Albina Y. Borisevich

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

Abstract 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.

Analysis of phase distributions in the Li 2 O–Nb 2 O 5 –TiO 2 system by piezoresponse imaging

The M -phase solid solutions Li 1+ x − y Nb 1− x −3 y Ti x +4 y O 3 ) (0.1 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.175) in the Li 2 O–Nb 2 O 5 –TiO 2 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 ( c -axis of the M -phase. Differences between the surface potential and the piezoresponse of ferroelectric multicomponent systems are discussed.

1:2 Cation order in A(Li1/3(Nb,Ta)2/3)O3 microwave perovskites

In a family of perovskites with the general stoichiometry (A2/32+La1/3)(B1/31+B2/35+)O3, three 1:2 ordered perovskites were prepared with A=Sr, B1+=Li, B5+=Nb, Ta and with A=Ca, B1+=Li, B5+=Nb. These compounds can be sintered to high density at temperatures ⩽1350 °C, have dielectric constants in the range 25–30, microwave quality factors as high as 26 000, and negative temperature coefficients of resonant frequency. A 1:2 polymorph was not observed for (Ca2/3La1/3)(Li1/3Ta2/3)O3 which adopted a 1:1 ordered structure. The larger charge difference between the ions involved in the B-site ordering in these systems compared to other 1:2 ordered microwave perovskites such as Ba(Zn1/3Nb2/3)O3, is reflected by a higher stability of the order which is stable up to their decomposition/melting temperature.