Carpy-Galy LaTaO4中的亚稳极性序与相竞争
Metastable polar order and phase competition in Carpy-Galy LaTaO4
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- Dankook University（丹阳大学）
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中文总结 AI 辅助
通过第一性原理计算发现Carpy-Galy LaTaO4中存在亚稳极性单斜P21相，作为连接反极性P21/c与极性Cmc21相的公度中间态，并揭示了稳定该相的机制及调控极性-反极性竞争的化学途径。
中文摘要 AI 辅助
Carpy-Galy LaTaO4经历了一个结构序列，该序列通过一个非公度调制区域将反极性单斜P21/c基态与极性正交Cmc21相连接起来。第一性原理计算确定了亚稳极性单斜P21相作为相变景观中的一个公度中间态。作为P21/c和Cmc21的共同子群，P21为已确立的多晶型物之间提供了一条对称连接的路径。这些对称破缺路径的模分辨能量面表明，各自的主序参量与一个同对称的Gamma_1+弛豫之间的耦合在两条路径上都稳定了P21极小值。因此，P21/c到P21的转变具有有限的能垒，而一个受限的软模模型在谐波刚度的说明性范围内保留了相互竞争的P21和Cmc21势阱。晶格度量和中子衍射比较表明，计算得到的公度态与实验上的IC-o调制具有共同的S_2+主导位移特征，支持将P21用作IC-o的公度结构参考。最后，依赖于组分的能量学为调节极性-反极性竞争提供了化学途径。
英文摘要
Carpy-Galy LaTaO4 undergoes a structural sequence linking the antipolar monoclinic P21/c ground state and the polar orthorhombic Cmc21 phase through an incommensurately modulated regime. First-principles calculations identify a metastable polar monoclinic P21 phase as a commensurate intermediate in the phase-transition landscape. As a common subgroup of P21/c and Cmc21, P21 provides a symmetry-connected route between the established polymorphs. Mode-resolved energy surfaces for these symmetry-breaking pathways show that coupling between the respective primary order parameters and an isosymmetric Gamma_1+ relaxation stabilizes the P21 minimum along both pathways. Consequently, the P21/c -> P21 transformation has a finite energy barrier, while a restricted soft-mode model retains competing P21 and Cmc21 basins over an illustrative range of harmonic stiffness. Lattice-metric and neutron-diffraction comparisons indicate a shared S_2+-dominated displacement character between the calculated commensurate state and the experimental IC-o modulation, supporting the use of P21 as a commensurate structural reference for IC-o. Finally, composition-dependent energetics suggest chemical routes for tuning polar-antipolar competition.
