POLAR FLUCTUATIONS AND 1ST-ORDER RAMAN-SCATTERING IN HIGHLY POLARIZABLE KTAO3 CRYSTALS WITH OFF-CENTER LI AND NB IONS

被引:106
作者
DIANTONIO, P [1 ]
VUGMEISTER, BE [1 ]
TOULOUSE, J [1 ]
BOATNER, LA [1 ]
机构
[1] OAK RIDGE NATL LAB,OAK RIDGE,TN 37831
来源
PHYSICAL REVIEW B | 1993年 / 47卷 / 10期
关键词
D O I
10.1103/PhysRevB.47.5629
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
Relatively low concentrations of randomly substituted off-center ions are known to induce ferroelectric order in highly polarizable crystals. In the case of potassium tantalate (KTaO3) doped with lithium or niobium, the results of first-order Raman scattering from two hard phonon modes (TO2 and TO3) show that polar microregions are formed at relatively high temperatures. At lower temperatures, and above a certain critical dopant concentration, the Raman results are consistent with the occurrence of a structural phase transition. These results can be reasonably explained by using a random-molecular-field theory that takes into account the indirect dipolar interactions mediated by the soft lattice. This approach accounts for the characteristic asymmetry of the TO2 Raman scattering detected at high temperatures and for the subsequent increase in the integrated scattering intensity with decreasing temperature. An analysis of the Raman results provides a means for determining the size of the polar microregions formed in the highly polarizable KTaO3 lattice. The good agreement obtained between the theoretical and experimental results provides support to the physical concepts embodied in the present theoretical approach to describing the onset of order in these systems.
引用
收藏
页码:5629 / 5637
页数:9
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