Impact of Defect Structure on ’Bulk’ and Nano-Scale Ferroelectrics

Ferroelectric materials offer a wide range of dedicated physical properties such as high dielectric constant, spontaneous polarisation, pyroelectric and piezoelectric effects which can be applied in thin-film non-volatile memories or ‘bulk’ actuators, multi-layer capacitors, thermal sensors and transducers (1–3). In that respect, desiredmaterials properties for specific applicationsmay be tailored by controlling the defect structure bymeans of aliovalent doping, rendering so-termed ’hard’ or ’soft’ piezoelectric materials (4–6). Another important impact on ferroelectric properties results from the confined size in nano-scale architectures (7). At the nanometer scale physical and chemical properties are expected to differ markedly from those of the ’bulk’ material. Owing to a size-driven phase transition, a critical particle size exists below which ferroelectricity does no longer occur (8). In this chapter, we will first outline the nature of the size-driven para-to-ferroelectric phase transition, as well as the concepts of defect chemistry. On that basis, the interplay between confined size at the nano-regime and the development of defect structure will be characterized. The here studied ferroelectric lead titanate nano-powders may be considered as a model system for more complex ferroelectric nano architectures (1; 2). Furthermore, the results discussed here may be transferred to large extent to other important perovskite oxides with divalent A- and tetravalent B-site, such as BaTiO3 or Pb[Zr,Ti]O3 (PZT). The defect chemistry of ferroelectric perovskite oxideswith monovalent A- and pentavalent B-site, such as the [K,Na]NbO3 (KNN) solid solution system, however has shown some important deviations from the defect structure characterized for PZT compounds (9; 10)

High-frequency electron paramagnetic resonance investigation of the Fe3+ impurity center in polycrystalline PbTiO3 in its ferroelectric phase

The intrinsic iron(III) impurity center in polycrystalline lead titanate was investigated by means of high-frequency electron paramagnetic resonance (EPR) spectroscopy in order to determine the local-environment sensitive fine structure parameter D. At a spectrometer frequency of 190 GHz, spectral analysis of a powder sample was unambiguously possible. The observed mean value D = +35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the B-site of the perovskite ABO3 lattice forming a directly coordinated iron - oxygen vacancy defect associate. A consistent fit of the multi-frequency data necessitated use of a distribution of D values with a variance of about 1 GHz. This statistical distribution of values is probably related to more distant defects and vacancies.Comment: 6 pages, 3 figures, 1 table, to appear in J. App. Phys, 96 (2004

Treatment of acute otitis externa with ciprofloxacin otic 0.2% antibiotic ear solution

R Mösges, M Nematian-Samani, A EichelInstitute of Medical Statistics, Informatics and Epidemiology, Faculty of Medicine, University of Cologne, GermanyBackground/objective: An inflammation of the cutis and subcutis of the external auditory canal is a primary symptom in cases of acute otitis externa. It is usually treated locally, since this type of therapy ensures a high concentration of the drug and interacts at the site of inflammation with no systemic effects. This systematic review compares the efficacy of treatment using a ciprofloxacin 0.2% solution with other therapeutic options.Methods: After compiling a catalog of search terms, medical databases were searched systematically for randomized, controlled studies. This search initially yielded a total of 38 studies which were then evaluated by three independent reviewers. The number of studies was subsequently reduced to 14: six studies using a ciprofloxacin 0.2% solution, and eight studies using both 0.2% and 0.3% solutions.Results: The studies included in the review demonstrate the statistical equivalence between the ciprofloxacin solution (0.2%) and the reference products PNH (a combination of polymyxin B, neomycin sulfate and hydrocortisone), auriculum powder, and a ciprofloxacin foam with respect to the cure rate. The research groups consistently observed high in vitro activity of ciprofloxacin against Pseudomonas aeruginosa.Conclusion: This systematic review confirms the hypothesis of ciprofloxacin's noninferiority in the treatment of otitis externa, in terms of the cure rate and microbiological eradication.Keywords: otitis externa, ciprofloxacin, antibiotic, ear solution, efficac

Effect of Nb-donor and Fe-acceptor dopants in (Bi1/2Na1/2)TiO3-BaTiO3-(K0.5Na0.5)NbO3 lead-free piezoceramics

The role of Fe as an acceptor and Nb as a donor in [0.94-x](Bi1/2Na1/2)TiO3-0.06BaTiO(3)-x (K0.5Na0.5)NbO3 (100xKNN) (x=0.02 and 0.03) lead-free piezoceramics was investigated. X-ray diffraction analyses show that all the profiles are best-fitted with a cubic symmetry where Fe doping tends to induce a lattice expansion, while Nb doping does the opposite. The strain and polarization characteristics are enhanced and suppressed by the acceptor and donor dopants, respectively. The improvement in the electrical properties with acceptor doping is accompanied by the stabilization of a ferroelectric order. Electron paramagnetic resonance spectroscopic analysis suggests that the stabilization of the ferroelectric order by the Fe dopant originates from the formation of (Fe-Ti'-V-O(center dot center dot))(center dot) defect dipoles.open211

Experimental evidence for the relaxation coupling of all longitudinal 7Li magnetization orders in the superionic conductor Li10GeP2S12

This contribution addresses the experimental proof of the relaxation coupling of the 7Li (I = 3/2) longitudinal magnetization orders in the solid-state electrolyte Li10GeP2S12 (LGPS). This effect was theoretically described by Korb and Petit in 1988 but has not yet been shown experimentally. In a 2D-T1/spin-alignment echo (SAE) experiment, the inverse Laplace transformation of the spectral component over two time dimensions revealed the asymmetric course of the spin-lattice relaxation following from the coupling of all longitudinal orders. These observations were supported by Multi-quantum-filter experiments and by simulations of the 2D-T1/SAE experiment with a lithium spin system. Since the asymmetric relaxation effects are directly dependent on the velocities and degrees of freedom of ion motion they could be used especially in fast Li-ion conductors as a separation tool for environments with different mobility processes