Search

Abstract: (Mg1−x Zn x )1.8Ti1.1O4 (x =0.03–1.00) ceramics were prepared via the conventional solid-state method and their dielectric properties were investigated in the microwave frequency region. Formation of solid solutions was confirmed by the X-ray diffraction analysis, the EDX analysis, and the measured lattice parameters. A small amount of Zn substitution for Mg produced a large increase in Q × f due to a high packing fraction as well as a high relative density of the ceramics. By increasing x from 0.00 to 0.06, the Q × f of the specimen could be tremendously improved from 141,000 to a maximum of 210,700GHz (at 10.52GHz), demonstrating an unique potential for low-loss microwave applications. The τ f values were found to retain in the range from −54.2 to −62.3ppm/°C for all compositions because the resultant change of unit cell volume was small. Also, a remarkable lowering of the sintering temperature down to ∼300°C was observed when Mg was totally substituted by Zn, thereby making it possible for low firing applications. [Copyright &y& Elsevier]

Abstract: High-relative-permittivity and low-loss ceramics in the (1− x)Ca(Mg1/3Ta2/3)O3–xCa0.8Sm0.4/3TiO3 system have been prepared by the conventional solid state route and their microwave dielectric properties have been investigated. (1− x)Ca(Mg1/3Ta2/3)O3–xCa0.8Sm0.4/3TiO3 solid solution exhibited orthorhombic crystal structures for all compositions. A rapid grain growth is observed at temperatures higher than 1450°C, which would lead to a decrease in the density and the Q × f of the ceramics. A near-zero temperature coefficient of resonant frequency can be achieved for Ca(Mg1/3Ta2/3)O3 with the addition of Ca0.8Sm0.4/3TiO3. The temperature coefficient of resonant frequency increases with increasing Ca0.8Sm0.4/3TiO3 content and tunes through zero at x =0.45. Specimen using 0.55Ca(Mg1/3Ta2/3)O3–0.45Ca0.8Sm0.4/3TiO3 possesses an excellent combination of microwave dielectric properties: ɛ r ∼44.96, Q × f ∼41,700GHz (where f =6.6GHz, is the resonant frequency) and τ f value of 0ppm/°C. It is proposed as a suitable candidate material for today''s 3G passive components and small-sized GPS patch antennas. [Copyright &y& Elsevier]

Abstract: The crystal structures, phase compositions and the microwave dielectric properties of the (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 perovskite-based composites have been investigated. The (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 solid solutions exhibited an 1:2 ordered monoclinic structure for all compositions. As (Ca0.8Sr0.2)TiO3 content increases, the ɛ r and τ f values increase gradually, while the Q × f values decreases. By appropriately adjusting the x value in the (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 ceramic system, a near-zero τ f value can be achieved. The optimal microwave dielectric properties with a dielectric constant (ɛ r ) value of 43.37, a Q × f value of 46,000GHz (where f =6.8GHz, is the resonant frequency), and a temperature coefficient of resonant frequency (τ f ) of −2.7ppm/°C can be obtained for specimen using (1− x)Ca(Mg1/3Ta2/3)O3–x(Ca0.8Sr0.2)TiO3 (x =0.4) sintered at 1425°C for 3h. It is proposed as a high-dielectric-constant, low-loss dielectric and in particular, a suitable candidate material for today''s 3G passive components and small-sized GPS patch antennas. [Copyright &y& Elsevier]