Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr0.25Ti0.75]O3 ceramic

Synthesis and characterization of ZnWO4 ceramic powder

We report on the structural, optical and dielectric characterization of solid state derived, pseudo-cubic nanoscale barium titanates (BTs) with gadolinium (Gd3+) as substitutional dopant. Referring to X-ray diffractograms, apart from the BT peaks related to perovskite structure, the non-existence of any additional peaks due to byproducts has revealed that Gd3+ has undergone substitutional doping into the BT host lattice. The well-separated BT nanoparticles of typical size ∼10–15 nm were observed through electron microscopy studies. Following a direct, allowed type carrier transition (n=1/2), a reduction in the optical band gap value (from 3.28 to 3.255 eV) was observed when the Gd-doping level was varied within 0–7 %. Conversely, the Urbach energy followed an increasing trend, from a value of 0.741 to 1.879 eV. Furthermore, the dielectric constant showed a decreasing tendency with doping content and with increasing frequency. However, in the low-frequency region, the loss tangent (tanδ), which is the combined result of orientational polarization and electrical conduction, was found to be quite high in the doped samples as compared to their un-doped counterpart. The frequency-dependent electrical data were also analyzed in the framework of conductivity and impedance formalisms. In particular, the ac conductivity which varies as ∼ω
 s
 approaches ideal Debye behavior (s→1) for a low Gd level and a higher doping concentration did not show improved dielectric feature of the host. The incorporation of rare-earth (Gd3+) ions into the BT host system could greatly manifest dielectric relaxation and carrier conduction mechanisms, in a given frequency range, and thus can find immense scope in miniaturized nanoelectronic elements including ceramic capacitors and transducers.

Effect of Gd 3+ doping on structural, optical and frequency-dependent dielectric response properties of pseudo-cubic BaTiO 3 nanostructures

https://tandfonline.com/doi/pdf/10.1080/21870764.2019.1579406

The structural and magnetic properties, non-Debye relaxation and hopping mechanism in PbxNd1−xFeO3 (where x = 0.1, 0.2 and 0.3) solid solutions

AC conductivity, dielectric constant, loss and electric modulus of Sodium nitrate system have been studied in the frequency range from 1Hz to 10MHz and in the temperature range from 303 K to 563 K by employing impedance spectroscopy. The frequency dependent ac conductivity follows Jonscher’s universal power law. Dimensionless frequency exponent (n), dispersion parameter (A) are determined. The change over frequency independent conductivity to frequency dependent conductivity at all temperatures shows the relaxation mechanism. The variation of real part of dielectric constant with frequency shows strong dispersion at low frequencies and saturation at high frequencies. The presence of peaks in the frequency plots of dielectric loss, imaginary parts of impedance and modulus are attributed to the relaxation processes. It is also confirmed by the temperature dependence study of real part of dielectric constant. The activation energy from relaxation processes and conductivity has been evaluated.

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Dielectric Relaxation, Ionic Conduction and Complex Impedance Studies on NaNo3 Fast Ion Conductor

The complex perovskite oxide barium–zinc–tungstate, Ba(Zn 1/2 W 1/2 )O 3 (BZW) is synthesized by a solid-state reaction technique. The X-ray diffraction study of the sample at room temperature shows a monoclinic phase. The field dependence of dielectric response and the conductivity of the sample are measured in a frequency range from 100 Hz to 1 MHz and in a temperature range from 143 to 650 K. An analysis of the real and imaginary parts of the dielectric permittivity with frequency was carried out assuming a distribution of relaxation times as confirmed by Cole–Cole plot as well as the scaling behaviour of the dielectric loss spectra. The frequency dependent maxima in the imaginary impedance are found to obey an Arrhenius law with an activation energy ≃ 0.82 eV. The frequency dependent electrical data are also analyzed in the frame work of conductivity and electric modulus formalisms. The scaling behaviour of imaginary electric modulus shows the temperature independent nature of the relaxation mechanism. All these formalisms provided for qualitative similarities in the relaxation time.

Dielectric relaxation in perovskite Ba(Zn1/2W1/2)O3

Polycrystalline BaCo 1/2 W 1/2 O 3 (BCW) is prepared by the solid-state reaction technique. The X-ray diffraction study of the compound at room temperature reveals the monoclinic phase. The field dependence of the dielectric constant and the conductivity are measured in the frequency range from 50 Hz to1 MHz and in the temperature range from 300 to 413 K. An analysis of the real and imaginary parts of the dielectric permittivity with frequency is performed. The frequency-dependent maxima in the imaginary impedance are found to obey an Arrhenius law with an activation energy=0.86 eV. The frequency-dependent electrical data are also analysed in the framework of the conductivity and modulus formalisms.

Ved Prakash

Papers

Dielectric relaxation in perovskite Ba(Zn1/2W1/2)O3

Dielectric relaxation in complex perovskite oxide BaCo1/2W1/2O3