Faculty Publications
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Item Evolutionary algorithm based structure search for hard ruthenium carbides(Institute of Physics, 2015) Harikrishnan, G.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.An exhaustive structure search employing evolutionary algorithm and density functional theory has been carried out for ruthenium carbides, for the three stoichiometries Ru1C1, Ru2C1 and Ru3C1, yielding five lowest energy structures. These include the structures from the two reported syntheses of ruthenium carbides. Their emergence in the present structure search in stoichiometries, unlike the previously reported ones, is plausible in the light of the high temperature required for their synthesis. The mechanical stability and ductile character of all these systems are established by their elastic constants, and the dynamical stability of three of them by the phonon data. Rhombohedral structure is found to be energetically the most stable one in Ru1C1 stoichiometry and hexagonal structure , the most stable in Ru3C1 stoichiometry. RuC-Zinc blende system is a semiconductor with a band gap of 0.618 eV while the other two stable systems are metallic. Employing a semi-empirical model based on the bond strength, the hardness of RuC-Zinc blende is found to be a significantly large value of ?37 GPa while a fairly large value of ?21GPa is obtained for the RuC-Rhombohedral system. The positive formation energies of these systems show that high temperature and possibly high pressure are necessary for their synthesis. © 2015 IOP Publishing Ltd.Item Microscopic and spectroscopic characterization of rice and corn starch(Wiley-Liss Inc., 2020) Govindaraju, I.; Pallen, S.; Umashankar, S.; Mal, S.S.; Kaniyala Melanthota, S.; Mahato, D.R.; Zhuo, G.-Y.; Mahato, K.K.; Mazumder, N.Starch granules from rice and corn were isolated, and their molecular mechanism on interaction with ?-amylase was characterized through biochemical test, microscopic imaging, and spectroscopic measurements. The micro-scale structure of starch granules were observed under an optical microscope and their average size was in the range 1–100 ?m. The surface topological structures of starch with micro-holes due to the effect of ?- amylase were also visualized under scanning electron microscope. The crystallinity was confirmed by X-ray diffraction patterns as well as second-harmonic generation microscopy. The change in chemical bonds before and after hydrolysis of the starch granules by ?- amylase was determined by Fourier transform infrared spectroscopy. Combination of microscopy and spectroscopy techniques relates structural and chemical features that explain starch enzymatic hydrolysis which will provide a valid basis for future studies in food science and insights into the energy transformation dynamics. © 2020 Wiley Periodicals, Inc.Item Entropy engineering in I-V-VI2 family: a paradigm to bestow enhanced average ZT in the entire operating temperature regime(Royal Society of Chemistry, 2024) Basu, R.; Shenoy, U.S.; Pathak, A.; Singh, S.; Jha, P.; Bhat, D.K.; Basu, H.; Singh, A.The design and development of n-type alloys in the mid-temperature regime (500-700) K with enhanced thermoelectric performance is of utmost necessity for the fabrication of thermoelectric devices. In this regard, the I-V-VI2 family reveals superior thermoelectric performance, owing to the fact that group V elements have non-bonded electrons and high Z (atomic number), with a high Grüneisen parameter, which cause amplified anharmonicity and subsequently low intrinsic lattice thermal conductivity. However, the irony is that the well-studied alloy of this family, AgBiSe2, undergoes phase transition in the operating temperature range. Thus, of paramount importance is restricting the phase transition and bringing it down below room temperature (RT), along with stabilizing a highly symmetrical crystal structure in the extended operating temperature range. Efforts were made to synthesize a cubic n-type AgBiSeS alloy belonging to the I-V-VI2 compounds (unlike AgBiSe2) that is stabilized throughout the temperature range, as the S element aids in strengthening of the chemical bonds. In addition, the alloy was further stabilized by forming a solid solution with PbSe, which aids in increasing the configurational entropy and thereby increases the chemical space of the system. The resultant alloys possess intrinsically low lattice thermal conductivity ranging from 0.38-0.74 W m−1 K−1 in the entire operating range. Consequently, the peak ZT was reported as ∼0.6 at 780 K, with an average ZT value of 0.3 for the alloy (AgBiSeS)0.5(PbSe)0.5 within 300-823 K. Although the reported ZT is low, the methodology of entropy-driven structural stabilization in the operating temperature regime was adapted to attain a highly symmetrical, stable structure for practical applications. © 2024 RSC.