Ambient Stable Tetragonal and Orthorhombic Phases in Penta-Twinned Bipyramidal Au Microcrystals

作者：Mettela Gangaiah; Bhogra Meha; Waghmare Umesh V; Kulkarni Giridhar U^*

来源：Journal of the American Chemical Society, 2015, 137(8): 3024-3030.

DOI：10.1021/ja512340m

Face-centered cubic (fcc) lattice is the only known crystal structure of bulk gold. In the present work, we report the presence of body-centered tetragonal (bct) and body-centered orthorhombic (bco) phases in bipyramidal Au microcrystals with penta-twinned tips. These microcrystals have been obtained by thermolysis of (AuCl4)- stabilized with tetraoctylammonium bromide (ToABr) in air at about 220 degrees C for 30 min. Using a laboratory monochromatic X-ray source, the non-fcc phases could be readily detected. The remarkable occurrence of non-fcc phases of Au grown in the temperature window of 200-250 degrees C results from the geometrically induced strains in the bipyramids. Having derived first-principles theoretical support for the temperature-dependent stability of non-fcc Au structures under stress, we identify its origin in soft modes. Annealing at high temperatures relieves the stress, thus destabilizing the non-fcc phases.

• 出版日期2015-3-4