Ferroelastic phase transition and the role of volume strain in the structural trapping of a metastable quenched low-spin high-symmetry phase in [Ru0.35Fe0.65(ptz)6](BF4)2,CrystEngComm

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Ferroelastic phase transition and the role of volume strain in the structural trapping of a metastable quenched low-spin high-symmetry phase in [Ru0.35Fe0.65(ptz)6](BF4)2
CrystEngComm ( IF 2.6 ) Pub Date : 2023-05-22 , DOI: 10.1039/d3ce00365e
Francisco Javier Valverde-Muñoz ₁ , Ricardo Guillermo Torres Ramírez ₁ , Abhilash Ulhe ₁ , Elzbieta Trzop _{1,

2} , Mousumi Dutta ₃ , Chinmoy Das ₃ , Pradip Chakraborty ₃ , Eric Collet _{1,

2,

4}

Affiliation

Spin-crossover (SCO) materials exhibit thermal conversion of their electronic state from low (LS) to high (HS) spin state, which also involves both intra- and inter-molecular structural reorganisations within the crystal. The occurrence of coupled SCO and symmetry-breaking (SB), also responsible for structural reorganisations, is a current topic of interest because it can generate exotic behaviours such as unsymmetric hysteresis loops, stepwise evolution of the spin conversion, or sequences of phase transitions. Here we study the coupling and decoupling of SCO and SB during the thermal conversion of the prototypical [Fe(ptz)₆](BF₄)₂ compound diluted in the isostructural ruthenium host lattice [Ru(ptz)₆](BF₄)₂. We show that the [Ru_0.35Fe_0.65(ptz)₆](BF₄)₂ system undergoes a SB between the high-spin high symmetry (HShs) phase (R [3 with combining macron]

space group) and the low-spin low symmetry (LSls) phase (P [1 with combining macron]

space group). We present a structural analysis of the ferroelastic R [3 with combining macron]

→ P

phase transition and highlight the structural SB signatures. We also study the metastable low-spin high symmetry (LShs) phase (R [3 with combining macron]

space group) reached upon fast cooling. In the framework of the Landau theory of phase transition adapted by Collet, and considering the elastic coupling between SCO and SB, we discuss the structural distortion between the HShs, LShs, and LSls phases and explain the metastable nature of the LShs phase.

中文翻译：

铁弹性相变和体积应变在 [Ru0.35Fe0.65(ptz)6](BF4)2 亚稳淬火低自旋高对称相的结构捕获中的作用

自旋交叉 (SCO) 材料表现出其电子态从低自旋态 (LS) 到高自旋态 (HS) 的热转换，这也涉及晶体内的分子内和分子间结构重组。耦合 SCO 和对称性破缺 (SB) 的发生也负责结构重组，是当前感兴趣的话题，因为它可以产生奇异行为，例如不对称滞后回线、自旋转换的逐步演化或相变序列。在这里，我们研究了在等结构钌主晶格 [Ru (ptz) ₆ ](BF ₄ )中稀释的原型 [Fe(ptz) ₆ ](BF ₄ ) ₂化合物热转换过程中 SCO 和 SB 的耦合和去耦合。₂ . 我们表明 [Ru_0.35 Fe_0.65 (ptz)₆ ](BF₄ )₂系统在高自旋高对称性 (HShs) 相（ R [3 结合马克龙]