Phase diagram, optical, nonlinear optical, and physicochemical studies of the organic monotectic system: Pentachloropyri
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The two immiscible liquid phases in equilibrium with a single liquid phase have been observed during the phase diagram study of an organic analog of a metal–nonmetal system involving pentachloropyridine (PCP)–succinonitrile (SCN). The phase equilibrium shows the formation of a monotectic and a eutectic, with large miscibility gap in the system, containing 0.0456 and 0.9658 mole fractions of SCN, respectively, and the consolute temperature being 99.0 °C above the monotectic horizontal line. The heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and excess thermodynamic functions were calculated based on enthalpy of fusion data determined via the differential scanning calorimetry method. The effects of solid–liquid interfacial energy on morphology of monotectic structure as well as the variation of interfacial energies with temperature have been discussed. The microstructures of monotectic and eutectic show peculiar characteristic features. The material properties of PCP and PCP doped with SCN crystals, grown by the Bridgman–Stockbarger method, have been studied via studying second harmonic generation efficiency, transparency range, and mechanical hardness.
I. INTRODUCTION
The repeated and considerable attempts are being made to study the microstructure and phase diagram of miscibility gap (monotectic) systems. The solidification behaviors of monotectic systems are of potential importance for both fundamental point of view and industrial application such as self-lubricating alloys.1,2 Although, metallic systems constitute an interesting area of investigations,3–5 they are not suitable for detailed study due to high transformation temperature, opacity, and density difference of the components that pose problem in clear observation during solidification resulting into erroneous results. However, low transformation temperature, transparency, wider choice of materials, and minimized density driven convection effects are the special features that have prompted a number of research groups6–7 to work on organic eutectics, monotectics, and molecular complexes. To start with, organic systems were studied as model systems but now-a-days they are being used in various applications ranging from conductors,8 transistors,9 to light emitting diodes,10 as well as the area in which the present work is concerned, nonlinear optical
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0181 1348
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 5, May 2004 Downloaded: 01 Mar 2015
(NLO) materials.11–13 The organic materials are in increasing demand as they offer various advantages over conventional inorganic NLO materials for their applications in the generation of new optical frequency, optical devices such as ultrafast modulators, amplifiers, and switches. Furthermore, binary organic materials are known to exhibit better optical properties than their parent components,14,15 as the NLO effect in molecular crystals depends mainly on the polarizability of the
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