Thermodynamic Optimization And Calculation Of BaO-SiO₂ And BaO-Lu₂O₃ Binary Systems

The novel single-phase full-color phosphor is expected to apply in white LEDs due to its low color temperature,high color rendering index,adjustable color coordinates and high luminous efficiency.However,recent work to optimize material preparation and promote luminescence of the single-phase full-color phosphor encountered some difficulties due to the lack of phase relationship and thermodynamics of BaO-Lu₂O₃-Si O2 ternary system.BaO-SiO₂ and BaO-Lu₂O₃ system as two important binary systems of BaO-Lu₂O₃-Si O2 ternary system,the phase diagram and thermodynamic data was assessed via the thermodynamic calculation by the CALPHAD method and experimental information of BaO-Lu₂O₃ system under low temperature Ionic Two-sublattice Liquid Model was chose to describehigh temperature solution to optimize and calculate BaO-SiO₂ and BaO-Lu₂O₃ system.The obtained self-consistent phase diagrams and thermodynamic data,thermodynamic model and its established method,will offer theoretical basis for the further research,but also provide new ideas for the related material and metallurgy systems.The main work and results are as follows:（1）BaO-SiO₂: BaO-SiO₂ system was assessed via the thermodynamic calculation by the CALPHAD method based on experimental phase diagram and the relevant thermodynamic data.The Gibbs energy of high temperature solution was determined by an ionic two-sublattice model as（Ba2+）P（O2–,Si O44–,Si O20）Q.The calculated Gibbs energies of seven intermediate phases（i.e.,Ba2 Si O4,Ba Si2O5,Ba Si O3,Ba2Si3O8,Ba3Si5O13,Ba3 Si O5,and Ba5Si8O21）are in reasonable agreement with the experimental data.In the Si O2-rich part,the optimized liquidus is in agreement with the experimental data and the calculated activities of Si O2 reproduce the experimental results within the error limits.The calculated activities of Ba O differ from the experimental data in range of 50mol% to 80mol% Ba O.which may be caused by the experimental error.The liquid Gibbs energy of mixing was also calculated.（2）BaO-Lu₂O₃: Only one intermediate compound Ba3Lu4O9 was identified at 1373,1573 and 1773 K.The Gibbs free energy of high temperature solution was described by an ionic two-sublattice model as（Ba2+,Lu3+）P（O2-）Q.The calculated phase diagram,Gibbs energy of intermediate phase Ba3Lu4O9,mixing free Gibbs energy at 900、1250 K are agree well with experimental results within error limits.The calculated activities at 2800 K was also calculated.Owing to the lack of experimental evidence,the calculated results should be regarded as tentative and more detailed experimental data are needed to verify the present study.