scispace - formally typeset
Search or ask a question
Author

C.K. Mahadevan

Bio: C.K. Mahadevan is an academic researcher from Hindu College, University of Delhi. The author has contributed to research in topics: Dielectric & Crystal. The author has an hindex of 23, co-authored 99 publications receiving 1586 citations. Previous affiliations of C.K. Mahadevan include Maharaja Sayajirao University of Baroda & Scott Christian College.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors show that L-arginine addition leads to reduction of electrical parameters of KDP and ADP single crystals which can be attributed mainly to the decrease of L-defects due to creation of additional hydrogen bonds by the impurity in random directions.
Abstract: Potassium dihydrogen orthophosphate (KDP) and ammonium dihydrogen orthophosphate (ADP) single crystals added with L-arginine have been grown by the solution methods. DC and AC electrical measurements were carried out at various temperatures along both a- and c- directions. Results indicate an increase of the electrical parameters with the increase of temperature which can be attributed mainly to the increase of thermally generated hydrogen bond vacancies (L. defects). Also, the present study indicates that L-arginine addition leads to reduction of electrical parameters of KDP and ADP single crystals which can be attributed mainly to the decrease of L-defects due to creation of additional hydrogen bonds by the impurity in random directions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

132 citations

Journal ArticleDOI
TL;DR: In this paper, the dielectric parameters increase with the increase in temperature but do not vary systematically with respect to impurity concentration, and they indicate that 0.6mole% urea addition to KDP leads to low permittivity value dielectrics.

97 citations

Journal ArticleDOI
TL;DR: In this paper, conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method.
Abstract: Pure and impurity added [with NH4CI, NH4NO3, NH44H2PO4, (NH4)2CO3 and (NH4)2SO4] KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for all the five dopants considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.

53 citations

Journal ArticleDOI
TL;DR: In this article, a comparative analysis of ZnS QDs synthesized by conventional and microwave heating techniques using zinc acetate and sodium sulphide reactants is presented, which reveals that the size of the quantum dots achieved by the latter technique (∼3nm) is at least 30 times smaller than the former technique.

53 citations

Journal ArticleDOI
TL;DR: In this article, a new organic nonlinear optical crystal l -alaninium tartrate (LAT) has been grown by slow evaporation method at room temperature, which is stable up to 118°C, SHG measurements and UV-Vis-NIR spectroscopy.
Abstract: A new organic nonlinear optical crystal l -alaninium tartrate (LAT) has been grown by slow evaporation method at room temperature. Single crystal X-ray diffraction studies reveal that the crystal has monoclinic structure with space group P21. From FT-IR spectrum, the CH vibrations of tartaric acid generate peaks at 2977 and 2960 cm−1. The thermal studies indicate that the grown LAT is stable up to 118 °C, SHG measurements and UV–Vis–NIR spectroscopy. Photoconductivity studies of LAT reveal its negative photoconducting nature. The second harmonic generation efficiency of LAT crystal is found to be 174 mV. The laser damage threshold is found to be 8.16 GW/cm2. The dielectric constant and dielectric loss of the crystal were studied as a function of frequency and the results are discussed. The AC/DC conductivity studies are carried out and reported for the first time.

46 citations


Cited by
More filters
Posted Content
TL;DR: In this article, the enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature has been reported.
Abstract: We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.

274 citations

Journal ArticleDOI
TL;DR: In this paper, a detailed discussion of the structural aspects of these species based upon X-ray data is presented. But emphasis is placed on detailed discussion on the structural properties of the species.

265 citations

Journal ArticleDOI
TL;DR: Geometry optimizations using all-electron density functional theory with scalar relativistic corrections at the second-order Douglas-Kroll-Hess and zeroth-order regular approximation (ZORA) levels result in excellent agreement with the experimentally determined structures and electronic spectra.
Abstract: The three diamagnetic square planar complexes of nickel(II), palladium(II), and platinum(II) containing two S,S-coordinated 3,5-di-tert-butylbenzene-1,2-dithiolate ligands, (L(Bu))(2-), namely [M(II)(L(Bu))(2)](2-), have been synthesized. The corresponding paramagnetic monoanions [M(II)(L(Bu))(L(Bu)(*))](-) (S = (1)/(2)) and the neutral diamagnetic species [M(II)(L(Bu)(*))(2)] (M = Ni, Pd, Pt) have also been generated in solution or in the solid state as [N(n-Bu)(4)][M(II)(L(Bu))(L(Bu)(*))] salts. The corresponding complex [Cu(III)(L(Bu))(2)](-) has also been investigated. The complexes have been studied by UV-vis, IR, and EPR spectroscopy and by X-ray crystallography; their electro- and magnetochemistry is reported. The electron-transfer series [M(L(Bu))(2)](2-,-,0) is shown to be ligand based involving formally one (L(Bu)(*))(-) pi radical in the monoanion or two in the neutral species [M(II)(L(Bu)(*))(2)] (M = Ni, Pd, Pt). Geometry optimizations using all-electron density functional theory with scalar relativistic corrections at the second-order Douglas-Kroll-Hess (DKH2) and zeroth-order regular approximation (ZORA) levels result in excellent agreement with the experimentally determined structures and electronic spectra. For the three neutral species a detailed analysis of the orbital structures reveals that the species may best be described as containing two strongly antiferromagnetically interacting ligand radicals. Furthermore, multiconfigurational ab initio calculations using the spectroscopy oriented configuration interaction (SORCI) approach including the ZORA correction were carried out. The calculations predict the position of the intervalence charge-transfer band well. Chemical trends in the diradical characters deduced from the multiconfigurational singlet ground-state wave function along a series of metals and ligands were discussed.

257 citations

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of hematite nanoparticles were investigated using a superconducting quantum interference device (SQUID) magnetometry, which showed a divergence between field-cooled (FC) and zero-field cooled (ZFC) magnetization curves below Tirr = 103 K (irreversibility temperature) and the ZFC magnetization curve showed maximum at TB = 52 K (blocking temperature).

237 citations

Journal ArticleDOI
TL;DR: In this article, various types of industrial lignins were characterized through elemental analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA).
Abstract: Lignin is a co-product of paper and lignocellulosic bioethanol industries. Structure and functionality of lignins differ from one another based upon the source material and isolation techniques adopted in various industries. Value added applications from lignins need a proper investigation of their inherent properties. Various types of industrial lignins were characterized through elemental analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) in order to understand the potential of these materials for future value added applications, with a major focus on compositae materials. All the grades of Protobind lignins exhibited lower sulphur content and higher carbon content. The highest value of sulphur content was observed for Arbo S01 lignin (lignosulphonate). Among all the industrial lignins, Protobind 2400 exhibited higher thermal degradation onset i.e. 174.5 °C followed by Arbo S01 (Sodium lignosulphonate, 164.4 °C). Derivative thermogravimetric (DTG) curves of the lignins demonstrated the differences in their thermal behaviour. The DTG curve of Polybind 300 was quite different from the other lignins.

211 citations