Competition between stimulated Brillouin scattering and two-photon absorption in dispersed boron nitride.

The design of transparent optical materials with stimulated Brillouin scattering (SBS) suppression is a topic of current interest. We measured two-photon absorption (2PA) cross-section σ2PA and Brillouin gain factor gB of a suspension of hexagonal boron nitride (hBN) in N-methyl-2-pyrrolidone at the second harmonic of a Nd:YAG laser. SBS exhibits a significant quenching with hBN concentration, like previously observed in graphene suspension. The melting of hBN flakes due to a large 2PA and the related changes in the acoustic damping coefficient explain the quenching mechanism.

Mineral Mimetic Material Sr-Exchanged Sitinakite of Different Crystallinity: Phase Transformations during Heat Treatment and the Strength of SR Fixation in a Ceramic Matrix.

A simple method for the direct transformation of Sr-exchanged titanosilicate with the sitinakite structure (IONSIV) into ceramic material through cold pressing and subsequent sintering at 1100 °C for 4 h is presented. The temperature transformation of Sr-exchanged sitinakite showed the stages of recrystallization of the material with the formation of Sr-Ti phases matsubaraite (Sr4Ti5[Si2O7]2O8), jeppeite (SrTi6O13), tausonite (SrTiO3), and rutile. Leaching experiments showed the efficiency of fixation of Sr cations in a ceramic matrix; extraction into water does not exceed 0.01% and desorption in 1 M HNO3 solution is only 0.19% within three days. The leaching rates of immobilized Sr demonstrate the structural integrity of the formed phases in the ceramic (2.8 × 10-5-1.0 × 10-5 g/(m2·day). The decrease in the crystallinity of the initial Na-sitinakite, which is achieved by reducing the synthesis temperature from 250 to 210 °C, does not affect the sorption capacity and the fixation of cations in the ceramic matrix. The obtained results confirm the prospect of using inexpensive precursors, titanium ore enrichment waste, for the synthesis of sorption materials.

Growth, crystal structure and IR luminescence of KSrY1-xErx(BO3)2.

A series of novel KSrY1-xErx(BO3)2 (x = 0-1) phosphors that emit near-infrared radiation was synthesized using solid-state methods. Pure Y and Er crystals were grown using a KF flux via the top-seeded solution growth technique. In situ high-temperature single crystal X-ray diffraction, Raman spectroscopy and DFT calculations were used for characterization. Within the series, a polymorphic phase transition from space group P21/m to R3m was discovered between 550 and 600°C. The concentration dependence of the luminescence intensity was measured for the samples. A strong emission of Er3+ electron transition 4I13/2 → 4I15/2 was detected within the 1529-1549 nm range, with the maximum observed for the KSrY0.4Er0.6(BO3)2 composition.

The Chemistry, Recrystallization and Thermal Expansion of Brannerite from Akchatau, Kazakhstan.

Numerous studies expose the potential of brannerite to become a good matrix, concentrating fission products and actinides. Minerals can complement the data collected from the synthetic materials and offer an advantage of a long-time exposure to radiation. Natural metamict brannerite from Akchatau, Kazakhstan, and its annealed sample were studied by EPMA, Raman spectroscopy, TGA, DSC, XRD and HTXRD. The radioactivity of pristine and annealed samples of brannerite was measured. Brannerite from Akchatau is characterized by the absence of significant amounts of REE and yttrium. The studied brannerite regains its structure at a temperature ~650 °C, revealed by the HTXRD and DSC. HTXRD was also performed on the annealed recrystallized brannerite. The thermal expansion for brannerite has been determined for the first time. The brannerite structure expands anisotropically with temperature increase. All the thermal expansion coefficients are positive except for αß. The decreasing beta parameter indicates a "shear structural deformation". The angle between the 1st axis of the tensor and the crystallographic a axis decreases with the increase of the temperature. The structure expands mostly in the α11 direction, approaching the bisector of the ß angle. Brannerite has a low CTE at room temperature-αv = 16 × 10-6 °C-1, which increases up to 39.4 × 10-6 °C-1 at 1100 °C. In general, the thermal stability of brannerite is comparable to that of the other perspective oxide radioactive waste-immobilizing matrices (e.g., Ln2Zr2O7, CePO4, CaTiO3, CaZrTi2O7). The calculated thermal expansion of brannerite and the understanding of its underlying crystal chemical mechanisms may contribute to the behavior prediction of the material (both metamict and crystalline) at high temperatures.

The AM-4 Family of Layered Titanosilicates: Single-Crystal-to-Single-Crystal Transformation, Synthesis and Ionic Conductivity.

Flexible crystal() structures, which exhibit() single-crystal()-to-single-crystal() (SCSC) transformations(), are attracting attention() in many applied aspects: magnetic() switches, catalysis, ferroelectrics and sorption. Acid treatment() for titanosilicate material() AM-4 and natural() compounds with the same structures led to SCSC transformation() by loss() Na+, Li+ and Zn2+ cations with large structural() changes (20% of the unit()-cell() volume()). The conservation() of crystallinity through complex() transformation() is possible due() to the formation() of a strong hydrogen bonding() system(). The mechanism() of transformation() has been characterized using single-crystal() X-ray() diffraction analysis(), powder() diffraction, Rietvield refinement, Raman spectroscopy and electron microscopy. The low migration() energy() of cations in the considered materials() is confirmed using bond()-valence and density() functional() theory() calculations, and the ion conductivity of the AM-4 family's materials() has been experimentally verified.