Frenkel A I, Pease D M, Budnick J I, Metcalf P, Stern E A, Shanthakumar P, Huang T
Department of Physics, Yeshiva University, New York, NY 10016, USA.
Phys Rev Lett. 2006 Nov 10;97(19):195502. doi: 10.1103/PhysRevLett.97.195502. Epub 2006 Nov 9.
Structural transformations around both V and Cr atoms in (V1-xCrx)2O3 across its metal-insulator transition (MIT) at x approximately 0.01 are studied by extended x-ray absorption fine-structure technique. Our new results for Cr made possible by the use of a novel x-ray analyzer that we developed reveal the substitutional mechanism of Cr doping. We find that this system has a buckled structure with short Cr-V and long V-V bonds. This system of bonds is disordered around the average trigonal lattice ascertained by x-ray diffraction. Such local distortions can result in a long range strain field that sets in around dilute Cr atoms in microscopic regions. We suggest that such locally strained regions should be insulating even at small x. The possibility of local insulating regions within a metallic phase, first suggested by Rice and Brinkman in 1972, remains unaccounted for in modern MIT theories.
利用扩展X射线吸收精细结构技术研究了(V1-xCrx)2O3在x约为0.01时跨越其金属-绝缘体转变(MIT)过程中V和Cr原子周围的结构转变。我们使用自行研发的新型X射线分析仪得到的关于Cr的新结果揭示了Cr掺杂的替代机制。我们发现该体系具有Cr-V键短、V-V键长的扭曲结构。由X射线衍射确定的平均三角晶格周围的这种键系是无序的。这种局部畸变会导致在微观区域中围绕稀Cr原子形成长程应变场。我们认为，即使在x较小时，这种局部应变区域也应该是绝缘的。1972年由赖斯和布林克曼首次提出的金属相中存在局部绝缘区域的可能性在现代金属-绝缘体转变理论中仍未得到解释。
