Temperature Stable, High-Quality Factor Li2TiO3-Li4NbO4F Microwave Dielectric Ceramics

In this work, (1-x)Li2TiO3-xLi4NbO4F ceramics were prepared by the conventional solid-state ceramic route. With the increase of Li4NbO4F content, the phase structure transformed from ordered monoclinic to disordered cubic. By increasing Li3NbO4F content, the temperature coefficient of resonant frequency (τf) was successfully adjusted closer to zero, while the dielectric constant (εr) and microwave quality factor (Qf) decreased to some degree. Outstanding microwave dielectric properties with a εr = 18.7, Qf = 61,388 GHz (6.264 GHz), and τf = 0.9 ppm/°C were obtained for 0.9Li2TiO3-0.1Li4NbO4F ceramics sintered at 1050 °C for 2 h, which indicated that these ceramics are suitable for practical applications in the field of microwave substrates and components.

Ferroelectric and Dielectric Properties of BaZr0.2[Ti(1-x)Mgx/3Ta2x/3]0.8O3 Solid Solution

BaZr0.2[Ti(1-x)Mgx/3Ta2x/3]0.8O3 (x = 0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) (BZTMT) ceramics were prepared through conventional solid state ceramic route. The crystal structure and microstructure of the compounds were investigated respectively using XRD and SEM. The dielectric properties were measured in the frequency range of 100 Hz–1 MHz. The ferroelectric Curie temperature of BaZr0.2Ti0.8O3 (x = 0) shifted from 21°C to -10°C with the addition of minute amount of dopant (x = 0.025) and the paraelectric transition temperature is diffusive in nature. The relative permittivity and dielectric loss of BZTMT at 1 MHz varies from 5205 to 24 and 1.8 × 10–2 to 2.0 × 10–5 respectively, as the value of x increases from 0 to 1.

Sodium Alanate Dehydrogenation Properties Enhanced by MnTiO3 Nanoparticles

In this study, we investigated the influence of MnTiO3 nanoparticles additive on hydrogen released performance of NaAlH4 for the first time. The MnTiO3 nanoparticles were successfully synthesized using conventional solid-state ceramic route. It was found that the hydrogen released performance of NaAlH4 can be significantly improved by the addition of MnTiO3 nanoparticles. Meantime, the composite of NaAlH4 doped 5 wt% MnTiO3 possessed excellent dehydrogenation properties, the onset dehydrogenation temperature was only 70.6 °C, reduced by about 105 °C in comparison with the pristine NaAlH4, and approximately 5.01 wt% of hydrogen could be released from composite with temperature heated to 220 °C. The isothermal dehydrogenation test results indicated that the amount of hydrogen released by NaAlH4-5 wt% MnTiO3 composite could reach 4.4 wt% under 200 °C within 25 min. According to the analysis of X-ray diffraction, the presence of MnTiO3 nanoparticles did not alter the overall dehydrogenation pathway of NaAlH4, and the Al3 Ti phases formed after dehydrogenation, which enhanced hydrogen desorption performances of NaAlH4 .

Raman spectroscopy and microwave dielectric properties of Sn substituted SrLa4Ti5O17 ceramics

SrLa4Ti5−xSnxO17 (0 ≤ x ≤ 2) ceramics were fabricated through solid state ceramic route and their microwave dielectric properties were investigated in an attempt to tune their temperature coefficient of resonant frequency (τf) to zero. The compositions were sintered to single phase SrLa4Ti5O17 and SrLa4Ti4.5Sn0.5O17 ceramics at x = 0 and x = 0.5, and SrLa4Ti4−xSnxO17 along with a small amount of La2Ti2O7 at x = 1. The major phase observed at x = 2 was La2Ti2O7 but along with SrLa4Ti4SnO17 and SrLa4Ti4O15 as the secondary phases. τf decreased from 117 to 23.0 ppm/°C but at the cost of dielectric constant (εr) and quality factor multiplied by resonant frequency (Qufo) which decreased from 65 to 33.6 and 11150 to 4191 GHz, respectively. The optimum microwave dielectric properties, i.e. τf = 38.6 ppm/°C, εr = 45.5 and Qufo = 7919 GHz, correspond to the SrLa4Ti5−xSnxO17 composition with x = 1.

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Ca2Ce2Ti5O16 dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO2 and another unidentified phase (that vanished at ≥ 1400 °C) as secondary phases along with the parent Ca2Ce2Ti5O16 phase. The amount of the parent Ca2Ce2Ti5O16 phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ɛr and Qu f o increased with sintering temperature. An er ~ 81.5, Qu fo ~5915 GHz and t f ~ 219 GHz were achieved for the sample sintered at 1450 °C.

DIELECTRIC BEHAVIOUR OF MANGANESE MODIFIED STRONTIUM TITANATE CERAMICS SYNTHESIZED BY SOLID STATE CERAMIC ROUTE

Various compositions with x=0.01, 0.05, 0.10, 0.20 and 0.30 in the system SrTi 1-x Mn x O 3 were prepared by solid state ceramic route. Compositions with x ≤ 0.10 were found to be single phase solid solution. In this paper, the result of investigations on the effect of manganese substitution in SrTiO 3 on dielectric behaviour for the compositions with x ≤ 0.10, which form single phase solid solution have been reported. Average grain size is small, this may be due to segregation of dopant at grainboundaries. Dielectric measurements were made in the temperature range 150–500K. Measurements of dielectric properties show that there is not much space charge polarisation across the grains and grainboundaries interface. This space charge polarisation only occurs at high temperature and one observes large dispersion of dielectric constant and dissipation factor. At low temperatures, dielectric behaviour follows the character of SrTiO 3 with only difference in the values of dielectric constant.

A NOVEL DIELECTRIC CERAMIC FOR MICROWAVE PASSIVE CIRCUITS

The tetragonal Ca 9 Nd 2 W 4 O 24 (CNW) ceramic was prepared by the conventional solid state ceramic route and their dielectric properties were investigated in the radio and microwave frequencies. The CNW ceramics sintered at 1450 °C for 4 h showed a densification 92 % with εr = 16 and tanδ = 0.004 at 15.1 GHz. The thermal conductivity of ceramic at room temperature was found to be 1.6 W m−1K−1 and coefficent of thermal expansion of CNW ceramics was 4.2 ppm/°C measured in the range of 25 to 600 °C. The dielectric and thermal properties of CNW ceramic are reported for the first time.

Novel glass free ceramic for LTCC applications

The LiZnPO4 ceramic has been prepared by the conventional solid state ceramic route. The ceramic sintered at 825 °C has an εr of 4.9, Qu×f of 65400 GHz, and τf of −80 ppm/°C. The LiZnPO4 ceramic shows low coefficient of thermal expansion (CTE) of 5.3 ppm/°C. The slightly large negative τf of LiZnPO4 has been tuned nearly to zero with TiO2 addition. LiZnPO4-TiO2 composite containing 0.15 volume fraction TiO2 sintered at 925 °C shows good microwave dielectric properties: εr = 7.8, Qu×f = 39800 GHz and τf = −6.8 ppm/°C. LiZnPO4−0.15 Vf TiO2 composite shows a CTE of 6.9 ppm/°C.

Microwave Dielectric Properties of Ca(Li1/3Nb2/3)O3-δ Ceramics with ZnO Additive

The complex perovskite compound Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics have received much attention due to the superior properties and relatively low sintering temperature 1150°C. In order to further low the sintering temperature of the CLN ceramics, enhance the Q · f values and other dielectric properties, the effects of the additive ZnO on the sinterability and dielectric properties of the CLN have been investigated. The CLN ceramics were prepared by conventional solid state ceramic route. With the addition of 1.0 wt% ZnO, the sintering temperature of Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics was effectively reduced from 1150◦C to 1090◦C，and the Q · f value was increased from 18920 to 20950 GHz (at 7.09 GHz). It also possesses compatible dielectric constant εrof 27.8 and τfvalue of -23.57 ppm/◦C. While with the addition of 1.25 wt% ZnO, the Q · f value of Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics sintered at 1150◦C for 3 hours was increased significantly to 32150 GHz (at 7.09 GHz), εrof 28.3 and τfvalue of -18.55 ppm/◦C. The relationship between microstructure and microwave dielectric characteristics was studied using X-ray diffractometer and Scanning electron microscope.