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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]

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]

Novel NaAGeO 4 (A = Sm, Y) ceramics with olivine structures were prepared and characterized. The phase composition, microstructural evolution, and densification behavior of the ceramics were investigated. The NaAGeO 4 (A = Sm, Y) ceramics possessed a single orthorhombic crystal system with Pbn21 and Pnma space groups. The NaSmGeO 4 ceramics had dense grains, clear boundaries, and low sintering temperatures, whereas a relatively wide range of sintering temperatures were feasible for the NaYGeO 4 ceramics. The NaSmGeO 4 ceramic material sintered at 1025 °C possessed excellent performance-related parameters, i.e., Q × f = 31,281 GHz, ε r = 6.29, and τ ƒ = −48.3 ppm/°C, whereas those for the NaYGeO 4 ceramic material were Q × f = 32,646 GHz, ε r = 6.74, and τ ƒ = −39 ppm/°C at 1200 °C. Furthermore, doping the NaYGeO 4 ceramic material with CaTiO 3 to obtain 0.12CaTiO 3 -0.88NaYGeO 4 yielded a τ ƒ value close to zero (−3 ppm/°C). The results demonstrate that NaAGeO 4 (A = Sm, Y) ceramics have substantial potential for application in microwave devices. [ABSTRACT FROM AUTHOR]

Owing to the rapid development of wireless communication technologies, microwave dielectric ceramics have been proposed to facilitate an increase in the performance of functional ceramic components. Herein, CaTiO 3 -LnAlO 3 (Ln=La, Nd) ceramics were synthesized via reaction sintering to produce low-cost, high-efficiency, materials. The reaction-sintering method, which imparts excellent comprehensive properties, was used to fabricate these ceramics. The subtle variations in the densification behavior, phase transformation, phase composition, microstructural evolution, and performance exhibited by the CaTiO 3 -LnAlO 3 (Ln=La, Nd) ceramics were systematically evaluated. The X-ray diffraction patterns obtained from each sample indicate that the Ca 0.61 La 0.39 Al 0.39 Ti 0.61 O 3 (CTLA) and Ca 0.7 Nd 0.3 Ti 0.7 Al 0.3 O 3 (CTNA) phases were generated under certain environmental conditions. The as-synthesized ceramics exhibited excellent performance parameters: ε r = 39.1, Q × f = 45 635 GHz, τ f = −1.48 ppm/°C and ε r = 44.03, Q × f = 46 269 GHz, τ f = +2.63 ppm/°C, respectively. In addition, the ceramics retained their strong performance parameters irrespective of external temperature fluctuations. The reaction sintering method provides an economical, convenient, and facile method for the fabrication of CaTiO 3 -LnAlO 3 (Ln=La, Nd) ceramics which, in turn, imparts broad prospects for the application and development of these materials. [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]

NaTaO 3 ferroelectric ceramics sintered at 1550 °C exhibit high relative permittivity and outstanding microwave dielectric properties of ε r = 113.76, Q × f = 8824 GHz, and τ ƒ = +645 ppm/°C in the low-frequency band (3.5195 GHz). The high relative permittivity is advantageous for the miniaturization of modern wireless communication devices. A near zero temperature coefficient of the resonance frequency (τ ƒ = +1.05 ppm/°C) and good microwave dielectric properties (Q × f = 54,680 GHz, ε r = 19.42) were obtained for 0.92MgTiO 3 -0.08NaTaO 3 ceramics. Moreover, the sintering temperature of MgTiO 3 could be decreased from 1350 °C to 1200 °C. Hence, NaTaO 3 is a high-potential microwave dielectric material for adjusting systems with a negative temperature coefficient of resonance frequency. [ABSTRACT FROM AUTHOR]