Homogeneity of 67P/Churyumov-Gerasimenko as seen by CONSERT: implication on composition and formation

Context. After the landing of Philae, CONSERT probed the nucleus of 67P/Churyumov-Gerasimenko (67P) and observed no heterogeneities at metric scale within the probed part of the small lobe of 67P. Further studies have then quantified the observed homogeneity in terms of maximum permittivity contrast versus the typical size of heterogeneities. Aims. The aim of this article is to interpret the sensitivity limits of CONSERT measurements in terms of composition, and to provide constraints on the maximum variability in composition, porosity, and local dust-to-ice ratio. Methods. The sensitivity of CONSERT measurements to local variations in density, dust-to-ice ratio, and composition was analyzed using permittivity modeling of mixtures. Results. We interpret the maximum detectable heterogeneity size and contrast in terms of composition and porosity of the nucleus. The sensitivity to porosity is ±10 percent points for heterogeneities with a characteristic length scale of a few meters; the sensitivity to local variations in the composition is limited. Conclusions. In terms of accretion, our results are compatible only with scenarios generating porosity heterogeneities at scales lower than one meter, or with porosity variations smaller than ±10 percent points. This is clearly compatible with an accretion model of a gentle gravitational collapse of a pebble cloud.

Effects of Bi3+ Doping on the Optical and Electric-Induced Light Scattering Performance of PLZT (8.0/69/31) Transparent Ceramics

Lanthanum modified lead zirconate titanate (abbreviated as PLZT) Electro-Optical ceramics with various Bi concentration were prepared by a hot-press process. The PLZT ceramic samples all present a single perovskite structure with no second phase detected. Bi3+ ion was considered to mainly enter the A-site of perovskite ABO3 structure of PLZT ceramics by the X-Ray Diffractionanalysis. The maximum permittivity (εm) of the PLZT samples decreased obviously as Bi concentration increased, while their remnant polarization (Pr) decreased slightly. In particular, the PLZT sample with 0.14 wt% Bi doping presented a higher optical transmittance 61.8% (λ = 633 nm), and its electric-induced light scattering performance was found to be improved obviously, the maximum light deduction value of ~47.6% was obtained.

Phase transition and dielectric properties of BaTiO3 ceramics containing 10 mol% BaGeO3

Dielectric properties and the cubic ? tetragonal phase transition temperature ofdense BaTiO3 ceramics containing 10 mol% BaGeO3, sintered between 840 and 1350 °C,have been investigated. The ceramic bodies were prepared from a nano-sized BaTi0.9/Ge0.1O3powder consisting of both BaTiO3 and BaGeO3 phases. The addition of BaGeO3 leads to areduction and broadening of the permittivity maximum, and to a small downshift of theparaelectric ? ferroelectric phase transition temperature, compared to a pure BaTiO3 ceramic.Lower sintering temperatures and thus small grain sizes of the ceramics cause an additionalreduction of the maximum permittivity down to 2800. Both DTA and dilatometricmeasurements reveal also a downshifting of the phase transition temperature, as well as adecrease of the latent heat.

Dielectric Properties of New Cd1-3xDy2x[]xMoO4 Molybdates (where 0 < x ≤ 0.2)

New scheelite type Cd1-3xDy2x[]xMoO4solid solution, where 0.0098 ≤ x ≤ 0.2 and [] denotes the cationic vacancies, was investigated by using UV-vis-NIR and dielectric spectroscopies at room temperature and in the temperature range 77-400 K, respectively. These studies showed the optical band gap energy Eg above 3.4 eV and relative low dielectric permittivity: εr ~ 6.0, 9.5, 7.0 and 8.2 for the x parameter 0.0098, 0.0839, 0.1667 and 0.2000, respectively. εr slightly decreases with increasing frequency and slightly increases at higher temperatures. All samples showed the maximum permittivity in the temperature range of 250-350 K. The loss tangent exhibited similar behaviour and its maximum value did not exceed 0.25. These results are discussed in a context of the shallow trap levels and the Maxwell-Wagner model.

The Microstructure and Dielectric Properties of SrTiO3 Modified 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Ceramics

The microstructure and dielectric properties of ferroelectric solutions which is formulated with (1-x)[0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3]-x mol% SrTiO3(x=0, 1, 3 and 5) have been investigated. The ceramics was fabricated by a modified columbite route sintered at 1200 °C. The effects of dopants on microstructure, maximum dielectric constant (εm) and diffuseness of the phase transition, etc. have been studied. It is found that the maximum permittivity (εm) increases to 24968 for the ST-doped (1 mol %) sample, subsequently decreases with ST addition and its corresponding phase-transition-temperature (Tm) shifts to the lower temperature. The variation of εmis caused by the decrease of polar nano-region size, increase of the fluctuation of the component and the increase of the effective spontaneous polarization. The enhancement of relaxor behavior in the PMN-PT sample is explained by the decrease of FE/AFE coupling.

Dielectric and Ferroelectric Properties of (Pb0.9Ba0.1) ZrO3 Ceramics

(Pb1-xBax)ZrO3(PBZ) ceramics forx= 0.10 were synthesized by the mixed oxide solid state reaction method. Phase transition was investigated by dielectric measurements in the temperature range from 27 to 350 °C at various frequencies. The permittivity of the solids corresponding to (Pb1-xBax) ZrO3showed the maximum value of 10220 atx= 0.10 at the phase transition temperature. The maximum permittivity gradually increasing concentration up tox= 0.10. The ferroelectric hysteresis loop of the PBZ ceramics forx= 0.10 is displayed at room temperature and 0.2 Hz.

Effects of CuO on the Preparation, Microstructure and Dielectric Response of CaCu3Ti4O12

CaCu3Ti4O12 (CCTO) barrier layer ceramic capacitor was prepared by a two-step sintering process. The CCTO powders were pre-synthesized at 900oC by solid-state reaction and the effects of the amount of CuO on the formation of the CCTO powders were investigated. The CCTO ceramics were prepared by the second-step sintering. It was found that the abnormal grain growth and inhomogeneous microstructure are controlled by the amount of excessive CuO. The optimized CuO content in the composites is ~14 wt%. The maximum permittivity is 115,000 (1 kHz, 210oC).

EFFECT OF RARE-EARTH (RE = La, Nd, Ce AND Gd) DOPING ON THE PIEZOELECTRIC of PZT(52:48) CERAMICS

The purpose of this research is to study the effect of doping some rare earth ions into PZT(52:48) ceramics. The ferroelectric Pb ( Zr x Ti 1-x) O 3 ceramics are well-known as piezoelectric materials for electro-mechanical transducers such as ultrasonic generator, electronic buzzer, and stress sensor, etc. The highest piezoelectric coupling coefficients as well as maximum permittivity are located near the morphotropic phase boundary (MPB). The region of phase transition between the tetragonal and rhombohedral structures in the Pb ( Zr x Ti 1-x) O 3 ceramic shows very adoptable piezoelectric characteristics due to the phase coexistence phenomena, and exhibits a sensitivity of properties to the preparation method, the composition, the firing temperatures and the kinds of additives. The purpose of this research is to study the effect of doping La , Nd , Ce and Gd into Pb ( Zr 0.52 Ti 0.48) O 3 ceramics prepared by solid state reaction. The properties include microstructure, physical properties, dielectric constant (εr) and piezoelectric properties (kp and Qm) of undoped and La , Nd , Ce and Gd doped PZT ceramics. Several effects, such as firing temperature, grain size and dopants, on the properties of PZT were also studied. The undoped PZT ceramics with Zr/Ti at 52/48 indicated the highest εr=1969 and kp= 0.381 for La doping. Doping with La , Nd , Ce and Gd led to an improvement in the εr but a reduced Qm value. The optimum values of electric properties were found in PZT (52/48) doped La with 10.0 mol% sintered at 1200°C for 2 h.

Effects of Mg2+ on Microstructure and Microwave Dielectric Properties of La2/3TiO3 Ceramics

(1-x)La2/3TiO3-xLa(Mg1/2Ti1/2)O3 ceramics with x ranging from 0.01 to 0.3 were prepared by the conventional solid-state reaction method. Microstructure and microwave dielectric properties were studied. The perovskite compound La2/3TiO3 is stabilized when x = 0.1. The content of La2/3TiO3 increases with increasing x from 0.01 to 0.1, and thereafter decreases when x > 0.1. The same tendency was also observed on measuring the dielectric constant, temperature coefficient of resonant frequency and Q× ƒ. A maximum permittivity of 77.35 was achieved with these stabilized La2/3TiO3 ceramics. Close to zero τf value (1 ppm/°C) was obtained at x=0.3, but its Q× ƒ value was relative low.

Anomalous Broad Dielectric Dispersion of 0.4PZN-0.3PSN-0.3PZN Relaxor Ceramics at Lower Temperatures

Dielectric properties of 0.4PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3-0.3PbMg1/3Nb2/3O3- (0.4PZN- 0.3PSN-0.3PMN) ceramics are presented for 200 < T < 500 K and 20 Hz < ν < 1 MHz. Dielectric constant is very high (more 14000) in the vicinity of the peak. Anomalous broad dielectric relaxation have been observed near the temperature of the maximum permittivity, Tm (at 1 kHz). External bias field considerably lowers the value of dielectric losses at low frequencies due to decrease of polar nano regions contribution to the dielectric permittivity.