Ferroelectric lead-free ${\mathrm{K}}_x{\mathrm{Na}}_{1-x}{\mathrm{NbO}}_3$ (KNN) perovskite, as the representative of the preferred oxides with good dielectric and piezoelectric behaviors, has attracted broad attentions in recent years. Here we systematically investigate the complete process of temperature dependent structural evolution in manganese (Mn)-doped ${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}{\mathrm{NbO}}_3\text{−}{\mathrm{LiBiO}}_3$ single crystals, presenting the ultrahigh piezoelectric coefficient of about 1050 pC ${\mathrm{N}}^{-1}$ and the excellent dielectric and ferroelectric performances, by demonstrating phonon thermodynamics associated with all Raman active modes at a wide temperature range of 80–800 K. All-round unpolarized and polarized scattering characteristics reflecting various phonon and structure properties are specified in detail. Symmetry difference, symmetry breaking, and structure rearrangement among the molecular vibrations have been proven to be related to a multiphase coexistence and the discontinuity of first-order phase transition. In comparison with the lattice dynamics, a complete phase transition ordering and the shift of transition point have been observed in $\mathrm{KNN}\text{−}{\mathrm{LiBiO}}_3$ crystals with the different Mn contents. This work aims at deeply revealing the details of good ferroelectric/dielectric performance, structure, and phonon thermodynamics, as well as understanding the mechanisms of first-order phase transition under the doping manipulation in KNN systems.

中文翻译：

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拉曼光谱研究锰掺杂K0.5Na0.5NbO3-LiBiO3压电晶体中的相变和声子热力学

铁电无铅 ${\mathrm{ķ}}_X{娜}_{\mathrm{1个}-X}{\mathrm{氧化铌}}_3$（KNN）钙钛矿作为具有良好介电和压电性能的优选氧化物的代表，近年来引起了广泛关注。在这里，我们系统地研究了掺杂锰（Mn）的温度依赖性结构演化的完整过程${\mathrm{ķ}}_{0.5}{娜}_{0.5}{\mathrm{氧化铌}}_3\text{-}{\mathrm{锂离子电池}}_3$ 单晶，呈现约1050 pC的超高压电系数 ${\mathrm{ñ}}^{-\mathrm{1个}}$通过演示与所有拉曼活性模式在80-800 K的宽温度范围内相关的声子热力学，以及出色的介电和铁电性能。详细说明了反映各种声子和结构特性的全方位非极化和极化散射特性。分子振动之​​间的对称性差异，对称性断裂和结构重排已被证明与多相共存和一阶相变的不连续性有关。与晶格动力学相比，已观察到完整的相变有序和相变点的偏移。$\mathrm{知识网络}\text{-}{\mathrm{锂离子电池}}_3$Mn含量不同的晶体。这项工作旨在深入揭示良好的铁电/介电性能，结构和声子热力学的细节，以及了解KNN系统中掺杂操作下的一阶相变机理。