A. Khodorov

Impedance spectroscopy study of a compositionally graded lead zirconate titanate structure

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure prepared by pulsed laser deposition was studied as a function of frequency and temperature (from room temperature up to 419u2009°C) using impedance spectroscopy. The analysis of combined impedance and modulus spectroscopy, as well as complex plane plots, revealed that the bulk grain relaxation was the dominant relaxation process over the frequency and temperature range studied. The calculated bulk grain capacitance of the graded structure shows an anomalous behavior near temperatures related to the phase transition temperatures of the corresponding PZT compositions. The hopping conduction obeying the “universal power law” and an exponent equal to 0.88 was observed to dominate in alternating current conductivity over the entire frequency range from 10 Hz to 2 MHz at room temperature. At higher temperatures the relaxation spectrum was found to be much influenced by the increased direct current (dc) conductivity. The meas...

Effect of Pt bottom electrode texture selection on the tetragonality and physical properties of Ba0.8Sr0.2TiO3 thin films produced by pulsed laser deposition

The effect of platinum (Pt) bottom electrode texture on the tetragonality, dielectric, ferroelectric, and polarization switching response of pulsed laser deposited Ba0.8Sr0.2TiO3 (BST) thin films has been studied. The x-ray diffraction and Raman analysis revealed the higher tetragonality of BST films when they were grown on higher (111) textured Pt layer. The properties like dielectric permittivity, polarization, switching time, and leakage currents were found to be correlated to tetragonality and orientation of the BST films. The polarization current was observed to be higher in BST films on Pt epitaxial layer and it exhibits exponential dependence on the electric field. The voltage-current measurements displayed Ohmic behavior of leakage current irrespective of Pt texture for low voltages (up to 1u2009V), whereas at higher voltages the conduction mechanism was found to be dependent on texture selection of bottom Pt electrode.

Mn-doped ZnO nanocrystals embedded in Al2O3: structural and electrical properties

We report on the structural and electrical properties of Mn-doped ZnO/Al(2)O(3) nanostructures produced by the pulsed laser deposition technique. Grazing incidence small angle x-ray scattering (GISAXS) and Rutherford backscattering spectrometry revealed the multilayered structure in as-deposited samples. Annealing of the nanostructures was shown to promote the formation of nanocrystals embedded in the Al(2)O(3) matrix, as was evidenced by GISAXS and high resolution transmission microscopy. Particle-induced x-ray emission analysis showed a doping of 8 at.% Mn in ZnO. Grazing incidence x-ray diffraction and Raman spectroscopy demonstrated that the nanocrystals have the pure wurtzite ZnMnO crystalline phase. Resonant Raman scattering displayed an increase of intensity of the 1LO mode as well as broadening of the 2LO mode related to the size effect. Capacitance-voltage measurements showed carrier retention with a voltage shift higher than those reported for similar systems.

Dielectric nonlinearity in a compositionally graded lead zirconate titanate structure

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure was studied as a function of frequency and amplitude of measuring field. The nonlinear behavior was observed above “threshold” value Et of electric field strength giving rise to field-dependent dielectric properties. Just above Et the nonlinearity was well fitted by the empirical Rayleigh relations. The values of Rayleigh coefficients were observed to be different from those of homogenous PZT films. The analysis of the nonlinearity allows us to suggest higher density of domain walls and/or their better mobility in graded structure.

Structural and Electrical Properties of Nanostructured Ba0.8Sr0.2TiO3 Films Deposited by Pulsed Laser Deposition

Barium Strontium Titanate Ba0.8Sr0.2TiO3 (BST) thin films have been deposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition technique. The X-ray diffraction (XRD) shows that the films crystallize in a perovskite phase. XRD and Atomic Force Microscopy (AFM) characterization reveal that the grains are nano-sized. Rutherford Backscattering Spectrometry (RBS) analysis shows the stoichiometry of the films to be close to the stoichiometry of the target. The Raman spectroscopy shows that the films exhibit the tetragonal structure by the presence of the Raman active modes at 301 cm-1 and 729 cm-1, at room temperature. Leakage current measurements of Au/ Ba0.8Sr0.2TiO3/Pt capacitors have been done, at room temperature, to investigate the conduction mechanisms of the films. We found that there are two different conduction regions in the capacitors, namely, an ohmic behavior at low voltages and a Schottky emission mechanism at high voltages. The Schottky barrier height has been estimated to be 0.99 eV.

Structural Study of Formation of Mn-Doped ZnO Nanocrystals Embedded in Alumina Matrix from ZnMnO/Al2O3 Multilayer Nanostructures

In this paper, the study of the formation of ZnMnO nanocrystals (NCs) embedded in an alumina matrix starting from ZnMnO/Al2O3 multilayers grown on a Si substrate by pulsed laser deposition with subsequent annealing is presented. The correlation between the morphology of grown NCs with the ratio R of the thickness of the ZnMnO layer to that of the Al2O3 layer in the as-grown multilayer structure was observed. The results show the possibility of controlling the strain, size, and distribution of grown NCs by setting the ratio R.

Optical Properties of PLZT 9/65/35 Thin Films on ITO-Coated Glass Substrate

Lanthanum modified lead zirconate titanate (PLZT) thin films were fabricated on indium doped tin oxide (ITO) - coated glass substrate by sol-gel method. The structure of the films was characterized with XRD and SEM. In the case of PLZT the dielectric function was modelled as a sum of Lorentzian oscillators and found by fitting the transmittance and reflectance spectra measured at normal incidence in the wavelength range of 220-2400 nm. The anomalous behaviour of dielectric function was observed below the absorption edge that was suggested to be due to formation of some defect states. The evolution of the absorption edge as well as dielectric function with film thickness was observed and discussed.