Subías G, Blasco J, García J, Herrero-Martín J, Sánchez M C
Instituto de Ciencia de Materiales de Aragón, Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza, Spain.
J Phys Condens Matter. 2009 Feb 18;21(7):075903. doi: 10.1088/0953-8984/21/7/075903. Epub 2009 Jan 23.
The nature of the para-antiferroelectric phase transition in Pb(2)MnWO(6) was investigated by x-ray absorption spectroscopy. Extended x-ray absorption spectra (EXAFS) and x-ray absorption near-edge structure (XANES) at the Pb L(3)-edge, W L(3)-edge and Mn K-edge were measured at temperatures above and below the transition temperature, T(c)∼445 K. The temperature dependence of the local geometrical and electronic structure around each of the three atoms was quantitatively determined. XANES spectra confirm the expected formal valence state as Pb(2+), W(6+) and Mn(2+) both above and below T(c). There are no significant changes of the local structure around the three atoms, which remains distorted in the whole temperature range. This indicates the existence of dynamic local distortions with a short-range order in the paraelectric phase. Below T(c), the local distortions (and the electrical dipoles) are static and their ordered arrangement gives rise to the orthorhombic crystallographic structure. Above T(c), these distortions are dynamically disordered, causing an average cubic crystallographic structure. Hence, the phase transition is of the order-disorder type.
通过X射线吸收光谱研究了Pb(2)MnWO(6)中准反铁电相变的性质。在高于和低于转变温度T(c) ∼ 445 K的温度下，测量了Pb L(3)边、W L(3)边和Mn K边的扩展X射线吸收光谱（EXAFS）和X射线吸收近边结构（XANES）。定量确定了三个原子周围局部几何结构和电子结构的温度依赖性。XANES光谱证实，在T(c)之上和之下，预期的形式价态分别为Pb(2+)、W(6+)和Mn(2+)。三个原子周围的局部结构没有显著变化，在整个温度范围内仍保持扭曲状态。这表明在顺电相中存在具有短程有序的动态局部畸变。在T(c)以下，局部畸变（和电偶极子）是静态的，它们的有序排列产生了正交晶系晶体结构。在T(c)以上，这些畸变是动态无序的，导致平均立方晶体结构。因此，该相变属于有序-无序类型。
