Heat treatment effects on domain configuration and strain under electric field in undoped Pb[ZrxTi1-x]O3 ferroelectrics

Undoped Pb[ZrxTi1-x]O3 (PZT) ceramics from the tetragonal and rhombohedral side of the morphotropic phase boundary (MPB) were examined. Temperature dependent changes in domain configuration were observed by in situ hot-stage transmission electron microscopy (TEM). In corresponding macroscopic ex situ strain measurements an enhanced influence of the electric field was detected after annealing

Inhibition of small G proteins of the Rho family by statins or Clostridium difficile toxin B enhances cytokine-mediated induction of NO synthase II

1. In order to investigate the involvement of Ras and/or Rho proteins in the induction of the inducible isoform of nitric oxide synthase (NOS II) we used HMG-CoA reductase inhibitors (statins) and Clostridium difficile toxin B (TcdB) as pharmacological tools. Statins indirectly inhibit small G proteins by preventing their essential farnesylation (Ras) and/or geranylgeranylation (Rho). In contrast, TcdB is a glucosyltransferase and inactivates Rho-proteins directly. 2. Human A549/8- and DLD-1 cells as well as murine 3T3 fibroblasts were preincubated for 18 h with statins (1–100 μM) or TcdB (0.01–10 ng ml(−1)). Then NOS II expression was induced by cytokines. NOS II mRNA was measured after 4–8 h by RNase protection assay, and NO production were measured by the Griess assay after 24 h. 3. Statins and TcdB markedly increased cytokine-induced NOS II mRNA expression and NO production. Statin-mediated enhancement of NOS II mRNA expression was reversed almost completely by cotreatment with mevalonate or geranylgeranylpyrophosphate. It was only slightly reduced by farnesylpyrophosphate. Therefore, small G proteins of the Rho family are likely to be involved in NOS II induction. 4. In A549/8 cells stably transfected with a luciferase reporter gene under the control of a 16 kb fragment of the human NOS II promoter (pNOS2(16)Luc), statins produced only a small increase in cytokine-induced NOS II promoter activity. In contrast, statins had a considerable superinducing effect in DLD-1 cells stably transfected with pNOS2(16)Luc. 5. In conclusion, our studies provide evidence that statins and TcdB potentiate cytokine-induced NOS II expression via inhibition of small G proteins of the Rho family. This in turn results in an enhanced NOS II promoter activity and/or a prolonged NOS II mRNA stability

The Impact of Heat Treatment on the Domain Configuration and Strain Behavior in Pb[Zr,Ti]O 3_{3} Ferroelectrics

The influence of heat treatment in lead zirconate titanate Pb(Zr,Ti)O3 (PZT) ferroelectrics on the domain structure and strain behavior has been investigated. Temperature-induced changes in the domain configuration, for example, appearance of nanodomains within microdomains, were observed by in situ hot-stage transmission electron microscopy. During the transient post annealing state the strain behavior under electric field differed from that of the nonheat-treated ferroelectrics. Directly after cooling the difference was most pronounced and decreased as a function of time. The enhanced response to an electric field of 4 kV/mm resulted in qualitatively different effects on strain for PZT from the tetragonal side and from the rhombohedral side of the morphotropic phase boundary

Iron-oxygen vacancy defect association in polycrystalline iron-modified PbZrO3PbZrO_{3} antiferroelectrics −- multi-frequency electron paramagnetic resonance and Newman superposition model analysis

By utilizing multifrequency electron paramagnetic resonance (EPR) spectroscopy, the iron functional center in Fe3+-modified polycrystalline lead zirconate (PbZrO3) was studied. The single phase polycrystalline sample remained orthorhombic and antiferroelectric down to 20 K as confirmed by high-resolution synchrotron powder diffraction. The Fe3+ ions were identified as substituting for Zr4+ at the B-site of the perovskite ABO3 lattice. Similarly as found for Fe3+:PbTiO3 [Meštrić et al., Phys. Rev. B 71, 134109 (2005)], the value of the fine-structure (FS) parameter B20 is only consistent with a model in which a charged (FeZr′–VO••)• defect associate is formed. In contrast to a well defined iron functional center in lead titanate (PbTiO3) with FS parameters exhibiting variances of less than 3%, a strong broadening of the EPR powder pattern was observed in lead zirconate, indicating a much larger variance of FS parameters. It is suggested that the apparent broad distribution of fine-structure parameters arises from the system’s capability to realize different oxygen vacancy positions in the first coordination shell around the iron site. This proposed model of a small number of distinct iron-oxygen vacancy sites is supported by the observation that corresponding B20 and orthorhombic B22 FS parameters of these sites are anticorrelated, a property not expected for random distributions of fine-structure parameters