钠磷酸盐精细结构的拉曼光谱解析

Hyperfine Structure Study of Binary Sodium Phosphates by Raman Spectroscopy

构建了钠磷酸盐精细结构团簇，应用量子化学从头计算方法，采用闭壳层Hatree-Fock（RHF）方法和6-31G（d, p）基组优化构型，进行了拉曼光谱的模拟计算。引入SIT应力指数标识磷酸盐局部微观精细结构，讨论和分析了磷酸盐在高频区的非桥氧对称伸缩振动的特征谱峰。结果表明SIT值与相应结构特征谱峰的拉曼位移呈良好相关性。采用高温拉曼光谱仪测定了Na5P3O10固态及熔体的变温拉曼光谱，观察到了Na5P3O10在873～1 073 K间的相变。Na5P3O10晶体的微结构单元为Q21与Q112, 其理论含量比例为2∶1。随着温度升高，Na5P3O10的主要峰包中心向低频移动，熔融后体系中出现了Q0,Q11,Q21,Q112,Q122,Q222等多种精细结构单元，导致其拉曼光谱的展宽与不对称性的出现。这些概念的建立和运用为磷酸盐熔体及玻璃的拉曼光谱的定量分析奠定了基础。

Quantum chemistry ab initio calculation was applied to study the hyperfine structure of binary sodium phosphates. A series of phosphate model clusters were designed to simulate the microstructure of phosphates with different components. Closed-shell Hatree-Fock method （RHF） and the basis sets of 6-31G （d, p） were employed to optimize structures and calculate Raman frequencies of these phosphate model clusters. SIT （stress index of tetrahedron）, which was well used in the study of silicate microstructures, had been adjusted before it was introduced to describe the microstructure of binary sodium phosphates. It was suggested that SIT of phosphates has good relationship with the Raman shift of the corresponding structures, which means SIT could also be used to study the hyperfine structure of binary sodium phosphates. Raman spectra of both solid and molten Na3P3O10 were determined in the range of room temperature to 1 473 K. A phase transition between 873 and 1 073 K was observed, and the main peaks of Na3P3O10 shifted to a lower frequency with increasing temperature. The microstrueture units of Na3P3O10 crystal are the types of Q1^2 and Q2^11 with a ratio of 2 ： 1. With the increase in the temperature, various new mierostructure units including Q0, Q1^1, Q1^2, Q2^11 , O2^12 and Q2^22 appeared while Na5P3O10 was heated above the melting point, which led to the broadening and asymmetry of Raman spectra of molten Na5P3O10. It came to an understanding that the microstructure units of phosphates may change at different temperature, especially above the melting points. The introduction of SIT and hyperfine structure could help analyze the Raman spectra of phosphates both qualitatively and quantitatively.