The difficulties in synthesizing phase pure BiFeO3 are well known. In this letter we are reporting the optimized synthesis conditions for obtaining phase pure BiFeO3 ceramic. The oxide mixing technique followed by leaching with dilute nitric acid has been used for the synthesis. X-ray diffraction pattern indicated that the sample is phase pure. Scanning electron microscopy along with energy dispersive x-ray fluorescence analysis confirmed the chemical homogeneity of the sample. No segregation of the impurity phase in the matrix was detected. Moreover, Bi/Fe atomic ratio is observed to be ∼1. The ferroelectric transition of the sample at 836 °C has been detected by differential thermal analysis.

We apply many criteria to estimate the diradical character of the ground state singlets of several oxyallyl derivatives. This is carried out as the oxyallyl derivatives like squaraine and croconate dyes can be represented by both mesoionic and diradical formulas, the domination of which would characterize its lowest energy transition. One criterion applied is the singlet-triplet gap, which is known to be inversely proportional to the diradical character. Another criterion is the occupation number; this is determined for the symmetry broken state of the molecules in the unrestricted formalism, and the difference of occupation in the HOMO and LUMO is related to the diradical character. The diradical character of all of the croconates and few squaraines is estimated to be large. All of these have absorption above 750 nm and can be classified as near infrared (NIR) dyes, leading to the inference that NIR absorptions in these molecules are largely due to the dominance of the diradical character. To understand the reliability of the DFT methods for the absorption property predictions of these molecules, TD-DFT studies to calculate the vertical excitation energies have been carried out, using the B3LYP/ BLYP exchange correlation functionals and the LB94 asymptotic functional with and without the inclusion of solvent. The deviations, in both the squaraine series (average lower diradical character), are found to be systematic, and with the inclusion of the solvent in the calculation, the deviations decrease. The best least-squares fit with the experimentally observed values using B3LYP /6-311G(d, p) for the symmetric squaraines yields an R value of 0.92 and, for the unsymmetric squaraines, an R value of 0.936. With inclusion of the solvent, the R value is 0.96 for the symmetric squaraines and 0.961 for the unsymmetric squaraines, indicating that these DFT functionals with linear scaling may be used to study these systems. The croconate dyes, however, have larger deviation from the experimentally observed values in all of the functionals studied even after inclusion of the solvent effects. The deviations are also not systematic. The deviation with respect to the experiment in this case is attributed to the average larger diradical character in this series.

With the aim of understanding the structural, electronic, and magnetic properties of nanocrystalline Co doped SnO2 diluted magnetic semiconductors, prepared by the tartaric acid gel route, a systematic investigation as a function of annealing temperature has been carried out. The precursor was characterized by TG-DTA to determine thermal decomposition and crystallization temperature. The XRD, TEM, FT-IR, and laser Raman studies revealed that all the samples have a tetragonal rutile structure with single phase. The average particle sizes obtained from TEM are in the range of 18−50 nm. The changes in Raman spectra were analyzed with varying crystallite size. The optical absorbance measurements revealed that the nanometric size of the materials influences the energy band gap values. From the XPS studies, the oxidation state of cobalt is found to be +2, and particle size induced implications in the core level XPS peaks of Co 2p and O 1s have been analyzed. The presence of room temperature ferromagnetism has been confirmed by the magnetization studies. Finally, it has been concluded that the ferromagnetic properties depend not only on the surface diffusion of Co ions and the distribution of defects such as oxygen vacancies or vacancy clusters but also on nanometric size of the materials and their surface conditions.

Complex impedance spectroscopic data were acquired on single crystals of the morphotropic phase boundary composition of 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 over a wide range of temperatures (25–525 °C) and frequencies 1 kHz–1 MHz. This study takes advantage of plotting ac data simultaneously in the form of impedance and modulus spectroscopic plots. This permits the easy interpretation of microscopic processes responsible for the measured ac response. Frequency explicit plots of imaginary components of impedance and modulus exhibit Debye-like peak shapes. The data for ac conductivity were computed from the impedance data and the activation energy for conduction at different frequencies was determined. Cole–Cole diagrams were plotted and these indicate the presence of a single relaxation process. The relaxation times determined from these plots followed an Arrhenius law, and the activation energy for relaxation was found to be 1.2 eV. The ac conductivity data was found to obey Jonscher’s universal power law and resulted in a value of the exponent “n”=0.95.