Li2Mg3TiO6 Ceramics Research Articles

The phase evolution, microstructure and microwave dielectric properties of non-stoichiometric Li2(1+x)Mg3TiO6 ceramics

The phase evolution, microstructure and microwave dielectric properties of non-stoichiometric Li2(1+x)Mg3TiO6 ceramics

Temperature Stable and Low Loss Microwave Dielectric Ceramics of Li2Mg3-xSrxTiO6

In this paper, a series of Li2Mg3-xSrxTiO6 (x = 0, 0.02, 0.04, 0.06, 0.08) ceramics were prepared by the conventional solid-state reaction method. The effects of Sr2+ substitution on the structure, morphology and microwave dielectric properties of Li2Mg3TiO6 ceramics were investigated. The X-ray diffraction (XRD) results indicated that Li2Mg3TiO6 and SrTiO3 phases stably coexisted with each other and formed composite materilas. The appearance of porous structure mainly originated from the volatilization of lithium at high sintering temperatures. As the Sr2+ content increased from 0 to 0.08, the optimum dielectric constant (ε r ) increased from 13.61 to 17.32, the quality factor (Q×f) decreased monotonously and the temperature coefficient of resonant frequency (τ f ) changed from -34.4 to +16.8 ppm/°C. The variations of ε r , Q×f and τ f could be explained by the Lichtenecker logarithmic model and mixing rule, respectively. In particular, optimal microwave dielectric properties of ε r = 16.08, Q×f = 82100 GHz, τ f = +1.7 ppm/°C were obtained for Li2Mg2.94Sr0.06TiO6 ceramic sintered at 1310 °C for 5h.

Structure and microwave dielectric properties of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 ceramics

Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al1/2Nb1/2)4+ substitution on the dielectric properties of Li2Mg3TiO6 ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al1/2Nb1/2)4+ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (εr) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τf|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li2Mg3Ti0.92(Al1/2Nb1/2)0.08O6 sample exhibited outstanding dielectric characteristics:εr = 15.256, Q × f = 174,300 GHz and τf = −19.97 ppm/°C.

Low temperature sintering and dielectric properties of Li2MgTiO4 microwave ceramics with BaCu(B2O5) addition for LTCC applications

The sintering behaviors and dielectric properties of the Li2MgTiO4 ceramics at microwave frequency were investigated as a function of BaCu(B2O5) in this paper. The addition of BaCu(B2O5) dramatically decreased the sintering temperature of Li2MgTiO4 ceramics from 1250 to 900 °C. No secondary phase was detected and single phase Li2MgTiO4 with NaCl structure in the 1.0–4.0 wt% BaCu(B2O5) doped Li2MgTiO4 ceramics was confirmed, while a small amount of BaCu(B2O5) phase was found in the 8.0 wt% BaCu(B2O5) doped Li2MgTiO4 ceramics. No much deterioration of dielectric properties at microwave frequency of the BaCu(B2O5) doped Li2MgTiO4 ceramics sintered at 900 °C for 3 h occurs and favorable dielectric properties (er = 15.8, Qf = 74,790 GHz and τf = − 24.3 ppm/°C) at microwave frequency were obtained for the Li2MgTiO4 ceramics with 4.0 wt% BaCu(B2O5) addition. Accordingly, such a favorable 4.0 wt% BaCu(B2O5)-doped Li2MgTiO4 ceramic might be a potential candidate material for LTCC applications.

Correlation between structure characteristics and dielectric properties of Li2Mg3-xCuxTiO6 ceramics based on complex chemical bond theory

A series of Li2Mg3-xCuxTiO6 (x = 0.00–0.20) ceramics were synthesized by a simple solid-state reaction. The influences of Cu2+ substitution on the microwave dielectric characteristics, structure characteristics and morphology of Li2Mg3TiO6 ceramics were investigated. The XRD results demonstrated that all samples displayed the pure Li2Mg3TiO6 phase with rock salt structure. The SEM results exhibited that a microstructure evolution from porous structure to nearly compact structure appeared with increasing Cu2+ content, indicating that the pores originated from lithium volatilization could be suppressed by Cu2+ substitution. Subsequently, the dependence of microwave dielectric properties on intrinsic factors was evaluated based on refinement results and P–V–L theory. The monotonic increase of dielectric constant (εr) was mainly correlated with the polarizability. The variation of quality factor (Q × f) was dependent on the total systematic lattice energy and packing fraction. In addition, the evolution tendency of the temperature coefficient of resonant frequency (τf) was explained by the linear thermal expansion coefficient α and EMg/Cu–O bond energy. All results suggested that the intrinsic factors play decisive roles on dielectric characteristics.

The temperature stable Li2Mg3TiO6 microwave dielectric ceramics with CaF2 addition

The Li2Mg3TiO6 (LMT)-x wt% CaF2 (x = 2, 4, 6, 8) ceramics were prepared by a conventional solid-state route. The effects of CaF2 addition on the sinterability, phase constitution, microstructure and microwave dielectric properties of LMT ceramics were investigated systematically. The results showed that CaF2 lowers the sintering temperature of LMT ceramics from 1280 to 900 °C and broadens their sintering range of LMT ceramics owing to the formation of LiF as a liquid sintering agent. Formation of CaTiO3 tuned the temperature coefficient of resonant frequency (τf) of LMT from − 39 to 1.5 ppm/°C. The LMT ceramics doped with 6 wt% CaF2 sintered at 1200 °C possess excellent microwave dielectric properties: er = 17.2, Q × f = 76,800 GHz, and τf = 1.5 ppm/°C.

Sintering behavior and microwave dielectric properties of low-loss Li2Mg3TiO6 ceramics doped with different glass agents

Abstract The Li2Mg3TiO6 ceramics doped with ZnO B2O3 SiO2 (ZBS)/Li2O B2O3 SiO2 (ZBS) glass were synthesized through the conventional solid-state reaction route. The phase compositions, microstructures, sintering characteristics and microwave dielectric properties of Li2Mg3TiO6-xwt%ZBS and Li2Mg3TiO6-xwt%LBS (0 ≤ x ≤ 8) were investigated. With the increase of low-melting ZBS/LBS glass, the densification of Li2Mg3TiO6 ceramics was improved significantly through the mechanism of liquid phase sintering. The addition of ZBS/LBS glass could effectively lower the sintering temperature from 1350 °C to 1025 °C/1050 °C and had slightly influences on microwave dielectric properties of Li2Mg3TiO6 ceramics. The dielectric constant ɛr and Q×f values correlated with bulk density strongly. The temperature coefficient of resonant frequency (τf) was reduced by adding ZBS/LBS glass, due to the formation of the second phase MgSiO4. Compared with Li2Mg3TiO6-4wt%LBS sintered at 1050 °C, Li2Mg3TiO6 ceramics with 4 wt% ZBS glass sintered at 1025 °C had higher densification and more uniform grain morphology, which displayed excellent microwave dielectric properties of ɛr∼13.35, Q×f∼138,800 GHz and τƒ∼-31.84 ppm/°C.

Sintering behavior, crystalline structure and microwave dielectric properties of Li2(Ni1-xMgx)3TiO6 (0 ≤ x ≤ 1) ceramics

Li2(Ni1-xMgx)3TiO6 (0 ≤ x ≤ 1) ceramics were synthesized via conventional solid-state reaction. The changes of phase compositions, crystalline structures, sintering behaviors and microwave dielectric properties were investigated firstly as the Li2Ni3TiO6 ceramics transformed into Li2Mg3TiO6 ceramics. With the addition of Mg2+ ions, the quality factor (Q × f) was improved greatly from 18,159 GHz to 152,189 GHz due to the expansion of cell volume. The dielectric constant εr had a similar trend with the electronic oxide polarizabilities, which was determined by the energy gap, the cation polarizability, and the molar volume. In addition, the octahedral distortion and bond energy were calculated and the temperature coefficient of resonant frequency (τf) correlated with the bond energy of Ni/Mg-O (ENi/Mg-O) primarily.

Low-temperature preparation and microwave dielectric properties of cold sintered Li2Mg3TiO6 nanocrystalline ceramics

This study aims to fabricate Li2Mg3TiO6 ceramics with ultrafine grains using a novel cold sintering process combined with a post-annealing treatment at a temperature < 950 °C. In this study, phase composition, sintering behavior, microstructure evolution, and microwave dielectric properties of the resultant nanocrystalline ceramics were investigated for the first time. The as-compacted green pellets at 180 °C yielded a high relative density of ~ 90% and the ceramics that were post-sintered over a broad temperature range (800–950 °C) possessed highly dense microstructure with a relative density of ~ 96%. The average grain size varied from 100 to 1200 nm for the samples sintered at 800–950 °C. Furthermore, the quality (Q × f) values of the obtained specimens exhibited a strong positive dependency on the grain size, which increased from 17,790 to 47,960 GHz for grain sizes ranging between 100 and 1200 nm, while the dielectric permittivity (εr) and temperature coefficient of the resonant frequency (τf) values did not undergo any significant changes over this range of grain size.

Low loss and temperature stable microwave dielectric ceramics in (1 − x)Li2TiO3–xLi2Mg3TiO6 (0.1 ≤ x ≤ 0.5) system

The (1 − x)Li2TiO3–xLi2Mg3TiO6 (x = 0.1, 0.15, 0.2, 0.3, 0.4, 0.5) ceramics system was fabricated by solid-state synthesis. Test results of X-ray diffraction and electron diffraction spectrum show that all ceramic samples only contain Li2TO3 and Li2Mg3TiO6 phase. Scanning electron microscope shows that pores were found in crystal grain due to Li volatilization in high temperature (> 1000 °C). With the rise proportion of Li2Mg3TiO6 in ceramics, dielectric constant (ɛr) decreases from 19.55 to 14.53, quality factor (Q×f) increases from 102,800 to 126,000 GHz and temperature coefficient (τf) decreases from + 15.9 to − 30.08 ppm/°C. High performance microwave dielectric properties of ɛr = 18.5, Q×f = 108,000 GHz, τf = 4.2 ppm/°C were obtained at 1390 °C for 0.85Li2TiO3–0.15Li2Mg3TiO6 ceramics. To suppress Li volatilization, LiF, a low temperature melting addition, was added to 0.85Li2TiO3–0.15Li2Mg3TiO6 ceramics. LiF effective lowers sintering temperature from 1390 to 1175 °C due to LiF liquid-phase sintering and restricts Li evaporation, and a well-developed grain morphology and excellent dielectric properties (ɛr = 18.5, Q×f = 87,000 GHz, τf = − 18 ppm/°C) was obtained which hold promise in 4G tele-communication applications.

Effect of Co-substitution on the sintering characteristics and microwave dielectric properties of Li2MgTiO4 ceramics

Rock-salt-structured Li2(Mg1−xCox)TiO4 (x = 0, 0.05, 0.10, 0.15 and 0.2) ceramics were successfully prepared via the conventional solid-state ceramic route in the present work. The effects of Co2+ content on sintering characteristics, crystal structure and microwave dielectric properties of Li2MgTiO4 ceramics were systematically investigated. Raman spectra and X-ray diffraction analysis revealed that the Li2(Mg1−xCox)TiO4 ceramics could form single phase within the range of 0.00 ≤ x ≤ 0.20. As the Co2+ content gradually increased, the dielectric constant of the solid solution gradually increased from 15.60 to 16.93, which was closely related with the variation of polarizability as well as the Raman shift in typical vibration modes. The thermal stability was also adjusted to a certain extent, and near-zero τf values could be found at x = 0.05 and 0.10. Although the dielectric loss gradually increased with the increasing Co2+ content, a good combination of microwave dielectric property of εr = 15.7, Q × f = 119,600GHz and τf = −2.67ppm/°C could be found in the Li2(Mg0.9Co0.1)TiO4 ceramics sintered at 1400°C.

Synthesis, characterization and microwave dielectric properties of rock-salt structure Li2Mg3TiO6 via aqueous sol–gel method

Rock-salt structure Li2Mg3TiO6 microwave dielectric ceramics were prepared via aqueous sol–gel method. The influences of sintering temperatures on the crystalline phase, microstructure and microwave dielectric properties of Li2Mg3TiO6 ceramics were investigated in detail. Microwave dielectric properties were strongly dependent on crystalline phases and grain sizes, which were affected by the powder preparation and the sintering process. The samples with nearly full density were obtained at 1150 °C and had an excellent microwave property of ɛ r = 14.78, Q × f = 162,260 GHz, and τ f = − 21.62 ppm/°C, observably decreasing the sintering temperature without deteriorating the acceptable properties. The relatively lower sintering temperature and excellent microwave dielectric properties would make these ceramics promising for microwave components application in the future.

Effects of (Mg1/3Ta2/3)-substitution for Ti-site on the microwave dielectric properties of Li2MgTiO4 ceramics

Novel high quality factor microwave dielectric ceramics Li2MgTi1−x(Mg1/3Ta2/3)xO4 (0 ≤ x ≤ 0.5) were successfully prepared via a conventional solid-state ceramic route. The effects of isovalent substitutions (Mg1/3Ta2/3)4+ at the Ti-site on the sintering behaviors, microstructures, and microwave dielectric properties of Li2MgTiO4 ceramics were investigated in this paper. The sintered samples exhibited the single phase with cubic rock-salt structure belonging to Fm-3m space group in the whole composition range. Rietveld refinement which could be performed by the Fullprof program was taken to explain the effects of (Mg1/3Ta2/3)4+ ion substitution on the crystal structures of Li2MgTiO4 ceramics. With the (Mg1/3Ta2/3)4+ content increasing from 0 to 0.5, the quality factor Q·f firstly increased and decreased thereafter, while the dielectric constant εr almost linearly decreased. In addition, the τf values shifted to positive value with the amount of (Mg1/3Ta2/3)4+ increasing. The best composition appeared to be Li2MgTi0.6(Mg1/3Ta2/3)0.4O4, which showed excellent microwave dielectric properties of εr = 15.73, Q·f = 184,000GHz and τf = − 12.54ppm/°C. This made the Li2MgTi0.6(Mg1/3Ta2/3)0.4O4 ceramic a very promising candidate for use as a low-loss microwave material.

Sintering characteristic and microwave dielectric properties of ultra-low loss Li2Mg3TiO6 ceramic prepared by reaction-sintering process

Microwave dielectric properties and microstructures of ultra-low loss Li2Mg3TiO6 ceramic prepared by reaction-sintering method (RS) and conventional solid-state reaction method (CS) have been investigated. The XRD patterns and SEM images revealed that the single phase of Li2Mg3TiO6 and uniform morphology are obtained by both RS and CS methods at the optimal sintering temperatures. In order to further investigate the effects of different sintering methods on the microwave dielectric properties of Li2Mg3TiO6 ceramics, the oxide polarizabilities and packing fraction were calculated based on the Rietveld refinement. The calculation results revealed that the RS method was more beneficial to the microwave dielectric properties of Li2Mg3TiO6 ceramics in comparison with CS method. Excellent microwave dielectric properties for Li2Mg3TiO6 ceramics with enhanced Q × f value of 157,036 GHz could be obtained using RS method sintered at 1250 °C for 6 h.

Effect of raw materials pretreated by physical grinding method on the sintering ability and microwave dielectric properties of Li2MgTiO4 ceramics

Li2MgTiO4-1 (abbreviated as LMT-1) ceramics were synthesized via the solid state reaction method using the pretreated raw materials. The unpretreated raw materials were used in the preparation of Li2MgTiO4-2 (abbreviated as LMT-2) ceramics. The particle size of LMT-1 powders is smaller and more uniform than that of LMT-2 powders and the porosity of LMT-1 ceramics is lower than that of LMT-2 ceramics. The microwave dielectric properties of LMT-1 ceramics keep a relatively stable value at a wide sintering temperature range. The slight fluctuation of sintering temperature will lead to great changes in the microwave dielectric properties of LMT-2 ceramics. The pretreatment of raw materials enhances the sintering ability and broadens the sintering temperature range of the Li2MgTiO4 ceramics.

Influence of CaTiO3 doping on the microwave dielectric properties of Li2MgTiO4 ceramics

In this article, Li2MgTiO4 + x wt% (x = 5–9) CaTiO3 microwave dielectric ceramics with high temperature stability were prepared by solid-state reaction. The crystal structure, microstructure, microwave dielectric properties were discussed systematically as function of x value and sintering temperature. The results show that Li2MgTiO4 and CaTiO3 phases coexist and the content of CaTiO3 phase increases, the dielectric constant increases, quality factor and temperature coefficient of resonant frequency decreases because of the increase of CaTiO3 content. The Li2MgTiO4 + 6 wt% CaTiO3 ceramics sintered at 1210 °C for 4 h show great properties: e r = 18.03, Q × f = 69,022 (at 7.886 GHz), τ f = − 3.03 ppm/°C.

A novel temperature-stable and low-loss microwave dielectric using Ca0.8Sr0.2TiO3- modified Li2Mg3TiO6 ceramics

Microstructure and microwave dielectric properties of (1-x)Li2Mg3TiO6-xCa0.8Sr0.2TiO3 (x = 0.03, 0.06, 0.08, 0.09, 0.12) ceramics prepared by the conventional solid state route have been investigated. XRD and SEM-EDS analysis confirmed that ceramics contain Li2Mg3TiO6 and Ca0.8Sr0.2TiO3 phases. The microwave properties exhibited a significant dependence on the sintering temperature and Ca0.8Sr0.2TiO3 content. With increasing addition of Ca0.8Sr0.2TiO3, the dielectric constant $$({\varepsilon _r})$$ increased from 14.3 to 17.4 when samples sintered at 1410 °C for 4 h; the quality factor (Q × f) decreased from 133,905 to 101,000 GHz, and the temperature coefficient of resonant frequency ( $${\tau _f}$$ ) significantly increased from −39 to 6.35 ppm/°C when samples sintered at 1370 °C for 4 h. Sample with 0.91Li2Mg3TiO6-0.09Ca0.8Sr0.2TiO3 sintered at 1370 °C for 4 h possess excellent microwave properties with $${\varepsilon _r}$$ of 16.4, a Q × f of 113,000 GHz and $${\tau _f}$$ of −3.65 ppm/°C. It is proposed as low-loss and low-cost dielectric materials for microwave and millimeter wave application.

The effect of sintering agents on the sinterability and dielectric properties of Li2Mg3TiO6 ceramics

ABSTRACTThe low-fired Li2Mg3TiO6 ceramics were fabricated via doping several multicomponent sintering agents. The effect of multicomponent sintering agents on the sinterability and microwave dielectric properties of Li2Mg3TiO6 ceramics were investigated. The results showed that the densification temperature of Li2Mg3TiO6 ceramics was reduced to 950°C, 975°C and 1000°C by doping LC, LV and LB as sintering agents, respectively. The optimum dielectric properties of ϵr = 15.7, Q × f = 70100 GHz and τf = −43 ppm/°C were obtained at 950°C for LC-doped Li2Mg3TiO6 ceramics. Such sample was compatible with Ag electrodes, suitable for the low-temperature co-fired ceramics (LTCC) applications.

Phase structure, sintering behavior and adjustable microwave dielectric properties of Mg1−xLi2xTixO1+2x solid solution ceramics

Mg1−xLi2xTixO1+2x (1/5 ≤ x ≤ 1/2) solid solution ceramics were prepared by the solid state reaction method. The sintering behavior, microstructure and microwave dielectric properties of ceramics were investigated. X-ray diffraction patterns showed that MgO and Li2TiO3 could form Mg1−xLi2xTixO1+2x solid solutions with a rock salt structure. With increasing x values, the unit cell parameters of ceramics decreased, both the Q×f value and bulk density increased firstly, reached the max value and then decreased. Most importantly, the thermal stability of microwave dielectric properties for ceramics was improved. When x = 1/4, Li2Mg3TiO6 ceramics exhibited good microwave dielectric properties with Q×f = 110,703 GHz, εr = 13.6 and τf = −35.1 ppm/°C.

Characterization on low loss dielectric Li2MgTiO4 ceramics based on chemical bond theory at microwave frequency

The low loss microwave dielectric materials Li2MgTiO4 with rock salt structure were prepared by the modified solid state method. Sintering characteristics and microwave dielectric properties were investigated under various sintering temperatures ranging from 1200 °C to 1375 °C. The crystal structure was studied by the X-ray diffraction and the micro-structure was studied by the scanning electron microscopy (SEM) techniques. Rietveld refinement was used to analyze the structure of the crystalline phase. Based on the cell parameters, the bond ionicity, lattice energy, bond energy and coefficient of thermal expansion were calculated to evaluate the structural characteristics. The εr values could be strongly dependent on the bond ionicity of the TiO bond. The Q·ƒ values were affected by the lattice energy of TiO bonds. As for the τf values, it could be mainly affected by the coefficient of thermal expansion of LiO bonds. At the sintering temperature of 1350 °C, Li2MgTiO4 ceramics exhibited the excellent microwave properties of εr = 15.07, Q·ƒ = 97,629 GHz (at 8.2 GHz) and τf = −3.81 ppm/°C. These results demonstrated that Li2MgTiO4 ceramics could be promising candidate materials for the application of highly selective microwave ceramic resonators and filters.