W0.5)-O1(1) and Ti/(Mn0.5W0.5)-O1(2) bond and Afc. The variation of quality factor strongly relies on the relative density, changing c/a value and valence state of Ti. The increase of c/a and elimination of Ti3+ contribute to the significant improvement of Q × f from 947 to 39,000 GHz. The τf dramatically decreases from 520 to 398 ppm/ºC because of the increase of unit cell volume. The excellent dielectric performance of Ti1-x(Mn0.5W0.5)xO2 ceramics can be achieved at x = 0.005 with εr = 105, Q × f = 39,000 GHz and τf = 464.4 ppm/ºC. [ABSTRACT FROM AUTHOR]

In this study, (Ti1/2W1/2)5+ ionic co-substitution effects on the crystal structural evolution, microstructure, and microwave dielectric characteristics of wolframite MgZrNb2O8 ceramics were studied in detail. From the Rietveld refinement analysis, the (Ti1/2W1/2)5+ cation diffuses into the Nb site and forms a solid solution; meanwhile, the increasing content of (Ti1/2W1/2)5+ cation from x = 0.02 to x = 0.08 decreases the volume cell, resulting in the shrinkage of the unit cell. The microstructures of ionic doped MgZrNb2O8 ceramics are compact; however, the sintering temperature benefits the growth of grain and the densification, where the highest density is achieved at x = 0.06. For the development of the microwave dielectric properties, the relative permittivity (εr) gradually declines as x increases, which is mainly ascribed to the small dielectric polarizabilities of (Ti1/2W1/2)5+ cation; however, the Q × f value is internally affected by the packing fraction and the size uniformity of grain distribution. The distortion of [NbO6] octahedral is mainly responsible for the variation of the τf value. [ABSTRACT FROM AUTHOR]

The Li 4 MgWO 6 ceramic was synthesized by the conventional solid-state reaction method, and its sintering behavior and microwave dielectric properties were studied for the first time. The XRD patterns and structural refinements indicated that Li 4 MgWO 6 formed an orthorhombic phase at temperatures above 900 °C, and TEM analyses confirmed the ordered and layered rock-salt superstructures for the orthorhombic Li 4 MgWO 6. The SEM photographs and relative density curve showed that the sample sintered at 950 °C had the highest densification. When sintered at 950 °C in a WO 3 -rich atmosphere for 4 h, Li 4 MgWO 6 had the following optimum properties: ε r = 15.06±0.33, Q × f = 28,300±600 GHz (f = 10.1 GHz), and τ f = 0.9±3.4 ppm/°C. Compared with other reported low permittivity compounds, Li 4 MgWO 6 shows more potential for the Low-Temperature Cofired Ceramics (LTCC) substrate materials due to its intrinsic low sintering temperature, novel temperature stability, and relatively low dielectric loss. [ABSTRACT FROM AUTHOR]

In this contribution, the Li 2 Sn 1- x Ge x O 3 (0 ≤ x ≤ 0.09) ceramics were synthesized by the conventional solid-state reaction method. The XRD patterns revealed that the solid solution was formed in the range of 0 ≤ x ≤ 0.07, and the Li 2 GeO 3 secondary phase was detected in the x = 0.09 sample. The Rietveld refinement results showed a decrease in the cell volume. The crystal structural changes were further verified by TEM and STEM-EDS technologies. Because of the lower atomic weight and smaller ion radius of Ge4+ to that of the Sn4+ ions, the increased ionic diffusion rate improved the average grain sizes and decreased the porosity, but led to abnormal grain growth for x ≥ 0.05. The relative density first increased and then decreased; the relative permittivity (ε r) decreased with the increase of x due to the pronouncedly decreasing ionic polarizability; the Q × f values increased first with the increasing x and deteriorated because of the abnormal grain growth in the x ≥ 0.05 samples; the temperature coefficient of the resonant frequency (τ f) decreased continuously owing to the "polarizability" effect. Typically, the optimum properties were achieved in the x = 0.07 sample that was sintered at 1175 °C for 4 h with ϵ r = 14.53, Q × f = 58,300 GHz (f = 9.9 GHz), and τ f = 2.4 ppm/°C, which is promising for industrial applications. [ABSTRACT FROM AUTHOR]

In this article, the (Mn 1/2 W 1/2)4+ complex cation co-doped ilmenite MgTiO 3 ceramics with improved microwave characteristics were synthesized. The correlations between the crystal structural evolution induced by ionic substitution and the microwave characteristics were investigated using the structural analysis and the P–V–L bond theory. Theoretically, the Mg–O bond should have a larger value of covalency than Ti–O bond, attributing to the distribution of densities of states, where the s and p states of the Mg atom overlap with those of the O atom. This conclusion fits well the bond theory estimation. The dielectric constant is dominated predominantly by the average bond covalency, which is intrinsically caused by the increase of doping contents. Moreover, the structural stability declines slightly with the increase of (Mn 1/2 W 1/2) contents. From the perspective of structural evolution, this dielectric performance is also reflected by the variations of the Raman shift and the FWHM value of A g 5 mode. The actual Q × f value, however, experiences a great enhancement at x = 0.010, which benefits generally from the uniformity of the grain size and the inhibition of reduction of Ti4+ valence. The excellent microwave characteristics of MgTi 0.99 (Mn 1/2 W 1/2) 0.01 O 3 ceramics were achieved: a ε r of 18.74, a Q × f value of 160992 GHz and a τ f of −58.2 ppm/°C, when sintered at 1325 °C. [ABSTRACT FROM AUTHOR]

The effects of LB glass on the sintering behavior, structure, and dielectric properties for the Ba3.75Nd9.5Ti17.5(Cr0.5Nb0.5)0.5O54 (BNTCN) ceramic were investigated. The results showed that the LB glass, as an effective sintering aid, successfully lowered the sintering temperature of BNTCN ceramic by formation of the liquid phase. Furthermore, the change of the structure and decrease in grain size had influences on the electrical conductivity, thermal stability, and microwave dielectric properties for the BNTCN ceramics doped LB glass. Finally, the excellent microwave dielectric properties with εr = 73.4, Q × f = 5277 GHz, and τf = +7.1 ppm/°C were obtained for samples sintered at 950°C when x = 5, indicating the BNTCN ceramic doped with 5 wt% LB glass is a promoting LTCC material. [ABSTRACT FROM AUTHOR]

In this paper, the (1−x)BaTiO3-xBi(Zn1/2Zr1/2)O3 (x = 0.04-0.20) solid solutions were prepared using conventional solid-state reaction method. The X-ray diffraction results showed that all samples were crystalized as the perovskite structure, and there was no secondary phase in whole compositional range. For x = 0.04, the ceramics were in tetragonal phase, and transformed to a pesudocubic phase for x ≥ 0.08 at ambient temperature. Temperature-dependent dielectric measurements indicated a crossover from ferroelectric behavior to relaxor-like characteristics. As the BZZ content increased, the polarization-electric field (P-E) hysteresis loops became slimmer, and the discharge energy density increased firstly, but dropped. For x = 0.12, the maximum discharge energy density was 0.758 J/cm3 at 100 kV/cm, and the corresponding energy efficiency was 98%, indicating that (1−x)BaTiO3-xBi(Zn1/2Zr1/2)O3 ceramics were promising candidates for energy storage applications. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric ceramic Li9Zr3NbO13 was found and investigated. Prepared via the solid‐state reaction method, the Li9Zr3NbO13 formed as a Li2ZrO3‐type solid solution at 880‐900°C, with monoclinic structure in C2/c space group and Z = 4. Typically, the Li9Zr3NbO13 sintered at 900°C exhibited the excellent microwave dielectric properties of εr = 21.3, Q×f = 43 600 GHz (at 7.4 GHz), τf = 7.3 ppm/°C. [ABSTRACT FROM AUTHOR]

In this paper, the Li2/3(1− x)Sn1/3(1− x)Mg xO (LSM xO) ceramic systems were prepared by solid-state reaction using novel atmosphere-controlled sintering ( x = 0-4/7). Pure Li2SnO3 was observed for x = 0, the Li2Mg3SnO6 and Li2SnO3 coexisted for x = 1/7, and the coexistence of three kinds of phases was detected for x = 1/5 and 1/4, including Li4MgSn2O7 impurity phase. Pure Li2Mg3SnO6-like phase with cubic rock salt structure in Fm-3 m space group was obtained in the range of 1/3-4/7. All samples showed well-dense and smooth microstructures. The microwave dielectric properties highly depended on the phase composition, bond valence, FWHM of Raman spectrum, Raman shift, average grain sizes, and octahedral distortion. The LSM xO ceramics sintered at 1250°C for 5 hours possessed excellent comprehensive properties of εr = 15.43, Q×f = 80 902 GHz and τ f = +5.61 ppm/°C for x = 1/7. Typically, the LSM xO ceramics sintered at 1350°C for 5 hours showed a maximum Q × f of 168 330 GHz for x = 1/2. [ABSTRACT FROM AUTHOR]

The BaNdTiCrO (0 ≤ z ≤ 3.0) ceramics were prepared using the solid-state reaction route. The influence of substitution of Cr for Ti on microstructure and microwave dielectric properties of BaNdTiCrO (BNTC z) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that pure BaNdTiO phase with tungsten bronze structure existed for z ≤ 1, but the secondary phase BaTiO was observed for 1.5 ≤ z ≤ 3. The substitution of Cr for Ti was confirmed by the results of scanning electron microscopy and energy dispersive spectrometer. The dielectric constant ( ε ) was deteriorated with the increment of substitution which was in accord with the tendency of apparent density. The quality factor value ( Q× f) was improved by a small amount of substitution for z ≤ 0.5, but deteriorated seriously when excessive Cr content was added ( z > 0.5). The temperature coefficient of the resonant frequency ( τ ) was effectively reduced from + 63 ppm/°C to − 7.1 ppm/°C with the increase of substitution content. At last, the excellent dielectric properties with ε = 81.53, Q× f = 11,294 GHz and τ = + 39.2 ppm/°C were obtained as z = 0.5 sintered at 1420 °C for 2 h. [ABSTRACT FROM AUTHOR]

In this study, the Li 2+ x Mg 3 SnO 6 (L x MS) ceramic systems were prepared by solid-state reaction using novel atmosphere-controlled sintering ( x = 0.00–0.12). The influences of extra lithium contents on the phase evolution, crystal structure and microwave dielectric properties of Li 2+ x Mg 3 SnO 6 (L x MS) ceramics were systematically investigated. As samples were calcined from 800 to 1000 °C, the Li 2 Mg 3 SnO 6 phase was formed from the chemical reaction between Li 2 SnO 3 and MgO phase. Pure Li 2 Mg 3 SnO 6 phase could be observed for samples calcined at 1000–1100 °C. But when it was exposed to high temperature air over 1100 °C, the Li 2 Mg 3 SnO 6 decomposed into Mg 2 SnO 4 , MgO and Li 2 O. Because of the protective atmosphere and extra lithium, the ε r , Q×f and τ f were significantly improved by the suppression of secondary phase and pores for 0.00 ≤ x ≤ 0.08 . However, comprehensive microwave characteristics were deteriorated for 0.08 < x ≤ 0.12 , which were correlated with dielectric polarization, bond valence, FWHM, packing fraction and octahedral distortion. The excellent microwave characteristics of L x MS ( x = 0.08) sintered at 1350 °C in novel controlled atmosphere were obtained : ε r = 12.7, Q×f = 168,330 GHz and τ f = −27.4 ppm/°C. [ABSTRACT FROM AUTHOR]

The microstructure and microwave dielectric characteristics of (BaSr)NdTi(ZnNb)O ceramics solid solutions (0 ≤ x ≤ 2.5) were investigated in this study. X-ray diffraction indicated that only BaNdTiO existed in the sintered samples when x value was lower than 2.0, but subsequently a new phase generated with increasing of x value. The dielectric constant (ε) of the samples increased slightly from 83.4 to 85.2 before falling down and quality factor value (Q × f) declined radically from 10,873 to 1321 GHz at optimum sintering temperature of 1450 °C, as x value increased from 0.0 to 2.5. And the temperature coefficient of resonant frequency (τ) could be adjusted to a minimum value and then rebounded because of the second phase NdNbTiO which also sharply deteriorated the quality factor of the samples. At last, the excellent microwave dielectric properties of the samples with values of ε = 85.2, Q × f = 5989 GHz, τ = +14.9 ppm/°C were obtained as x was 1.0 sintered at 1450 °C for 3 h in air. [ABSTRACT FROM AUTHOR]

This study introduced a novel low-loss tungstate ceramic, La 7 Nb 3 W 4 O 30 (LNWO), synthesized using the solid-state techniques. The structural analysis of the La 7 Nb 3 W 4 O 30 ceramic material, utilizing X-ray diffraction (XRD) patterns and followed by detailed structural refinement, validated its rhombohedral structure. Transmission electron microscopy (TEM) was utilized to confirm the ordered layer arrangement characteristic of the rhombohedral structure. The internal structure was characterized by scanning electron microscopy (SEM), with the sample's relative density reaching 97.5 %. The correlation between the full width at half maximum (FWHM) of the Raman matrix at 901 cm−1 corresponding to the symmetric bending mode vibrations of WO 5 and the Q × f value was discussed. Furthermore, the main factors affecting the dielectric constant, including density, bond valence, secondary phases, and variations in porosity, were analyzed. Encouragingly, the ceramic showed significant microwave dielectric properties when it was sintered at 1425 °C (ε r = 23.68, Q × f = 26,687 GHz (f = 7.2 GHz), τ f = −35.2 ppm/°C). [ABSTRACT FROM AUTHOR]

A novel Li 4 AlSbO 6 (LASO) microwave dielectric ceramic with a monoclinic structure and space group C12/c1 was successfully prepared using traditional solid-state methods. When the sintering temperature was 1200 °C, it had excellent microwave dielectric properties, with ε r = 8.2, Q × f = 22,098 GHz, and τ f = −15.53 ppm/°C. Raman spectroscopy analysis showed that the FWHM of the strong peak at 691 cm−1 reflected the variation trend of Q × f value and was opposite to the variation trend of Q × f value. Additionally, the augmentation in the Q × f value can be attributed to a higher relative density. As per the bond valence analysis, ε r is closely connected to the rattling and compressing effects of A-site cations, and the higher ε theo than ε r in Li 4 AlSbO 6 can be attributed to the strong compression effect induced by Li+. Additionally, τ f may be influenced by both the Sb–O bond and relative density. [ABSTRACT FROM AUTHOR]

The CaMg 1 -x Cr 2 x /3 Si 2 O 6 (0 ≤ x ≤ 0.1) microwave dielectric ceramics were synthesized via conventional solid state reaction. In this study, the effects of Cr3+ substituting for Mg2+ on morphology, crystal structure and microwave dielectric properties of CaMg 1 -x Cr 2 x /3 Si 2 O 6 ceramics were explored. XRD diffraction patterns exhibited that the CaMg 1 -x Cr 2 x /3 Si 2 O 6 ceramics possessed the pure phase of CaMgSi 2 O 6 when x ≤ 0.06 and a small amount of secondary phase Ca 3 Cr 2 (SiO 4) 3 for 0.08 ≤ x ≤ 0.1. SEM micrographs revealed that the substitution of Mg2+ with Cr3+ could decrease the grain size. The apparent density was affected by the concentration of Mg vacancies. The correlation between crystal structure and microwave dielectric properties was investigated through the Rietveld refinement and Raman analysis. The microwave dielectric properties were mainly dependent on relative density, ionic polarizabilities, internal strain Ƞ, disordered structure and MgO 6 octahedron distortions. Finally, CaMg 1 -x Cr 2 x /3 Si 2 O 6 (x = 0.02) ceramics sintered at 1270 °C for 3 h exhibited excellent microwave dielectric properties of ε r = 8.06, Q × f = 89054 GHz, τ f = −44.92182 ppm/ºC. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation into the dielectric properties of LiY 9 Si 6 O 26 ceramics, which were prepared for the first time using the solid-state method. XRD patterns and Rietveld refinement analysis conclusively demonstrate that LiY 9 Si 6 O 26 adopts a hexagonal crystal structure with space group P63/m (176). Furthermore, Raman spectroscopy reveals a significant correlation between the quality factor and the FWHM of the A 1g (O) mode at 879 cm−1. Transmission electron microscopy (TEM) was employed to verify the ordered layered structure inherent in the hexagonal LiY 9 Si 6 O 26 ceramics. The microstructure of the ceramic grains was analysed using scanning electron microscopy (SEM), which revealed a remarkably high relative density of 96.4% for the LiY 9 Si 6 O 26 ceramic. The Si–O bond valences (V Si – O) were found to be closely associated with the τ f in LiY 9 Si 6 O 26 ceramics. Remarkably, the microwave dielectric properties of LiY 9 Si 6 O 26 ceramics sintered at 1425 °C were ascertained to be ε r = 10.54, Q × f = 25,579 GHz (f = 10.3 GHz), and τ f = 2.64 ppm/°C. These outstanding properties position LiY 9 Si 6 O 26 ceramics as promising candidates for high-performance dielectric materials. [ABSTRACT FROM AUTHOR]

Abstract: The microwave dielectric ceramic Li9Zr3NbO13 was found and investigated. Prepared via the solid‐state reaction method, the Li9Zr3NbO13 formed as a Li2ZrO3‐type solid solution at 880‐900°C, with monoclinic structure in C2/c space group and Z = 4. Typically, the Li9Zr3NbO13 sintered at 900°C exhibited the excellent microwave dielectric properties of εr = 21.3, Q×f = 43 600 GHz (at 7.4 GHz), τf = 7.3 ppm/°C. [ABSTRACT FROM AUTHOR]

Novel walstromite-type MCa 2 Si 3 O 9 (M = Ba, Sr) ceramics, with triclinic space group P-1 , were prepared through a solid-state reaction method. The P–V-L theory proves that the lattice energy and bond energy of the Si–O bond play a leading role in the quality factor and the dielectric constant is mainly determined by the ionic polarization. Excellent microwave dielectric properties of BaCa 2 Si 3 O 9 and SrCa 2 Si 3 O 9 ceramics could be obtained: ε r = 8.99 ± 0.23, Q × f = 44,542 ± 500 GHz, and τ f = −25.9 ± 3.0 ppm/°C and ε r = 7.39 ± 0.23, Q × f = 48,772 ± 500 GHz, and τ f = −27.5 ± 3.0 ppm/°C, when sintered at 1240/1280 °C for 4 h. Then SrCa 2 Si 3 O 9 ceramic is applied to a new microstrip bandpass filter, because of its high microwave dielectric properties and low thermal expansion coefficient. With reduced dimension, the filtering performance of the circuit is also highly improved, including reduced capacitor parasitic effect and the optimized stopband insertion loss. Accordingly, the SrCa 2 Si 3 O 9 ceramic is a promising candidate for sub-6 GHz a filter of microstrip bandpass applications. [ABSTRACT FROM AUTHOR]

This research demonstrates the microwave dielectric properties of Ba 2 Bi 2/3 TeO 6 ceramics, synthesized for the first time via the solid-state method, for LTCC applications. The analysis of X-ray diffraction (XRD) patterns and structural refinement verify the double perovskite structure of Ba 2 Bi 2/3 TeO 6 ceramics. Transmission electron microscopy (TEM) validates the ordered layered structure of the double perovskite Ba 2 Bi 2/3 TeO 6 ceramics. Scanning electron microscopy (SEM) characterizes the grain microstructure, revealing a relative density of 99.1% for the sample. An inverse proportionality is observed between the Raman full-width at half maximum (FWHM) and the Q × f value. X-ray photoelectron spectroscopy (XPS) elucidates the chemical composition and valence states of the Ba 2 Bi 2/3 TeO 6 ceramic elements. The microwave dielectric properties of Ba 2 Bi 2/3 TeO 6 ceramics calcined at 935 °C were discovered to be ε r = 11.94, Q × f = 21,579 GHz (f = 9.8 GHz), and τ f = −22.4 ppm/°C. Ba 2 Bi 2/3 TeO 6 ceramics emerge as an excellent candidate for LTCC applications. [ABSTRACT FROM AUTHOR]

Ceramics of Y 2 GaSbO 7 (YGSO) were prepared by the solid-state reaction method. The ceramics were confirmed by XRD and TEM to exhibit the Fd-3 m (227) space group and a cubic pyrochlore structure within the temperature range of 1420–1500 °C. XPS verified that the valence states of Y, Ga, and Sb in the ceramics were + 3, + 3, and + 5, respectively. Additionally, the relationship between the FWHM of the notable peak at 775 cm−1 and the Q × f value was elucidated through Raman spectroscopic analysis. The analysis of the P-V-L theory revealed that the Sb-O bond is crucial in determining ε r , while the values of τ f and Q × f are affected by the Y-O bond. At 1460 °C, YGSO ceramics obtained the maximum relative density (97.5%) and the best microwave dielectric properties (ε r = 14.78, Q × f = 50,153 GHz, and τ f = –22.3 ppm/°C). • For the first time, a Y 2 GaSbO 7 microwave dielectric ceramic with a pyrochlore structure was discovered. • The Raman spectra of the ceramics were analyzed, and the valence state was studied using XPS. • TEM analysis confirmed the cubic structure of Y 2 GaSbO 7 ceramics. • SEM images revealed the microstructure of the ceramic grains, with the maximum relative density reaching 97.5%. • The relationship between α , f i , E b , U b , and the dielectric properties of Y 2 GaSbO 7 ceramics was examined using P-V-L theory. [ABSTRACT FROM AUTHOR]

Novel lead-free ceramics of (1- x)BaTiO 3 - x Bi(Mg 1/2 Sn 1/2)O 3 (abbreviated as (1- x)BT- x BMS, with x = 0–0.20) were fabricated through a solid-state reaction route. Introducing BMS into the BT host triggered a ferroelectric-to-relaxor phase transition, which yielded slim polarization-electric field (P - E) loops and enhanced energy-storage performances. The large recoverable energy density with 2.25 J/cm3 and high energy efficiency of 94% were obtained simultaneously under 240 kV/cm with x = 0.12. Furthermore, the energy storage characteristics of the 0.88BT-0.12BMS ceramics exhibited good temperature stability in the range of −55–150 °C, and great frequency stability in the range of 10–1000 Hz. Meanwhile, by means of pulsed charging-discharging evaluation, the 0.88BT-0.12BMS ceramics displayed a fast discharge period of 73 ns and a large power density of 27.7 MW/cm3. The results indicate that the elaborately designed 0.88BT-0.12BNS ceramics have promising potential for high-power pulsed capacitor applications. • Bi(Mg 1/2 Sn 1/2)O 3 doping can trigger a phase transition from ferroelectric to relaxor ferroelectric. • A large recoverable energy density of 2.25 J/cm3 and a high energy efficiency of 94% can be obtained simultaneously. • The energy properties show excellent thermal and frequency stability. • A large power density of 27.7 MW/cm3 can be obtained at 100 kV/cm. [ABSTRACT FROM AUTHOR]

Electrocaloric (EC) refrigeration materials have seen significant progress recently, with efficient Barium titanate-based (BT-based) lead-free materials particularly promising for microelectronics applications. However, their performance still lags behind their lead-based counterparts, highlighting the need for further improvements. This study employs a novel density adjustment strategy (DAS) to enhance the EC performance of (0.5- x)BCT-BTZ- x BST ceramics by carefully balancing the relationships among density, dielectric breakdown strength (BDS), and Δ T. Although Δ T intuitively decreases with increasing density, enhanced BDS can partially compensate for this decrease. An excellent EC performance with Δ T of 2.21 K and Δ T /Δ E of 0.471 K mm kV−1 is obtained in x = 0.5, together with a broader temperature span of 50.3 °C near room temperature, which surpasses or is comparable to other lead-free or lead-based ones. The results suggest that the DAS provides a promising approach for developing efficient EC, making speediness of application in EC devices. [Display omitted] • Developed innovative density adjustment strategy (DAS) for (0.5- x)BCT-BTZ- x BST ceramics to reconcile ρ and Δ T relationship. • Excellent EC properties (Δ T = 2.21 K, Δ T /Δ E = 0.471 K mm kV−1, T span =50.3 ℃) achieved by balancing ρ, BDS, and Δ T. • Identified physical mechanisms responsible for enhanced EC properties. [ABSTRACT FROM AUTHOR]

In this paper, Sr 2 Ga 2 GeO 7 (SGG) ceramics were prepared by the solid-state method, and their microwave dielectric properties were studied. The XRD and TEM analyses show that the ceramic samples all acknowledged a tetragonal structure with the P-412 m (113) space group. The refinement results show that the lattice parameters of the ceramics sintered at 1360 °C are a = b = 8.04553 Å, c = 5.39084 Å and V = 348.9517 Å3. The Sr 2 Ga 2 GeO 7 ceramics sintered at 1360 °C have a compact microstructure, and the optimum relative density is 97.5 %. Raman spectroscopy exhibited that the quality factor shows a close connection with the FWHM of the A 1 g mode at 785 cm–1. The microwave dielectric properties of Sr 2 Ga 2 GeO 7 ceramics sintered at 1360 °C were found to be ε r = 6.52, Q × f = 32,685 GHz (f = 12.99 GHz), and τ f = –37.15 ppm/°C. • A novel tetragonal Sr 2 Ga 2 GeO 7 microwave dielectric ceramic with low dielectric constant and low loss was first discovered: ε r = 6.52, Q × f = 32,685 GHz (f = 12.99 GHz), and τ f = –37.15 ppm/°C. • We analyzed the relationship between Raman spectroscopy and microwave dielectric properties. • TEM analysis confirmed the ordered layered structure of tetragonal Sr 2 Ga 2 GeO 7 ceramics. • SEM images revealed the microstructure of the ceramic grains, with the maximum relative density reaching 97.5 %. [ABSTRACT FROM AUTHOR]

Abstract The Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x (Zn 1/3 Ta 2/3) x O 3 (0 ≤ x ≤ 0.12) ceramics were prepared using the solid-state reaction route. The influence of substitution of (Zn 1/3 Ta 2/3)4+ for Ti4+ on microstructure and microwave dielectric properties of Ca 0.35 Li 0.25 Nd 0.35 Ti 1- x (Zn 1/3 Ta 2/3) x O 3 (CLNT(ZT) x) ceramics was investigated in this study. The X-ray diffraction patterns (XRD) of the specimens showed that the ceramics with x ≤ 0.06 were crystallized as an orthorhombic perovskite structure in Pnma space group. However, the secondary phase of Nd 2 Ti 2 O 7 was observed with properties of 0.08 ≤ x ≤ 0.12. The analysis results of Raman spectra revealed the existence of oxygen octahedral distortion and the short-range ordering occurred in CLNT(ZT) x ceramics with the change of (Zn 1/3 Ta 2/3)4+ content. The dielectric constant (ε r) increased firstly and then decreased gradually when substitution increased, and the variation of ε r was affected by the B-site bond valence. The quality factor value (Q × f) was improved by right amount of substitution when x ≤ 0.08, but deteriorated seriously as excessive (Zn 1/3 Ta 2/3)4+ content was added (x ≥ 0.10). The temperature coefficient of the resonant frequency (τ f) was effectively reduced from +90.9 ppm/ºC to +30.3 ppm/ºC with the increasing of substitution due to the declination of tolerant factor (t). At last, the CLNT(ZT)0.08 ceramics sintered at 1250 °C for 4 h exhibited the excellent comprehensive dielectric properties with ε r = 120.63, Q × f = 3889 GHz, τ f = +60.9 ppm/ºC. [ABSTRACT FROM AUTHOR]

In this contribution, we synthesized a novel Li 5 ZnSnNbO 8 ceramics with the traditional solid-state reaction. The correlations between microwave performance and crystal structures were systematically studied. According to the XRD result, the Li 5 ZnSnNbO 8 formed a rock salt structure, belongs to Fm-3m (225) space group, which can be further confirmed by the Rietveld refinement method. By observing the SEM photograph and measuring the density, it is found that the sample has the highest degree of densification. Typically, the Li 5 ZnSnNbO 8 ceramic sintered at 1250 °C for 4 h exhibited the excellent microwave dielectric performance of ε r = 17.17, Q × f = 51519 GHz and τ f = −28.2 ppm/°C. [Display omitted] • The sintering behavior of a new compound Li 5 ZnSnNbO 8. • The structure-property relationship via Structural Rietveld refinement. • The excellent microwave dielectric properties of Li 5 ZnSnNbO 8. • The three-component solid solution system. [ABSTRACT FROM AUTHOR]

The structure and properties of Ca 0.61 Nd 0.26 Ti 1- x Al x O 3 (0 ≤ x ≤ 0.05) ceramics are explored by using XRD, SEM, Raman spectrometer, TEM, XPS, etc. All compositions are formed the main phase with orthorhombic perovskite structure, whereas the second phase TiO 2 exists in the range of x = 0.02–0.05. The Rietveld refinement results show that the lattice parameters and the unit cell volume decrease as x value increases, and the ε r and τ f values decline. The Raman spectra prove that the A g (3) mode related to the Ti O bending is blunted, owing to the increasing average lattice energy values of Ti/Al-O bond. This result implies the oxygen octahedral structure becomes more stable with increasing content of Al3+, which is in favor of the decline of the positive τ f values for Ca 0.61 Nd 0.26 Ti 1- x Al x O 3 samples. The generation of Ti3+ has been restrained when x = 0.01, which is confirmed by XPS results. Meanwhile, the 1:1 ordered areas are detected in sample at x = 0.05 by HRTEM, and the corresponding SAED patterns present faint spots among the bright diffraction spots, indicating the super-lattice structure. Consequently, the Q × f value dramatically increases from 11,356 GHz at x = 0 to 18,128 GHz at x = 0.05 for Ca 0.61 Nd 0.26 Ti 1- x Al x O 3 samples. [Display omitted] • The reduction of Ti4+ has been suppressed at x = 0.01. • The 1:1 ordered areas have been observed by TEM. • The suppression of Ti3+ and the Ti/Al 1:1 ordering areas contribute to the improvement of Q × f value for Ca 0.61 Nd 0.26 Ti 1- x Al x O 3 ceramic. [ABSTRACT FROM AUTHOR]

We studied the phase constitutions, microstructure, chemical bond and microwave dielectric properties for Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 (0 ≤ x ≤ 0.03) ceramics synthesized by solid-state reaction using SEM, X-ray diffractometer, Raman spectroscopy, microwave measuring system, etc. Although the second phase TiO 2 appeared when x ≥ 0.015 as presented in XRD patterns, TiO 2 was confirmed to have no effects on the tendency of microwave dielectric properties as a function of x value. The SEM images showed that the grain size decreased as Cr content increased, which could be explained by that doping Cr increased the grain boundary energy or decreased surface energy for Ca 0.61 Nd 0.26 TiO 3 ceramic. The SRO effects enhanced with increase of Cr substitution, which was verified by Raman spectra. The dielectric constant and τ f value were concerned with the average ionicity of chemical bond and the ionic polarizability for Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 ceramics. The SEM images suggested that the optimized sintering temperatures was 1400 °C for samples with x = 0.01. The XPS spectra and the trend of Q × f value indicated that the balanced amount of Cr substitution could restrain the generation of Ti3+. Hence, the Q × f value of Ca 0.61 Nd 0.26 Ti 1- x Cr x O 3 ceramics reached the maximum of 16,078 GHz at x = 0.01 compared with that of 11,425 GHz in pure Ca 0.61 Nd 0.26 TiO 3 ceramic. • The Ca 0.61 Nd 0.26 Ti 0.99 Cr 0. 0 1 O 3 ceramic had maximum Q × f value of 16,078 GHz. • The SRO effect enhanced with increase of Cr3+. • The balanced amount of Cr substitution could restrain the generation of Ti3+. [ABSTRACT FROM AUTHOR]