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.

Dielectric Relaxation and Conductivity of Ba(Mg_(1/3)Ta_(2/3))O_3 and Ba(Zn_(1/3)Ta_(2/3))O_3

The frequency dependent dielectric properties of barium magnesium tantalate （BMT）, Ba（Mgl/3Ta2/3）03 and barium zinc tantalate （BZT）, Ba（Znl/3Ta2/3）03 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy. BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm, respectively. The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides. The relaxation in the samples is polydispersive in nature. The temperature dependence of dc conductivity, the most probable relaxation frequency （corn） obtained from tanδ vs logo） plots and ωm obtained from imaginary parts of the complex electrical modulus vs Iogω plots follow the Arrhenius behavior. According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV, respectively. Thus the results indicate that samples are semiconducting in nature. The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation time. Our study points that for complex perovskite oxides with general formula A（B＇B＇）03, the dielectric properties significantly depend on the atomic radii of both A and B type cations. BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts. They may find several technological applications such as in capacitors, resonators and filters owing to their high dielectric constant and low loss tangent.

Octahedral distortion-driven electrical and vibrational properties of A_(2)ErTaO_(6)(A=Sr and Ca)double perovskite oxides

Rietveld refinement analysis indicates that A_(2)ErTaO_(6)(A=Sr^(+2),Ca^(+2)ceramics prepared by a solid-state route are crystallized in monoclinic perovskite phase with space group P21=n.Raman scattering and infrared spectroscopy are used to investigate the structure and phonon modes of the samples.Using Lorentzian lines,we have fitted the Raman spectra and the major Raman modes are assigned.Phonon vibrational frequency is modulated with the A-site cationic change.Impedance spectra of the samples over the frequency range of 100 Hz–1.1 MHz are investigated at different temperatures from 303 K to 573 K.Cole–Cole relaxation of dielectric constant is modified with the electrical conduction parameter to describe the temperature dependence of dielectric constant.The frequency-dependent conductivity spectra follow the double power-law.