摘要
Si3N4是一种具有多种优越物化性能的多功能材料.采用基于密度泛函理论(DFT)的第一性原理计算对Si3N4的高低温相(β、α)进行了对比研究.对于d相,计算得晶格常数a=0.7678nm、c=0.5566nm,弹性刚度系数C11=4.232×1011N/m2、c33=4.615×1011N/m2,压电应变常量d33=0.402pC/N;而对于β相,a=0.7536nm、c=0.2874nm,弹性刚度系数c11=4.241×1011N/m2、C33=5.599×1011N/m2,压电应变常量则几乎为零.分析表明Si3N4的α、p两相均为高硬高强材料,这与其结构由四面体组成的网络架构有关.而Si3N4高低温相的压电性能都很差,特别是β相的压电系数几乎为零,这与其结构的对称性有关,高温相结构的对称性更高,形变引起的离子位移响应抵消更多.
Abstract
Si3N4 is a popular material with many excellent physicochemical properties. This present work make a comparative study on its low and high temperature phases (α- and β-Si3N4) by first-principles calculation based on density functional theory (DFT). As for α phase, the calculated lattice parameters are a=0.7678nm, c=0.5566nm; elasticstiffness coefficients are c11=4.232×1011N/m2, c33=4.615×1011N/m2; piezoelectric strain coefficients are d33= 0.402pC/N. While for β phase, they are a =0.7536nm, c = 0.2874nm, c11=4.241×1011N/m2, c33=5.599×1011N/m2 and the piezoelectric strain coefficients are nearly zero. The analysis shows that both α and β phases are high strength and high hardness, relating to their network structures of tetrahedron. The piezoelectricity is poor, especially for β-Si3N4.This can be attributed to the structural symmetry, higher symmetry and lower piezoelectricity.
基金项目
国家自然科学基金(50772121)
中国科学院知识创新工程重要方向性项目(KGCX-2-YW-206)
万方数据