title: Ambient stable tetragonal and orthorhombic phases in penta-twinned bipyramidal au microcrystals.
abstract: 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 °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 °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.
authors: Thematic Unit of Excellence on Nanochemistry and Chemistry and Physics of Materials Unit and ‡Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) , Jakkur P.O., Bangalore 560 064, India.
authors: Gangaiah
authors: G
authors: Mettela
authors: Meha
authors: M
authors: Bhogra
authors: Umesh V
authors: UV
authors: Waghmare
authors: Giridhar U
authors: GU
authors: Kulkarni