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Ca 1.15 RE 0.85 Al 0.85 Ti 0.15 O 4 (RE = Nd, La, Y) ceramics were prepared by a reaction sintering method. The sintering behavior, phase composition, microstructure and microwave dielectric performances of ceramics were investigated. X-ray diffraction patterns illustrated that both the Ca 1.15 Nd 0.85 Al 0.85 Ti 0.15 O 4 (CNAT) and Ca 1.15 Y 0.85 Al 0.85 Ti 0.15 O 4 (CYAT) ceramics are single-phase structures, and the Ca 1.15 La 0.85 Al 0.85 Ti 0.15 O 4 (CLAT) ceramic contain LaAlO 3 and CaO phases. The apparent morphology and elemental distribution of the ceramic samples were analyzed by using scanning electron microscope and energy dispersive spectrometer. When the sintering temperature is 1500 °C, the CNAT and CYAT ceramics have the best microwave dielectric properties with ε r = 19.2, Q × f = 74924 GHz, τ f = −1.21 ppm/°C and ε r = 17.5, Q × f = 27440 GHz, τ f = −5.79 ppm/°C, respectively. And the best microwave dielectric properties of ε r = 17.5, Q × f = 22568 GHz, τ f = −14.69 ppm/°C were obtained for the CLAT ceramic sintered at 1525 °C. The reaction sintering method provides a low-cost, economical and straightforward method for the preparation of the Ca 1.15 RE 0.85 Al 0.85 Ti 0.15 O 4 (RE = Nd, La, Y) ceramics, which has promising potential for application. [ABSTRACT FROM AUTHOR]

MNdTiNbO7 (M = Ca, Sr) ceramics were prepared by a conventional solid-state reaction method. Single-phase dense CaNdTiNbO7 (CNTN) ceramic was obtained at 1400 °C and displayed outstanding microwave dielectric properties of Q × f = 6710 GHz, τf = 205 ppm/°C, and εr = 65.1. While the excellent microwave dielectric properties of Q × f = 8088 GHz, τf = 305 ppm/°C, and εr = 56.5 were obtained for the SrNdTiNbO7 (SNTN) ceramic at 1375 °C. The GSAS analysis software was used to investigate the ion occupancy of the ceramic samples and the changes in their phase structure. When the sintering temperature was 1400 °C, the lattice energy and packing fraction of the CNTN ceramic reached the maximum values of 41,779.7 kJ/mol and 65.35%. The CNTN ceramic resistance is mainly influenced by the grain boundaries. The substitution of Ta for Nb could adjust the τf value of CNTN ceramic. As x = 0.8, the τf values of CaNdTi(Nb1−xTax)O7 ceramics sintered at 1400 °C would be decreased from + 205.18 to + 20.27 ppm/°C. [ABSTRACT FROM AUTHOR]

We use reaction sintering method (RS) to prepared 0.85(1 − xCaTiO3−xLnAlO3)–0.15Ca1.15Ln0.85Al0.85Ti0.15O4 (Ln = Nd, Y) ceramics. CLnC ceramics have two phase structures of perovskite and K2NiF4. The ceramic grains are obvious solid solutions, and gradually enlarge with increasing the sintering temperature. CNdC ceramics exhibit good microwave dielectric properties in the sintering temperature range of 1475–1575 °C. As the sintering temperature increases from 1475 to 1500 °C, the density of CNdC ceramics tends to be stable, fluctuates around 4.6 g/cm3. The εr reaches maximum value at 1500 °C then gradually decreases. As the sintering temperature increases from 1500 to 1550 °C, the Q × f keeps a stable value from 41,953 to 44,188 GHz. As the sintering temperature was 1500 °C, the CNdC ceramics achieved the best microwave dielectric properties with εr = 37.15, Q × f = 44,188 GHz, τf = − 4 ppm/°C. The sintering temperature of CYC ceramics was relatively low and the ceramics sintered at 1450 °C achieved good microwave dielectric properties of εr = 38.3, Q × f = 29,620 GHz, τf = 0.03 ppm/excellent. It is worth noting that CYC ceramics have an excellent τf, which can ensure excellent temperature stability during application. [ABSTRACT FROM AUTHOR]

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]

Novel 0.695CaTiO 3 -0.305SmAlO 3 + x wt% CeO 2 (x = 0, 0.5, 1.0, 1.5) ceramics were fabricated using a reaction-sintering (RS) approach. The crystal structure, morphology, and microwave dielectric properties of ceramics were systematically studied. The addition of CeO 2 could effectively improve the sintering behavior of 0.695CaTiO 3 -0.305SmAlO 3 (CTSA) ceramics. When x = 0.5 wt%, the ceramics exhibited optimal microwave dielectric properties, with ε r = 43.9, Q × f = 48 779 GHz, and τ ƒ = −0.24 ppm/°C, thereby indicating that the samples prepared via the RS route possess superior dielectric properties compared to those prepared by the conventional solid phase reaction. The results demonstrate that CaTiO 3 -SmAlO 3 ceramics can be prepared simply and efficiently through a reaction-sintering process. [ABSTRACT FROM AUTHOR]