Effect of dysprosium substitution on structural and dielectric properties of BiFeO_3-PbTiO_3 multiferroic composites

0.5BiDyxFe1-xO3-0.5PbTiOa（0.5BDxF1-x-0.5PT） （x=0.00, 0.05, 0.10, 0.15, 0.20） multiferroic composites were pre- pared by conventional solid state reaction method. Structural characterization was performed by X-ray diffraction and the mate- rials showed tetragonal structure at room temperature. Surface morphology of the composites was studied by a scanning electron microscope （SEM）. Frequency and temperature dependence of dielectric constant （er） and dielectric loss （tan~） of 0.5BDxF1_x- 0.5PT were measured in a wide range of frequency （100 Hz to 1 MHz） and temperature （25 to 400 ~C）. The analysis of the study showed that the er and tang decreased with increasing frequency in the given range for all the samples which could be explained through the occurrence of dipole relaxation process. The effect of substitution of rare earth element dysprosium （Dy） showed increase in er in all the samples prepared for different concentrations from 0.00 to 0.20. An explanation for high value of er for Dy modified 0.5BiFeO3-0.5PbTiO3 （0.5BF-0.5PT） compared to Gd modified 0.5BF-0.5PT was provided. The variation of AC conductivity with inverse temperature found to obey the Arrhenius equation and the composites showed negative temperature coefficient of resistance （NTCR） behavior. The activation energy was found to be in the range from 0.25 to 0.40 eV for all the studied samples.

Complex impedance properties of LiSr_(2)Nb_(5)O_(15) ceramic

The polycrystalline sample of LiSr2Nb5O15(LSN)was prepared by a high-temperature solid state reaction technique.The impedance parameters were studied using an impedance analyzer in a wide range of frequencies(102-106 Hz)at different temperatures(28-500℃).Nyquist plot reveals the presence of bulk effect only.The bulk resistance of the compound decreases with rise in temperature which shows the negative temperature coefficient of resistance(NTCR)like a semiconductor.The ac conductivity spectrum was found to obey Jonscher’s universal power law.DC conductivity(bulk)with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity and the activation energy found to be 0.97 eV.

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5（Bi LaxFe1-xO3）–0.5（Pb Ti O3）（x = 0.05,0.10,0.15,0.20）（BLxF1-x-PT） were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La（x = 0.05–0.20） concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range（102–106Hz） at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures（200–300 ℃）.

Effect of Zn Concentration on Microstructural,Optical,and Hyperfine Properties of Nanocrystalline a-Fe_(2)O_(3)

Efforts have been made to prepare nanocomposites of a-Fe2O3-ZnO by wet chemical route with varying concentrations of the precursors.The microstructural properties of the samples are investigated by powder X-ray diffractometry（PXRD） and Transmission electron microscopy.Initial concentration of Zn ions（up to 20 at%） leads to the formation of nanocomposites of a-Fe2O3 and ZnO.Evolution of ZnFe2O4 phase is detected by the substitution of higher concentration of Zn2？（30 at%） in the sample.The average size of the nanoparticles remains in the range of 22–27 nm as obtained from XRD data.The results obtained from electron microscopic studies are also close to these values.Photoluminescence measurement shows the excitonic peak of ZnO around 390 nm which gets strengthened with Zn addition.FTIR spectra show the metal–oxygen band below 700 cm-1.Room temperature Mssbauer studies of the samples show the transition of iron oxide form antiferromagnetic state to paramagnetic state with increasing concentration of Zn2？.Sharp quenching of hyperfine field with Zn concentration is observed as the Hintvalue reduced to zero from 51 T.

Dielectric and electrical properties of Na_(2)Pb_(2)La_(2)W_(2)Ti_(4)Ta_(4)O_(30) electroceramics

The polycrystalline sample of complex tungsten-bronze type compound(Na_(2)Pb_(2)La_(2)W_(2)Ti_(4)Ta_(4)O_(30))was prepared by a high-temperature solid-state reaction technique.Room temperature preliminary structural study using X-ray diffraction(XRD)data exhibits the formation of a single-phase new compound.The SEM micrograph of the compound exhibits non uniform rectangular grains distributed throughout the sample surface.Detailed studies of dielectric parameters(εr,tanδ)as a function of temperature and frequency,and P-E hysteresis(spontaneous polarization)confirmed the existence of ferroelectricity in the material.Complex impedance spectroscopy analysis,carried out as a function of frequency at different temperatures,established a correlation between the microstructure and electrical properties of the material.The electrical relaxation process occurring in the material is temperature dependent.The activation energy found from the Arrhenius plot that the conduction process in the material is of mixed type.The nature of frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.