The structure and dielectric properties of the so-called M-phase solid solutions in the Li2O–Nb2O5–TiO2system have been investigated Detailed studies of the lattice parameters of these phases agree well with structure models based on intergrowths of LiNbO3slabs with a titanium-rich corundum-type layer The relative permittivity ranges from ∼80 to ∼55; microwave quality factors increase with the titanium content, reaching values of Q×f= 9000 at 6 GHz The temperature coefficient of the resonant frequency changes sign within the solid solution region, thus permitting tunability to a zero value All the compositions can be sintered to high density at temperatures ≤1100°C

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Crystalline Structure and Dielectric Properties of Li1+x−yNb1−x−3yTix+4yO3M-Phase Solid Solutions

Compound and solid-solution formation in the system Li2ONb2O5TiO2

A series of new low sintering temperature microwave resonator ceramics were investigated in the Li 1+ x – y Nb 1– x –3 y Ti x +4 y O 3 solid solution system. Ceramics with high relative permittivities (78–55), Q × f values up to 9000 (6 GHz), and zero temperature coefficients in the microwave region could be obtained via sintering at 1100°C. Similar phases were identified in the Li 2 O–Ta 2 O 5 –TiO 2 system and their stability region at 1100°C was determined. The microwave dielectric properties of the tantalates were similar to those of their Nb counterparts. The addition of ⩾ 2 mol% V 2 O 5 to the Nb solid solutions was effective in producing a large reduction in the sintering T and dense ceramics could be prepared at T ⩽ 900°C. The addition of V did not induce any significant degradation of the microwave properties and their apparent compatibility with Ag powder may indicate potential applications as co-fired circuit components.

Microwave dielectric properties of Li1+x–yM1–x–3yTix+4yO3 (M=Nb5+, Ta5+) solid solutions

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.

A New Microwave Dielectric Ceramic for LTCC Applications

The effect of the addition of V2O5 on the structure, sintering and dielectric properties of M-phase (Li1+x−yNb1−x−3yTix+4y)O3 ceramics has been investigated. Homogeneous substitution of V5+ for Nb5+ was obtained in LiNb0.6(1−x)V0.6xTi0.5O3 for x≤ 0.02. The addition of V2O5 led to a large reduction in the sintering temperature and samples with x= 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M-phase system and the x= 0.02 ceramics had [alt epsilon]r= 66, Q×f= 3800 at 5.6 GHz, and τf= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V2O5-doped M-phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.

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A. Aragón-Piña

Papers

Compound and solid-solution formation in the system Li2ONb2O5TiO2

Solid solutions with rock salt related structures on the join Li2TiO3-Li3NbO4