研究目的
To clarify phase equilibria of the pure oxides Nb2O5 and Ta2O5, as well as the two pseudo-binary systems Nb2O5–V2O5 and Nb2O5–Ta2O5, and to grow doped Nb2O5 crystals using the optical floating zone technique.
研究成果
The study successfully clarified phase equilibria in the Nb2O5–Ta2O5 and Nb2O5–V2O5 systems, confirming solid solution formation and identifying intermediate compounds. Doped Nb2O5 crystals with Ta and V were grown up to 10 mm in size, but challenges like crown formation and cracking remain. Future work should optimize growth conditions and investigate crown causes.
研究不足
The phase transformation in Nb2O5 is kinetically inhibited, requiring long-term sintering. Crystal growth was unstable due to crown formation, leading to cracked crystals. The phase width of intermediate compounds like Ta2Nb4O15 was not fully verified, and some thermodynamic assessments (e.g., azeotropic point) lack experimental confirmation.
1：Experimental Design and Method Selection:
The study employed thermal analysis (DTA/TG), X-ray powder diffraction (XRD), and thermodynamic simulations using FactSage software to investigate phase equilibria and solid solution formation in the systems Nb2O5–Ta2O5 and Nb2O5–V2O5. Crystal growth was performed using the optical floating zone (OFZ) technique.
2：Crystal growth was performed using the optical floating zone (OFZ) technique.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Samples were prepared from powdered chemicals: Nb2O5 (99.995% purity), Ta2O5 (99.99% purity), and V2O5 (99.99% purity). Mixtures of varying compositions were analyzed.
3：995% purity), Ta2O5 (99% purity), and V2O5 (99% purity). Mixtures of varying compositions were analyzed.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment included NETZSCH STA 449C Jupiter and STA 429C thermal analyzers, XRD 3003 TT diffractometer, Bruker M4 TORNADO spectrometer, and FZ-T-10000-H-VII-VPO-PC optical floating zone furnace. Materials included platinum and tungsten crucibles, and various powdered oxides.
4：Experimental Procedures and Operational Workflow:
DTA/TG measurements involved three heating/cooling cycles at 10 K/min rates. XRD samples were sintered at specific temperatures and times, then ground and analyzed. Crystal growth used pre-molten feed-rods, growth rate of 6 mm/h, rotation rate of 30 rpm, and dried air atmosphere.
5：Data Analysis Methods:
Data were analyzed using thermodynamic simulations with FactSage 7.1, employing Redlich-Kister polynomials for excess Gibbs free energy calculations. XRD patterns were compared to literature data for phase identification.
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