Dielectric Properties Of Ca Research Articles

Dense and strong plasma initiated by Ca0.7Sr0.3TiO3 ceramic

In order to find a kind of material that is able to initiate plasma avalanches, Ca0.7Sr0.3TiO3 ceramic, which possesses high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier to decompose CO2 in order to investigate the efficiency and characteristics of this ceramic. The results were compared with commercial alumina and silica glass, which possess lower permittivities, but however, were widely used in previous studies. The mechanical and dielectric properties of Ca0.7Sr0.3TiO3 were greatly enhanced by adding 0.5 wt. % Li2Si2O5 as a sintering additive. Although Ca0.7Sr0.3TiO3 without an additive was fractured before the arcing plasma, that which was sintered with 0.5 wt. % Li2Si2O5 successfully generated a dielectric barrier discharge (DBD) plasma and the CO2 conversion was much higher than with those using an alumina or silica glass barrier. The plasma behaviors of using different dielectric materials were studied during the processes of the DBD plasma burst. It was found that the density and strength of current pulses increased with increasing permittivity, and as a consequence, very dense and strong current pulses were initiated by this Ca0.7Sr0.3TiO3 with 0.5 wt. % Li2Si2O5 ceramic because of its high permittivity; likewise, they were efficient in reducing CO2. The density and strength of current pulses are also found to be the dominative parameters of the plasma reaction. This Ca0.7Sr0.3TiO3 ceramic was sintered using Li2Si2O5 as a sintering additive and used as a dielectric barrier of DBD for the first time.

Sintering and characterization of Ca0.9Sr0.1TiO3 ceramics with sintering additive

Abstract Ca 0.9 Sr 0.1 TiO 3 was sintered using Li 2 Si 2 O 5 as a sintering additive for the first time. Although Ca 0.9 Sr 0.1 TiO 3 could not be fully sintered even at 1400 °C, the densification temperature could be decreased to 1200 °C by using Li 2 Si 2 O 5 , which possesses low melting temperature of ca. 1030 °C. Consequently, the mechanical and dielectric properties of Ca 0.9 Sr 0.1 TiO 3 ceramics were improved. The microstructure, mechanical properties, and dielectric properties greatly changed depending on the amount of additive. The optimum concentration to obtain high density and high dielectric strength was 0.5 wt.%. In addition, the results suggested that relative density was the most important parameter to the dielectric properties.

Dielectric properties of [Ca 1− x(Li 1/2Nd 1/2) x] 1− yZn yTiO 3 ceramics at microwave frequencies

Dielectric properties of Ca 1− x (Li 1/2Nd 1/2) x TiO 3 (0.0≤ x≤0.6, CLNT) and [Ca 0.6(Li 1/2Nd 1/2) 0.4] 1− y Zn y TiO 3 (0.5≤ y≤1.0, CLNZT) ceramics were investigated at 4–10 GHz. For the CLNT system, a single perovskite phase was detected in the entire composition range. The dielectric constants ( K), and the temperature coefficients of the resonant frequency (TCF) were dependent on the B-site bond valence. Qf value decreases with the increase in (Li 1/2Nd 1/2)TiO 3 content ( x) due to a decrease in grain size. For the CLNZT system, Qf value and TCF were improved with Zn content ( y) due to the formation of Zn 2TiO 4. Typically, K of 47, Qf of 13 000 GHz, TCF of 14 ppm per °C were obtained for [Ca 0.6(Li 1/2Nd 1/2) 0.4] 0.4Zn 0.6TiO 3 sintered at 1150 °C for 4 h.

Microwave dielectric properties of Bi2O3-doped Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics

The effect of the additive on the densification, low temperature sintering, and microwave dielectric properties of the Ca[(Li 1.3 Nb) 2/3 ) 1-x Ti x ]O 3-δ (CLNT) was investigated. Bi 2 O 3 addition improved the densification and reduced the sintering temperature from 1150 to 900 C of CLNT microwave dielectric ceramics. As the Bi 2 O 3 content increased, the dielectric constant (e r ) and bulk density increased. The quality factor (Q.f 0 ), however, was decreased slightly. The temperature coefficient of resonant frequency (τ f ) shifted to a positive value with increasing Bi 2 O 3 content. The dielectric properties (e r , Q.f 0 , τ f ) of Ca[(Li 1.3 Nb 2/3 ) 0.95 Ti 0.05 ]O 3-δ and Ca[(Li 1.3 Nb 2/3 ) 0.8 Ti 0.2 ]O 3-δ with 5 wt.% Bi 2 O 3 sintered at 900 °C for 3 were 20, 6500 GHz, -4 ppm/C. and 35, 11,000 GHz, 13 ppm/°, respectively. The relationship between the microstructure and dielectric properties was studied by X-ray diffraction (XRD), and SEM.

Low-temperature sintering and microwave dielectric properties of Ca(Li1/3Ta2/3)O3−δ–CaTiO3 ceramics

New Ca[(Li 1/3 Ta 2/3 ) 1-x Ti x ]O 3-δ (0.5≥x≥0) solid solutions with the addition of B 2 O 3 were prepared by a conventional oxide mixture method to develop a microwave resonator with a low sintering temperature. It was shown that Ca(La 1/3 Ta 2/3 )O 3-δ ceramics did not occur as a single phase but rather as a mixture of a perovskite-type phase with a minor amount of Li 3 TaO 4 . The perovskite phase exhibited 1:2 ordering of Li and Ta on the B-sites. The substitution of Ti 4+ for Li 1+ and Ta 5+ stabilized the perovskite phase, destabilized 1:2 ordering, and improved the grain growth of Ca[(Li 1.3 Ta 2.3 ) 1-x Ti x ]O 3-δ (x=0.2, 0.3) ceramics. As the x composition increased from 0 to 0.5, the dielectric constant, e, increased from 24 to 48, the quality factor, Q×f, decreased from 42,000 to 11,000 GHz, and the temperature coefficient of resonator frequency, τ f , increased from a negative value to a positive one. A new microwave dielectric material with e=35, Q×f = 22,800 GHz, and τ f = -4.1 ppm/°C was obtained in the Ca[(Li 1.3 Ta 2.3 ) 0.7 Ti 0.3 ]O 3-δ ceramics doped with B 2 O 3 sintered at a temperature as low as 1050 C.

Microwave dielectric properties of B2O3 doped Ca[(Li1/3Nb2/3)0.9Ti0.1]O3-δ ceramics

The effect of B2O3 doping on microwave dielectric properties of Ca[(Li1/3Nb2/3)0.9Ti0.1]O3-δ was investigated. The Ca[(Li1/3Nb2/3)0.9Ti0.1]O3-δ ceramics was sintered at 1150°C. In order to decrease the sintering temperature for using as a low temperature co-firing ceramics (LTCC), B2O3 was added in the Ca[(Li1/3Nb2/3)0.9Ti0.1]O3-δ. As the content of B2O3 increased, the sintered density, the dielectric constant and Q·f0 value increased and the temperature coefficient of resonance frequency (τf) shifted to the negative value. When the B2O3 of 0.7 wt% added, the dielectric properties were ϵr of 35, Q·f0 of 22100 GHz, and τf of-5.6 ppm/°C at the sintering temperature of 1000°C.

Conductivity and dielectric relaxation in hydrated fused salts

The dielectric properties of Ca(NO3)2· 2.9H2O, Cd(NO3)2· 2.37H2O and (Ca + Cd)(NO3)2· 2.92H2O have been measured in the supercooled liquid state immediately above their respective calorimetric glass-transition temperatures. Over the frequency range 12–105 Hz, their permittivity and loss spectra are featureless. By subtracting the contributions from electrode impedance and dc conductivity, the remaining Iµ*, which is due to a polarization process, is described well by a Davidson–Cole relaxation function with β in the range 0.26–0.40 (± 0.05). The activation energies for conduction are 200–220 kJ mol–1. β decreases with decreasing temperature, as does the contribution to permittivity from orientation polarization. The latter, which differs from the behaviour of most liquids, indicates a decrease in the number densities of the molecular and ion-pair dipoles and/or their dipole moments with decreasing temperature. Analyses of the data in Iµ* and M*(=Iµ*–1) formalisms give the same results. The former is direct, although it requires knowledge of the exponent for the electrode impedance. The data also fit an asymmetric distribution of conductivity relaxation times at least as well as in the literature, but this fit appears to be misleading.

Dielectric Studies on Phase Transition of Ca2Sr(CH3CH2COO)6Crystals Doped with HCF2CF2COO/HCF2COO Ion

Dielectric properties of Ca 2 Sr(CH 3 CH 2 COO) 6 (DSP), Ca 2 Sr(CH 3 CH 2 COO) 6(1- x ) (HCF 2 CF 2 COO) 6 x (HCF 2 CF 2 -DSP) and Ca 2 Sr(CH 3 CH 2 COO) 6(1- x ) (HCF 2 COO) 6 x (HCF 2 -DSP) crystals have been studied in the temperature range from 4 K to room temperature at several frequencies between 1 and 100 kHz. The DSP crystal underwent I-II, II-III and III-IV phase transitions near 281.2, 76 and 58 K, respectively. In HCF 2 CF 2 -DSP and HCF 2 -DSP crystals, the phase transition temperature decreased for the I-II phase transition and increased for the II-III phase transition with the increase in the content of HCF 2 CF 2 COO/HCF 2 COO ion (x). These results were qualitatively explained by the motion of propionate group associated with the phase transitions.

Pressure-Induced Ferroelectricity in Ca2Ba(C2H5CO2)6 (DBP)

Dielectric properties of Ca 2 Ba(C 2 H 5 CO 2 ) 6 single crystals have been studied at hydrostatic pressure of about 0.9 kbar. It has been found that the high-pressure phase V is ferroelectric. D - E hysteresis loop at 60 Hz is observed only on annealed specimens, but not on as-grown crystals. It is suggested that the ferroelectric phase V of Ca 2 Ba(C 2 H 5 CO 2 ) 6 corresponds to those well-known ferroelectric phases II of Ca 2 Sr(C 2 H 5 CO 2 ) 6 and Ca 2 Pb(C 2 H 5 CO 2 ) 6 which are realized at atmospheric pressure.