【正文】 ms do not have a longrange order (～ 1nm).252。≠βOrthorhombic a≠b≠c ， α＝ β＝ γ＝ 90176。Cubic a＝ b＝ c ， α＝ β＝ γ＝ 90176。 Space LatticeuⅠ. Crystals versus noncrystals 1. Classification of functional materialsChapter ⅡFundamentals of CrystallographyLesson three2. Classification of materials based on structure Regularity in atom arrangement —— periodic or not (amorphous)216。Rhombohedral a＝ b＝ c ， α＝ β＝ γ≠90176。 Lattice Types If a rotation around an axis passing through the crystal by an angle of 360o/n can bring the crystal into coincidence with itself, the crystal is said to have a nfold rotation symmetry. And axis is said to be nfold rotation axis. We identify 14 types of unit cells, or Bravais lattices, grouped in seven crystal systems.uⅠ.Seven crystal systems All possible structure reduce to a small number of basic unit cell geometries.① There are only seven, unique unit cell shapes that can be stacked together to fill threedimensional.