Search

In the present work, a high quality (Q) Ca 1.15 Sm 0.85 Al 0.85 Ti 0.15 O 4 (CSAT) ceramic was prepared via reaction sintering (RS) method. The phase structure, surface morphology, packing fraction (PF), and valence bond of the ceramic were systematically investigated. By studying the X-ray diffraction (XRD) pattern of the ceramic, it was determined to exhibit a single-phase tetragonal structure with the dimensions of a = b = 3.6943(13)Å and c = 12.0320(23)Å and volume of V = 164.22(10) Å3. The influence of the intrinsic quality loss factor on the Q × f value was investigated by calculating the PF. Simultaneously, the bond valence of the samarium (Sm) sites was evaluated to elucidate the relationship with the temperature coefficient of resonant frequency (τ f). The CSAT ceramic was sintered at 1550 °C for 6 h and exhibited exceptional characteristics in terms of the relative dielectric constant (ε r) = 17.5, quality factor (Q × f) = 66700 GHz, and τ f = −6.93 ppm/°C. These results highlighted the excellent suitability of the RS method for preparing CSAT ceramics with outstanding microwave dielectric properties. [ABSTRACT FROM AUTHOR]

0.85(0.74CaTiO3–0.26SmAlO3)–0.15Ca1.15Sm0.85Al0.85Ti0.15O4 (CSC) composite ceramics were prepared by a reaction-sintering method. The phase structure, sintering behavior and microwave dielectric properties of CSC ceramics were investigated. The preparation process of reaction-sintering route (RS) is simple. XRD patterns show that Ca0.74Ti0.74Sm0.26Al0.26O3 (similar to CaTiO3), SmAlO3 and Ca1.15Sm0.85Al0.85Ti0.15O4 phases are formed in the CSC ceramics. The grain size and dielectric constant of CSC ceramics increase with rising the sintering temperature. As the sintering temperature increases, the quality factor (Q × f) and τf value of the CSC ceramics increase to the maximum values first and then decrease. The bulk density fluctuates up and down around a value, but little change. The ceramics sintered at 1500 °C got the best microwave dielectric performances with εr = 35.9, Q × f = 49,221 GHz, τf = − 0.53 ppm/°C. [ABSTRACT FROM AUTHOR]

A novel La 2 MgGeO 6 ceramic was synthesized through a solid-state reaction process within a sintering temperature range of 1450–1550 °C. By a combination of X-ray diffraction and Rietveld refinement analyses, the ceramics were found to have a pure hexagonal phase structure belonging to space group R3/146. The scanning electron microscopy images revealed that the ceramic grains were closely connected. The effects of internal (lattice energy, valence bond, and fraction packing) and external factors (density) on the microwave properties of ceramics were also studied. The ceramic exhibited excellent microwave dielectric performances, with a relative permittivity (Ɛ r) of 21.2, a quality factor (Q × f) of 52 360 GHz, and a temperature coefficient of resonant frequency (τ f) of −44.2 ppm/°C, when sintered at 1500 °C for 4 h. The τ f value of the La 2 MgGeO 6 ceramic doped with CaTiO 3 could be adjusted to zero. Particularly, 0.2La 2 MgGeO 6 -0.8CaTiO 3 ceramics have good microwave dielectric properties with τ f = +2.1 ppm/°C, Q × f = 15 610 GHz, and Ɛ r = 40.3. [ABSTRACT FROM AUTHOR]