[Hyperfine structure study of binary sodium phosphates by Raman spectroscopy].
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 Na5P3O10 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 Na5P3O10 shifted to a lower frequency with increasing temperature. The microstructure units of Na5P3O10 crystal are the types of Q1(2) and Q2(11) with a ratio of 2 : 1. With the increase in the temperature, various new microstructure units including Q0 , Q1(1), Q1(2), Q2(11), Q2(12) and Q2(22) appeared while Na5 P3 O10 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.
Zhao
Si-Jie
SJ
School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China. zhaosijie@hotmail.com
You
Jing-Lin
JL
Chen
Hui
H
Jiang
Guo-Chang
GC