Geirhos K, Langmann J, Prodan L, Tsirlin A A, Missiul A, Eickerling G, Jesche A, Tsurkan V, Lunkenheimer P, Scherer W, Kézsmárki I
Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany.
CPM, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany.
Phys Rev Lett. 2021 May 7;126(18):187601. doi: 10.1103/PhysRevLett.126.187601.
We report the observation of an antipolar phase in cubic GaNb_{4}S_{8} driven by an unconventional microscopic mechanism, the cooperative Jahn-Teller effect of Nb_{4}S_{4} molecular clusters. The assignment of the antipolar nature is based on sudden changes in the crystal structure and a strong drop of the dielectric constant at T_{JT}=31 K, also indicating the first-order nature of the transition. In addition, we found that local symmetry lowering precedes long-range orbital ordering, implying the presence of a dynamic Jahn-Teller effect in the cubic phase above T_{JT}. Based on the variety of structural polymorphs reported in lacunar spinels, also including ferroelectric phases, we argue that GaNb_{4}S_{8} may be transformable to a ferroelectric state, which would further classify the observed antipolar phase as antiferroelectric.
我们报道了在立方相GaNb₄S₈中观察到的一种反极相，该反极相由一种非常规的微观机制——Nb₄S₄分子簇的协同 Jahn - Teller 效应驱动。反极性质的确定基于晶体结构的突然变化以及在T₍JT₎ = 31 K时介电常数的急剧下降，这也表明了该转变具有一级相变的性质。此外，我们发现局部对称性降低先于长程轨道有序化，这意味着在高于T₍JT₎的立方相中存在动态 Jahn - Teller 效应。基于在缺位尖晶石中报道的多种结构多晶型物，包括铁电相，我们认为GaNb₄S₈可能可转变为铁电态，这将进一步把观察到的反极相归类为反铁电相。
