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A route for production of fine Bi4Ge3O12 (BGO) powder is sought after to lower the cost of scintillation devices and make their shapes more versatile. A systematic study of highly dispersed BGO crystallization under the hydrothermal-microwave (HTMW) conditions was carried out in the present work. Anionic, cationic and non-ionic surfactants, chelating agents and polyols were used to modify the synthesis and their respective effects on phase composition and morphology were determined. It was shown that chelating agents or other additives that are capable of forming complexes with the bismuth ions allow the production of smaller, non-aggregated particles and have the procedure be scaleable. BGO powders of various morphology were synthesized and study of the optical properties of the product discovered their advantages over traditional single-crystal material. The BGO powders obtained in optimal HTMW conditions are characterized by the presence of a single intense fast scintillation component with a flash time of about 11 ns which is by an order of magnitude less than that observed in single-crystal BGO (327 ns). This suggests the suitability of these powders for the production of scintillation materials with improved properties. This material is promising for creating highly sensitive composite detectors with a high rate of counting events.

A comparative analysis has been made for the dielectric and electrorheological properties of suspensions of highly dispersed powders of bismuth ferrites BiFeO3 and Bi2Fe4O9 in polydimethylsiloxane PMS-300. Dielectric characteristics (dielectric constant, dielectric loss tangent) for the suspensions in frequency range 2.5–106 Hz have been determined and non-Debye character of relaxation processes in these systems has been revealed. The measured values of dielectric constant for the disperse bismuth ferrites at zero and infinite frequency (e0 and e∞) are 150 and 59 for BiFeO3, 22 000 and 14 for Bi2Fe4O9, respectively. Electrorheological properties of bismuth ferrite suspensions in static electric field (up to 5 kV) in tension, compression, and shear modes have been analyzed. It has been found that the values of electrorheological effect for BiFeO3 suspensions in polydimethylsiloxane PMS-300 are small even at high concentrations of disperse phase (60 wt %). On the contrary, the suspensions of highly disperse Bi2Fe4O9 exhibit distinct electrorheological effect. For 80 wt % Bi2Fe4O9 suspension, the tensile yield point reached ~7 kPa in electric field of 5 kV, while compressive stress was 12 kPa.

We report on the first experimental evidence of the electrorheological effect in suspensions of superfine pyrochlore-type Bi1.8Fe1.2SbO7 powders. Tensile-compressive and shear stress studies of the electrorheological fluids, with various filler contents, revealed an exceptionally high electrorheological effect in the materials – the tensile yield strength at 5 kV/mm reached about 20 kPa. The frequency dependencies of dielectric permittivity, dielectric loss tangent, and the conductivity of the suspensions with various filler contents allowed estimation of the dielectric permittivity values for superfine Bi1.8Fe1.2SbO7 particles at zero and infinite frequencies. The study reveals new oxide materials as promising fillers for electrorheological fluids.

The series of La1-xPrxGa0.5Sb1.5O6 solid solutions (x = 0–1) with PbSb2O6 structure was synthesized. The comparative study of the La1-xPrxGa0.5Sb1.5O6 morphology showed all compounds have net microstructures. Herein the Pr concentration increasing leads to particles size decreasing from 400 up to 200 nm in the samples with low Pr content and to recrystallization and coarsening of the particles in Pr-rich ones. Using LaGa0.5Sb1.5O6 as an example, it was shown that the compounds have a wide transmission region in the visible and IR spectral ranges and are characterized by a low-energy phonon spectrum. An analysis of the spectral-luminescent characteristics revealed the presence of a cross-relaxation process (1D2→1G4) → (3H4→3F4) of Pr3+ ions for La1-xPrxGa0.5Sb1.5O6 at x ≥ 0.07. It was showed that a broadband radiation of thermal nature is observed under laser excitation with λ = 457 nm and a power density of J = 4.65 kW/cm2 for the samples with high (x = 0.4–1) praseodymium content.

—We have synthesized needle- and platelike α-Bi2O3 and Bi2O2CO3 nanoparticles. The bulk density of the α-Bi2O3 and Bi2O2CO3 powders is 8.5 and 6.9 g/cm3. The dielectric permittivity of α-Bi2O3 and Bi2O2CO3 has been calculated using dielectric permittivity and dielectric loss tangent dispersion measurements in the frequency range from 2.5 × 101 to 1 × 106 Hz for 40% suspensions (0.05 and 0.08 volume fractions of α-Bi2O3 and Bi2O2CO3, respectively) in PMS-300 polydimethylsiloxane. The value of e∞ has been found to be 5.4 for α-Bi2O3 and 4.9 for Bi2O2CO3. Dielectric spectra of the suspensions have been shown to exhibit no relaxation behavior in the frequency range studied. We have compared the effects of the shape and dielectric permittivity of the particles on the magnitude of the electrorheological effect in them. Using a simple polarization model, we have analyzed the effect of the dielectric characteristics of the filler material on the yield stress τ0 of the suspensions in electric fields from 0 to 4 kV/mm. Using a combination of rheometric and direct microscopic observations, we have explained the effect of the type of filler on the electrorheological effect: the Bi2O2CO3-based ERFs have higher shear and compressive yield stresses, whereas the α-Bi2O3-based ERFs have a higher tensile yield stress.

We have prepared glasses in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) and HfF4–BaF2–LaF3–AlF3–NaF (HBLAN) systems in which fluorine anions are partially replaced by chlorine and bromine anions. Structural changes in the chlorine-substituted glasses have been investigated by Raman spectroscopy and their crystallization behavior has been studied by differential thermal analysis and X-ray diffraction. The results demonstrate a characteristic decrease in glass transition temperature (Tg) and the precipitation of fine-particle crystalline chloride and bromide phases in a temperature range well below the crystallization temperature (Tx) of the fluoride analogues. We have identified phases that crystallize during heat treatment of the glasses at various temperatures.

Anhydrous basic bismuth nitrate Bi6(NO3)2O7(OH)2 was shown to be produced by reacting bismuth nitrate with aqueous ammonia under microwave-assisted hydrothermal treatment as a result of hydrolysis. The composition of the basic nitrate was verified by titration, CHNS analyses, DTG, and IR spectroscopy. Photocatalytic tests showed that Bi6(NO3)2O7(OH)2 has a photocatalytic activity, but its properties are interior to those of α-Bi2O3.

We have developed a process for the synthesis of fine bismuth orthogermanate, Bi4Ge3O12 (BGO), powders in a NaCl/KCl melt and examined the effect of synthesis conditions on the phase composition and morphology of the powders. Our results demonstrate that the synthesized materials compare well in scintillation performance with single-crystal BGO: their scintillation efficiency is 90% relative to single-crystal BGO, with a decay time of 300 ns.

In this work, novel phosphors LaGa0.5Sb1.5O6 and BiGeSbO6 doped with Eu3+, Tb3+, and Dy3+ were synthesized, and the luminescent properties were studied. The impact of the host type on the emission properties was demonstrated for compositions singly doped with Eu3+ and Dy3+ ions. For the La1−xEuxGa0.5Sb1.5O6 and Bi1−xEuxGeSbO6 (x = 0.05–0.5) solid solutions, there were evident differences in the luminescence intensity ratio of the bands caused by the 5D0→7F1 and 5D0→7F2 transitions of Eu3+ that may have resulted from a different rare earth (RE) ion coordination environment. The spectra of all the bismuth-containing solid solutions were characterized by the appearance of an additional band related to the intrinsic luminescence of the bismuth-containing host. The intensity ratio of this band and the RE ion emission lines for dysprosium-containing compounds was much higher than that for compositions doped with praseodymium and europium. Co-doping with Eu3+, Dy3+, and Tb3+ ions led to a shift in the emission colour to orange (when doped with two types of RE ions) and yellow-orange (when doped with three types of RE ions).

The isobaric heat capacity of pyrochlore-related compounds RE2FeTaO7 (RE = Sm and Gd) was measured using an adiabatic and a differential scanning calorimetry over a wide temperature range using adiabatic and differential scanning calorimetry. An anomaly on the curves of all the compounds is clearly observed within the low-temperature range, T

Reactions of nitric acid solutions of bismuth with alkalis have been studied. The effect caused by coprecipitation conditions in the presence of additional agents (EG, PEG 400, or PEG 8000) and without on the phase composition and morphology of α- and γ-Bi2O3 has been determined.

A process for the growth of VSe2 and VTe2 single crystals using VCl3 as a transport agent is proposed and experimentally demonstrated. X-ray diffractometry and Laue X-ray photography results indicate that the crystals thus grown are identical in properties to chalcogenide crystals grown using I2 as a transport agent. The mechanism of chemical vapor transport is discussed and the process conditions are optimized.

In this work, Bi1-xPrxGeSbO6 (x = 0–0.5) solid solutions were synthesized, and the corresponding properties were compared to those of La1-xPrxGa0.5Sb1·5O6. The lattice parameters of the La1-xPrxGa0.5Sb1·5O6 solid solutions decrease linearly as the activator concentration increases. This linear reduction is only observed for the a parameter for Bi1-xPrxGeSbO6. Parameter c shows non-linear growth, which is related to the structural features of BiGeSbO6. Increasing the activator content leads to a decrease in the particle size, which is 0.5–8 μm for Bi1-xPrxGeSbO6. The influence of the host composition on the spectral-luminescent properties of the solid solutions was determined. The difference in the phonon frequencies of BiGeSbO6 and LaGa0.5Sb1·5O6 leads to different luminescence quenching processes for Pr3+ ions. Interactions between Pr3+ ions and Bi3+ were observed for Bi1-xPrxGeSbO6 solid solutions. These processes give rise to changes in the ratios of the luminescence bands of these ions. All the bismuth-containing solid solutions are characterized by the appearance of an additional band in the spectrum related to the luminescence of the bismuth centres of the BiGeSbO6 host. An evaluation of the colour coordinates (CIE 1931) of the Bi1-xPrxGeSbO6 luminescence showed that the colour of the radiation depends on the praseodymium content: as the praseodymium content increases, the luminescence changes from orange (x = 0.005, 0.01) to yellow-green (x = 0.05–0.5). Broadband thermal emission is observed for Bi0.5Pr0.5GeSbO6 under laser excitation with λ = 457 nm and a power density of J = 6 kW/cm2.

The region of pyrochlore existence in the Bi-Mn-Sb-O system, Mn valence state and magnetic properties of pyrochlore compounds have been studied. It is shown that a pyrochlore phase exists in the vide range х = 0.2–0.8 along the Bi(2−x)Mn(1+x/2)Sb(1+x/2)O7 section. Rietveld structure refinement, XANES and EXAFS data show that Bi-Mn-Sb-O pyrochlores are structurally disordered and manganese is in Mn2+/Mn3+mixed-valence state. Mn2+ ions occupy a part of eight coordinated Bi sites while Mn3+ ions are in strongly distorted octahedra. Magnetic measurements confirm the structural data and reveal strong dependence of magnetic properties on Mn concentration. According to dc and ac susceptibility data all studied pyrochlores demonstrate a transition to the conventional spin glass state at Tf ≤ 7 K. The transition temperature decreases with the decrease of Mn3+ amount in the pyrochlore octahedral sublattice. It was also revealed that there exists a threshold Mn concentration above which we detected an antiferromagnetic transition at TN = 42 K along with an SG transition.

A technique has been developed for fluorinating the pyrochlore oxide Bi1.8Fe0.2FeSbO7, and a compound with the composition Bi1.8Fe1.2SbO7–x/2Fx has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) A (R wp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe3+ to Fe2+ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below T f = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe3+ ions and changes in the dynamic properties of the spin glass phase.

Optical and vibrational spectra of Bi1.8Fe1.2(1 – x)Ga1.2x SbO7 solid solutions with pyrochlore structure have been studied. It has been shown that the compounds have strongly disordered structure. It has been established that a decrease in iron content causes a marked shift of Bi1.8Fe1.2(1 – x)Ga1.2x SbO7 absorption edge. According to assessment of band gap width, Bi1.8Ga1.2SbO7 is the most wide-band compound (2.90 eV), while Bi1.8Fe1.2SbO7 is the most narrow-band compound (1.88 eV).

The Bi–La–Fe–Sb–O, Pr–Fe–Sb–O, and Bi–Pr–Fe–Sb–O systems have been shown to contain pyrochlore solid solutions. We have determined the limits of the Pr2–xFe1 + xSbO7 and Bi2–xLnxFeSbO7 (Ln = La, Pr) solid solutions and shown that there is no compound corresponding to the “ideal” composition Pr2FeSbO7. Analysis of the magnetic properties of the synthesized compounds indicates that rare earth substitution for bismuth ions has no effect on the spin glass transition and that the spin glass state is only determined by the interaction between the Fe3+ spins on the octahedral site. The Pr3+ paramagnetic ion in Pr2–xFe1 + xSbO7 does not participate in the formation of the spin glass state but makes a paramagnetic contribution to the total magnetic susceptibility, which is especially significant at low temperatures.

Phase equilibria in the La 2 O 3 -Fe 2 O 3 –Sb 2 O 5 system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe 0.5 Sb 1.5 O 6 was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe 0.5 Sb 1.5 O 6 crystallizes in a trigonal layered structure relating to PbSb 2 O 6 type (space group P-31m, a=b=5.2446(3) A, c=5.1930(3) A, Z=1). The fine powder of LaFe 0.5 Sb 1.5 O 6 was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe 0.5 Sb 1.5 O 6 in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe 0.5 Sb 1.5 O 6 indicates an unusual critical behavior near phase transition at T

The crystallization mechanism of chlorine-containing fluorohafnate glasses with the compositions (65–56)HfF4 · (20–x)BaF2 · xBaCl2 · 4LaF3 · (3–y)AlF3 · yInF3 · (5–18)NaF has been studied by X-ray diffraction and differential thermal analysis. The results demonstrate that characteristic features of the glasses are a decrease in glass transition temperature and the precipitation of fine-particle crystalline chloride phases at temperatures below the crystallization temperature of their fluoride analogs. We have studied the effect of the Cl/F ratio in the glass batch and the melt cooling rate on the crystallization behavior of the glasses and determined the heat treatment temperature and time for the formation of transparent glassceramic materials. The luminescence properties of Er3+-doped fluoride and fluorochloride glasses and glassceramics prepared from them have been investigated in the 1.5-µm range.

Crystallization processes in the Bi2O3-Fe2O3-NaOH system upon microwave-assisted hydrothermal synthesis have been studied to reveal the effect of the mineralizer concentration, temperature, degree of filling of the autoclave, and the preparation of precursors on the phase composition and the morphology of the reaction product. Submicron powders of bismuth ferrite Bi2Fe4O9 have been synthesized.

It was shown that it is possible to obtain by coprecipitation a complex ternary oxide containing elements dissimilar in their chemical nature. The interaction of acidic solutions of bismuth, iron, and antimony with monoethanolamine and ammonia was studied, and the effect of the coprecipitation conditions on the phase composition and morphology of the reaction products was determined. Samples of nanocrystalline pyrochlore containing bismuth, iron, and antimony were produced for the first time.

The refinement of the Bi2O3–Fe2O3–Sb2O5 system phase diagram has been performed and the existence of the two ternary compounds has been confirmed. The first one with a pyrochlore-type structure (sp. gr. Fd 3m) exists in the wide solid solution region, (Bi2−xFex)Fe1+ySb1−yO7±δ, where x=0.1–0.4 and y=−0.13–0.11. The second one, Bi3FeSb2O11, corresponds to the cubic KSbO3-type structure (sp. gr. Pn 3) with unit cell parameter a=9.51521(2) A. The Rietveld structure refinement showed that this compound is characterized by disordered structure. The Bi3FeSb2O11 factor group analysis has been carried out and a Raman spectrum has been investigated. According to magnetization measurements performed at the temperature range 2–300 K it may be concluded that the Bi3FeSb2O11 magnetic properties can be substantially described as a superposition of strong short-range antiferromagnetic exchange interactions realizing inside the [(FeSb2)O9] 3D-framework via different pathways.

60B2O3-32CaF2-8Bi2O3 glasses codoped with chromium and neodymium have been prepared for the first time, and their luminescence properties have been studied. The glasses have been shown to contain chromium in two oxidation states. We have obtained luminescence spectra of Cr3+ in octahedral coordination and Cr4+ in tetrahedral coordination. Energy transfer from Bi3+ to Nd3+ and Cr3+ has been demonstrated.

The subsolidus phase equilibria of the Bi 2 O 3 –Fe 2 O 3 –Sb 2 O x system have been investigated by X-ray powder diffraction. The isothermal section of the system at 775–800 °C has been constructed. It can be represented by 9 phase assemblage triangles. Ternary compound formation is limited to pyrochlore which forms a substantial solid solution region of Bi-deficient compositions relative to Bi 2 FeSbO 7 . As follows from the phase diagram, approximately 7–25% of Bi positions in pyrochlore may be occupied with Fe 3+ ions that was confirmed by Mossbauer data. Magnetic measurements were carried out on the pyrochlore specimen of quasi-chemical formula (Bi 1.8 Fe 0.2 )(FeSb)O 7 . The existence of the strong short-range antiferromagnetic superexchange interactions and spin-glass magnetic transition at around 9 K were revealed.

We have studied the effect of mechanochemical activation on the reactivity of Bi2O3 + Fe2O3 oxide mixtures, assessed the temperature effect on the kinetics of BiFeO3 formation in the oxide mixtures before and after mechanochemical activation, and optimized the conditions of bismuth ferrite synthesis by solid-state reaction. A material with a BiFeO3 content of at least 98.3 wt % has been obtained, and its magnetic properties have been investigated.

Single crystals of a new compound, Ba2Bi3B25O44, were grown by cooling a melt of non- stoichiometric composition. The crystal structure was solved by direct methods and refined to R ¼ 0.030

Crystals of BSO doped with Se in two different concentrations (BSO:Se(I) and BSO:Se(II)) were grown by the Czochralski method. It is established that doping with Se is accompanied with preferential absorption of Fe from the melt. According to the in-depth chemical analysis, it is assumed that the doping Se ions enter the tetrahedral positions by means of the substitution of 3Si4+ by (Se6+ + 2Fe3+) ions. The measured absorption spectrum of the low-concentration Se-doped crystal (BSO:Se(I)) confirms such a conclusion as the absorption coefficient is increased in a broad spectral interval (1.4–3.1 eV) – an effect typical for all Fe-doped Bi12SiO20 crystals. The polarized Raman spectra of BSO:SeI show that the doping-induced lattice distortions are small. The IR spectrum of the BSO:SeI crystal yields indications for local lowering of the symmetry of the Fe-occupied tetrahedral positions. Doping with Se at high concentration (BSO:Se(II)) leads to occasional second phase inclusions and to a downshift of practically all modes in the Raman spectrum by 2–5.5 cm−1. It is concluded that the doping with Se at high concentrations follows the same mechanism as that at low concentrations but the introduced lattice distortions are more significant, and lead to an enlargement of the unit cell while preserving the overall cubic symmetry.

We have prepared europium-doped BaO-Bi2O3-B2O3 glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω2, Ω4, and Ω6), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for 5 D 0 → 7 F J transitions.

A physicochemical study of glasses based on the MO-Bi2O3-B2O3 and SrO-Bi2O3-B2O3 systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.

This work examines the effect of KBF4 additions on the crystallization behavior of glasses based on the multicomponent systems MO-Bi2O3-B2O3 with M = Ca, Sr, and Ba. The glass-ceramic composites obtained contain a δ-Bi2O3-based crystalline phase with a crystallite size of ≃7 nm, evenly distributed over the glass matrix. The 400°C electrical conductivity of the nanocomposites reaches 2 × 10−4 S/cm, and the activation energy is 1.1 eV, typical of anion conduction. These values are comparable to those reported for δ-Bi2O3 ceramics.

Single crystals of α- and β-polymorphs of Bi2B8O15 were grown by Czochralski method from a charge of the stoichiometric composition. The crystal structure of β-Bi2B8O15 was solved by direct methods from a twinned crystal and refined to R1=0.081 (wR=0.198) on the basis of 1584 unique observed reflections (I>2σ(I)). The compound is triclinic, space group P 1 ¯ , a=4.3159(8), b=6. 4604(12), c=22.485(4) A, α=87.094(15)°, β=86.538(15)°, γ=74.420(14)°, V=602.40(19) A3, Z=2. The B–O layered anion of β-Bi2B8O15 is topologically identical to the anion of α-Bi2B8O15 but the orientation of neighboring layers is different. Thermal expansion of α-Bi2B8O15 has been investigated by X-ray powder diffraction in air in temperature range from 20 to 700 °C. It is strongly anisotropic, which can be explained by the hinge mechanism applied to chains of Bi–O polyhedra. While the anisotropy of thermal expansion is rather high, the volume thermal expansion coefficient αV=40×106 °C−1 for α-Bi2B8O15 is close to those of other bismuth borates.

Phase equilibria in the SrO-Bi2O3-B2O3 system were studied using powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Quasi-binary sections were determined, and an isothermal section of the system in the subsolidus region at 600°C was constructed using the crossing spections method. A new ternary compound was found: SrBi2B4O10. The existence of SrBi2B2O7 was verified. Bi2O3-SrB2O4 and Bi4B2O9-2SrO: 3B2O3 polytherms were constructed.

It is shown using Bi12TiO20 as an example that doping of a sillenite phase leads to the formation of a solid solution between it and the Bi12M x O20 ± δ phase corresponding to the dopant. This gives rise to structural features characteristic of the second phase and, accordingly, results in the formation of the corresponding optical centers. Dopant atoms occupy tetrahedral (M) sites. In addition, in the case of heterovalent substitutions the M site is partially occupied by the Bi atoms of [BiO3] groups. The structural features of sillenites are governed by the oxidation state of the M cation. Accordingly, doping with ions in the same oxidation state leads to the formation of similar optical centers and, as a consequence, produces similar changes in the properties of the material. The results obtained are supported by experimental studies of the absorption, circular dichroism, photoinduced absorption, and photoconductivity spectra of doped sillenite crystals in a wide spectral range.

A new compound, SrBi 2 B 4 O 10 , has been grown by cooling a melt with the stoichiometric composition. It is triclinic, P −1, a =6.819(1), b =6.856(1), c =9.812(2) A, α= 96.09(1), β =109.11(1), γ =101.94(1)°, V =416.5(1) A 3 , Z =2. The crystal structure of the compound has been solved by direct methods and refined to R 1 =0.050 (w R 2 =0.128). The structure contains Bi–O pseudolayers build up from Bi–O chains involving oxocentred OBi 3 triangles. Sr atoms and [B 4 O 9 ] 6− isolated anions (4B:3 Δ □: Δ □> Δ ) are located between the Bi–O packages. The thermal treatment as well as DSC experiment showed that the compound melts above 800 °C presumably according to the peritectic reaction: SrBi 2 B 4 O 10 ↔ SrB 2 O 4 +SrB 4 O 7 + Liquid. According to high-temperature X-ray powder diffraction study thermal expansion of SrBi 2 B 4 O 10 structure is anisotropic ( α 11 =13, α 22 =9, α 33 =2, α V =24×10 −6 °C −1 ).

Three-dimensional opal-matrix nanocomposites containing various bismuth selenides and tellurides with a particle size from 25 to 150 nm have been produced by reducing oxygen-containing compounds with supercritical isopropanol. The bismuth: chalcogen ratio in the reduction products has been shown to correlate with that in the starting mixtures, indicating that targeted synthesis in opal pores can be used to controllably fabricate nanocomposites.

The 600°C (subsolidus) section of the CaO-Bi2O3-B2O3 phase diagram has been studied by x-ray diffraction and differential thermal analysis. A new calcium bismuth borate of composition CaBi2B4O10 has been identified, and the existence of CaBi2B2O7 has been confirmed. According to T-x phase diagram data, these compounds form peritectically at 700±5 and 783±5°C, respectively.

We studied the influence of doping with 4d and 5d elements on the optical and photo-induced properties of Bi12SiO20 (BSO) crystals. Doping with Ru, Rh and Re does not significantly influence BSO absorption spectra as well as photo-induced absorption and photocurrent in BSO. On the other hand, doping with Os with concentration of 0.0004 mass% increases by more than an order of magnitude the illumination response time, the strength of the photochromic effect and photocurrent, all this being accompanied by only a slight change of the absorption coefficient as compared to undoped BSO. The observed effects are explained in the framework of the Rose model assuming that doping with Os creates deep levels in the gap that act as recombination centers with a very little cross-section of electron capture. We also studied the kinetic curves of photocurrent increase and decrease in BSO:Os which enabled us to determine the magnitude of the cross-section of a photon capture at an impurity center. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The crystal structure of a new bismuth aluminoborate Bi0.96Al2.37(B4O10)O is studied by single-crystal X-ray diffraction. The Bi0.96Al2.37(B4O10)O single crystals are hexagonal (space group $$P\bar 6$$ 2m). The unit cell parameters are as follows: a = b = 4.587(4) A, c = 2.253(9) A, α = β = 90°, γ = 120°, V = 168.60 A3, Z = 1.

Phase equilibria in the BaO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction analysis and DTA. Quasi-binary sections have been determined, and an isothermal section of the system in the subsolidus region has been constructed. The BaO-Bi2O3-B2O3 ternary system has been divided into 22 triangles of coexisting phases. It has been found that four bismuth barium borates exist, namely, Ba3BiB3O9, BaBi2B4O10, BaBiB11O19, and BaBiBO4. Ba3BiB3O9 undergoes a phase transition at 850°C and exists up to 885°C, where it decomposes in the solid state. BaBiB11O19 and BaBi2B4O10 melt congruently at 807 and 730°C, respectively. BaBiBO4 melts incongruently at 780°C. X-ray powder diffraction data for the low-temperature polymorph of Ba3BiB3O9 are presented.

The phase equilibria in the concentration triangle Bi2O3-BaB2O4-B2O3 of the BaO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction and DTA. Barium bismuth borates of the composition BaBi2B4O10 and BaBiB11O19 have been found to exist. These borates melt at 730 and 807°C, respectively. The quasi-binary sections have been determined. It has been shown that the isothermal section of the Bi2O3-BaB2O4-B2O3 in the subsolidus region at 600°C is characterized by 13 triangles of coexisting phases.

Single crystals of Bi 2 Ga 4 O 9 are grown from a solution in a bismuth oxide melt. The structure (orthorhombic, space group Pbam , a = 7.918(2) A, b = 8.299(2) A, c = 5.894(2) A, Z = 2) is refined to R = 0.052 in the anisotropic approximation based on single-crystal X-ray diffraction data. The structure is a framework. The bismuth(III) atoms are sixfold coordinated; gallium(III) exists in both tetrahedral and octahedral coordina- tions. The thermal expansion of Bi 2 Ga 4 O 9 is studied by high-temperature X-ray powder diffraction method and is found to be sharply anisotropic. A structural interpretation of the anisotropy is proposed. Chemical distortion in the Bi 2 M 4O9 compounds with M = Fe(III), Al, or Ga is analyzed and compared with the thermal expansion of Bi2Ga4O9.

The axial circular-dichroism spectrum of a synthetic amethyst crystal has been studied for the first time. Bands both of the positive and negative signs are revealed. New information on the color centers of amethyst and their electronic structure is obtained.

The vibrational spectra of crystals of bismuth borates Bi24B2O39, Bi4B2O9, BiBO3, and Bi2B8O15 were obtained for the first time, and the spectra of Bi3B5O12 and BiB3O6 crystals measured in the range 30–1600 cm−1 at room temperature were refined. The lines observed were assigned to the corresponding vibrational transitions on the basis of the theoretical group analysis and comparison of the obtained results with the vibrational spectra of borates of different composition. The complication of the structure of bismuth borates with increasing content of B2O3 was traced by the example of vibrational spectra.

The photoinduced absorption in a Ca-doped bismuth titanate crystal is measured as a function of temperature in the red (660 nm), yellow (570 nm), and green (505 nm) spectral regions.

Evidence that local ordered magnetic fields from 30 to 250 G exist in bismuth-based diamagnetic compounds comprising neither d- nor f-elements was given by 209Bi NQR spectroscopy and supported by SQUID measurements of α-Bi2O3. The NQR experiments involved a study of the zero-field line shapes, analysis of the Zeeman-perturbed patterns, and examination of the zero-field spin-echo envelopes in single crystals and powders. The results of the experiments followed by computer modeling of the observed spectra were interpreted assuming that ordered magnetic fields are located at the bismuth sites in α-Bi2O3, Bi3O4Br, Bi2Al4O9, Bi4Ge3O12, Bi2Ge3O9 and perhaps in Bi3B5O12. A survey of the related 209Bi NQR data is here presented.

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi 3 B 5 O 12 . The Bi 3 B 5 O 12 single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi 3 B 5 O 12 was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma , a =6.530(4), b =7.726(5), c =18.578(5) A, V =937.2(5) A 3 , Z =4, R =3.45%. Bi 3+ atoms have irregular coordination polyhedra, Bi(1)O 6 ( d (B–O)=2.09–2.75 A) and Bi(2)O 7 ( d (B–O)=2.108–2.804 A). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O 3 (2.09–2.20 A) and tetragonal Bi(2)O 4 (2.108–2.331 A) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO 4 polyhedra form zigzag chains along b -axis. These chains alternate with isolated anions [B 2 IV B 3 III O 11 ] 7− through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi–O chains. The Bi 3 B 5 O 12 thermal expansion is sharply anisotropic ( α 11 ≈ α 22 =12, α 33 =3×10 −6 °C −1 ) likely due to a straightening of the flexible zigzag chains along b -axis and decreasing of their zigzag along c -axis. Thus the properties like cleavage and thermal expansion correlate to these chains.

Results of investigations into the dynamics of light-induced absorption in bismuth titanium oxide crystals doped with calcium (Bi12TiO20:Ca) illuminated with quasimonochromatic light of semiconductor light-emitting diodes at two wavelengths from the set λ = 870, 660, and 525 nm are presented. Based on an analysis of the experimental data, a model of charge transfer by defect centers describing the observed phenomena is suggested.

The results of experimental investigations into the dynamics of light-induced absorption for coherent incident light (the wavelength λ = 633 nm) and incoherent radiation of a light emitting diode (λ ≈ 660 nm) in single bismuth titanate crystals with different stoichiometric structures are presented. It is demonstrated that the dynamics of two-wave interaction on the photorefractive reflection grating in (100)-cut samples illuminated with coherent light is nonmonotonic in character. Light-induced changes in the absorption coefficient and the efficiency of interaction on the reflection grating increase when the titanium oxide content in the examined samples decreases.

Absorption and circular-dichroism spectra of iron-doped AlPO4 crystals have been studied. For the first time, the experimental data on the electronic states of the [FeO4]5− complex are obtained in the range from 190 to 350 nm with due regard for the interactions that cannot be described within the one-electron approximation. The bands observed in the absorption and circular-dichroism spectra are attributed to corresponding electronic transitions. The advantages of the use of crystal-field-induced circular dichroism in comparison with other spectroscopic methods in the analysis of the electronic states of impurity ions in gyrotropic crystalline matrices are considered on the [FeO4]5− complex.