| Symbol | Structure Name | Space Group (Example) | Representative Substances | Description | |
|---|---|---|---|---|---|
| A1 | Face-Centered Cubic Structure Cubic Close Packing fcc | \(Fm\bar{3}m\) | Al, Cu, Ni, Sr, Rh, Pd, Ag, Ce, Tb, Ir, Pt, Au, Pb, Th | One of the close-packed structures. Atoms are positioned at the vertices of the unit cell and at the centers of all faces. It can also be thought of as dense planar layers stacked in the order ABCABC… along the body diagonal direction. | |
| A2 | Body-Centered Cubic Structure bcc | \(Im\bar{3}m\) | Na, K, V, Cr, Fe, Rb, Nb, Mo, Cs, Ba, Eu, Ta, W | Atoms are positioned at the vertices of the unit cell and at the body center (center of the lattice). This is not a close-packed structure. | |
| A3 | Hexagonal Close Packing HCP | \(P6_3/mmc\) | Be, Mg, Sc, Ti, Co, Zn, Y, Zr, Tc, Ru, Cd, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Re, Os, Tl | One of the close-packed structures. Dense planar layers are stacked in the order ABAB…. The unit cell is a right prism with a rhombic base (interior angles of 60° and 120°). | |
| A3′ | \(P6_3/mmc\) | α-La, Pr, Nd, Pm, Ce, Am, Cm, Bk, Cf | One of the close-packed structures. Dense planar layers are packed in the order ABACABAC…. The unit cell is a hexagonal lattice. | ||
| A4 | Diamond type | \(Fd\bar{3}m\) | C, Si, Ge, α-Sn | In addition to atoms at the face-centered cubic lattice points, atoms also exist at the body-center positions of 4 non-adjacent sub-lattices out of 2×2×2 subdivisions. All atoms are equivalent and tetrahedrally bonded. | |
| A5 | β-Tin Structure, White Tin Structure | \(I4_1/amd\) | β-Sn | Has a structure like the diamond structure (A4) compressed along one axis direction. A \(4_1\) screw axis remains along the compressed axis, resulting in a tetragonal crystal system. | |
| A6 | Indium type | \(I4/mmm\) | In | A body-centered tetragonal lattice. This is the A2 structure elongated in one direction. | |
| A7 | α-Arsenic type | \(R\bar{3}m\) | α-As, Sb, Bi | Distorted eight-coordination structure. | |
| A8 | Selenium type | \(P3_121\) | γ-Se, Te (SeTe) | A simple structure where atoms are located along the \(3_1\) screw axis. | |
| A9 | Graphite type | \(P6_3/mmc\) | C (LiB) | A structure of stacked sheets of planar hexagonal lattice with honeycomb bonding. The sheets are weakly bonded to each other and easily exfoliated. | |
| A10 | α-Hg ABC Packing | \(R\bar{3}m\) | α-Hg | Like the A1 structure, dense planar layers are stacked in the order ABCABC…, but the interlayer distance is larger. Can also be thought of as the A1 structure elongated along the stacking direction. Similar to the Ai structure. | |
| A11 | α-Ga | \(Cmce\) | α-Ga | Difficult to describe verbally. Orthorhombic crystal system. | |
| A12 | α-Mn | \(I\bar{4}3m\) | α-Mn | A structure containing 58 atoms per unit cell. Difficult to describe verbally. Cubic crystal system. Stable below 742°C for Mn. | |
| A13 | β-Mn | \(P4_132\) | β-Mn | A structure containing 20 atoms per unit cell. Difficult to describe verbally. Cubic crystal system. Stable between 742–1095°C for Mn. | |
| A14 | Iodine type | \(Cmce\) | I2, Br2 | A structure consisting of diatomic molecules. The molecular centers coincide with the lattice points of an orthorhombic face-centered lattice. There are two molecular orientations, perpendicular to one lattice axis. | |
| A15 | β-Tungsten | \(Pm\bar{3}n\) | β-W (Distinguishing A and B: Nb3Al, CdV3, Cr3O, Ti3Sb, Ti3Au) | In addition to atoms (A) at the body-centered lattice points, atoms (B) exist at two positions on each face. The former (A) are surrounded by 12 atoms (B), and atoms (B) are linearly arranged in three mutually orthogonal but non-intersecting directions. | |
| A16 | α-Sulfur | \(Fddd\) | α-S8 | Eight atoms bond together to form molecules. | |
| A17 | Black Phosphorus | \(Cmca\) | P | Atoms bond in layers, with weak bonding between layers. | |
| A18 | Cl2 Structure | \(P4_2/ncm\) | Cl2 | Diatomic molecules are arranged nearly in one direction (along the \(4_2\) screw axis). Similar to the A14 structure. | |
| A20 | α-Uranium | \(Cmcm\) | α-U, Tb, Dy, (Ag,Cd), γ–Ti | Zigzag atomic chains are arranged in a fixed direction (along the c-axis). | |
| Aa | α-Protactinium | \(I4/mmm\) | α-Pa | A body-centered tetragonal lattice. This is the A2 structure compressed along one axis direction. (Note: A6 is the elongated structure.) | |
| Ab | β-Uranium | \(P4_2/mnm\) | β-U | A structure where layers with near-close-packed planar arrangement are stacked along the c-axis direction. | |
| Ac | α-Neptunium | \(P4/nmm\) | α-Np | Each atom is bonded with two types of distorted 4-fold coordination. | |
| Ad | β-Neptunium | \(P4/nmm\) | β-Np | A structure where sheets of distorted square lattice are stacked along the c-axis direction. | |
| Af | Simple Hexagonal Lattice | \(P6/mmm\) | HgxSn | A simple structure where atoms are located at the lattice points of a hexagonal lattice. | |
| Ag | Boron | \(P4_2/nnm\) | B | A complex structure containing 50 atoms per unit cell. | |
| Ah | Simple Cubic Lattice | \(Pm\bar{3}m\) | α-Po | A structure where atoms exist at the lattice point positions of a simple cubic lattice. Despite such a simple structure, it is somewhat remarkable that its numbering is in the latter half (meaning it was discovered late). | |
| Ai | ABC Packing | \(R\bar{3}m\)td> | β-Po | Like the A1 structure, dense planar layers are stacked in the order ABCABC…, but the interlayer atomic distance is shorter. Can also be thought of as the A1 structure compressed along the stacking direction. Similar to the A10 structure. | |
| Ak | γ-Selenium | \(P2_1/c\) | γ-monoclinic Se | A complex structure containing 64 atoms per unit cell. Eight atoms form ring-shaped molecules. | |
| Al | β-Selenium | \(P2_1/c\) | β-monoclinic Se | A complex structure containing 32 atoms per unit cell. Eight atoms form ring-shaped molecules. |