The resistivity switching of iron doped strontium titanate single crystals and thin films

The main objective of this work was to identify and understand the physical mechanisms underlying the phenomenon of the RS in the Fe doped SrTiO3 material. Two basic types of materials were investigated: the single crystals and thin lms. The main reason for this approach was to obtain the information about both: the fundamental physics (single crystals) and the material more suited for the applications (thin lms). The samples with di erent iron concentrations, were modi ed by the temperature, electric eld and chemical gradients. Resulting changes were investigated by a number of techniques that are characteristic to the solid state physics in the macro- and nano- scales. Completed studies have shown that: Crystallographic structure of the starting crystals was in good agreement with the literature. Surprisingly high level of the Fe concentration variation, even for the relatively low Fe doping, was found. Local conductivity in nanoscale showed characteristic conducting stripes, not observed previously. Fe valence state was found to be a mixture of 2+ and 3+, contrary to the most of the reports on similar systems. Moderately high temperature treatment under oxidizing and reducing conditions led to huge chemical modi cation of the crystal surface, including formation of new phases and the decomposition of STO phase. High mobility of the Fe ions above 700 C allowed for signi cant iron migration and preferential atoms localization (close to the extended defects). Especially interesting is that the crystals exposed to the high temperaturę under various conditions undergone transformation and decomposition to other phases. This remains in the contrary to conventional model, where only the oxygen content in the form of SrTiO3 was changing. Moreover, the a nity of the Fe ions to locate close to the extended defects was shown, as an formation of lament like Fe structure. The nanoscale RS behavior was also evident and did not di er signi cantly from the behavior in the undoped STO crystals. It was concluded, that the basic mechanism of RS in Fe doped STO is not in uenced by the iron doping. Similar results can be observed under the electrical stress. The electroformation and subsequent electro-coloration phenomena were investigated. The most prominent results showed: Electrical stimuli led to the I-M transition. I-M transition was connected to changes in the oxygen vacancy concentration and the movement of the oxigen ions along the extended defect network. Evolution of the color front was documented, and compared to the removal of oxygen ions from the material. Total number of the oxygen ions removed from the material during electroreduction experiment was estimated. RS behavior was found and measured both in macro- and nano-scales. Fast reaction of the electrical behavior to the surrounding atmosphere conrmed, that the oxygen can be removed and introduced to the system quite easily. Strong connection between the evolution of the color front and the electrical properties of the samples were shown. Also the fact that the Fe doped STO crystal is in fact 'open' to the removal and introduction of the oxygen ions from the surrounding atmosphere was found. The investigation of the thin lms yielded promising results, especially in the similarities with the single crystal behavior. The most interesting ndings consist of: Many hints that the Fe ions were inhomogeneously distributed in the STO matrix was found. Fe was found to be very mobile and typically was found to migrate away from the surface into the bulk. High susceptibility of the electrical parameters to the electrical stress led to high variation in the measured activation energy values. The RS behavior was con rmed and no clear voltage threshold for the set and reset voltage was found (up to several mV). This results showed many similarities of the STO thin lm and single crystals behavior. It seems possible to maintain good single crystal properties in more applicative thin lms. What is more, the pursue for the 'perfect' or defect-free thin lms is not always necessary, since it can be bene cial for the RS materials to posses slightly di erent structure or defect concentration. Nevertheless, there is still a long way from the basic investigations and prototypes to the commercial applications. It is also important to be more careful measuring the electrical properties of the RS material, since the properties of the investigated material can change during the experiment itself, leading to unreliable results. Outlook Investigation presented in this work showed that the RS is complicated phenomena. The complexity of the RS even increases, when one moves his attention from the macroscale, typically used to describe the properties of the materials, into nanoscale. In many cases, only the nanoscale experiments can provide crucial data necessary for better understanding of the fundamental physics. What is more, the observations in nano-scale clearly shows that the perfect crystals are really not so perfect as one could expect, which is strongly connected to structure defects and inhomogeneity of the dopant. The knowledge of the imperfection and the real state of the materials is not only useful from the fundamental point of view. I strongly believe it is necessary for the future investigation and the development of new technologies. As the case of the STO (and the Fe doped STO) shows, the extended defects, such as dislocations, are crucial for the RS behavior. Therefore a careful investigations, mostly in nanoscale, can provides the ideas and the means to exploit the defects and imperfections for the bene t of new materials with outstanding properties

Computational complexity of the semantics of some natural language constructions

AbstractWe consider an example of a sentence which according to Hintikka's claim essentially requires for its logical form a Henkin quantifier. We show that if Hintikka is right then recognizing the truth value of the sentence in finite models is an NP-complete problem. We discuss also possible conclusions from this observation

Stability of ferrous fumarate in medicaments for women : application of Mossbauer spectroscopy

Determination of the iron state (Fe2+ or Fe3+) and content of iron in commercial pharmaceutical products containing ferrous fumarate FeC4H2O4 was made by the Mössbauer spectroscopy and X-ray fluorescence method. Also, influence of thermal treatment on stability of ferrous fumarate in selected medicaments has been investigated. The investigated samples were annealed in definite temperature: 373, 473, and 573 K for 5 h. Room temperature Mössbauer spectra of initial samples gave clear evidence that two phases of iron were presented. The major component was connected with ferrous fumarate with a contribution from 85% to 50%, depending on investigated medicaments. Ferrous fumarate was stable up to annealing temperature 473 K. Above this temperature significant oxidation of Fe2+ to Fe3+ was observed

ДВОРЯНСТВО ЛІВОБЕРЕЖНОЇ УКРАЇНИ І ЛІТЕРАТУРА ДРУГОЇ ПОЛОВИНИ XIX –ПОЧАТКУXX СТ.

В статті розглядається внесок представників дворянських родів Лівобережної України в розвитоклітератури пореформенного періоду. Окреслено основні їх здобутки та подана коротка характеристика літературних розвідок .Стороженка О.П., Ганни Барвінок, Марка Вовчка, СтарицькогоМ.П.. та ін.In the article payment of representatives of the Left-bank nobility is examined in development of literature of poreformennogoperiod.Outlined their basic achievements and short descriptionof literary secret services of .StorozhenkoO. P.,Hanna Barvinok,MarkVovchka, StarickogoM. but insh

Mössbauer spectroscopy study in characterization of steel production dusts

Steel production involves processes and alloys based on iron. Metallurgy is one of the most energy-intensive branches of industry and it also generates a lot of damage. The aim of the research was to recognize magnetic properties, mineral composition, and phase content of dusts from a de-dusting station, steel mill, sinter strand and filter press located in a steel metallurgical foundry in Upper Silesia, the most urbanized, industrialized and also the most polluted region of Poland. The following methods were applied: X-ray fluorescence, X-ray diffraction and the Mössbauer spectroscopy measurements

Inhomogeneity and Segregation Effect in the Surface Layer of Fe-Doped SrTiO3 Single Crystals

The e ect of Fe doping on SrTiO3 single crystals was investigated in terms of crystal and electronic structure over a wide temperature range in both oxidizing and reducing conditions. The electrical properties were thoroughly studied with a special focus on the resistive switching phenomenon. Contrary to the undoped SrTiO3 crystals, where isolated filaments are responsible for resistive switching, the iron-doped crystals showed stripe-like conducting regions at the nanoscale. The results showed a non-uniform Fe distribution of as-received crystals and the formation of new phases in the surface layer of reduced/oxidized samples. The oxidation procedure led to a separation of Ti(Fe) and Sr, while the reduction resulted in the tendency of Fe to agglomerate and migrate away from the surface as seen from the time of flight mass spectroscopy measurements. Moreover, a clear presence of Fe-rich nano-filament in the reduced sample was found

Structure and Properties of Copper Pyrophosphate by First-Principle Calculations

Investigated the structural, electronic, and magnetic properties of copper pyrophosphate dihydrate (CuPPD) by the first-principle calculations based on the density functional theory (DFT). Simulations were performed with the generalized gradient approximation (GGA) of the exchangecorrelation functional (Exc) supplemented by an on-site Coulomb self-interaction (U–Hubbard term). It was confirmed that the GGA method did not provide a satisfactory result in predicting the electronic energy band gap width (Eg) of the CuPPD crystals. Simultaneously, we measured the Eg of CuPPD nanocrystal placed inside mesoporous silica using the ultraviolet–visible spectroscopy (UV–VIS) technique. The proposed Hubbard correction for Cu-3d and O-2p states at U = 4.64 eV reproduces the experimental value of Eg = 2.34 eV. The electronic properties presented in this study and the results of UV–VIS investigations likely identify the semiconductor character of CuPPD crystal, which raises the prospect of using it as a component determining functional properties of nanomaterials, including quantum dots

Electrical polarization switching in bulk single crystal GaFeO3_{3}

The electrical polarization switching on stoichiometric GaFeO$_{3}$ single crystal was measured, and a new model of atomic displacements responsible for the polarization reverse was proposed. The widely adapted mechanism of polarization switching in GaFeO$_{3}$ can be applied to stoichiometric, perfectly ordered crystals. However, the grown single crystals, as well as thin films of Ga-Fe-O, show pronounced atomic disorder. By piezoresponse force microscopy, the electrical polarization switching on a crystal surface perpendicular to the electrical polarization direction was demonstrated. Atomic disorder in the crystal was measured by X-ray diffraction and M\"ossbauer spectroscopy. These measurements were supported by ab initio calculations. By analysis of atomic disorder and electronic structure calculations, the energies of defects of cations in foreign cationic sites were estimated. The energies of the polarization switch were estimated, confirming the proposed mechanism of polarization switching in GaFeO$_{3}$ single crystals