SUMMARY Teleseismic data from six broad‐band stations on the south Indian shield have been analysed, primarily to examine the differences in the crustal structure between the eastern and western units of the Archaean Dharwar craton. SV receiver functions for these stations have been computed and modelled down to the Moho level in terms of Poisson's ratio and shear wave velocities. Results show that the crust for the entire Dharwar craton is mainly simple, and has a low (about 0.25) Poisson ratio. It is usually thinner and less complex than the adjacent Proterozoic crust. However, the western Dharwar craton crust (thickness ∼41 km) with a gradational Moho boundary, is substantially (>7 km) thicker than its eastern counterpart (thickness ∼34 km). No substantial differences in average crustal S velocities (3.6–3.8 km s−1) were found. The eastern Dharwar crust below the Proterozoic Cuddapah basin was also found to have remained relatively simple and undisturbed. The continental margin to the west of the Dharwar craton appears to have shifted further west off the coast, where a possible west coast fault has down‐thrown a continental crustal block under the seas. The crust constituting the Deccan volcanic province in the western Indian shield is found to be similar to that of the eastern Dharwar craton. The crust underneath the neighbouring Godavari graben is significantly different from the Dharwar crust and resembles that of a typical rift‐valley.

Abstract. Teleseismic earthquake waveform data from 10 broadband stations spread over the Indian shield and in operation since 1997, were analyzed to infer the crustal structure, using the receiver function technique. The South Indian shield is characterized by a 33-39 km thick, and remarkably simple crust, with an average Poisson's ratio close to 0.25. The Archaean crust is devoid of any prominent intra-crustal discontinuities. The velocity contrast at the well developed Moho is large, resulting in very clear P-to-S conversions as well as first-order multiples. In contrast, the predominantly Proterozoic crust in the northern part of the shield exhibits a complex character, due to the presence of additional seismic discontinuities. Moho conversions, which are considerably weaker compared to the Archaean terrains, indicate crustal thicknesses of more than 40 km.

Solid polymer electrolyte films (SPEs) based on poly(methyl methacrylate) are prepared using a solution cast technique. The temperature-dependent behavior of dielectric, modulus spectra and ac conductivity has been investigated. The long tail of the real part of modulus (M 0 ) in the low frequency indicates the capacitive nature of the samples. The frequency dependence of imaginary part of modulus (M 00 ) shows a non-Debye relaxation that has been explained using the Kohlrausch-Williams-Watts stretched exponential function. The activation energy for the relaxation is almost same as the activation energy for the conduction. The relaxation time obtained from the tangent loss graph (τ δ ) is about two orders of magnitude larger than that obtained from the imaginary part of modulus graph (τ m ). The ac conductivity has been found to obey Jonscher's universal power law. Transport parameters show that addition of filler creates additional hopping sites for the charge carriers and also increases the charge carrier density. It is also observed that the higher ionic conductivity at higher temperature is due to increased thermally activated hopping rates accompanied by a significant increase in carrier concentration. The contribution of carrier concentration to the total conductivity is also confirmed from Summerfield scaling. POLYM. ENG. SCI., 60:297-305, 2020.

We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C) than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

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