0.67 PbMg1/3Nb2/3O3-0.33 PbTiO3单晶中软模模式指认

应用显微拉曼技术对弛豫型铁电体0.67PbMg1/3Nb2/3O3-0.33PbTiO3(0.67PMN-0.33PT)的偏振拉曼光谱随温度变化的研究表明,在-196到600°C温度范围内0.67PMN-0.33PT存在两次相变:三方到四方(R-T)相变和四方到立方(T-C)相变。R-T相变的特征是106cm-1软模(-196°C时)随温度的升高而湮没到80cm-1"静态"模式中。依照群论分析,0.67PMN-0.33PT的80cm-1和106cm-1(-196℃时)两个模式分别为E(1TO)和A1(1TO)模。文章对三方相的对称结构(C3v点群)在背向散射配置下不同偏振方向的拉曼散射效率进行了计算。计算结果表明晶体中的A1(1TO)和E(1TO)模式能够通过使用不同的散射配置进行识别。理论计算和实验结果相比较得到了很好的吻合。

The Assignment of Soft Mode in 0.67 PbMg1/3Nb2/3O3-0.33 PbTiO3 Single Crystal

Polarized Raman spectra of ferroelectric relaxor 0.67Pb(Mg1/3Nb2/3)O3 - 0.33 PbTiO3 (0.67 PMN-0.33 PT) single crystals have been systematically investigated in a wide temperature range from -196 to 600 ℃ by micro-Raman scattering technique. The two structural phase transitions in the crystal were clearly revealed. One is the rhombohedral-tetragonal (R-T) phase transition, other one is the tetragonal-cubic (T-C) phase transition. The characteristic of the R-T phase transition is the soft mode at 106 cm-1 (at -196℃) which merges to the "static" mode at 80 cm-1 as temperature increases. According to the analysis of the group theory, the two modes at about 80 cm-1 and 106 cm-1 (at -196℃), respectively, are attributed to E(1TO) and A1(1TO) in the 0.67PMN-0.33PT. Raman scattering efficiencies of the rhombohedral symmetry structure (C3v point group) for the crystal in backscattering geometry with different polarization directions are calculated. The analytic results indicate that A1(1TO) and E(1TO) modes in the crystal can be identified by using different scattering geometry. A comparison of experimental results with theoretical predictions shows satisfactory agreement.