Crystal structure of KTi0.93Sn0.07OPO4

To reveal correlations between the atomic structure and properties of the KTi_1-x SnxOPO₄ solid solutions, single crystals of the KTi_0.93Sn_0.07OPO₄ composition were synthesized and their structure was determined. The crystals belong to the KTiOPO₄ family; orthorhombic, sp. gr. Pna2₁. The unit-cell parameters are a = 12.831, b = 6.410, and c = 10.584 Å. The partial substitution of Sn atoms for Ti atoms results in the formation of more symmetric coordination polyhedra in the structure framework and the change of the physical properties of the crystals.     

Crystal structure of potassium titanyl phosphate doped with zirconium

This paper reports on the results of precision X-ray structural investigations of single crystals of the compounds KTi_0.96Zr_0.04OPO₄ (at 293 K) and KTi_0.97Zr_0.03OPO₄ (at 293 and 105 K). No significant splitting of the positions occupied by potassium atoms is revealed. This result is in agreement with a considerable decrease in the electrical conductivity of potassium titanyl phosphate KTiOPO₄ (KTP) crystals doped with zirconium (KTP: Zr) as compared to crystals of undoped potassium titanyl phosphate. It is established that the difference between the Ti-O bond lengths in chains formed by titanium octahedra is not a single structural parameter responsible for the nonlinear optical properties of crystals in this series.     

Structural reasons for the nonlinear optical properties of KTi<Subscript>0.96</Subscript>Zr<Subscript>0.04</Subscript>OPO<Subscript>4</Subscript> single crystals

This paper reports on the results of the precision X-ray structural investigations of KTi_0.96Zr_0.04OPO₄ single crystals at room temperature. It is established that the incorporation of zirconium atoms into the structure of KTiOPO₄ (KTP) crystals does not lead to substantial changes in the framework structure and results only in an insignificant decrease in the scatter of the distances in the PO₄ tetrahedra and the formation of more symmetric (TiZr)O₆ octahedra as compared to the TiO₆ octahedra. However, the incorporation of zirconium atoms into the KTP structure is accompanied by the redistribution of the electron density in the crystal as a whole, so that the electron density increases in the region of the positions occupied by the potassium atoms. This changes the nonlinear optical properties of the given series of crystals, which are estimated from the intensity of the second harmonic generation signals.     

On the effect of structural and symmetrical features of potassium titanyl phosphate crystals with different contents of niobium,antimony, and zirconium on the second-harmonic intensity

A model is proposed, which shows that, at small deviations from the centrosymmetric state of the atomic structure, the quadratic nonlinear susceptibility of a crystal monotonically decreases with approach of the degree of central symmetry \(\eta _{\overline 1 } \)[φ(r)] of the electric potential function of the crystal structure to unity. The quadratic nonlinear susceptibility of K_{1 ? x} Ti_{1 ? x} Nb _x OPO₄ (x = 0, 0.02, 0.04, 0.11), K_{1 ? x} Ti_{1 ? x} Sb _x OPO₄ (x = 0.01, 0.07, 0.17), and KTi_{1 ? x} Zr _x OPO₄ (x = 0.03, 0.04) crystals has been measured. The degree of central symmetry \(\eta _{\overline 1 } \)[φ(r)] has been calculated for the structures of K_{1 ? x} Ti_{1 ? x} Nb _x OPO₄ (x = 0, 0.04, 0.11), K_{1 ? x} Ti_{1 ? x} Sb _x OPO₄ (x = 0.01, 0.07, 0.17), and KTi_{1 ? x} Zr _x OPO₄ (x = 0.03, 0.04) crystals. It is shown that, at \(\eta _{\overline 1 } \)[φ(r)] > 0.7, the relationship between the quadratic nonlinear susceptibility of the investigated crystals and the degree of their central symmetry \(\eta _{\overline 1 } \)[φ(r)] is in qualitative agreement with the proposed model.     

Crystal growth of zirconium‐doped KTiOPO4 crystals in the K2O‐P2O5‐TiO2‐ZrF4 system

Zirconium‐doped KTiOPO₄ (KTP) crystals were grown using a high temperature flux method in the K₂O‐P₂O₅‐TiO₂‐ZrF₄ system. The dopant content in the single crystals with general composition KTi_1‐xZr_xOPO₄ (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO₄ containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF₄ precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Incorporation of hafnium (IV) into KTP framework from phosphate‐fluoride fluxes

Solid solutions KTi_1‐XHf_XOPO₄ (х = 0.008 – 0.107) possessing the KTiOPO₄ structure, have been synthesized in molten system K₂O‐P₂O₅‐TiO₂‐HfF₄. The crystal growth experiment of Hf‐doped KTP crystal has been reported. The X‐ray powder diffraction data and chemical analysis are also presented. It has been shown that KTiOPO₄ crystal structure slightly changes when Hf incorporates into the framework. Transmission/absorption spectra of KTi_0.974Hf_0.026OPO₄ crystals have been recorded. The incorporation of Hf ions shifts the optical absorption edge in the UV‐visible spectrum towards the long‐wavelength region with absorption near 387 nm.     

X-Ray diffraction study of KTiOPO<Subscript>4</Subscript> single crystals doped with hafnium

Single crystals of KTi_{1 − x} Hf _x OPO₄ (x = 0.015(2), 0.035(1), and 0.128(1) are reinvestigated by precision X-ray diffraction at room temperature. It is found that the implantation of hafnium atoms in the crystal structure of KTiOPO₄ does not lead to significant changes in the framework and affects only the positions of the potassium atoms in the channel. Our studies reveal the displacements of the potassium atoms from their main and additional positions in the structure of pure KTP in all three structures studied. The largest displacements from the K1′ and K1″ additional positions are observed in the structure with x = 0.035. At this hafnium concentration, the occupancy of the main positions of potassium atoms decreases and the occupancy of the additional positions increases in relation to those in KTP. This redistribution of potassium atoms enhances the nonuniformity of distribution of the electron density in the vicinity of their positions, which is probably responsible for the increase in the nonlinear susceptibility of KTP crystals that contain 3.5% hafnium in relation to crystals of pure KTP.     

Electrical and nonlinear optical properties of KTiOPO<Subscript>4</Subscript> single crystals doped with niobium,antimony, and tantalum

Single crystals of K_{1 ? x}Ti_{1 ? x}Nb_xOPO₄ (KTP: Nb), K_{1 ? x}Ti_{1 ? x}Sb_xOPO₄ (KTP: Sb), and K_{1 ? x}Ti_{1 ? x}Ta_xOPO₄ (KTP: Ta) solid solutions are grown and their dielectric, conducting, and nonlinear optical properties are investigated. The maximum contents x of niobium, antimony, and tantalum impurities in the crystals are equal to 0.11, 0.23, and 0.25, respectively. The doping of the KTiOPO₄ crystals with niobium, antimony, and tantalum brings about the formation of additional potassium vacancies and additional potassium positions and, as a consequence, an increase in the ionic conductivity σ₃₃. An increase in the doping level leads to a smearing of the ferroelectric phase transitions and a decrease in the phase transition temperatures. The permittivity of the doped crystals exhibits a broad relaxation peak in the temperature range 200–600°C.     

Synthesis,properties, and structure of potassium titanyl phosphate single crystals doped with hafnium

Single crystals of potassium titanyl phosphate doped with hafnium are grown by spontaneous flux crystallization. Their physical properties are studied, and the structure of three KTi_{1 − x} Hf _x OPO₄ crystals (x = 0.01, 0.03, and 0.12) is determined. In the crystals studied, hafnium mostly occupies the second titanium position. The doping of KTP crystals with hafnium results in an elongation of K-O bonds in the potassium polyhedra and, as a consequence, in a considerable (by approximately 180°C) decrease in the temperature of ferroelectric phase transition. The magnitude of anomalous permittivity substantially decreases. The electrical conduction in the specimens studied decreases by approximately half an order of magnitude in the low-temperature region but remains almost unchanged in the high-temperature region. Even at minor concentrations, the presence of a hafnium additive in the specimens considerably (by 35%) enhances the intensity of the second harmonic generation of laser radiation.     

Mössbauer investigation of tin-containing chalcogenide glasses and glass-ceramics

The parameters of Mössbauer spectra, namely isomer shift, quadrupole splitting and linewidth were obtained before and after crystallization of glass samples of composition xSn_0.5Se_0.5 (100x) (As_0.1Ge_0.3Se_0.6) with x = 5 ～ 30 mol.%. It is demonstrated that the higher the crystallinity, the more the isomer shift decreases, this is probably due to the variation of average SnSe bond length. An electric field imbalance in the Sn nucleus caused by distortion of (Sn Se₆) octahedra in glasses showed a greater quadrupole splitting as compared with glass-ceramics of the same tin content.     

Synthesis and properties of zirconium-doped RbTiOPO<Subscript>4</Subscript> single crystals

Single crystals of the solid solutions RbTi_{1 ? x} Zr _x OPO₄ (0.015 < x < 0.034) were grown and their physical properties were studied. In the presence of zirconium in the crystals with the maximum content x = 0.034, the ferroelectric phase transition and the high-temperature transition from the orthorhombic to the cubic phase are shifted to lower temperatures by 100 and 50°C, respectively. In the temperature range from 700°C to room temperature, the conductivity of doped crystals decreases compared to that of the undoped crystals. It is of particular interest that the intensity of the second-harmonic generation of the doped crystals is substantially higher than that of RbTiOPO₄.     

Precipitation of nanometer-sized SnO2 crystals and Sn depth profile in heat-treated float glass

The effect of oxygen diffusion from the atmosphere on tin depth profile in the bottom face of a soda-lime-silica float glass at temperatures above T_g was investigated. The heat treatment was performed in ¹⁸O₂/N₂ and argon (Ar) atmospheres. The significant diffusion of tin to the surface was observed for the glass heat-treated in ¹⁸O₂/N₂ atmosphere, resulting in the formation of a tin-enriched layer near the surface region. It was found that the tin was supplied from the region shallower than the ‘hump’ which is commonly observed in the tin profile of a commercial soda-lime-silica float glass. No significant change in the tin depth profile was observed for the glass heat-treated in Ar atmosphere. These results indicate that ¹⁸O diffusion into the glass, which causes the change in chemical state of tin from Sn²⁺ to Sn⁴⁺, induces the significant diffusion of tin. Furthermore, the precipitation of crystalline SnO₂ particles with a diameter of ∼1 nm was clearly recognized in the tin-enriched layer. This fact indicates that a phase separation was induced by the oxygen diffusion into the glass. Consequently, Sn²⁺ may be supplied to the surface in order to compensate for the marked decrease in Sn²⁺ concentration in the glass system. The significant diffusion of tin to the surface was suppressed by increasing the iron content in the glass. This suppression was ascribed to the increase in Sn⁴⁺ concentration as a result of the redox reaction between tin and iron because the diffusion coefficient of Sn⁴⁺ is much smaller than that of Sn²⁺.     

Synthesis,physical properties,and atomic structure of niobium-doped RbTiOPO<Subscript>4</Subscript> crystals

Single crystals of solid solutions Rb_1?xTi_1?xNb_xOPO₄(RTP: Nb) were grown and the temperature dependences of their dielectric and nonlinear optical properties and electric conductivity were studied. The maximum possible niobium content in these crystals is close to x = 0.1. The niobium impurities decelerate growth of {100} faces, and crystals take a plate-like habit. With increasing doping level, ferroelectric phase transitions diffuse and their temperature decreases. A specific feature of the dielectric properties of RTP: Nb crystals is the appearance of a broad relaxation maximum ε₃₃ in the temperature range 200–600°C caused by the formation of vacancies in the rubidium cation sublattice. The intensity of second-harmonic generation under laser irradiation decreases with increasing niobium content. The atomic structure of a crystal with x = 0.01 is studied and it is established that niobium substitutes for titanium only in Ti(1) positions.     

Spontaneous growth of single crystals of various shapes in tin-fullerite films

Changes in the structure and elemental and phase compositions of tin-fullerite films after their storage in air are investigated by X-ray diffraction, scanning electronic microscopy, atomic force microscopy, X-ray spectroscopic microanalysis, and Auger electron spectroscopy. Formation of the new phase Sn_xC₆₀, whisker tin and Sn_xC₆₀ crystals, and petal and flowerlike fullerite crystals under the action of internal stress is established.     

Crystal structure of chloro[1-hydroxyethane-1,1-diphosphonato(3−)]ditin(II) monohydrate Sn2(HL)Cl · H2O

The synthesis and X-ray structure analysis of Sn₂(HL)Cl · H₂O, where HL ^3? is the anion of 1-hydroxyethane-1,1-diphosphonic acid, are reported. The coordination polyhedra of two independent tin(II) atoms are the Sn(1)O₂Cl and Sn(2)O₃ trigonal pyramids, in which one of the vertices is occupied by a lone electron pair (Sn-O, 2.144–2.218 Å and Sn-Cl, 2.573 Å). The pyramids are complemented by weaker Sn?O and Sn?Cl contacts to form severely distorted (3 + 3) octahedra. The SnO₂Cl and SnO₃ pyramids are linked by the HL ^3? bridging ligands into the [Sn₂(HL)Cl]₆ cyclic molecules, which, in turn, are joined by additional Sn?O, Sn?Cl, O(H₂O)?O(L), and O(H₂O)?Cl contacts with each other and with crystallization water molecules into a three-dimensional framework.     

The effect of alumina on the Sn/Sn redox equilibrium and the incorporation of tin in Na2O/Al2O3/SiO2 melts

Glasses with the basic compositions 10Na₂O · 10CaO · xAl₂O₃ · (80 − x)SiO₂ (x=0, 5, 15, 25) and 16Na₂O · 10CaO · xAl₂O₃ · (74 − x)SiO₂ (x=0, 5, 10, 15, 20) doped with 0.25-0.5 mol% SnO₂ were studied using square-wave-voltammetry at temperatures in the range from 1000 to 1600 °C. The voltammograms exhibit a maximum which increases linearly with increasing temperature. With increasing alumina concentration and decreasing Na₂O concentration the peak potentials get more negative. Mössbauer spectra showed two signals attributed to Sn²⁺ and Sn⁴⁺. Increasing alumina concentrations did not affect the isomer shift of Sn²⁺; however, they led to increasing quadrupole splitting, while in the case of Sn⁴⁺ both isomer shift and quadrupole splitting increased. A structural model is proposed which explains the effect of the composition on both the peak potentials and the Mössbauer parameters.     

One‐step fabrication of SnxTi1‐xO2 rutile‐type core‐shell microspheres and their electrochemical properties

Sn_xTi_1‐xO₂ core‐shell microspheres were synthesized through a simple one‐step hydrothermal method. The structural and morphologic properties were unambiguously characterized, and the electrochemical performance of the Sn_xTi_1‐xO₂ microspheres was determined by cyclic voltammetry. The possible formation mechanism of Sn_xTi_1‐xO₂ microspheres was also proposed.     

Growth and characterization of Fe1 ? x M x VO4 single crystals (M = Al, Cr, Co, Ga)

Triclinic Fe_{1 ? x} M _x VO₄ single crystals (M = Al, Ga, Co, Cr) have been grown by the flux method from systems based on PbO-V₂O₅. Their crystallographic parameters are determined by powder X-ray diffraction. Fe_{1 ? x} Ga _x VO₄ single crystals (x = 0?C0.3) with a volume more than 1cm³ are grown using the seeding technique. The temperature and field dependences of magnetization and magnetic susceptibility of the grown Fe_{1 ? x} Ga _x VO₄ and Fe_{1 ? x} Al _x VO₄ single crystals (x = 0.3 in the solution-melt) are reported. It is shown that the magnetizations of these crystals exceed that of FeVO₄, and both of their antiferromagnetic phase transitions are shifted to lower temperatures.     

Tin valence and local environments in silicate glasses as determined from X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) was used to characterize the tin (Sn) environments in four borosilicate glass nuclear waste formulations, two silicate float glasses, and three potassium aluminosilicate glasses. Sn K-edge XAS data of most glasses investigated indicate Sn⁴⁺O₆ units with average Sn-O distances near 2.03 Å. XAS data for a float glass fabricated under reducing conditions show a mixture of Sn⁴⁺O₆ and Sn²⁺O₄ sites. XAS data for three glasses indicate Sn-Sn distances ranging from 3.43 to 3.53 Å, that suggest Sn⁴⁺O₆ units linking with each other, while the 4.96 Å Sn-Sn distance for one waste glass suggests clustering of unlinked Sn⁴⁺O₆ units.     

Square-wave voltammetry and impedance spectroscopy in tin doped melts with the compositions xNa2O · 15Al2O3 · (85 − x)SiO2 (x = 8.5, 11 and 16)

Glasses with the base compositions xNa₂O · 15Al₂O₃ · (85 ? x)SiO₂ (x = 8.5, 11 and 16) doped with 0.5 mol% SnO₂ were investigated by both square-wave voltammetry and impedance spectroscopy in the temperature range from 1300 to 1600 °C. Each recorded square-wave voltammogram exhibits a well pronounced peak attributed to the Sn²⁺/Sn⁴⁺-redox pair. Impedance spectra were measured in a frequency range from 0.1 to 10⁵ s^?1 as a function of the superimposed dc-potential and were simulated using an equivalent circuit taking into account the resistivity of the melt, the electrochemical double layer, a resistor attributed to a kinetically hindered electron transfer and a Warburg parameter which accounts for the diffusion process of Sn⁴⁺ and Sn²⁺ to and from the electrode. Additionally, two impedance elements, a resistor and a capacitance both attributed to adsorption processes were necessary to fit the impedance spectra.