ON THE DISPERSIVE NATURE OF F2-REGION TIDs OVER WALTAIR

A ternary system of lead niobate–lead zirconate–lead titanate with composition xPN–yPZ–(x-y)PT where x=0.5 and y=0.15, 0.25, and 0.35 known as PNZT has been prepared by conventional mixed oxide route at a temperature of 1100°C. The formation of the perovskite phase was established by X-ray diffraction analysis. The surface morphology studied by scanning electron microscopy shows the formation of fairly dense grains and elemental composition was confirmed by energy dispersive X-ray analysis. Dielectric properties like dielectric constant and dielectric loss (ε′ and tan⁡δ) indicate poly-dispersive nature of the material. The temperature dependent dielectric constant (ε′) curve indicates relaxor behaviour with two dielectric anomalies. The poly-dispersive nature of the material was analysed by Cole-Cole plots. The activation energy follows the Arrhenius law and is found to decrease with increasing frequency for each composition. The frequency dependence of ac conductivity follows the universal power law. The ac conductivity analysis suggests that hopping of charge carriers among the localized sites is responsible for electrical conduction. The ferroelectric studies reveal that these ternary systems are soft ferroelectric.

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Thermodynamics of Dislocation Pattern Formation at the Mesoscale

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.592-593.79 ◽

2013 ◽

Vol 592-593 ◽

pp. 79-82

Author(s):

Roman Gröger

Keyword(s):

Strain Field ◽

Elastic Strain ◽

Strain Energy ◽

Elastic Strain Energy ◽

The Body ◽

Dislocation Network ◽

Length Scale ◽

Displacement Fields ◽

Elastic Strain Field ◽

Dispersive Nature

We introduce a mesoscopic framework that is capable of simulating the evolution of dislocation networks and, at the same time, spatial variations of the stress, strain and displacement fields throughout the body. Within this model, dislocations are viewed as sources of incompatibility of strains. The free energy of a deformed solid is represented by the elastic strain energy that can be augmented by gradient terms to reproduce dispersive nature of acoustic phonons and thus set the length scale of the problem. The elastic strain field that is due to a known dislocation network is obtained by minimizing the strain energy subject to the corresponding field of incompatibility constraints. These stresses impose Peach-Koehler forces on all dislocations and thus drive the evolution of the dislocation network.

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Collecting Quality Infrared Spectra from Microscopic Samples of Suspicious Powders in a Sealed Cell

Applied Spectroscopy ◽

10.1177/0003702816666286 ◽

2016 ◽

Vol 71 (3) ◽

pp. 438-445

Author(s):

Brooke W. Kammrath ◽

Pauline E. Leary ◽

John A. Reffner

Keyword(s):

Barium Fluoride ◽

Experimental Conditions ◽

Minimal Sample ◽

Dispersion Effects ◽

Toxic Agents ◽

Sample Spectrum ◽

Dispersive Nature ◽

Absorption Measurements ◽

Absorption Mode

The infrared (IR) microspectroscopical analysis of samples within a sealed-cell containing barium fluoride is a critical need when identifying toxic agents or suspicious powders of unidentified composition. The dispersive nature of barium fluoride is well understood and experimental conditions can be easily adjusted during reflection–absorption measurements to account for differences in focus between the visible and IR regions of the spectrum. In most instances, the ability to collect a viable spectrum is possible when using the sealed cell regardless of whether visible or IR focus is optimized. However, when IR focus is optimized, it is possible to collect useful data from even smaller samples. This is important when a minimal sample is available for analysis or the desire to minimize risk of sample exposure is important. While the use of barium fluoride introduces dispersion effects that are unavoidable, it is possible to adjust instrument settings when collecting IR spectra in the reflection–absorption mode to compensate for dispersion and minimize impact on the quality of the sample spectrum.

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