Structure of Pb(Fe2/3W1/3)O3 Single Crystals with Partial Cation Order

Despite intensive studies on the complex perovskite Pb(Fe2/3W1/3)O3 (PFWO) relaxor, understanding the exact nature of its multifunctional properties has remained a challenge for decades. In this work we report a comprehensive structural study of the PFWO single crystals using a combination of synchrotron X-ray diffraction and high-resolution electron microscopy. The set of {h + ½, k + ½, l + ½} superlattice reflections was observed for the first time based on single-crystal synchrotron X-ray experiments (100–450 K) and transmission electron microscopy investigations, which indicates some kind of B-cation ordering in PFWO which had been thought to be totally disordered. It was found that (1) the crystal structure of PFWO should be described by a partly ordered cubic perovskite (i.e. Fm − 3m), (2) the weak ferromagnetic properties and excess magnetic moment of PFWO can be understood based on non-random distribution of Fe cations between the 4a and 4b sites, and (3) the Pb displacement disorder is present in this material and the cations are probably displaced along the <100> directions. The X-ray diffraction results of this investigation show that partial cation ordering indeed exists in PFWO, which makes it necessary to revisit the generally accepted interpretations of the results obtained up to date. In agreement with X-ray diffraction study the main results of TEM study include: (1) a long range order that can be described with the Fm − 3m symmetry is reliably detected, (2) the coherence length of that long range order is in the order of 1–2 nm and (3) no remarkable chemical inhomogeneity is found in the tested PFWO crystal, excluding the possibility of a compositional ordering arising from substitutional defects in the perovskite structure

The δ-phase of SrTeO3 at 780 K1

As part of a structural investigation of strontium tellurate(IV) (STO), SrTeO3, with particular emphasis on the crystal chemistry and phase transitions, the structure of the δ-phase has been determined at 780 K using a single-crystal analysis. Both structural and non-linear optical measurements indicate that STO undergoes a γ→δ second-order ferroelectric phase transition at 633 K from the C2 (γ) to the C2/m (δ) modification. Systematic differences between the similar γ- and δ-phase structures were determined and it was found that this phase transformation can be described by a displacive mechanism

Potencijalna upotreba izotopa važnih za okoliš u ispitivanju migracije onečišćujućih tvari

This article presents the use of natural abundance stable isotope (hydrogen, carbon, nitrogen, oxygen, chlorine) analysis data as a tool for providing important information about the origin of contaminants, the contribution of different sources to a multi-source plume, characterisation of their complex transport (rate and mechanisms) and for evaluating the success of contaminated site remediation. Isotopic signatures of contaminants are useful tracers of their sources, while isotopic fractionation can be used to quantitatively assess the progress of an environmental process such as biodegradation. This new isotopic approach is reliable and can offer more information than traditional techniques in pollutant migration studies, particularly after waste disposal. During biological degradation of any organic compound, molecules containing lighter isotopes are degraded, and the portion of heavier isotopes in the substrate is increased, identifying specific microbial roles in biogeochemical cycling. Since isotopic fractionation is proportional to degradation, depending on the type of contamination, a microbial degradation of 50 % to 99 % of the initial concentration can be quantified using isotope ratio measurements.Cilj ovog rada je da se prikaže korištenje podataka analize prirodne obilnosti stabilnih izotopa (vodika, ugljika, dušika, kisika i klora) kao alata za dobivanje važnih informacija o porijeklu onečišćujućih tvari, doprinosu različitih multikomponentnih onečišćivača, karakterizaciji njihova kompleksnog transporta (brzine i mehanizma) i praćenja uspjeha remedijacije onečišćenih mjesta. Izotopski sadržaji onečišćujućih tvari koriste se kao traseri za određivanje njihovih izvora, dok se izotopsko frakcioniranje može iskoristiti za kvantitativnu procjenu toka procesa kao što je biodegradacija. Takav nov izotopski pristup je pouzdan i nudi više informacija od tradicionalnih tehnika kontrole putovanja onečišćivala, napose nakon odlaganja opasnog otpada na zemljištu. Za vrijeme biodegradacije nekog organskog spoje molekule koje sadržavaju lake izotope lakše se degradiraju, a dio težih izotopa u supstratu se povećava, što upućuje na mikrobiološku ulogu u biokemijskom ciklusu. Kako je izotopsko frakcioniranje proporcionalno degradaciji zavisno od tipa onečišćenja, korištenjem podataka mjerenja izotopskih odnosa može se procijeniti mikrobiološka degradacija od 50 % do 99 % od početne koncentracije

Modern means of endoscopic diagnosis for dysplastic changes of gastric lining

Modern endoscopic technologies at careful mucous surface examination make possible diagnosis of early gastric cancer, or even absolutely small flat superficial epithelial neoplasms. Various endoscopic methods were worked out to improve primary and precise clarifying diagnosis for dysplastic gastric lining changes and early gastric cancer. The international recommendations developed by the group of experts allow to define uniform tactics for maintaining patients with dysplastic changes of mucous membrane and early cancer. Wide-ranging studies of diagnostic endoscopy possibilities are going on together with development and improvement of available endoscopic technologies. In the present article we present a review of the modern endoscopic techniques for gastric mucosa dysplastic changes and early gastric cancer

Bis(N-nitroso-N-pentylhydroxylaminato-κ2 O,O′)copper(II)

In the centrosymmetric title compound, [Cu(C5H 11N2O2)2], the Cu2+ ion, located on an inversion centre (Wyckoff position 2b), is in a square-planar environment, surounded by four O atoms of the N-O groups of two N-nitroso-N- pentylhydroxylaminate ligands [Cu-O = 1.9042(17) and 1.9095(16)Å]. The hydroxylaminate monoanions are bidentate chelating ligands. The Cu2+ cations form stacks along [010], with intermolecular Cu..N contacts of 3.146(2) and 3.653(2)Å

Diaquabis[N-(2-fluorobenzyl)-N-nitrosohydroxylaminato-κ2 O,O′]nickel(II)

In the centrosymmetric title compound, [Ni(C7H 6FN2O2)2-(H2O) 2], the NiII cation is in a slightly distorted octahedral environment and is surrounded by four O atoms from the N - O groups of the organic ligands [Ni - O = 2.0179 (13) and 2.0283 (12) Å], and two water molecules [Ni - O = 2.0967 (14) Å]. The N-(2-fluorobenzyl)-N- nitrosohydroxylaminate monoanions act as bidentate chelating ligands. In the crystal, the Ni cations in the columns are shifted in such a way that the coordinated water molecules are involved in the formation of hydrogen bonds with the O atoms of the organic species of neighbouring molecules. Thus, a two-dimensional network parallel to (100) is built up by hydrogen-bonded molecules

Bis(N-nitroso-N-pentylhydroxylaminato-κ2 O,O′)copper(II)

In the centrosymmetric title compound, [Cu(C5H 11N2O2)2], the Cu2+ ion, located on an inversion centre (Wyckoff position 2b), is in a square-planar environment, surounded by four O atoms of the N-O groups of two N-nitroso-N- pentylhydroxylaminate ligands [Cu-O = 1.9042(17) and 1.9095(16)Å]. The hydroxylaminate monoanions are bidentate chelating ligands. The Cu2+ cations form stacks along [010], with intermolecular Cu..N contacts of 3.146(2) and 3.653(2)Å