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The detailed study of magnetic properties, including dc and ac measurements, has been carried out on the Bi-Cr-Sb-O pyrochlore. The region of pyrochlore phase existence was determined and photocatalytic properties have been also studied. We revealed that the Bi-Cr-Sb-O pyrochlore phase occurs along Bi2−xCr1+xSbO7 section within the region x = 0.1–0.4. The Cr3+ ions oxidation state in Bi-Cr-Sb-O pyrochlore was confirmed by XANES spectra. The best Rietveld refinement results for Bi1.8Cr1.2SbO7 composition were achieved for the disordered structure model (space group Fd-3m). According to the magnetic data Bi1.8Cr1.2SbO7 is a highly frustrated pyrochlore with short-range antiferromagnetic exchange interactions between the nearest Cr3+ ions. At Tg = 4 К this compound undergoes spin-glass transition.

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.

New complex Cr-containing pyrochlores Ln2CrTaO7, Ln = Y, Sm, Gd, were synthesized. The Rietveld refinement of the Ln2CrTaO7 composition confirmed the pyrochlore type of the structure. The Cr3+ oxidation state is corroborated by XANES spectra. The detailed study of DC and AC magnetization of Ln2CrTaO7, Ln = Y, Sm, Gd, was carried out in the temperature range 2–300 K and magnetic field up to 5 T. FM phase transitions at 143, 192, and 163 K were observed in pyrochlores with Y, Sm, and Gd, respectively. It is shown that these transitions are due to canted antiferromagnetism or weak-ferromagnetism in the Ln2CrTaO7 pyrochlores. AFM interactions between Ln- and Cr-sublattices in Sm2CrTaO7 and Gd2CrTaO7 causes AFM transition at T = 42 K, after which magnetization continues increasing. Unusual magnetic properties were observed for Gd2CrTaO7 at low temperatures. Competitive FM and AFM interactions in Cr-and Gd-sublattice give rise to the occurrence of reentrant spin glass at T

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.

The thermal behavior of barium and bismuth borate BaBiBO4 is studied by X-ray powder and single-crystal diffraction in a wide temperature range, as well as by the methods of differential scanning calorimetry and dielectric spectroscopy. Thermal expansion is anisotropic, which is caused by the orientation of BO3 boron-oxygen groups. With increasing temperature, the degree of anisotropy of thermal expansion increases up to negative. In the temperature range of 700–800 K, an anomaly of the dielectric properties is observed, accompanied by the change of the temperature dependence of the coefficients of thermal expansion and the heat capacity.

Phase equilibria in the Bi2O3–NiO–Sb2O5 system have been investigated. The isothermal section of the system (650°) has been constructed. For the first time the existence of the pyrochlore structure solid solution, (Bi2−xNix)Ni2/3−ySb4/3+yO7±δ, x=0.1−0.35, y=0−0.1, and a new compound Bi3Ni2/3Sb7/3O11 of KSbO3 structure type have been discovered. The structures and properties of these compounds were studied by XRD, XAFS, diffuse reflection spectroscopy and magnetic methods. Rietveld refinement of synchrotron radiation-based powder XRD data for pyrochlore sample of 38.43Bi2O3–33.0NiO–28.57Sb2O5 composition and Bi3Ni2/3Sb7/3O11 compound was performed. The best possible refinement of the positional parameters for both pyrochlore and Bi3Ni2/3Sb7/3O11 structures was achieved for disordered models. Magnetic, diffuse reflection and an X-ray absorption spectroscopy study confirmed that in both compounds nickel ions are mainly in a 2+ oxidation state. According to magnetic data, Bi1.84Ni0.16(Ni0.63Sb1.37)O7 pyrochlore and Bi3Ni2/3Sb7/3O11 are overall paramagnetic in nature.

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.

A new composite material consisting of BiFeO3 crystallites inside a nonmagnetic glass-like matrix has been synthesized using the glass crystallization method. The phase equilibrium and glass formation region of the Bi2O3–Fe2O3–B2O3 system (0–50 mol % B2O3) have been investigated. The optimal compositions for glass–ceramic synthesis are within the 25–85 mol % BiFeO3 range on the Bi4B2O9–BiFeO3 section. The obtained ceramics were studied by X-ray diffraction, Raman spectroscopy, microscopic and magnetic methods. It was shown that the BiFeO3 crystallites grow according to a dendrite mechanism resulting in anisotropic glass–ceramic. Magnetic properties of the synthesized samples depend upon their morphology and crystallinity.

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.

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

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.

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 ).

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 polarization structure of the signal wave that interacts with a circularly polarized pump wave on the reflection holographic gratings in the (112)-, (111)-, and (110)-cut Bi12TiO20 (BTO) crystals is experimentally and theoretically analyzed. An analytical expression for the vector field of the signal wave that is valid for an arbitrary orientation of the cubic refractive crystal is derived using approximation of the nondepleting circularly polarized pump wave. The contribution of the absorption component of the reflection hologram into the counter interaction is estimated for the crystals under study using the approximation of the experimental data with theoretical curves. Based on the experiments with incoherent quasi-monochromatic radiation, it is demonstrated that the real BTO crystals exhibit weak induced linear birefringence.

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.

Single crystals of Bi 12 TiO 20 doped with Cu, Ca, Zn, Cd, B, Al, Ga, V, P, Nb, Cr, Mn, Fe, Co, Ni, and their mixtures were grown by a conventional high-temperature flux method. Absorption, circular dichroism, light-induced absorption, optical activity, photoconductivity, dark conductivity and the two-beam coupling on the reflection grating are studied.

The Bi 12 TiO 20 thin films with high optical quality were grown from the melt on a substrate of Bi 12 SiO 20 and Bi 12 GeO 20 single crystals by two methods: LPE and crystallization from finite volume (CFV). The results of experimental investigation of time evolution of light-induced absorption in BTO:Cu waveguide are presented. All structures show a nearly equidistant spectrum of n eff with intervals from 2×10 −3 to 5×10 −3 . The time evolution of light-induced absorption is qualitatively different for the lowest and the highest modes in the waveguide.

Bi12 SiO20 crystals doped with Os, Re, Ru, and Rh were grown by the Czochralski technique, and their conductivity (real and imaginary parts) was measured as a function of temperature and frequency. The results are interpreted as evidence that the charge transport in the crystals is due to hopping along chains of localized states.

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.

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.

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.

The absorption and circular dichroism spectra of Nd-doped Bi12SiO20 crystals were measured in the range 10 000 to 20 000 cm–1. The spectra showed electronic transitions related to only one type of Nd-related center: Nd substituting for Bi in position with symmetry C1. The bands due to the transitions from the first Stark component of the ground state to Stark components of excites states (4I9/2 → 4G5/2 , 4I9/2 → 2G7/2 , and 4I9/2 → 4G7/2) were analyzed in detail. The dipole strength D0k , rotatory power R0k , and anisotropy factor G0k of these transitions were calculated. The intensities of transitions to Stark components were shown to vary by more than one order of magnitude within an excited-state multiplet. The anisotropy factors of the 4I9/2 → 2G7/2 and 4I9/2 → 4G7/2 transitions, allowed in the magnetic dipole approximation, are, on the average, larger than that of the 4I9/2 → 4G5/2 transition, which points to a significant contribution of the magnetic moment (λ λ2) to the total intensity of the transition.

Raman spectra of a Bi3B5O12 monocrystal are investigated for the first time and compared with the Raman spectra of crystals α-Bi2O3 and Bi12SiO20. The most intensive lines observed in the Raman spectrum of Bi3B5O12 are identified. Promising prospects of use of Bi3B5O12 crystals as SRS converters of radiation are shown.

The Raman spectra of Bi24AlPO40 and Bi38ZnO58 crystals have been studied for the first time. The polarization Raman spectra of Bi12GeO20, Bi12TiO20, Bi24AlPO40, and Bi38ZnO58 crystals are also studied. The lines in the Raman spectra of Bi12TiO20, Bi24AlPO40, and Bi38ZnO58 are identified and compared with the lines of the Bi12GeO20 spectra studied earlier. It is shown that the differences in the Raman spectra of the crystals studied are associated with the specific features of their atomic structures.

The experimental data on the optical and chiro-optical properties of crystals with the sillenite structure Bi12MxO20 ± δ (M= elements of II–VIII groups) have been reviewed. The relations between the changes in the chemical composition, the crystal structure of Bi12MxO20 ± δ compounds, absorption, circular dichroism, and optical rotation spectra of sillenites have been established. A model taking into account the contribution of the electronic transitions of optically active tetrahedral [MO4]n− complexes to the total optical rotation in sillenites is suggested. The data on the state (oxidation degree) and the recharging processes of 3d-elements in sillenites are systematized. The models of optical centers responsible for the photochromic effect in sillenites are critically analyzed.

Bi12SiO20 crystals doped with Cu were grown by the Czochralski method along 〈 001 〉 from a melt. The concentration of the impurities was determined by electro–thermal and flame atomic absorption spectroscopy. The lattice parameter a o = 10.165 A was determined by single-crystal diffractometry. Results from Raman measurements in different scattering configurations lead to the conclusion that distinguishable structural distortions of the bismuth–oxygen framework of the sillenite lattice take place due to Cu doping.

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 a-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 a-Bi2O3, Bi3O4Br, Bi2Al4O9, Bi4Ge3O12, Bi2Ge3O9 and perhaps in Bi3B5O12. A survey of the related 209Bi NQR data is here presented.

In this work we studied experimentally the dynamics of beam-coupling amplification on a reflection gratings at light-induced absorption in Bi12TiO20 crystals doped by different impurities. Doping with different impurities modifies the photorefractive properties of these crystals

Cr-doped Bi12TiO20 (BTO) single crystals have been grown by the Czochralski technique. The optical absorption at 4.2 K of as-grown crystals is compared to that observed after vacuum annealing of the samples. This treatment modifies the visible and near infrared optical absorption. The absorption spectrum of Cr-doped BTO crystals before vacuum annealing is interpreted as the superposition of the crystal-field transition bands of (CrO4)4- and (CrO4)3- and charge transfer bands of (CrO4)3-. Annealing in vacuum leads to Cr5+ → Cr4+ conversion. Chromium reduction to lower oxidation states has not been observed. The optical absorption shows a vibrational character. The energy shifts of Cr4+ bands are as expected from the coupling with the T2(v3) fundamental mode of (CrO4)4- clusters. On the other hand, it is proposed that the series of sharp lines observed in the 9500 to 11500 cm-1 range arises from the interaction with a vibration of about 300 cm-1, which seems to be the T2(v4) fundamental mode of (CrO4)3- and with the lattice modes.

An evidence that local ordered magnetic fields from 30 to 200 G exist in diamagnets α-Bi2O3, Bi3O4Br, Bi4Ge3O12, Bi2Al4O9 which comprise neither d- nor f-elements was earlier given by the zerofield and Zeeman-perturbed209Bi nuclear quadrupole resonance (NQR) spectra. With a view to find similar spectroscopic effects in other compounds, we examined the209Bi NQR Zeeman-perturbed spectra of the Bi3B5O12 oriented single crystal as well as the zero-field spin echo envelopes in Bi3B5O12 and Bi2Ge3O9. Distinctive modulations were displayed by the zero-field209Bi spin echo envelopes in Bi2Ge3O9 powder. The modeling of the spin echo envelopes within the density matrix formalism explained the observed effect by the presence of local ordered magnetic field of the order of 65 G at the Bi atoms. The zero-field modulations of the209Bi spin echo envelopes were also observed in Bi3B5O12 indicating the presence of the internal source of line splitting. This finding and considerable deviation of the resonance intensity ratios from that in a pure NQR, found in the zero-field209Bi spectrum of the single crystal, were understood as indirect evidences that a local ordered magnetic field exists also in Bi3B5O12. The zero-field209Bi spin echo envelopes assigned to the lines split by the local magnetic fields in α-Bi2O3 and Bi4Ge3O12 were observed to display modulations on the appropriate curves.