When describing the structure of a material, we make a clear distinction between its crystal structure and its microstructure. The term“crystal structure”is used to describe the average positions of atoms within the unit cell, and is completely specified by the lattice type and the fractional coordinates of the atoms. In other words, the crystal structure　describes the appearance of the material on an atomic length scale. The term “microstructure”is used to describe the appearance of the material on the nm-cm length scale. A reasonable working definition of microstructure is“the arrangement of phases and defects within a material." 1. The term“crystal structure”is used to describe the all positions of atoms within the unit cell, and is specified by the lattice type and the fractional coordinates of the atoms.（T/F)