High Qf Value Research Articles

Structures and microwave dielectric properties of Ba6−3x(Nd,Biy)8+2xTi18O54 (x = 2/3) solid solution

The effects of Bi substitution for Nd in Ba6−3xNd8+2xTi18O54 (x = 2/3) solid solution upon the microstructures and microwave dielectric properties were investigated. The solid solubility limit of Bi in Ba6−3xNd8+2xTi18O54 (x = 2/3) solid solution was about 15 mol%, the same as that for x = 0.5, and densification of the present solid solutions could be performed well at lower temperatures. However, the variation tendency of microwave dielectric properties with composition in the present ceramics quite differed from that for x = 0.5: (1) The temperature coefficient of resonant frequency in the present ceramics showed a continuous variation from positive to negative and did not indicate extreme value at the solid solubility limit. (2) Near-zero temperature coefficient of resonant frequency combined with high-ε and high-Qf values could be obtained in the present ceramics, while that for x = 0.5 had a lower limit of +15 ppm/°C. (3) The dielectric constant also showed a continuous increase for the present compositions, while that in x = 0.5 had an extreme at solid solubility limit. Ceramics with composition of Ba6−3x(Nd0.85,Bi0.15)8+2xTi18O54 (x = 2/3) showed excellent dielectric properties of ε = 99.1, Qf = 5290 GHz, and τf = −5.5 ppm/°C.

Bismuth/Samarium Cosubstituted Ba6−3xNd8+2xTi18O54 Microwave Dielectric Ceramics

Modification of the microwave dielectric properties in Ba6−3xNd8+2xTi18O54 (x= 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near‐zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3xNd8+2xTi18O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3xNd8+2xTi18O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf= 4110 GHz, and very low τf) were achieved in the composition Ba6−3x(Nd0.7Bi0.18Sm0.12)8+2xTi18O54.

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na1/2Ln1/2)TiO3> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (τf) (where Ln represents a lanthanide: La+3, Pr+3, Nd+3 and Sm+3). On the other hand, MgTiO3 ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO3-(1 − x)(Na1/2 Ln1/2) TiO3. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO3 and Na1/2 Ln1/2)TiO3 phases. Its dielectric characteristics (Q*f, temperature coefficient and dielectric constant) are intermediate between (Na1/2 Ln1/2) TiO3 and MgTiO3 and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.