Dielectric behavior and PTCR effect in nanocrystallite PMN ferroelectric ceramics

Abstract

The ac behavior of a nanocrystallite lead magnesium niobate (PMN) ceramic sample was studied over a wide range of temperatures and frequencies. The results revealed a diffuse phase transition and very high dielectric constant at lower frequencies. The high value of the dielectric constant at lower frequencies is shown to be due to barrier layer formation. A positive temperature coefficient of resistivity (PTCR) was observed in the temperature dependence of the ceramic resistivity. The results are explained on the basis of the Heywang and Jonker models. The Schottky barrier formed at grain boundary regions acts as a trap for the electrons available from oxygen vacancies in the ceramics. This provides PTCR characteristics from the transition temperature to about 208 C.

Effect of Fiber Orientation on the Mechanical Behavior of E-Glass Fibre Reinforced Epoxy Composite Materials

“…From stress-strain curves, it seems that by increasing compression in unidirectional fiber orientation(0°), this bonding becomes greater and the role of matrix against microbuckling of fibres is more highlighted. As shown in the figure, significant nonlinear deformation was often observed before the maximum load, and this behavior was associated to the plastic deformation of the polymeric matrix [23,29]. [17], who reported that unidirectional glass/epoxy (%V f = 35%) composites achieved higher (c. a.…”