Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, China.
Argonne National Laboratory, X-Ray Science Division, Argonne, Illinois 60439, USA.
Phys Rev Lett. 2013 Mar 15;110(11):115901. doi: 10.1103/PhysRevLett.110.115901. Epub 2013 Mar 14.
Tetragonal PbTiO(3)-BiFeO(3) exhibits a strong negative thermal expansion in the PbTiO(3)-based ferroelectrics that consist of one branch in the family of negative thermal expansion materials. Its strong negative thermal expansion is much weakened, and then unusually transforms into positive thermal expansion as the particle size is slightly reduced. This transformation is a new phenomenon in the negative termal expansion materials. The detailed structure, temperature dependence of unit cell volume, and lattice dynamics of PbTiO(3)-BiFeO(3) samples were studied by means of high-energy synchrotron powder diffraction and Raman spectroscopy. Such unusual transformation from strong negative to positive thermal expansion is highly associated with ferroelectricity weakening. An interesting zero thermal expansion is achieved in a wide temperature range (30-500 °C) by adjusting particle size due to the negative-to-positive transformation character. The present study provides a useful method to control the negative thermal expansion not only for ferroelectrics but also for those functional materials such as magnetics and superconductors.
四方相 PbTiO(3)-BiFeO(3) 在 PbTiO(3) 基铁电体中表现出强烈的负热膨胀，该铁电体由负热膨胀材料家族中的一个分支组成。随着粒径的略微减小，其强烈的负热膨胀大大减弱，然后异常转变为正热膨胀。这种转变是负热膨胀材料中的一种新现象。通过高能同步辐射粉末衍射和拉曼光谱研究了 PbTiO(3)-BiFeO(3) 样品的详细结构、单元胞体积的温度依赖性和晶格动力学。由于铁电性减弱，这种从强负到正热膨胀的异常转变是高度相关的。通过调整粒径，可以在很宽的温度范围内（30-500°C）实现有趣的零热膨胀，这是由于负到正的转变特性。本研究为控制不仅是铁电体而且是磁性和超导等功能材料的负热膨胀提供了一种有用的方法。
