NH4H2PO4和ND4D2PO4晶体微结构的拉曼光谱研究

本文利用偏振拉曼光谱和第一性原理, 对磷酸二氢铵(NH₄H₂PO₄, ADP)和不同氘含量磷酸二氢铵DADP晶体的晶格振动模式进行了研究. 实验测得了不同几何配置、200–4000 cm^-1范围的偏振拉曼光谱, 分析在不同氘含量条件下921 cm^-1和3000 cm^-1附近拉曼峰的变化. 在ADP晶体中, 基于基本结构单元NH₄⁺ 和H₂PO₄^-基团的振动模, 用第一性原理进行了数值模拟, 进一步明确拉曼峰与晶体中原子振动的对应关系; 通过洛伦兹拟合不同氘含量DADP晶体的拉曼光谱中2000–2600 cm^-1处各峰的变化讨论了DADP 晶体的氘化过程, 结果表明氘化顺序是先NH₄⁺ 基团后H₂PO₄^-基团, 研究结果为今后此类材料的生长和性能优化奠定了基础.

Raman spectroscopic study on the micro-structure of NH4H2PO4 and ND4D2PO4 crystals

In this paper, the lattice vibration modes of ammonium dihydrogen phosphate NH₄H₂PO₄ (ADP) and its deuterated analog DADP are studied by using polarized Raman spectra and the first-principles calculation in the framework of the density functional theory. The vibration modes of ADP crystal, in which the basic structural units are the NH₄⁺ and H₂ PO₄^-groups, have been simulated by using a plane-wave pseudo potential method. Result shows that the peaks of 921 and near 3400 cm^-1 are assigned as the vibrational H₂ PO₄^-and NH₄⁺ groups, respectively. In order to investigate the deuteration process, the polarized Raman spectra are obtained in different polarization configurations and recorded in the range of 200-4000 cm^-1, so that we can study the variation of Raman peaks at 921 and 2600–3400 cm^-1. For example, in the scattering geometryX(YY)X , with increasing degree of deuterated, the peak of 921 cm^-1 red shifts and decreases in intensity, while the peaks ranging from 2600 to 3000 cm^-1 decrease in intensity. Moreover, a new broadened line appears in the range of 2000–2600 cm^-1, and the intensity of the new line increases with the degree of deuterated, but no change occurs in the peak position. With Lorentz analysis, it can be inferred that the deuterated of NH₄⁺ group is prior to that of H₂ PO₄^-group. We also study the spectra for other Raman scattering geometry of these crystals, and the result shows that the site symmetries of NH₄⁺ (ND₄⁺) and H₂ PO₄^-(D₂ PO₄^-) groups are determined to be C₂, which means that the site symmetry of the two groups in crystals have no change during the deuteration process. These results will be a foundaton for optimizing the growth and property of this kind of material.