Prabhakaran Sreekumari Anjana

CeO2–La0.5Sr0.5CoO3−δ composites for giant permittivity applications

CeO2?La0.5Sr0.5CoO3?? (LSCO) composites with different LSCO loadings were prepared by the conventional solid-state ceramic route. X-ray diffraction and scanning electron microscopy results show that the composite is a mixture of CeO2 and LSCO. The variation of relative permittivity (measured at 27??C) with sintering temperature shows that the permittivity is maximum when sintered at 1150??C for the volume fraction of 0.4 (?r ? 105). The permittivity is decreased when sintering temperature increases above 1150??C. For all volume fractions of LSCO, the relative permittivity of CeO2?LSCO composites is almost independent of temperature in the range ?30 to 70??C. CeO2?LSCO composites can be a suitable substitute for cermets used in electromechanical and embedded passive devices.

Polyethylene-ceramic composites for electronic packaging applications

Summary form only given. The recent rapid progress in microwave communication accelerates the search of new materials to meet the present challenging performance requirements. In order to maintain high signal conveying efficiency, the dielectric substrate should have low relative permittivity and low dielectric loss. Several low loss low permittivity ceramics such as silicates and aluminates have been developed. However, they have high processing temperature and are brittle. Polymers are flexible having low processing temperature and exhibit excellent microwave dielectric properties. However, they have low thermal conductivity and high coefficient of thermal expansion. The composite strategy of combining the advantages of both polymer and ceramic phase can offer excellent property. Polymer ceramic composite offers excellent material characteristics such as flexibility, low processing temperature, and good microwave dielectric and thermal properties. In the present study we have taken polyethylene as the polymer because it has low processing dielectric properties. The relative permittivity of the individual phases and volume fraction of the filler are the most important factors determining the effective dielectric properties of the composites. In this paper we report the effect of ceramic fillers having relative permittivity in the range 10 to 110 (Sm2Si2O7, CeO2, Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-delta, Sr2Ce2Ti5O15) in polyethylene. The effect of frequency and temperature and volume fraction of fillers in polyethylene on the dielectric properties of the composites are studied. The ceramic reinforced polyethylene composites are prepared by melt mixing and hot pressing techniques. The microstructure of the composite is studied using a scanning electron microscope. The dielectric properties at high frequency (8 GHz) are analyzed using the cavity perturbation method. The relative permittivity and dielectric loss increased with increase in the ceramic loading for all the ceramic polymer composites. The experimentally observed results are compared with theoretical models.

Microwave dielectric properties of Ca 5-x Mg x Nb 4 TiO 17 (x = 0–3) ceramics

The Ca_5-xMg_xNb₄TiO₁₇ (x = 0-3) ceramics were prepared by conventional solid state ceramic route. The microstructure of the ceramic was studied using scanning electron spectroscopy. The microwave dielectric properties (Q_uxf, epsiv_r and tau_f) were measured using a vector network analyser. Ca₅Nb₄TiO₁₇ ceramics have a relative permittivity(epsiv_r) of 45, quality factor (Q_uxf) of 17600 GHz (at 4.13 GHz), and coefficient of temperature variation of resonant frequency (tau_f)-113 ppm/degC. The variation in the microwave dielectric properties of Ca₅Nb₄TiO₁₇ ceramics were investigated with the increase in magnesium content. The sintering temperature reduced from 1475degC for x = 0 to 1200degC for x = 3. The quality factor increased with magnesium content and maximum Q_uxf was obtained for the composition x = 2 (22500 GHz (at 3.99 GHz)). The epsiv_r and tau_f of Ca₃Mg₂Nb₄TiO₁₇ ceramics were found to be 37.5 and -4.3 ppm/degC respectively. Hence Ca₃Mg₂Nb₄TiO₁₇ ceramics are very much useful for practical applications like Dielectric resonators in filters and oscillators.