ANALYSIS OF QUASIELASTIC LIGHT-SCATTERING IN LINBO3 NEAR TC
ANALYSIS OF QUASIELASTIC LIGHT-SCATTERING IN LINBO3 NEAR TC
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DOI：
10.1103/physrevb.32.6787
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发表时间：
1985-01-01
影响因子：
3.7
通讯作者：
SCOTT, JF
中科院分区：
文献类型：
--
作者：
OKAMOTO, Y;WANG, PC;SCOTT, JF
我们对铌酸锂在293 ~ 1224 K范围内的拉曼光谱进行了研究，特别强调了0 ~ 50 cm−1范围内准弹性散射的定量分析。我们发现完整的谱，包括准弹性“翼”和两个最低频率的A - 1对称光学声子，可以拟合到具有松弛自能系统的预测谱分布函数；当这样做时，所有拟合的参数随温度缓慢而单调地变化。耦合参数δ 2 (T)的变化近似为(T C-T)−1.4，符合Halperin和Varma [Phys]的预测。Rev. B 14, 4030(1976)]。这只是第二个满足缺陷理论预测的中心模式研究。检查了全等和化学计量标本。相同样品的逆弛豫时间为540±30 GHz，与温度无关；它显然受到由于缺乏化学计量而产生的缺陷的限制。化学计量样品显示出温度相关的弛豫时间τ−1 (T)= τ 0−1 [(T - C-T)/T C], τ 0−1= 1740±430 GHz（即τ 0−1= 58±14 cm−1）；这是二阶相变所期望的平均场依赖性。数据显示了为什么非弹性中子散射研究[例如，MR Chowdhury， GE Peckham和DH Saunderson， J. Phys]。C 11, 1671(1978)]可能无法探测到最低A -对称光学声子的软化，从而有助于解决关于拉曼和中子散射数据的定性分歧的长期争议。
We have performed Raman studies of lithium niobate from 293 to 1224 K with special emphasis upon quantitative analysis of the quasielastic scattering from 0–50 cm− 1. We find that the complete spectrum, including both the quasielastic ‘‘wing’’and the two lowest-frequency A 1-symmetry optical phonons, can be fitted to the spectral distribution function predicted for a system with a relaxing self-energy; when this is done all the parameters fitted vary slowly and monotonically with temperature. The coupling parameter δ 2 (T) varies approximately as (T C-T)− 1.4 in accord with the predictions of Halperin and Varma [Phys. Rev. B 14, 4030 (1976)]. This is only the second central-mode study to satisfy that defect-theory prediction. Both congruent and stoichiometric specimens were examined. The congruent sample exhibits an inverse relaxation time of 540±30 GHz that is independent of temperature; it is apparently limited by defects arising from the lack of stoichiometry. The stoichiometric sample exhibits a temperature-dependent relaxation time of the form τ− 1 (T)= τ 0− 1 [(T C-T)/T C] with τ 0− 1= 1740±430 GHz (ie, τ 0− 1= 58±14 cm− 1); this is the expected mean-field dependence for a second-order phase transition. The data show why inelastic neutron scattering studies [eg, MR Chowdhury, GE Peckham, and DH Saunderson, J. Phys. C 11, 1671 (1978)] may have been unable to detect the softening of the lowest A 1-symmetry optical phonon and thereby help resolve a long-standing controversy concerning the qualitative disagreement of Raman and neutron scattering data.