0.67PbMg_(1/3)Nb_(2/3)O_3-0.33PbTiO_3单晶中软模模式指认(英文)

The Assignment of Soft Mode in 0.67PbMg_(1/3)Nb_(2/3)O_3-0.33PbTiO_3 Single Crystal

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。

Polarized Raman spectra of ferroelectric relaxor 0. 67Pb （ Mg1/3 Nb2/3 ） 03 - 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 differ- ent polarization directions are calculated. The analytic results indicate that As （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.