Mixtures of zinc metatitanate and rutile (ZnTiO 3 + xTiO 2 , where x = 0-0.5) have been prepared via the conventional mixed-oxide method. Centrifugal planetary milling with zirconia beads 1 mm in diameter produced very fine powders (mean particle size of 0.2 µm), which allowed the synthesis of ZnTiO 3 and sintering at temperatures <945°C, which is the decomposition temperature of ZnTiO 3 . Sintering of the mixtures was enhanced further by the addition of B 2 O 3 . Densities of >94% of the theoretical density have been attained for the specimens that were sintered at 875°C for 4 h with B 2 O 3 additions of <1 wt%. Microwave dielectric properties of the aforementioned compositions were as follows: dielectric constant of 29-31, normalized quality factor of 56000-69000 GHz, and a temperature coefficient of resonance frequency between −10 and +10 ppm/°C. Sintering was enhanced by the formation of a ZnO-B 2 O 3 liquid phase, which affected the microwave properties, because of variation in the phase composition.
A dielectric ceramic comprised of (Zn 1−x Mg x )TiO 3 (x = 0 to x = 0.5) with low sintering temperature and promising microwave properties was prepared by applying a semichemical synthesis route and a microbeads milling technique. X-ray diffractometry and thermal analyses results indicated that the phase stability region of the hexagonal (Zn,Mg)TiO 3 extended to higher temperatures as the amount of magnesium increased. The dielectric properties in this system exhibited a significant dependence on the sintering conditions, especially near the phase decomposition temperature. From 950°C, the temperature compensation characteristics occurred as the phase composition changed from hexagonal (Zn,Mg)TiO 3 to two phases: (Zn,Mg) 2 TiO 4 and rutile. The magnesium content for zero temperature coefficient ( f ) was ∼3 mol% at 950°C; however, f increased with the sintering temperatures because of the shift of the decomposition temperature.
Crystal structure and microwave dielectric properties of a xCaTiO3–y(Li1/2Nd1/2)TiO3–z(Ln1/3Nd1/3)TiO3 (Ln=La, Dy) ternary system were studied. Crystal structures were
refined by the Rietveld method using X-ray and neutron diffraction
data. (Li1/2Nd1/2)TiO3 and 0.2CaTiO3–0.8(La1/3Nd1/3)TiO3 ceramics showed the most reliable
R-values with a tetragonal structure with a space group P-4b2 and lattice constants of
a=b≈5.4 Å, and c≈7.6 Å. The A-site cations were ordered along the c-axis. When
x≥0.3, the crystal structure changed to an orthorhombic CaTiO3 type. The
xCaTiO3–y(Li1/2Nd1/2)TiO3–z(La1/3Nd1/3)TiO3
system showed microwave dielectric properties of
ε
r=133, Q·f=1,450 GHz and τf=-17 ppm/°C
at a composition of x=0.2, y=0.68, z=0.12. In
xCaTiO3–y(Li1/2Nd1/2)TiO3–z(Dy1/3Nd1/3)TiO3,
dielectric properties of ε
r=97.6, Q·f=5,150 GHz and τf=+0.4 ppm/°C were obtained at x=0.30, y=0.40, z=0.30. The effect of each ternary system component on the dielectric properties is discussed.
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