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Electron paramagnetic resonance study of impurities and point defects in oxide crystals

Stefaniuk I.

Opto-Electronics Review

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2018

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Vol. 26, No. 2

81--91

EN

In this topic review the results of the X-band electron paramagnetic resonance (EPR) measurements of Mn, Co, Cr, Fe ions in YAlO₃ (YAP) crystals and Fe ions in LiNbO₃ (LNO) crystals and of chromium doped Bi₁₂GeO₂₀ (BGO) and Ca₄GdO(BO₃)₃ single crystals, are presented. It is well known that the oxide crystals (for example:YAP, LNO, BGO) are one of the most widely used host materials for different optoelectronic applications. The nature of point defect of impurities and produced in the oxide crystal after irradiation by bismuth ions and after irradiation by the ²³⁵U ions with energy 9.47 MeV/u and ﬂuency 5 × 10¹¹ cm⁻¹ is discussed. The latter is important for applications of these oxide crystal as laser materials.

2

Electron paramagnetic resonance studies of manganese and cobalt ions in YAlO3 crystals

Stefaniuk I., Rogalska I, Suchocki A, Berkowski M., Cieniek B., Potera P.

Optica Applicata

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2014

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Vol. 44, nr 1

113--121

EN

The results of X-band electron paramagnetic resonance measurements of Mn2+ and Mn4+ ions in YAlO3 (YAP) crystals in the temperature range 100–300 K are presented. Additionally, we observe electron paramagnetic resonance spectra of unintentional impurities Fe3+ and Cr3+ in YAP crystals. The angular dependence for Mn ions in YAP crystals can be presented. We aim at obtaining a better insight into the spectroscopic properties of paramagnetic Mn centers and structural information about their nearest environment in YAP host and at determining the valence of manganese ion. In this paper we compare electron paramagnetic resonance spectra for Co and Mn ions in YAP crystals.

3

Wpływ modyfikacji zeolitów na ich właściwości fizykochemiczne

Świderska-Dąbrowska R., Schmidt R.

Rocznik Ochrona Środowiska

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2012

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Tom 14

460--470

EN

Zeolites are crystalline, hydrated aluminosilicates of alkali and alkaline earth metals (Na, K, Mg, Ca, Sr, Ba), in which the pore size is 0.3-1.2 nm and depends on the structure of the zeolite. They consist of tetrahedrons of [AlO4]-5- and [SiO4]4-, which make ordered crystal lattice of rings, channels and chambers. Variable degree of oxidation of silicon (IV) and aluminum (III) causes their electronegative character. The size of the charge may determine the adsorption, ion exchange and catalytic capacities of zeolite. The structure made of ring tetrahedron units contains open tunnels, making zeolites also molecular sieves. Zeolites are mostly used for adsorption of ammonium ions from aqueous solutions, removal of radioactive elements and heavy metals, and recent studies suggest the possibility of application of zeolites for removal of chloroorganic compounds and oily pollutants. The most widely used zeolite in practice for water and wastewater treatment is clinoptilolite, which is characterized by large ion exchange and adsorption capacity. Authors of many works explain the adsorption process with ion exchange. But when interpreting the results the authors do not consider that the zeolites have also tunnels that make them also molecular sieves. As a result of ion adsorption on clinoptilolite in hydrogen or sodium form, pH of the solution decreases, resulting in possible formation of electropositive, electronegative complexes and dissociated ions which make up aquaions, increasing or decreasing the effectiveness of their removal. During usage of modified zeolites for the adsorption of ions from aqueous solutions, many accompanying processes take place, such as precipitation, coprecipitation and catalytic adsorption. The influence of the physicochemical properties of natural zeolite and zeolite in the hydrogen form on an aqueous solution in the process of washing out is presented in the paper. Presented results clear prove that the decisive factor affecting the quality of the aqueous solution after the washing out process is initial pH of the solution. Depending on method of modification, physicochemical properties of zeolites can vary considerably. Transformation of natural zeolite into the hydrogen form increases its acidity and physical and chemical resistance. Modification of zeolite with HCl may also increase the content of pure zeolite by dissolution of other, non-zeolite materials. Zeolite H has a greater content of of silicon and aluminum compounds in relation to total mass which is a result of introduction of protons into the zeolite. This is confirmed by lower content of alkali metals and alkaline earth metals (sodium, calcium and potassium) in ZH. Exchange of ions of sodium, potassium, calcium for protons is a result of modification of ZN with HCl. Examination of washing out process showed that there is a small migration of impurities (Fe and Ca) from ZH as compared to ZN. At the same time increase of iron content in the solution increases its turbidity. And also turbidity depends on the initial pH of the solution. It's highest value was observed when the initial pH was equal to 6. Significant increase of turbidity as a function of pH is mainly caused by abrasion of zeolite grains in the process of shaking and by formation of precipitable complexes of iron and calcium. The paper presents also the results of zeta potential measurements. potential of H zeolite in the investigated range of pH has a much higher absolute values compared to ZN and vary in the range from -20 mV to -30 mV. H zeolite has a higher electrostatic activity than natural zeolite. Potential creating ions such as H+ and OH- have decisive influence on the zeolite surface charge.

4

Simultaneous kinetic-potentiometric determination of Fe3+ and Al3+ using H-point standard addition and partial least squares methods

Karimi M. A., Ardakani M. M., Behjatmanesh-Ardakani R., Monfared M. R. Z.

Chemia Analityczna

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2009

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Vol. 54, No. 6

1321-1337

EN

H-point standard addition method (HPSAM) and partial least squares (PLS) method were used for simple, accurate and simultaneous determination of two cations: Fe3+ and Al3+ using kinetic data obtained in a novel potentiometric method. The measurement principle of the methods was based on a difference between complexation reaction rates of Fe3+ and Al3+* with fluoride ion. The reaction rate of Fe3+ and A13+ with F~ was monitored using a fluo-ride ion-selective electrode (FISE). The results demonstrated that the simultaneous determination of Fe3+ and Al3+ was possible in the concentration ranges of 2.0-50.0 and 0.5-40.0 μg mL-1, respectively. Total relative standard error was 1.55%. The effects of certain foreign ions upon the reaction rate were determined in order to assess selectivity of the method. The proposed methods (HPSAM and PLS) were successfully applied to the simultaneous determination of Fe3+ and Al3+ in water, tea, alloy and plant samples. Recoveries were satisfactory and statistically comparable to those obtained applying the reference ' flame atomic absorption spectrometry method.

PL

Opracowano nową potencjometryczną metodę, która w kombinacji z metodą dodatku wzorca w punkcie H (HPSAM) i metodą częściowych, najmniejszych kwadratów (PLS) pozwoliła na proste, dokładne i jednoczesne oznaczanie kationów Fe3 i Al3+. W metodzie wykorzystano różnicę między szybkością kompleksowania Fe3+ i Al3+ przez jony fluorkowe. Reakcje kompleksowania monitorowano elektrodą jonoselektywną na fluorki. Stwierdzono, że jednoczesne oznaczanie było możliwe w zakresie stężeń 2-50 (Fe3+) 0.5-40 (Al3+) mg mL-1 Względny całkowity błąd standardowy wyniósł l .55 %. Zbadano wpływ niektórych obcych jonów na selektywność metody. Opracowaną metodę zastosowano do oznaczania wymienionych kationów w wodzie, herbacie, i próbkach stopów i roślin. Odzyski były satysfakcjonujące i statystycznie równocenne do tych otrzymanych metodą atomowej spektrometrii absorpcyjnej.