M. Pilch

Resistance Switching Induced in BiMnO3 Ceramics

In our study BiMnO3 ceramics has been sintered. The X-ray diffraction test has shown that the crystal lattice symmetry is monoclinic and centrosymmetric. Grain structure and stoichiometry has been determined by scanning electron microscopy whereas local disorder by X-ray photoemission spectroscopy. Leakage currents dominated the D–E hysteresis loop. Electric conductivity has been measured in the 85–770 K range. The studied fresh ceramics shows semiconductor properties. Charge-order transition occurrence has been deduced. The dc resistance switching occurs following the application of electroformation at a high temperature range. This effect is reversible, i.e. the Rdc(T) recovers semiconductor properties after thermal and electric field treatment.

Glycine modified graphene oxide as a novel sorbent for preconcentration of chromium, copper, and zinc ions from water samples prior to energy dispersive X-ray fluorescence spectrometric determination

A novel and selective sorbent for micro-solid phase extraction was synthesized by chemical functionalization of graphene oxide with glycine. The structure of this nanomaterial, referred to as GO-Gly, was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. GO-Gly was used for preconcentration of chromium, zinc, and copper ions from water samples prior to their determination by energy dispersive X-ray fluorescence spectrometry (EDXRF). The proposed procedure is based on dispersion of micro amounts of GO-Gly in aqueous samples. After adsorption of metal ions on its surface, samples were filtered under vacuum and then membrane filters were directly submitted to energy dispersive X-ray fluorescence spectrometric measurements. In order to obtain optimal preconcentration conditions, some parameters affecting sorption process, such as pH, amount of GO-Gly, sorption times, and sample volume, were examined. Under optimal conditions the calibration curves were linear in a 1–150 ng mL−1 range with recoveries higher than 97%. The obtained detection limits for Cr(III), Zn(II), and Cu(II) determinations are 0.15, 0.07, and 0.08 ng mL−1, respectively. A relative standard deviation of the proposed procedure (at a 10 ng mL−1 level for n = 10) is lower than 2.3%. The proposed method was successfully applied for determination of Cr(III), Zn(II), and Cu(II) ions in water samples.

Local conductivity of epitaxial Fe-doped SrTiO3 thin films

Atomic Force Microscopy (AFM) measurements have been performed for Fe-doped SrTiO3 thin films with an Fe concentration of 1 and 2 at%. Thin films with a thickness of 15–50 nm were grown by pulsed laser deposition on single crystalline SrTi0.99Nb0.01O3 substrates. Low-energy electron diffraction examination showed that the films are single crystalline. The regions treated with the AFM tip (applied dc voltage up to 6 V) showed inhomogeneity of the electrical conductivity. Resistive switching was studied by the use of local conductive atomic force microscopy and was present in all samples. Fe doping was found to influence the character of switching.

Influence of nitrogen flow during sintering of bismuth manganite ceramics on grain morphology and surface disorder

ABSTRACT Bismuth manganite ceramics, consisted of two phases: cubic I23 and orthorhombic Pbam, were obtained by high-temperature sintering in the air. The powdered ceramics were sintered in gaseous nitrogen flow at stabilized temperature of TS = 870–1120 K for 4 h. Grain structure and chemical composition were checked by scanning electron microscopy (SEM). We observed changes in the grain shapes, the number and size of the hexagon-based parallelepipeds increased. The X-ray diffraction (XRD) test has shown that the orthorhombic BiMn2O5 phase formation was favored. The local disorder was tested by X-ray photoemission spectroscopy. Multi-component lines assigned to O 1s, Mn 2p, Bi 4f were detected. The ratio of intensities of particular components was influenced by the sintering conditions. The shape of valence band was not influenced by the sintering conditions. Electric resistivity was measured in 200–750 K range with the use of Ag and In electrodes. The activation energy increased slightly when the sintering temperature increased.

Resistance switching in rejuvenated NaNbO3:Mn crystals

In this paper, the resistance switching effect has been studied in NaNbO3:Mn crystals. Samples were rejuvenated in ambient air, below and above antiferroelectric phase transition. Dielectric spectroscopy has exhibited weak dispersion. The influence of annealing on the electronic structure has been determined with the use of X-ray photoelectron spectroscopy. Na2s, Nb3d, O1s, and Mn2p lines of the aged as-grown crystal and the rejuvenated samples spectra have been analyzed. Nb4+ states observed in the samples point to the presence of oxygen vacancies in the surface layer. Na ions migrate toward the surface due to rejuvenation. Switching from an insulator high-resistance state to a semiconductor medium resistance and finally to a metallic-type low-resistance state has been observed. The results are discussed within the framework of the extended defects model. We propose that the aliovalent Mn2+ dopant ions stabilize the oxygen vacancies and enable the resistive switching.

Influence of Proton Exchange on LiNbO3Crystals Structure

Proton exchange reaction (Li+/H+) was carried out on LiNbO3 crystals (z-cut). Reaction was conducted in concentrated environment of HNO3, at stabilized temperature 110°C. Portion of acid was added after each 24 h interval. The reference LiNbO3 crystal sample and etched for 240 h HxLi1−xNbO3 crystals were used for surface sensitive studies. SIMS test proved that H and Li the proton exchange reaction took place. Electronic structure was checked by XPS. The Li, Nb, O core lines, and VB line were analyzed. Substitution of Li by H ions deformed shape of the XPS lines that indicated crystal structure change.

Influence of post-sintering annealing on relaxor properties of BaBi2Nb2O9 ceramics

The effect of thermal treatment on the properties of Bi-layered ceramics, and particularly of the BaBi2Nb2O9 ceramics was considered to be marginal, despite the fact that their dielectric and relaxor properties are strongly related to the degree of heterogeneity. The aim of this article is to determine the influence of defects, especially the concentration of oxygen vacancies, on the relaxor properties of BaBi2Nb2O9. The results show that the oxygenation, taking place in the first phase of post-sintering annealing, do not affect significantly the values of the parameters characteristic of ferroelectric relaxors. The parameters undergo changes only after prolonged annealing, when the content of barium and bismuth were slightly changed.

PLZT microfibers volume gradients and anisotropy

ABSTRACT Electrocaloric materials for a new generation of cooling elements utilize the temperature dependence of spontaneous polarization in crystalline materials to harvest waste heat. From published results in particular (Pb0.93La0.07)(Zr0.65Ti0.35)O3 composition, have the largest pyroelectric coefficient. The most effective form for such applications is micro-fiber form, due to small heat capacitance allowing quick response time, even for nano second laser excitation. The presented work provides a consistent set of examinations of structural, ferroelectric and piezoelectric properties of damaged ceramics in fiber form and its comparative analysis to bulk to get practical knowledge of the processes occurring during fiber manufacture, to effectively prevent its destruction.

Thermal Treatment Effects in PbTiO3 Crystals Studied by XPS and Electric Conductivity Tests

The as-grown aged and thermally annealed at 720 K and 820 K PbTiO3 crystals were prepared. The ɛ′(T,f) and σAC(T,f) were measured at radio frequencies. Samples heated at 720 K shown resistive switching to metallic-type σAC(T). The resistivity switching was confirmed by RDC(T) measurement. The samples annealed at 820 K were rejuvenated, exhibited Curie-Weiss dependence above TC = 750 K and semiconductor conductivity. Annealing induced changes in shape of the Pb 4f, Ti 2p, O 1s, and VB XPS lines. We propose a model related to ionic migration toward FE domain walls and to vortices which provide conducting channels.

Technology of PLZT ceramics microfibers for multiferroics composites

Compactness and large energy conversion capacity are the main reasons of development of sophisticated ceramics materials in microfibers form, which are prepared for high-speed multiferroic systems and devices. These multifunctional composite applications are owing to coupling of electrical and magnetic properties, as well as additional thermal and mechanical properties. So that, they are suitable for magnetic sensors, electrically tunable non-linear transducers, and non-volatile memories. In our experiment, the thin fibers ceramics have been produced using special environmental chamber where the high temperature sintering can be protected by controlling such parameters as temperature and sintering atmosphere. Consequently, for these purposes structural and physical properties, preparation and thermal synthesis of micrometer sized lead lanthanum zirconate titanate (PLZT) fibers were investigated thoroughly. Since the phase transition properties of PLZT fibers differ much, the production process of fibers suffers from lack of proper high temperature control. Consequently, our experiments should help to eliminate this drawback, so that various technological conditions, parameters, and subsequent sintering atmosphere with different mixtures of PbO and ZrO were experimentally tested. Final conclusions include comparative analysis of obtained PLZT fibers ferroelectric phase transition properties to specific sintering atmosphere.