Local structure and dynamics in relaxor-ferroelectric PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 single crystals
Local structure and dynamics in relaxor-ferroelectric PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 single crystals
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弛豫铁电 PbSc1/2Nb1/2O3 和 PbSc1/2Ta1/2O3 单晶的局部结构和动力学
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
L. Konstantinov
中科院分区：
文献类型：
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作者：
B. Mihailova;U. Bismayer;B. Güttler;M. Gospodinov;L. Konstantinov
利用拉曼光谱研究了弛豫铁电体PbSc1/2Nb1/2O3和PbSc1/2Ta1/2O3的局部结构排列及其动力学效应。测量了单晶在不同温度和不同散射构型下的偏振拉曼光谱。观测到的峰值是根据正常模式计算分配的。通过计算结构单元在不同原子位置的模态，分析了小的结构偏差对原子振动的影响。结果表明，在几个单元格的局部尺度上，结构单元的加倍总是可能的。源自F2u模式的两个拉曼峰的存在表明，PbSc1/2B " 1/2O3中发生了电子-声子耦合，从而导致了动态的非中心对称结构波动。结构扰动包括Pb和O原子在垂直于体对角线的平面上的非共面性和B阳离子偏离BO6八面体中心。两个峰的强度比对Pb- o平面内的孤对Pb原子的取向有序程度敏感，而取向有序程度与组分B′/B”有序程度有关。由不对称O-B-O弯曲、BO3平移和pb局域模式产生的峰对温度的依赖性表明，两种材料在冷却过程中有不同的结构变化。在PbSc1/2Nb1/2O3中，温度的降低有利于B阳离子偏离中心。在PbSc1/2Ta1/2O3中，温度降低稳定了Pb和O原子在垂直于体对角线平面上的非共面性，增强了Pb电子孤对之间的相关性。
Local structural arrangements and corresponding dynamical effects in relaxor ferroelectrics PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 were studied by Raman spectroscopy. Polarized Raman spectra of single crystals were measured at different temperatures in several scattering configurations. The peaks observed are assigned on the basis of normal-mode calculations. The effect of small structural deviations on the atomic vibrations is analysed by calculating the modes of structural units at various atomic positions. It is shown that doubling the structural unit is always possible on a local scale of a few unit cells. The presence of two Raman peaks originating from the F2u mode shows that electron-phonon coupling occurs in PbSc1/2B''1/2O3, thus leading to dynamical off-centre-symmetrical structural fluctuations. The structural perturbation consists of the non-coplanarity of Pb and O atoms in the planes perpendicular to the body diagonal and deviations of B cations from the centre of BO6 octahedra. The intensity ratio of the two peaks is sensitive to the degree of orientational ordering of the lone pairs of Pb atoms within the Pb-O planes, which is related to the degree of compositional B'/B'' ordering. The temperature dependence of the peaks arising from asymmetrical O-B-O bending, BO3 translation and Pb-localized modes shows that on cooling different structural changes are preferential in the two materials studied. In PbSc1/2Nb1/2O3 the lowering of the temperature favours the off-centre deviations of the B cations. In PbSc1/2Ta1/2O3 the temperature decrease stabilizes the non-coplanarity of the Pb and O atoms in the planes perpendicular to the body diagonal and enhances the correlation between the electronic lone pairs of Pb.