Small concentrations of impurities can create profound differences in the thermodynamic stability and the physical behavior of crystalline materials. The dramatic changes produced by chemical substitutions are perhaps best illustrated by the discovery of high-Tc superconducting oxides by Bednorz and Müller in 1986. As a pure endmember, the cuprate that revolutionized solid state physics is an insulator. However, when small amounts of Ba2+ or Sr2+ replace La3+ in La2CuO4, the doping induces a series of surprising transformations. At low levels of substitution, La2−x(Sr,Ba)xCuO4−y remains insulating, but...

First Page Preview

First page PDF preview
You do not currently have access to this article.