Li2O Nb2O5 TiO2 Research Articles

Structural, dielectric and optical analysis of Li1.1−yNb0.9-3yTi0.1+4yO3 M-phase solid solutions

Abstract The present paper reports the structural, dielectric and optical analysis of the M-phase Li1.1−yNb0.9-3yTi0.1+4yO3 (y=0.00, 0.045, 0.09, 0.11, 0.135) solid solutions in the Li2O–Nb2O5–TiO2 ternary system prepared by conventional solid state reaction method. High density (relative density>91%) ceramics were obtained by sintering the solid solutions at 1100 °C. XRD spectra revealed these ceramics to exhibit hexagonal structure and the superstructure formation was observed for higher Ti content (≥28 mol%) samples. Plate-like shape and closely packed grains were formed with low porosity (≤10%). Particle size was obtained in the range of 392–235 nm using TEM images. Relative permittivity changed from 46 to 31 while temperature coefficient of resonant frequency ranged from −93.5 to 57.5 at 1 MHz frequency. The maximum photoluminous intensity of 203.13 for the emission peak at 453 nm (blue emission) was observed for the sample y=0.00.

Dielectric and optical study of the M-phase LNT (Li-Nb-Ti-O) solid solutions

The M-phase Li1+xNb1−xTixO3 (x=0.06, 0.10, 0.14, 0.18) solid solutions have been successfully synthesized in the Li2O–Nb2O5–TiO2 system by solid state reaction method. XRD patterns of the samples have shown that these possesses hexagonal structure. Spherical shaped and closely packed grains were formed with low porosity (<5%). These ceramics can be considered as low-sintering dielectrics as they were sintered to high density (relative density >94%) at 1100°C. Particle size was obtained in the range of 401.5–351.3nm using TEM images. The values of the relative permittivity varied from 42 to 51 while loss tangent ranged from 0.0212 to 0.0701 at 1MHz frequency. The highest PL intensity of 203.13 that exhibits the blue emission (453nm) was obtained for the composition of Li1.1Nb0.9Ti0.1O3.

Effect of Li–B–Si glass on the low temperature sintering behaviors and microwave dielectric properties of the Li-modified ss-phase Li2O–Nb2O5–TiO2 ceramics

The effects of Li amount on the phase structures and microwave dielectric properties of the Li2.081Ti0.676Nb0.243O3 (LNT) ceramics were studied. And also the effects of the Li2O–B2O3–SiO2 (LBS) glass on the low temperature sintering behaviors, microstructures and microwave dielectric properties of the Li-modified LNT ceramics have been investigated. The results show that there is a phase boundary between cubic and monoclinic phase (so called ss-phase LNT) with different amount of Li. The LBS glass effectively lowered the sintering temperature and improving the microwave dielectric properties of the ss-phase LNT. The ss-phase LNT ceramic doped with 5 wt% LBS glass can be well sintered at 850 °C and has excellent microwave dielectric properties of e r = 19.16, Q × f = 41,413 GHz, and τ f = −1.62 ppm/°C.

Effect of B2O3 on the aqueous tape casting and microwave properties of Li2O–Nb2O5–TiO2 ceramics

The effect of B2O3 addition on the aqueous tape casting, sintering, microstructure and microwave dielectric properties of Li2O–Nb2O5–TiO2 ceramics has been investigated. The tape casting slurries exhibit a typical shear-thinning behavior without thixotropy, but the addition of B2O3 increases the viscosity of the slurries significantly. It was found that doping of B2O3 can decrease the tensile strength, strain to failure and density of the green tapes. The sintering temperature could be lowed down to 900°C with the addition of 2wt% B2O3 due to the liquid phase effect. No secondary phase is observed. The addition of B2O3 does not induce much degradation on the microwave dielectric properties. Optimum microwave dielectric properties of εr=67, Q×f=6560GHz are obtained for Li2O–Nb2O5–TiO2 ceramics containing 2wt% B2O3 sintered at 900°C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.

Microwaves Dielectric Properties of 3Li2O-Nb2O5-6TiO2 Ceramics with B2O3 Addition

The effects of B2O3 addition of on sintering behavior, microstructure, and microwave dielectric properties of a new Li2O-Nb2O5-TiO2 (LNT) ceramics: 3Li2O-Nb2O5–6TiO2 has been investigated. The compound is composed of two phases, TiO2 and ‘‘M-phase’’ solid solution phase. The low-amount doping of B2O3 can effectively lower the sintering temperature from 1125°C to 900°C without inducing obvious degradation of microwave dielectric properties. The 1 wt.% B2O3-doped ceramic sintered at 900°C has better microwave dielectric properties of ϵr = 52, Q × f = 12000 GHz, τf = 32.3 ppm/°C. Moreover, there is no reaction occurred when co-firing the LNT ceramic with Ag electrode, which suggests that the ceramics can be applied to microwave LTCC devices.

A new microwave dielectric ceramic for LTCC applications

A new low-sintering temperature microwave dielectric ceramic was found and investigated in the Li2O–Nb2O5–TiO2 (Li2O:Nb2O5:TiO2 = 5.7:1:14.7, by mole, abbreviated as LNT) system. This new microwave dielectric ceramic shows a relatively high permittivity (47), high Q × f values up to 17,800 GHz, and low temperature coefficients (57 ppm/°C), which were obtained via sintering at 1,125 °C. With the low-level doping of B2O3–CuO (BCu) (below 2 wt%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The addition of BCu does not induce apparent degradation in the microwave properties but lowers the τf value. Typically, the 2.0 wt% BCu-doped ceramics sintered at 900 °C have better microwave dielectric properties of er = 48.7, Q × f = 16,350 GHz, τf = 32 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.

Microwave dielectric properties of the 5.5Li2O–Nb2O5–7TiO2 ceramics

A new Li2O–Nb2O5–TiO2 (LNT) ceramic with the Li2O:Nb2O5:TiO2 mole ratio of 5.5:1:7 was prepared by solid state reaction route. The phase and structure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The microwave dielectric ceramic has low sintering temperature (∼1075°C) and good microwave dielectric properties of er=42, Q×f=16900 GHz (5.75 GHz), and τf=63.7 ppm/°C. The addition of B2O3 can effectively lower the sintering temperature from 1075 to 875°C and does not induce degradation of the microwave dielectric properties. Obviously, the LNT ceramics can be applied to microwave low temperature-cofired ceramics (LTCC) devices.

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li2O–Nb2O5–TiO2 (LNT) ceramic with the Li2O:Nb2O5:TiO2 mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li2TiO3 and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li2O–0.17V2O5 (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of er = 51.3, Q × f = 7235 GHz, τf = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.

A new Li2O–Nb2O5–TiO2 microwave dielectric ceramic composite

AbstractIn the Li2O–Nb2O5–TiO2 (LNT) system, a new dielectric ceramic composite with special structure has been found and investigated. The compound is composed of two phases, the “M‐phase” and Li2TiO3 solid solution phase. This ceramic composite has a low sintering temperature (∼1100 °C) and good microwave dielectric properties of high permittivity (∼49), high Q × f value up to 9500 GHz, and small tempe‐ rature coefficient (∼22 ppm/°C). Furthermore, by adding 1 wt% B2O3, the ceramic could be densified at very low sintering temperatures (≯900 °C) and also have good microwave dielectric properties of ϵ r = 49.2, Q × f = 8839 GHz, which suggests that the ceramic could be a promising candidate for multilayer low‐temperature co‐fired ceramics applications. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A New Microwave Dielectric Ceramic for LTCC Applications

A new low‐sintering temperature microwave dielectric ceramic, the Li2TiO3 solid solution, was found and investigated in the Li2O–Nb2O5–TiO2 system. The compound with the composition of Li2.081Ti0.676Nb0.243O3 crystallizes as a monoclinic structure. This new microwave dielectric ceramic shows a relatively low permittivity (∼20), high Q×f values up to 50 000 (7.8 GHz), and near‐zero temperature coefficients (13 ppm/°C), which were obtained via sintering at 1100°C. The addition of ≤2 wt% B2O3 was very effective in lowering the sintering temperature (Ts), and dense ceramics could be obtained at Ts≤900°C. The addition of B2O3 does not induce apparent degradation in the microwave properties but lowers the τf value to near zero. It is obvious that the ceramics could be promising candidates for multilayer low‐temperature co‐fired ceramics applications.

Structural Study of Li1+x−yNb1−x−3yTix+4yO3 Solid Solutions

The structures of Li1+x−yNb1−x−3yTix+4yO3 solid solutions within the so-called M-phase field in the Li2O–Nb2O5–TiO2 system were investigated using high-resolution transmission electron, microscope (HRTEM) and single-crystal X-ray diffraction. The results demonstrated that the phase field is not a solid solution but rather a homologous series of commensurate intergrowth structures with LiNbO3-type (LN) slabs separated by single [Ti2O3]2+ corundum-type layers. The thickness of the LN slab decreases with increasing Ti-content from ∼55 to 3 atomic layers in the metastable H-Li2Ti3O7 end-member. The LN slabs accommodate a wide range of Ti4+/Nb5+ substitution, and for a given homolog the distribution of Ti and Nb is not uniform across the slab. A single-crystal X-ray diffraction study of a structure composed of nine-layer LN slabs revealed preferential segregation of Ti to the slab surfaces which apparently provides partial compensation for the charge on the adjacent [Ti2O3]2+ corundum layers. The extra cations in phases with x>0 are accommodated through the formation of Li-rich Li2MO3-type layers in the middle of the LN slabs. The fraction of layers with extra cations increases with increasing Ti-content in the structure.

Analysis of phase distributions in the Li2O–Nb2O5–TiO2 system by piezoresponse imaging

The M-phase solid solutions Li1+x−yNb1−x−3yTix+4yO3) (0.1 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.175) in the Li2O–Nb2O5–TiO2 system have promising microwave dielectric properties. However, these compounds can contain small quantities of ferroelectric impurities that affect the polarization response of the material. Due to their low concentration and their chemical similarity to the host material, the impurities cannot be detected by x-ray diffraction or local elemental analysis. Scanning surface potential microscopy and piezoresponse imaging were used to analyze phase compositions in this system. Piezoresponse imaging demonstrated the presence of thin (&lt;200–300 nm) ferroelectric layers on the grain boundaries oriented along the c-axis of the M-phase. Differences between the surface potential and the piezoresponse of ferroelectric multicomponent systems are discussed.