V. Sridharan

Wide band gap tunability of bulk Cd1−xCaxO

We report the lattice parameter variation and the band gap tuning of CdO with Ca by preparing thermodynamically stable Cd1−xCaxO solid solution in the entire composition range 0≤x≤1. The functional dependence of the lattice parameter on Ca concentration is found to deviate from Vegard’s law. The principal band gap is found to vary nonmonotonically over a wide range, from 1.4 to 3.9 eV for 0≤x≤0.8. First principles density functional theory calculations, using full potential linearized augmented plane wave methods also predict a nonlinear variation for the lattice parameter and the optical band gap with Ca concentration. From these calculations, contributions from volume deformation, electron transfer, and structural relaxation are estimated and the results are compared with experiments.

Possible magnetic phase separation in Ru-doped La0.67Ca0.33MnO3

Abstract X-ray diffraction, resistivity, AC susceptibility and magnetization studies on La0.67Ca0.33Mn1−xRuxO3 (0⩽x

Transport and thermal properties of La0.67Ca0.33Mn1−xMxO3 (M=Fe, Zr and Hf)

Mn site substitution with Fe, Zr and Hf (1 at.%) were carried out in colossal magneto-resistive material La 0.67 Ca 0 33 MnO 3 . It is found from the resistivity, ac susceptibility and specific heat (C p ) measurements that Zr and Hf substitutions suppress the transition temperature (T c ) more effectively than Fe substitution. The excess entropy under the C p curve associated with the magnetic transition also substantially lowered compared to that of undoped and Fe-doped systems. From the consideration of the excess entropy under the C p curve and the ionic radii, it is speculated that both Zr 4+ and Hf 4+ ions predominantly substitute Mn 3+ site. Larger suppression of T c is attributed to local strain produced due to larger ion substitution as well as hole filling due to replacement of trivalent ion (Mn 3+ ) with tetravalent ions (Hf 4+ and Zr 4+ ).

Structural, magnetic, and dielectric studies on Gd0.7Y0.3MnO3.

Structural, magnetic, specific heat, and dielectric studies were carried out on Y substituted (30 at. %) GdMnO(3) compound as a function of temperature. Anomalies occur at ~41 and 18 K, in the specific heat measurements and are ascribed to paramagnetic, to sinusoidal incommensurate antiferromagnetic transition (ICAFM) and ICAFM to commensurate antiferromagnetic transitions, respectively. Changes in the lattice parameters across these temperatures indicate magneto-elastic coupling present in the compound. However, in the dielectric measurements, an anomaly at 18 K alone is observed and is ascribed to a ferroelectric transition, giving rise to spontaneous ferroelectric ordering at low temperatures. This observation is supported by an anomaly in lattice parameters, across the transition temperature. From the frequency dependent dielectric studies, a strong coupling between Gd(3+) and Mn(3+) magnetic sublattices is inferred and Y substitution results in substantial changes in the relaxation process compared to that of GdMnO(3).

Local structural studies of the cubic Cd1–xCaxO system through Cd K-edge extended X-ray absorption spectroscopic studies

Local structure studies about Cd in the Cd1–xCaxO solid solution through Cd K-edge EXAFS studies are described, indicating a bimodal distribution of the first nearest neighbour distance for Cd and that the optical properties should belong to a persistence type.

Raman Scattering of Cadmium Oxide: in B1 Phase

Raman spectra of polycrystalline Cadmium Oxide (CdO) have been measured between 100 and 2000 cm−1 over the temperature range 80 to 300 K. The observed modes are reconciled with the results of the earlier reports. The observed Raman modes are ascribed to the structural disorder (static/dynamic (thermal)) and the resonance Raman processes. The Raman modes are assigned to forbidden longitudinal optical excitations, which are allowed under resonance conditions by a Frohlich interaction mechanism, and two‐phonon excitations.

Effect of Sn substitution on structural and transport properties of (La0.67Sr0.33)MnO3

We investigate the effects of Sn substitution on structural and electrical transport mechanism of polycrystalline samples La0.67Sr0.33Mn1-xSnxO3 (x = 0, 0.05, 0.10, 0.15). Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of Sn in the series leads to a decrease in conductivity of the doped manganites samples, with conduction being controlled by the disorder induced localization of charge carriers. The value of M-I transition temperature (TP) decreases while resistivity increases with Sn substitution.

Properties of Cd1-xCaxO disordered alloy

Structural, optical and vibrational properties of disordered ternary Cd1-xCaxO alloys have been calculated using the density functional formalism (DFT). We obtain a nonlinear variation (non Vegards law behavior) of the lattice parameter and the optical band gap with Ca concentration. The reasons for this are enumerated. The calculated phonon dispersions and dielectric spectra for the end compounds and the Cd0.5Ca0.5O alloy show that the signatures of both the end compounds are preserved and additional phonon modes are observed due to the disordered nature of the alloy. Thus the alloy belongs to the persistent class.