研究目的
To explore new birefringent crystals in bismuth d0 transition metal selenites by synthesizing and characterizing novel compounds, and to understand their structural and optical properties, particularly birefringence.
研究成果
Five new bismuth fluoride selenites with d0 transition metals or Te(VI) were successfully synthesized and characterized, exhibiting large birefringence values, particularly for isostructural compounds 1-3 (Δn > 0.19 at 1064 nm). The asymmetric SeO3/TeO3 groups were identified as the primary contributors to the birefringence, offering insights for designing new birefringent materials. Future work should focus on enhancing stereoactivity of lone-pair cations, increasing distortion of d0-TM octahedrons, and raising the density of SeO3 groups to improve birefringence further.
研究不足
The study is limited to the specific synthesized compounds; generalizability to other systems may be constrained. The DFT calculations have limitations in accurately predicting band gaps due to the use of GGA methods. Thermal stability varies among compounds, with decomposition temperatures ranging from about 295°C to 432°C, which may limit high-temperature applications. The birefringence values are theoretical and may not fully match experimental measurements; further experimental validation is needed.
1：Experimental Design and Method Selection:
Hydrothermal synthesis was used to synthesize five new bismuth fluoride selenites with d0 transition metals or Te(VI) through aliovalent substitution. Single-crystal X-ray diffraction, thermal analysis, IR and UV-Vis-NIR spectrometry, and DFT-based theoretical calculations were employed for characterization.
2：Sample Selection and Data Sources:
Polycrystalline materials were synthesized from commercial reagents including Bi2O3, SeO2, TiF4, NbF5, Na2TeO3, ZrF4, MoO3, and HF. Single crystals were grown under hydrothermal conditions at 220°C for 4 days.
3：List of Experimental Equipment and Materials:
Equipment includes Miniflex600 powder X-ray diffractometer, FESEM (JSM6700F) with EDS, Magna 750 FT-IR spectrometer, PE-Lambda 900 UV-vis-NIR spectrophotometer, Netzsch STA 499C TGA, Agilent Technologies SuperNova Dual Wavelength CCD diffractometer, Bruker D8 Quest/Venture diffractometer. Materials include Bi2O3 (
4：9%, AR), SeO2 (99+%, AR), TiF4 (99%, AR), NbF5 (99%, AR), Na2TeO3 (5%, AR), ZrF4 (99%, AR), MoO3 (5+%, AR), HF (40+%, AR), deionized water, KBr pellets, BaSO4 plate, Al2O3 crucibles. Experimental Procedures and Operational Workflow:
Mixtures of reagents with deionized water and HF were sealed in Teflon-lined autoclaves, heated at 220°C for 4 days, slowly cooled, filtered, washed, and dried. Powder X-ray diffraction, elemental analysis, IR spectra, UV-Vis-NIR spectra, TGA, and single-crystal XRD data collection and refinement were performed. DFT calculations were conducted using CASTEP code.
5：Data Analysis Methods:
Data were analyzed using SHELX-97 for structure refinement, PLATON for symmetry checking, and CASTEP for electronic structure and optical property calculations. Bond valence sums were calculated to confirm oxidation states.
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