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首页> 外文期刊>Physical review >Damped soft phonons and diffuse scattering in (Bi_(1/2)Na_(1/2))TiO_3
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Damped soft phonons and diffuse scattering in (Bi_(1/2)Na_(1/2))TiO_3

机译：（Bi_（1/2）Na_（1/2））TiO_3中的阻尼软声子和扩散散射

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摘要

Neutron-scattering studies of (Bi_(1/2)Na_(1/2))TiO_3 (BNT) have been performed to elucidate the microscopic mechanism of the broad maximum in the temperature dependence of the dielectric constant at TM ～ 600 K and the reduction in the piezoelectric properties above the depolarization temperature, 460 ～ 480 K. We observed diffuse scattering near the T point below 700 K, which competes with the superlattice peak at the M point of the tetragonal phase but coexists with the superlattice peak at the R point of the rhombohedral phase. The diffuse scattering shows an anisotropic Q shape extending along the <100> direction transverse to the scattering vector Q, which is explained by atomic shifts bridging the tetragonal and rhombohedral structures. We propose that the broad maximum in the dielectric constant is associated with a diffusive first-order transition between the competing tetragonal and rhombohedral phases. In addition, we found that the diffuse scattering is reduced for single crystals grown under high oxygen pressure, which suggests an analogy with the central peak in hydrogen-reduced SrTiO_3. Inelastic neutron scattering near the T point reveals a heavily overdamped soft mode similar to those reported in lead-based relaxors, the "waterfall" feature. Moreover, a damped soft transverse acoustic mode is observed for the <100> direction as the anisotropic diffuse scattering, indicating phase instabilities with the same origin as that of the diffuse scattering. The recovery of the soft mode is observed near the depolarization temperature, which coincides with the disappearance of the superlattice peak at the M point. These results indicate that the depolarization and the waterfall feature originate in the dynamic nature of ferroelectric clusters in the coexisting tetragonal/rhombohedral phase.
机译：（Bi_（1/2）Na_（1/2））TiO_3（BNT）的中子散射研究已经阐明了介电常数在TM〜600 K和在去极化温度460〜480 K之上，压电性能下降。我们观察到700 K以下T点附近的散射，与四方相M点的超晶格峰竞争，但与R处的超晶格峰共存。菱面体相的点。漫散射显示出沿垂直于散射矢量Q的<100>方向延伸的各向异性Q形状，这可以通过桥接四边形和菱形结构的原子位移来解释。我们提出介电常数的宽泛最大值与竞争四方相和菱面体相之间的扩散性一阶跃迁有关。此外，我们发现，在高氧气压力下生长的单晶，其散射散射降低了，这与氢还原SrTiO_3的中心峰相似。 T点附近的非弹性中子散射显示出严重过阻尼的软模，类似于铅基弛豫器中报道的软模，即“瀑布”功能。此外，在<100>方向观察到阻尼软横波模态为各向异性扩散，表明相位不稳定性与扩散的起源相同。在去极化温度附近观察到软模式的恢复，这与M点处超晶格峰的消失相符。这些结果表明，去极化和瀑布特征起源于共存的四方/菱面体相中铁电团簇的动力学性质。

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  • 来源
    《Physical review》 |2013年第6期|064109.1-064109.10|共10页
  • 作者

    M. Matsuura; H. Iida; K. Hirota; K. Ohwada; Y. Noguchi; M. Miyayama;

  • 作者单位

    Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan;

    Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan;

    Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, 560-0043, Japan;

    Synchrotron Radiation Research Center (SPring-8), Quantum Beam Science Directorate, Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan;

    Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8904, Japan;

    Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8904, Japan;

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    ferroelectricity and antiferroelectricity;

    机译：铁电和反铁电;

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