Crystal Lattice (IMAGE)
Caption
This is a crystal lattice of ferroelectric ammonium sulfate [(NH4)2SO4] with tilted ammonium (NH4+) tetrahedra (nitrogen: blue, hydrogen: white) and sulfate (SO42-) tetrahedra (sulfur: yellow, oxygen: red). The green arrow shows the direction of macroscopic polarization P. Blue arrows: local dipoles between sulphur and oxygen atoms. The electron density maps shown in the bottom left panel, in Fig. 2, and the movie are taken in the plane shown in grey. Bottom left: Stationary electron density of sulfur and oxygen atoms, displaying high values on the sulfur (red) and smaller values on the oxygens (yellow). Bottom right: Change of local dipoles at a delay time of 2.8 picoseconds (ps) after excitation of the ammonium sulfate crystallites. An anisotropic shift of charge reduces the dipole pointing to the right and increases the other 3 dipoles.
Credit
MBI Berlin
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