固体物理学英文-SSP-2（一）.pptxVIP

ELEMENTARY CRYSTALLOGRAPHY Review Solid: Crystal vs. Amorphous (glassy) Ordered array of atoms Disordered arrangement Competition between attractive (binding) force and repulsive force. Regular array lowers system energy. Deals with the geometric description of crystals and their internal arrangement. The branch of science crystallography Symmetry of a crystal can have a profound influence on its properties. Any crystal structure should be specified completely, concisely and unambiguously. Structures should be classified into different types according to the symmetries they possess. For SSP crystal structure ? CONTENTS Periodic arrays of atom lattice translation vectors Basis and crystal structure Primitive lattice cell Fundamental types of lattices 2D lattice types 3D lattice type What is crystal (space) lattice? Platinum Platinum surface Crystal lattice and structure of Platinum one replaces each atom by a geometrical point located at the equilibrium position of that atom. An infinite array of points in space, Each point has identical surroundings to all others. Arrays are arranged exactly in a periodic manner. Crystal structure can be obtained by attaching atoms, groups of atoms or molecules which are called basis (motif) to the lattice sides of the lattice point. crystal structure different choices for the basis Lattice +basis=crystal structure Dont mix up atoms with lattice points Lattice points are infinitesmal points in space Lattice points do not necessarily lie at the centre of atoms To describe a CS, there three important question to answer: Attention a. Lattice translation vectors Crystal periodic array of atoms: Point lattice –mathematical points in space point lattice + basis Lattice +basis=crystal structure From the point r Lattice? r r ’ The choice of lattice vectors is not unique. Thus one could equally well take the vectors a and b’ as a lattice vectors. S a b S ⊗ One lattice point pe