Effect of La substitution on the structural and electrical properties of BaBi4−xLaxTi4O15

Pure and lanthanum doped barium bismuth titanate BaBi_4−xLa_xTi₄O₁₅ (BBLT, x=0, 0.05, 0.15, 0.30) ceramics were prepared utilizing solid state method. The X-ray diffraction (XRD) data confirmed formation of single-phase Aurivillius compounds while SEM micrographs did not show evident grain size change of doped ceramics. Dielectric properties were investigated in 1.21 kHz to 1 MHz frequency range and in the temperature range of 20 to 727 °C. When Bi³⁺ is substituted with La³⁺, a significant disorder was induced and the material exhibited broadening of the phase transition. Impedance analysis confirmed the presence of two semicircular arcs in doped samples suggesting the existence of grain and grain-boundary conduction. The dc-conductivity and activation energies were evaluated for all compositions.     

PZT-nickel ferrite and PZT-cobalt ferrite comparative study: Structural,dielectric, ferroelectric and magnetic properties of composite ceramics

Comparative study of different PZT-based composite materials ((x)PbZr_0.52Ti_0.48O₃ + (1-x)CoFe₂O₄ and (x)PbZr_0.52Ti_0.48O₃ +(1-x)Ni_0.7Zn_0.3Fe₂O₄ (x = 0.8 and 0.9)) is presented in the frame of structural, dielectric, ferroelectric and magnetic properties. PZT and NZF/CF powders were synthesized by auto combustion technique. The composites were synthesized by mixing the appropriate amount of individual phases using conventional sintering. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF, without the presence of undesirable phases. SEM micrographs revealed a uniform grain distribution of both, ferroelectric and ferromagnetic phases. Non-saturated hysteresis loops are evident in all samples due to the existence of non-ferroelectric ferrite phase. All the samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Dielectric investigations revealed that ferrites are the main source of charge carriers, which must be of electronic origin. The activation energy of effective electrical resistivity is heavily influenced by the ferroelectric phase.     

Antimony doping effect on barium titanate structure and electrical properties

Nanopowders of pure and antimony doped barium titanate (BaTiO₃-BT) were synthesized by polymeric precursors method based on Pechini process. Obtained powders were pressed and sintered at 1300 °C for 8 h. XRD analysis showed the formation of cubic crystal structure in all nanopowders and tetragonal in BT ceramics. The influence of antimony concentration on structure change, grain size reduction and microstructure development was analyzed. Dielectric behavior of pure and antimony doped ceramics was studied as a function of temperature and frequency. The significant dielectric properties modification as a consequence of doping with different antimony concentration was noticed. The electrical resistivity measurements pointed out that antimony concentration influenced also on materials change from insulator to semiconductor.     

Dielectric investigations and theoretical calculations of size effect in lead titanate nanocrystals

The dielectric properties of nanograin ferroelectric lead titanate crystals are presented. The PbTiO3 samples were prepared by pressing nanopowders into plates and were studied experimentally by dielectric permittivity measurements in a wide frequency and temperature range. The TC dependence obtained showed a critical change of behavior with increasing mean nanoparticle size in the 9-nm region. The theoretical calculations based on Monte Carlo simulation were performed to describe the behavior of this material. It was shown that the distribution of nanoparticle sizes in the sample taken into account with the Monte Carlo method describes the dielectric properties of PbTiO3 nanocrystals quite well.     

Self-efficacy and illicit opioid use in a 180-day methadone detoxification treatment.

Self-efficacy ratings coincided with illicit opioid use across the 3 phases of a 180-day methadone detoxification treatment. Efficacy ratings increased after patients received their first dose of methadone, did not change while they were maintained on a stable dose of methadone, and declined during the taper as they attempted to face high-risk situations without the full benefit of methadone. Efficacy ratings measured at a point before a phase of treatment predicted illicit opioid use across that phase. For clarification of the relation between self-efficacy and illicit opioid use, 3 conceptual models proposed by J. S. Baer, C. S. Holt, and E. Lichtenstein (see record 1987-13846-001) were tested. Self-efficacy influenced subsequent drug use in parallel with previous behavior, but this influence was found only at the start of the stabilization phase and immediately before the start of the taper phase. These findings highlight the usefulness of the self-efficacy concept for the treatment of opioid addiction (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dielectric spectroscopy of nano BaTiO3 confined in MCM-41 mesoporous molecular sieve materials.

Dielectric properties of barium titanate (BaTiO3) particles, synthesized directly in the pores of MCM-41 materials, have been investigated in the frequency range from 20 Hz to 1 MHz for temperature intervals from 100 K to 500 K. The dielectric spectra of BaTiO3 confined in these molecular sieves were compared with the results obtained from the investigation of pure MCM-41 materials. Obtained results confirmed successful incorporation of BaTiO3 into porous matrix, but no phase transition from paraelectric to ferroelectric phase was observed due to the particle size being smaller than the critical size. Also, the overall dielectric response of investigated materials is strongly influenced by adsorbed water molecules.     

Dielectric properties of a novel high absorbing onion-like-carbon based polymer composite

A novel lightweight onion-like carbon (OLC) based Poly(methyl metacrylate) (PMMA) composite with high electromagnetic (EM) absorption capability determined earlier in microwave range is studied in low frequencies from 20 Hz to 1 MHz by dielectric spectroscopy. The investigation of dielectric properties of PMMA films with incorporated OLC in small concentration (0.5–2 wt.%) have been carried out by varying the temperature between 240 and 520 K. The temperature behavior of the complex permittivity at a given frequency is found to be strongly dependent on the OLC concentration. The experimental data are in quantitative agreement with the results of modified effective medium calculations of OLC-based polymer film's permittivity. Both the experimental observations and theoretical simulation demonstrate that small additions of onion-like carbon particles to a polymer matrix can noticeably modify the composite response to low-frequency EM radiation as well as improve its thermal stability (increased glass transition and melting temperatures, correspondingly).     

Dielectric properties of onion‐like carbon and detonation nanodiamond/polydimethysiloxane composites

Results of dielectric investigations of onion‐like carbon (OLC) and detonation nanodiamond (DND)/polydimethysiloxane composites in wide frequency (20 Hz–3 THz) and temperatures (26–300 K) ranges are presented. The percolation threshold in OLC composites is 6.8 vol%. Electrical conduction in the OLC composites above the percolation threshold occurs mainly due to electron tunneling between OLC clusters and quasi‐one‐dimensional hopping inside the clusters. Hopping almost vanishes at frequencies above 100 GHz, where phonon contribution to the dielectric permittivity dominates. At low concentrations of nanocarbon particles (concentrations below the percolation threshold for OLC), the dielectric properties of the OLC and DND composites are similar. However, DNDs provide a noticeable improvement of the mechanical properties of the composites, in contrast with OLC. Therefore, a combination of the two nanomaterials in the composites could be beneficial. POLYM. COMPOS., 36:2084–2092, 2015. © 2014 Society of Plastics Engineer