六方晶系Ln2CuTiO6（Ln=Y，Dy，Ho，Er，Yb）的电、磁极化率
Electric and magnetic polarizabilities of hexagonal Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb)
摘要：
我们研究了稀土过渡金属氧化物系列Ln_2CuTiO_6（Ln=Y，Dy，Ho，Er和Yb）的多铁性，其晶体结构为六方晶系，空间群为非中心对称的P63 cm。我们的研究结果表明，而这些化合物，除了Ln=Y，表现出低温反铁磁转变由于稀土矩的有序，预期的铁电转变是受挫的Cu和Ti之间的大尺寸差异在B-网站。有趣的是，这导致这些化合物获得了罕见的和独特的理想的顺电性能与高介电常数，低损耗和弱温度和频率依赖性的组合。第一性原理计算确定这些特殊性质是由两种效应的组合产生的。M = Cu和M = Ti的MO 5多面体尺寸的显著差异抑制了铁电转变所需的这些多面体的预期合作倾斜模式，导致在该系列中研究的每个化合物的介电常数的相对较大的值。此外，它示出的介电常数的大部分贡献来自中频极性振动模式，使其相对稳定，对任何温度变化。示出了在该系列的不同成员之间的介电常数的温度稳定性的变化所产生的软极性模式的相对贡献的变化。
英文摘要：
We investigated the rare-earth transition metal oxide series, Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb), crystallizing in the hexagonal structure with non-centrosymmetric P63cm space group for possible occurrences of multiferroic properties. Our results show that while these compounds, except Ln=Y, exhibit a low temperature antiferromagnetic transition due to the ordering of the rare-earth moments, the expected ferroelectric transition is frustrated by the large size difference between Cu and Ti at the B-site. Interestingly, this leads these compounds to attain a rare and unique combination of desirable paraelectric properties with high dielectric constants, low losses and weak temperature and frequency dependencies. First-principles calculations establish these exceptional properties result from a combination of two effects. A significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti suppress the expected co-operative tilt pattern of these polyhedra, required for the ferroelectric transition, leading to relatively large values of the dielectric constant for every compound investigated in this series. Additionally, it is shown that the majority contribution to the dielectric constant arises from intermediate-frequency polar vibrational modes, making it relatively stable against any temperature variation. Changes in the temperature stability of the dielectric constant amongst different members of this series are shown to arise from changes in relative contributions from soft polar modes.
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