Negative Τf Value Research Articles

Investigations of crystal structure, phase compositions and intrinsic dielectric properties of novel Ba2RE2Si4O13 ceramics by bond theory and infrared spectroscopy

Novel Ba2RE2Si4O13 (RE = La, Nd, Sm, Eu, Gd, Ho, Er and Yb) ceramics were prepared by traditional solid reaction methods. The phase compositions of Ba2RE2Si4O13 ceramics were explored. The triclinic structure with P1¯ space group of Ba2RE2Si4O13 ceramics was confirmed by TEM and Rietveld refinement analyses, and the decrease in the ionic radius of RE3+ induced the phase transition from low symmetry (triclinic) to high symmetry (monoclinic) between Ba2Sm2Si4O13 and Ba2Eu2Si4O13. εr-exp of the Ba2RE2Si4O13 ceramics was significantly affected by ionic polarisability. The ‘rattling and compressing effects’ of cations also affected the εr-exp of Ba2RE2Si4O13 ceramics. The intrinsic dielectric loss of Ba2RE2Si4O13 ceramics were evaluated by the far-IR reflectivity spectrum, and high Q × f values of the Ba2Nd2Si4O13 and Ba2Eu2Si4O13 ceramics were attributed to their large total lattice energy and activation energy. The average bond valence of RE3+ played an important role in controlling the τf values of the Ba2RE2Si4O13 single-phase ceramics, and the high average bond valence of RE3+ corresponded with the small negative τf values. Great microwave dielectric properties (εr = 11.52, Q × f = 33,600 GHz at 11.80 GHz and τf = ‒25.6 ppm/ °C) were obtained in the Ba2Nd2Si4O13 single-phase ceramic.

Phase composition, crystal structures and enhanced microwave dielectric properties of Mg2+/Zr4+ co-doped Al2Mo3O12 ceramics

In this work, the substitution of Al3+ by Zr/Mg in Al2Mo3O12 was designed to enhance the quality factor while simultaneously adjusting the thermal stability of the resonant frequency. The Al2–2x(Zr0.5Mg0.5)2xMo3O12 (AMZM) (0.1 ≤ x ≤ 0.5) ceramics were synthesized using a simple solid-state method, resulting in all components exhibiting single-phase crystallinity and a dense structure. A phase transition temperature below room temperature was observed when x ≥ 0.4. Furthermore, the quality factor of the synthesized samples, compared to pure-phase Al2Mo3O12 (εr = 6.79, Q×f = 28471 GHz, τf = −48.77 ppm/℃), increased by nearly threefold. A detailed investigation of the crystal structure of the samples was conducted through Rietveld refinement. The composition with x = 0.3 (monoclinic phase) exhibited optimal dielectric performance after sintering at 800 ℃ for 6 h: εr = 7.84, Q×f = 86511 GHz, τf = −42.08 ppm/℃. By forming a composite ceramic with (Li1/2Sm1/2)MoO4, the negative τf value was further adjusted to near zero.

Microwave dielectric properties of NaMgF3 ceramic

Microwave dielectric properties of NaMgF3 ceramics prepared by reactive sintering (RS) and conventional sintering (CS) processes have been reported in this paper. Phase pure NaMgF3 ceramics with relative densities of ∼95% could be obtained at 800–950 °C/2h by both sintering processes. The RS sample demonstrates lower sintering activation energy and a much large grain size compared with the CS sample. Both densified samples exhibit similar microwave dielectric properties: εr ∼ 6.9, Q × f value ∼63000 GHz, and τf ∼ −114 ppm/°C. However, the large negative τf value needs to be further improved for practical applications.

Microwave dielectric properties of LiZn4V3O12 composite ceramics sintered at low temperature and its LTCC application

The solid-state method was used to prepare LiZn4V3O12 ceramics. The phase composition, crystal structure and micromorphology of ceramics were studied in detai. The XRD data and rietveld refinement revealed that LiZn4V3O12 ceramics were composed of LiZnVO4 and Zn3V2O8, with a content ratio of 1:3. The results indicate that the εr and Q × f value of LiZn4V3O12 ceramics were related to the relative density. When the LiZn4V3O12 ceramics sintered at, 720 °C for 4 h, possessed a high relative density (96.71%), a low εr value (11.51), a high Q × f value (53891 GHz (11.5 GHz)), and a negative τf value (−25.58 ppm/°C). The XRD and SEM analyses have demonstrated that LiZn4V3O12 ceramic can coexist with the Ag electrode, indicating there is the great potential for application in the field in LTCC application.

Evolution of Phase Transformation on Microwave Dielectric Properties of BaSixO1+2x Ceramics and Their Temperature-Stable LTCC Materials

BaSixO1+2x (1.61 ≤ x ≤ 1.90) and LiF-doped BaSi1.63O4.26 ceramics were prepared by using a traditional solid-state method at the optimal sintering temperatures. The evolution of phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.9) ceramics was revealed. The coexistence of Ba5Si8O21 and Ba3Si5O13 phases was obtained in BaSixO1+2x (1.61 ≤ x ≤ 1.67) ceramics. The BaSi2O5 phase appeared inBaSixO1+2x (1.68 ≤ x ≤ 1.90) ceramics. At 1.68 ≤ x ≤ 1.69, only BaSi2O5 and Ba3Si5O13 phases existed. With the further increase in x, the Ba5Si8O21 phase appeared, and BaSi2O5, Ba5Si8O21 and Ba3Si5O13 phases coexisted in BaSixO1+2x (1.70 ≤ x ≤ 1.90) ceramics. The phase compositions of BaSixO1+2x (1.61 ≤ x ≤ 1.90) ceramics were controlled by the ratio of Ba:Si. The BaSixO1+2x (x = 1.68) ceramics with 98.15 wt% Ba3Si5O13 and 1.85 wt% BaSi2O5 phases exhibited a negative τf value (−37.53 ppm/°C), and the good microwave dielectric properties of εr = 7.51, Q × f = 13,038 GHz and τf = +3.95 ppm/°C were obtained for BaSi1.63O4.26 ceramics with 70.05 wt% Ba5Si8O21 and 29.95 wt% Ba3Si5O13 phases. The addition of LiF sintering aids were able to reduce the sintering temperatures of BaSi1.63O4.26 ceramics to 800 °C. The phase composition of BaSi1.63O4.26 ceramics was affected by the sintering temperature, and the coexistence of Ba5Si8O21, Ba2Si3O8, BaSi2O5 and SiO2 phases was achieved in BaSi1.63O4.26-3 wt% LiF ceramics. The BaSi1.63O4.26-3 wt% LiF ceramics sintered at 800 °C exhibited dense microstructures and excellent microwave dielectric properties (εr = 7.10, Q × f = 12,463 GHz and τf = +5.75 ppm/°C), and no chemical reaction occurred between BaSi1.63O4.26-3 wt% LiF ceramics and the Ag electrodes, which indicates their potential for low-temperature co-fired ceramic (LTCC) applications.

ZnZr1−xHfxNb2O8-yTiO2-ZnZr1−xHfxNb2O8 (0.000 [formula omitted] x [formula omitted] 0.030, 0.01 [formula omitted] y [formula omitted] 0.06): An high-Q and temperature-stable microwave dielectric ceramic through laminated co-firing technique

In order to better fulfill the requirements high-performance dielectric devices for low insertion loss, compact size, and excellent temperature stability, we propose a strategy to maximize the comprehensive regulation of microwave dielectric properties. Since TiO2 has a relatively large and positive τf value, direct addition of TiO2 has often been utilized to modify the negative τf value in previous studies. In this paper, TiO2 and the laminated co-firing technique are applied to monoclinic wolframite structural ceramics. Tri-layer architectural ZnZr1−xHfxNb2O8-yTiO2-ZnZr1−xHfxNb2O8 (0.000 ≤ x ≤ 0.030, 0.01 ≤ y ≤ 0.06) ceramics were synthesized by the laminated co-firing technique. Firstly, Hf4+ ions substituted for Zr4+ ions to significantly enhance the Q×f value of ZnZrNb2O8 system. The modulation effect of Hf4+ on the crystal structure and the influence on the dielectric constant (εr), Q×f, and τf values were reasonably demonstrated by combining several characterization approaches with complex chemical bond theory. Compared with pure ZnZrNb2O8, the ZnZr0.990Hf0.010Nb2O8 ceramic achieved a nearly 65% increase in the Q×f value without excessive deterioration of other dielectric parameters. The laminated co-firing technique was then used to further modulate its εr and τf values. Notably, the ZnZr0.990Hf0.010Nb2O8-0.05TiO2-ZnZr0.990Hf0.010Nb2O8 tri-layer architectural ceramic achieved prominent comprehensive microwave dielectric characteristics: εr = 34.34, Q×f = 53,860 GHz, and τf = + 2.29 ppm/°C, making the tri-layer architecture ceramics attractive for usage in modern microwave communications.

An evaluation of the impact of crystal structure on microwave dielectric properties of novel titanite-type CaMGeO5 ceramics

Novel titanite-type CaMGeO5 (M = Ge, Hf, Zr) microwave dielectric ceramics were prepared using solid-state reaction. A CaGe2O5 single-phase ceramic with a triclinic structure was obtained, and the main phase compositions and crystal structure of CaMGeO5 (M = Hf, Zr) ceramics were confirmed. The CaGe2O5 single-phase ceramic exhibited a high Q×f value (92,400 GHz), and its Q×f values were controlled by the rc (Ge-O) and the packing fraction. For CaMGeO5 (M = Hf, Zr) multi-phase ceramics, the Q×f values were deteriorated by the second phase. The τf and τε values of the CaMGeO5 ceramics were directly controlled by the εr anomaly peaks, and the phase transitions were controlled by −δ. The τf values of the CaMGeO5 (M = Ge, Hf, Zr) ceramics were mainly related to −δ, and the small −δ corresponded to the nearer-zero τf values for the titanite-type CaMGeO5 ceramic with negative τf values. The optimal microwave dielectric properties (εr = 10.57, Q×f = 92,400 GHz at 13.22 GHz, and τf = 68.3 ppm/°C) were obtained by the CaGe2O5 ceramic.

L2Ti0.85(Mg1/3Nb2/3)0.15O3/MgTiO3/L2Ti0.85 (Mg1/3Nb2/3)0.15O3 tri-layer co-fired microwave dielectric ceramics: A strategy to suppress non-linear variation of resonant frequency with temperature and achieve a high Q value

In many microwave dielectric ceramics systems, like MgTiO3–CaTiO3, MgTiO3–SrTiO3, and tri-layer MgTiO3/TiO2/MgTiO3, the resonant frequency shows a non-linear variation over a wide temperature range (−40 – 105 °C), indicating that the negative τf (−40 – 25 °C) value deviates from zero when the positive τf (25–105 °C) value is tuned to zero. To suppress the non-linear variation of resonant frequency in the range of −40 – 105 °C, a well-established and efficacious method has been proposed by introducing Li2Ti0.85(Mg1/3Nb2/3)0.15O3 ceramic to the MgTiO3 system. Furthermore, a tri-layer architecture ceramic was designed to improve the dielectric properties. Compared with randomly distributed samples, the Q × f value can be increased by up to 51%. Moreover, the electric field distribution was simulated by the finite element method with the aid of the eigenmode solver of high frequency structure simulator (HFSS) to clarify the dielectric mechanism and predict the microwave dielectric characteristics of the tri-layer structure ceramics. Finally, tri-layer Li2Ti0.85(Mg1/3Nb2/3)0.15O3/MgTiO3/Li2Ti0.85(Mg1/3Nb2/3)0.15O3 ceramic with wide temperature stability and high Q × f value was obtained [εr = 18.4, Q × f = 85 000 GHz, τf+ = −3.8 ppm/°C (25–105 °C), τf− = 4.0 ppm/°C (−40 – 25 °C)], which refines the theory of non-linear variation of resonant frequency and holds promise for application in the 5G communication system.

LiCuVO4: A low-firing microwave material with promising dielectric properties and chemical compatibility with silver

Dense LiCuVO4 ceramics with a relative density of 95% were facilely fabricated using a conventional solid-state method at low temperatures (∼660 °C). Promising microwave dielectric properties were obtained with a moderate relative permittivity (εr) of 16.9 ± 0.3 and a quality factor (Q × f) of 15,200 ± 300 GHz, but poor temperature stability of the resonance frequency (τf ∼ −61.5 ± 3 ppm/°C). To compensate for the negative τf value, rutile TiO2 with a positive τf value was added to form a series of composite ceramics (1-x)LiCuVO4-xTiO2. As regards, a zero-close τf value (∼−1.4 ppm/°C) was achieved at x = 0.6 compositions with an εr of 18.6 ± 0.3 and a Q × f of 18,000 ± 400 GHz. Additionally, the LiCuVO4 ceramic has good chemical compatibility with silver electrodes. All results support the prospective applications of LiCuVO4 in low-temperature cofired ceramics (LTCC) as substrates.

Characterization of structure and chemical bond in high-Q microwave dielectric ceramics LiM2GaTi2O8 (M = Mg, Zn)

LiM2GaTi2O8 (M = Mg, Zn) ceramics with the Fd-3m space group were synthesized using the solid-state method. In comparison with Mg2+ that fully occupied the tetrahedral (A) site in LiMg2GaTi2O8, LiZn2GaTi2O8 was jointly occupied by Zn2+ and Li+ at the A site. Excellent microwave dielectric properties of Q×f = 133,400 ± 500 GHz, 101,800 ± 500 GHz, εr = 17.1 ± 0.2, 15.8 ± 0.2, and τf = −60.1 ± 3.0 ppm/°C, − 42.2 ± 3.0 ppm/°C for LiZn2GaTi2O8 and LiMg2GaTi2O8 were obtained, respectively. The large deviations (30.3% for LiMg2GaTi2O8 and 19.6% for LiZn2GaTi2O8) between the corrected εcorr and theoretical εth were observed, which might be attributed to the underestimated Shannon’s ionic polarizability of Ti4+ in Ti-containing spinels. Their intrinsic microwave dielectric properties were discussed based on bond valence, lattice energy (U), and B-site bond energy (E). Besides, their large negative τf values were compensated to near-zero by CaTiO3.

Temperature stable Li5.5Nb1.5O6F-based microwave dielectric ceramics for LTCC applications

Herein, low-fired (1−x)Li5.5Nb1.5O6F–xBa3(VO4)2 (x = 0, 0.15, 0.2, 0.25 and 0.3) composite ceramics were fabricated using a standard solid-state reaction method. The X-ray diffraction and Rietveld refinement results demonstrated that the Li5.5Nb1.5O6F ceramics crystallised in a cubic rock-salt structure. Based on the refined crystal parameters, the calculated εr was highly close to the measured value. The variation in Q × f values was mainly controlled by the density and packing fraction. The single-phase Li5.5Nb1.5O6F ceramic sintered at 875 °C displayed satisfactory dielectric properties: εr = 17.05, Q × f = 77,500 GHz and τf = −44.1 ppm/°C. Considering of the relatively large negative τf value of the Li5.5Nb1.5O6F ceramic, different mole ratios of Ba3(VO4)2 were added to enhance its temperature stability. The τf value increased continuously as the Ba3(VO4)2 amount increased. When x = 0.25, the optimal microwave dielectric properties were achieved for the composite ceramics at 875 °C, with εr = 16.68, Q × f = 55,800 GHz and τf = −1.7 ppm/°C at a frequency of 7.68 GHz. Such samples were compatible with the Ag electrodes and would be a promising candidate for low-temperature cofired ceramics applications.

Modulation of microwave dielectric properties in melilite-structured SrREGa3O7 (RE = La, Pr) ceramics

Gallium-based SrREGa3O7 (RE = La, Pr) melilite ceramics were prepared and selected to modify their microwave dielectric properties. Sintered at 1425 °C for 6 h, SrLaGa3O7 (SLGO) and SrPrGa3O7 (SPGO) ceramics exhibited high relative densities of 98.33 and 95.23%, low εr values of 11.8 and 10.9, Q×f values of 32,500 GHz (at 12.1 GHz) and 26,400 GHz (at 12.7 GHz), negative τf values of −32 and −54 ppm/°C. As a compensator, CaTiO3 can tune the τf values of SLGO and SPGO to near zero (+2 and −4 ppm/°C). In SrREGa3O7 melilite ceramics, the εr and τf values are mainly dependent on ionic polarizability, crystal structure and the “rattling” effect. The micromorphology, XPS, Raman spectrum and A-site bond valence (VRE) of SrREGa3O7 (RE = La, Pr) microwave dielectric ceramics have also been comprehensively reported.

Compositional modulation in ZnGa2O4 via Zn2+/Ge4+ co-doping to simultaneously lower sintering temperature and improve microwave dielectric properties

AB2O4-type spinels with low relative permittivity (εr) and high quality factor (Q × f) are crucial to high-speed signal propagation systems. In this work, Zn2+/Ge4+ co-doping to substitute Ga3+ in ZnGa2O4 was designed to lower the sintering temperature and adjust the thermal stability of resonance frequency simultaneously. Zn1+xGa2−2xGexO4 (0.1 ⩽ x ⩽ 0.5) ceramics were synthesised by the conventional solid-state method. Zn2+/Ge4+ co-substitution induced minimal variation in the macroscopical spinel structure, which effectively lowered the sintering temperature from 1385 to 1250 °C. All compositions crystallized in a normal spinel structure and exhibited dense microstructures and excellent microwave dielectric properties. The compositional dependent quality factor was related to the microstructural variation, being confirmed by Raman features. A composition with x = 0.3 shows the best dielectric properties with εr ≈ 10.09, Q × f ≈ 112,700 THz, and τf ≈ −75.6 ppm/°C. The negative τf value was further adjusted to be near-zero through the formation of composite ceramics with TiO2.

Temperature‐stable BaAl2Si2O8–CaSnSiO5 microwave dielectric ceramics

AbstractIn the present study, (1 − x)BaAl2Si2O8−xCaSnSiO5−y wt.% LiF microwave dielectric ceramics were prepared through the traditional solid‐state sintering at 950−1395°C for 5 h. The BaAl2Si2O8 phase could coexist with the CaSnSiO5 phase at (1 − x)BaAl2Si2O8−xCaSnSiO5 (.2 ≤ x ≤ .6) ceramics, and no other secondary phase was observed. The CaSnSiO5, as a τf regulator, adjusted the negative τf value of BaAl2Si2O8 to near zero. Excellent microwave dielectric properties (εr = 8.1, Q × f = 37 560 GHz, and τf = −1.5 ppm/°C) were obtained from the 0.6BaAl2Si2O8−0.4CaSnSiO5 ceramic. The sintering temperature of 0.6BaAl2Si2O8−0.4CaSnSiO5 ceramic decreased from 1375°C to 950°C by introducing 2 wt.% LiF. The 0.6BaAl2Si2O8−0.4CaSnSiO5−2 wt% LiF ceramic exhibited remarkable microwave dielectric properties (εr = 7.6, Q × f = 17 420 GHz, and τf = −12.2 ppm/°C) and could be applied to the low‐temperature co‐fired ceramic (LTCC) field.

Impedance and Mössbauer spectroscopy study of BiCu3Ti3FeO12 dielectric matrix

In the present work, an electroceramic of the perovskite family, BiCu3Ti3FeO12 (BCTFO), was synthesized by the solid-state reaction method. The structural study was performed by X-ray diffraction and Mossbauer and Raman spectroscopy. Electric and dielectric properties were analyzed by impedance spectroscopy and the Hakki-Coleman method. Due to the BCTFO is isostructural of the CaCu3Ti4O12 (CCTO), the BCTFO presents as a promissory electroceramic. Mossbauer spectroscopy reveals paramagnetic spectra to BCTFO, with two octahedral sites for iron ions. Regarding dielectric properties, for 1 Hz, BCTFO presents a high relative dielectric permittivity (er ≈ 1 × 104) and dielectric loss (tan δ > 1) and er = 230.88, tan δ ≈ 1 × 10–2 in the microwave range. The produced ceramic exhibited a high resonance frequency temperature coefficient (τf) with a value of + 2852 ppm °C−1, making it a candidate for fabrication of the thermostable electroceramic composites with other ceramic matrices with negative τf values improving the thermal stability.

Two novel garnet Sr3B2Ge3O12 (B = Yb, Ho) microwave dielectric ceramics with low permittivity and high Q

Two cubic garnet-structured Sr3B2Ge3O12 (B = Yb, Ho; called SYG and SHG) ceramics synthesised by the high-temperature solid-phase reaction method were investigated in terms of phase formation, sintering behaviour and microwave dielectric performance. At their optimal sintering temperatures, SYG had low dielectric constant (εr) = 9.30, high quality factor (Q × f) = 129,360 GHz and negative temperature coefficient of resonant frequency (τf) =−42 ppm/℃, whereas SHG exhibited low εr = 9.23, Q × f = 104,600 GHz, and comparatively near-zero τf =−26 ppm/℃. The difference in microwave dielectric performance of both ceramics was discussed by the packing fraction, full width at half maximum (FWHM) of A1g Raman mode at 779 cm−1 (775 cm−1) and bond valence. The intrinsic dielectric properties of SYG and SHG ceramics were investigated by the infrared reflectivity spectra, and their negative τf values were tuned to near-zero.

Ca3Al2O6: novel low-permittivity microwave dielectric ceramics with abnormally large negative τf

Ca3Al2O6 ceramics are synthesized using a standard solid-state reaction method and their microwave dielectric properties are systematically investigated. Pure phases with space group of Pa_3 are confirmed from X-ray diffraction patterns (XRD) and Rietveld refinements. er and Qf values of the present ceramics are mainly determined by the porosity, and the optimal values (er = 14.5, Qf = 24,500 GHz) are achieved when sintered at 1425 °C. Abnormally large negative τf values in the range of − 322 to − 354 ppm/°C are obtained, which are rare and extremely important in adjusting the positive τf values of other material systems. In addition, a large temperature sensitivity of − 4.19 MHz/°C is also confirmed in the present ceramics, which indicates great potential for temperature sensor applications. Moreover, the dielectric spectra measured under various radio frequencies reveal similar positive τe values of 715.5 ppm/°C, which could account for the large negative τf values in the operating temperatures.

High-Q and near-zero τf composite Li2Mg2TiO5-Sr3(VO4)2 ceramics for low-temperature co-fired ceramic applications

In the first part of this study, the effects of LiF additives on the phase constitution, microstructure, and microwave dielectric properties (MDPs) of Li2Mg2TiO5 ceramic were studied systematically. The addition of LiF not only effectively lowered the sintering temperature but also considerably improved sinterability and quality factor simultaneously. The Li2Mg2TiO5+4 wt% LiF ceramic sintered at 900 °C for 4 h presented optimum MDPs with εr = 14.6, Q × f = 128,500 GHz and τf = -35.6 ppm/°C. Its relatively large negative τf value could be counteracted to near zero by Sr3(VO4)2 for the first time. In the second part of the study, a series of (1-x)[Li2Mg2TiO5+4 wt% LiF]-x[Sr3(VO4)2+1 wt% B2O3] (abbreviated as (1-x)[LMT+4LiF]-x[SV+1B2O3]) (0.25 ≤ x ≤ 0.4) composite ceramics were designed and prepared through the traditional solid-state sintering route. The XRD patterns revealed that Li2Mg2TiO5 and the Sr3(VO4)2 phase could be well coexisted and no impurity phase was detected. A near-zero τf value of -1.6 ppm/°C was obtained in the 0.65[LMT+4LiF]-0.35[SV+1B2O3] ceramic with εr of 13.4 and high Q×f of 91,860 GHz. The excellent chemical compatibility of the ceramic with Ag was confirmed through co-firing at 900 °C for 2 h. All results indicate that the composite 0.65[LMT+4LiF]-0.35[SV+1B2O3] ceramic can be applied to low-temperature co-fired ceramic technology.

Two low-permittivity melilite ceramics in the SrO-MO-GeO2 (M = Mg, Zn) system and their temperature stability through compositional modifications

Two melilite ceramics Sr2AGe2O7 (A = Mg, Zn) with low permittivity were prepared by a solid-state reaction method. The crystal structure and microstructure of the ceramics were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and scanning electron microscopy. Both ceramics crystallized in a single melilite structure with a tetragonal space group P-42m (113) and exhibited homogeneous microstructures. Optimum microwave dielectric properties with relative permittivity (εr) of 8.56, quality factor (Q × f) of 28,800 GHz, and temperature coefficient of resonance frequency (τf) of −70.5 ppm/°C were obtained in Sr2MgGe2O7 sintered at 1330 °C. Sr2ZnGe2O7 possessed εr of 8.81, Q × f of 35,700 GHz, and τf of −84.4 ppm/°C when sintered at 1290 °C. Thermal stability of resonance frequency was accessible when the negative τf values of Sr2AGe2O7 were adjusted after the formation of composite ceramics with CaTiO3.

Low temperature sintering of Li2Zn3Ti4O12–xTiO2 microwave dielectric ceramics without glass addition

The sintered densities, crystal structure, surface topography, and microwave dielectric properties of B2O3 and TiO2 dual-doped Li2Zn3Ti4O12 ceramics were investigated. Small amount of B2O3 addition (0.25 wt%) can remarkably improve the densification process of Li2Zn3Ti4O12 ceramics at about 900 °C. The sintered Li2Zn3Ti4O12 ceramics with B2O3 added have a cubic spinel structure. With the addition of 0.25 wt% B2O3, Li2Zn3Ti4O12 ceramics exhibit high Qf value of about 62,500 GHz at sintering temperature of 900 °C, while a relatively large negative τf value of about − 40.5 ppm/°C still limit its application. Based on the addition of 0.25 wt% B2O3, TiO2 was also added in Li2Zn3Ti4O12 ceramics for further improving the τf value. Finally, doped with 0.25 wt% B2O3 and sintered at 900 °C, Li2Zn3Ti4O12–1.75TiO2 ceramics exhibited near zero τf value of 0.5 ppm/°C as well as a high Qf value of 55,000 GHz, which is attractive for applications in low temperature co-fired ceramic technologies.