Research On Mechanical And Electrical Properties Of Niobium Phosphate Glass-ceramics

Phosphate glass has the advantages of low melting temperature,moderate phonon energy,good nonlinear optical performance,good biocompatibility,and high conductivity.So,it is often used in developing new functional materials.The niobate crystal whose structure is perovskite type or tungsten bronze type,such as NaNb O₃,Ba₂NaNb₅O₁₅,etc.usually has a high dielectric constant and play an important role in developing capacitors.For the purpose of combining the advantages of the both,study on synthesis,mechanical,electrical properties and correlation between structure and property of the niobium phosphate glass-ceramics was carried out in this paper.The P₂O₅-Nb₂O₅-BaO-Na₂O system glass was prepared by the melt-quenching method.And the glass-ceramics were obtained successfully after the glasses were heat-treated.The methods such as differential scanning calorimetry,X-ray diffraction analysis,Raman spectra analysis and scanning electron microscopy analysis,along with microhardness test,flexural strength test,dielectric and ferroelectric test,were used to characterize the structure,mechanical and electrical properties of the glass and glass-ceramics.In this paper,we explored the influence of phosphorus content on glass formability;the influence of nucleation parameters and crystal growth temperature on density,mechanical and electrical properties of the glass-ceramics,and the effect of rare earth ceria on this system glass and glass-ceramics.The main results are as follows:（1）The phosphorus content had a great influence on the glass formability.The increase of phosphorus content will reduce T_g and increase the melting temperature.Therefore,the phosphorus content should be controlled less than 40 mol%.Under this condition,not only the glass processability is guaranteed,but also keep the melting temperature low.The T_g of the glass was about 670℃and the crystallization temperature was about 810℃.XRD showed that the glass is homogeneous amorphous phase.Raman spectra analysis showed that there is chain structure of Nb-O-P-O,which indicates that Nb₂O₅ and P₂O₅ build the glass network together.Niobium Oxide Octahedron became the main unit of the three-dimensional glass structure.Phosphorus existed in the glass network in the form of Q¹ and Q².（2）The research of nucleation parameters showed that the glass was suitable for nucleation at 700℃for 0.5 h to get the largest number of crystal nuclei.The mechanical properties of glass-ceramics treated at 810℃are the best.And the glass-ceramics treated at 910℃had better performance on dielectric properties.XRD showed that two crystal phases appeared after the crystallization,the main phase is Ba Nb₂P₂O₁₁,and the secondary phase is Nb PO₅.The addition of CeO₂ can inhibit the formation of the second phase.But when the addition amount was higher than 1 mol%,it had an inhibitory effect on the crystallization.SEM showed that CeO₂ had the effect of grain refinement,but the addition of more than 1 mol%will cause the increase of pore defects.（3）The density,hardness and flexural strength of the glass reached the maximum when the CeO₂ addition is 1 mol%.At this time,the glass structure was the densest.And the changes in hardness and strength indicate that CeO₂ enhanced the mechanical properties of the glass.The dielectric properties of the glass were also the best when the CeO₂ addition is 1 mol%.The polarization curve indicated that the glass was a linear dielectric material.（4）The parameters such as density,Knoop hardness,Vickers hardness,dielectric constant of the glass-ceramics all reached the maximum when CeO₂ addition is 1 mol%.The molar volume and fracture toughness had the lowest value when CeO₂ addition is 1 mol%.The addition of CeO₂ will reduce the dielectric loss of the glass-ceramics and keep it stable.Impedance analysis showed that the glass phase was a high-resistance and low-capacitance phase,while the crystal phase was a low-resistance and high-capacitance phase.The polarization curve proves that there is ferroelectric phase in the glass-ceramic.So,the niobium phosphate glass-ceramics is a potential dielectric material to develop capacitors.