Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Science. 2010 Dec 17;330(6011):1660-3. doi: 10.1126/science.1192759.
We report the observation of local structural dipoles that emerge from an undistorted ground state on warming, in contrast to conventional structural phase transitions in which distortions emerge on cooling. Using experimental and theoretical probes of the local structure, we demonstrate this behavior in binary lead chalcogenides, which were believed to adopt the ideal, undistorted rock-salt structure at all temperatures. The behavior is consistent with a simple thermodynamic model in which the emerging dipoles are stabilized in the disordered state at high temperature due to the extra configurational entropy despite the fact that the undistorted structure has lower internal energy. Our findings shed light on the anomalous electronic and thermoelectric properties of the lead chalcogenides. Similar searches may show that the phenomenon is more widespread.
我们报告了在升温过程中观察到局部结构偶极子的出现，这与传统的结构相变不同，在结构相变中，结构扭曲是在冷却过程中出现的。通过对局部结构的实验和理论探测，我们在二元铅硫属化物中证明了这种行为，这些铅硫属化物被认为在所有温度下都采用理想的、无扭曲的岩盐结构。这种行为与一个简单的热力学模型一致，即由于额外的组态熵，尽管无扭曲结构具有更低的内能，但在高温无序态下，新出现的偶极子得以稳定。我们的发现揭示了铅硫属化物异常的电子和热电性质。类似的搜索可能表明，这种现象更为普遍。
