Insulator-to-metal transition in RCoO_(3)(R=Pr,Nd)

We report a straightforward tool to investigate insulator-metal transition in RCoO_(3)(R=Pr,and Nd)nanoparticles prepared by a sol-gel technique.Thermogravimetric analysis(TGA)of the as-prepared gel is performed to get the lowest possible calcination temperature of RCoO_(3)nanoparticles.The Rietveld refinement of the powder X-ray diffraction(XRD)patterns for both samples shows that the samples crystallize in the orthorhombic(Pnma)phase at room temperature.The particle size of the sample is determined by scanning electron microscopy.Ac conductivity of the materials is analyzed in the temperature range from 303 K to 673 K and in the frequency range from 42 Hz to 1.1 MHz.The insulator-to-metal transition of PrCoO_(3)and NdCoO_(3)is analyzed by ac impedance spectroscopy.DC resistivity measurement is also done to cross check the insulator-metal transition in RCoO_(3)system.

Structural and electrical transport properties of a rare earth double perovskite oxide:Ba_2ErNbO_6

The double perovskite oxide barium erbium niobate, Ba2ErNbO6 （BEN） was synthesized by solid state reaction technique. Rietveld refinement of the X-ray diffraction pattern of the sample showed cubic （Fm3m） phase at room temperature. Fourier trans-form infrared spectrum showed two primary phonon modes of the sample at around 387 and 600 cm-1. Raman spectrum of the sam-ple taken at 488 nm excitation wavelength showed four primary strong peaks at 106, 382, 747 and 814 cm-1. Lorentzian lines with 10 bands were used to fit the Raman spectrum. A group theoretical study was performed to assign all the Raman modes. Impedance spectroscopy was applied to investigate the ac electrical conductivity of BEN in a temperature range from 303 to 673 K and in a fre-quency range from 100 Hz-1 MHz. The dielectric relaxation mechanism was discussed in the frame work of permittivity, conduc-tivity, modulus and impedance formalisms. The complex plane plot of the impedance data was modeled by an equivalent circuit con-sisting of two serially connected R-CPE units, （one for the grain and the other for the grain boundary）, each containing a resistor （R） and a constant phase element （CPE）. The R-CPE units were used to incorporate the non-ideal character of the polarization phenome-non instead of an ideal capacitive behaviour. The relaxation time corresponding to dielectric loss was found to obey the Arrhenius law with activation energy of 0.85 eV. The frequency dependent conductivity spectra followed the Jonscher power law. The Cole-Cole model was used to investigate the dielectric relaxation mechanism in the sample.