霞石NaAlSiO_4的压缩性及其机理研究

Investigation on the Compressibility of Nepheline NaAlSiO_4 and Its Mechanism

NaAlSiO_4高压相CF相的结构和性质近年来被广为关注,然而对其低压相霞石的高压行为研究并不深入。为进一步认识碱金属在CF相中的赋存状态,采用金刚石压腔和同步辐射X射线衍射,开展了霞石NaAlSiO_4(P63,Z=8)常温、20GPa时的压缩性质研究。结果显示,在实验压力范围内,霞石没有发生结构相变,其三阶等温状态方程参数为:V0=0.715(2)nm^3,K0=53(3)GPa,K'=4.1(3),a和c轴的压缩系数Ka=3.8(1)×10^(-3)nm/GPa,Kc=2.42(6)×10^(-3)nm/GPa。通过第一性原理计算模拟,印证了实验压缩性的结果,揭示了霞石的压缩机制,即SiO_4和AlO_4四面体呈刚性行为,这些四面体之间的扭转导致结构中伪正交空隙通道的畸变。

CF phase（ NaAlSiO_4） ＇s structure and physical properties has attracted a wide attention,however,the high pressure behavior of nepheline is quite unclear. For further understanding on the occurrence of the alkali metal in CF phase,investigation on the compressibility of nepheline NaAlSiO_4（ P63,Z = 8） at room temperature with pressure up to20GPa has been carried out by using diamond anvil cell and synchrotron X-ray diffraction. No phase transition of nepheline occurs in present experimental conditions,and its parameters of isothermal equation of state are V0= 0. 715（ 2） nm^3,K0= 53（ 3） GPa,K＇ = 4. 1（ 3）. The compressional coefficients are 3. 8（ 1） × 10^-3nm/GPa for the a axis and 2. 42（ 6） ×10^-3nm/GPa for the c axis,respectively. The results from first-principle calculations not only underpin the experimental observations,but also reveal the compressional mechanism of nepheline,i.e. the rigid behavior of SiO_4 and AlO_4 tetrahedron,and their tilting resulting in the distortion of pseudo-orthogonal channel alone the c-axis direction.