Ba3Al2P4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to one P(2), two equivalent P(3), and three equivalent P(1) atoms. In the second Ba site, Ba(2) is bonded to two equivalent P(2) and four equivalent P(1) atoms to form distorted BaP6 octahedra that share corners with eight equivalent Al(1)P4 tetrahedra, edges with two equivalent Al(1)P4 tetrahedra, and faces with two equivalent Ba(2)P6 octahedra. Al(1) is bonded to one P(2), one P(3), and two equivalent P(1) atoms to form AlP4 tetrahedra that share corners with four equivalent Ba(2)P6 octahedra,  an edgeedge with one Ba(2)P6 octahedra, and edges with two equivalent Al(1)P4 tetrahedra. The corner-sharing octahedral tilt angles range from 20-64°. There are three inequivalent P sites. In the first P site, P(3) is bonded in a 6-coordinate geometry to four equivalent Ba(1) and two equivalent Al(1) atoms. In the second P site, P(1) is bonded in a 7-coordinate geometry to two equivalent Ba(2), three equivalent Ba(1), and two equivalent Al(1) atoms. In the third P site, P(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Al(1) atoms.
Ba3Al2P4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 6-coordinate geometry to one P(2), two equivalent P(3), and three equivalent P(1) atoms. The Ba(1)-P(2) bond length is 3.45 Å. There is one shorter (3.17 Å) and one longer (3.25 Å) Ba(1)-P(3) bond length. There are a spread of Ba(1)-P(1) bond distances ranging from 3.34-3.55 Å. In the second Ba site, Ba(2) is bonded to two equivalent P(2) and four equivalent P(1) atoms to form distorted BaP6 octahedra that share corners with eight equivalent Al(1)P4 tetrahedra, edges with two equivalent Al(1)P4 tetrahedra, and faces with two equivalent Ba(2)P6 octahedra. There is one shorter (3.18 Å) and one longer (3.22 Å) Ba(2)-P(2) bond length. There are two shorter (3.24 Å) and two longer (3.42 Å) Ba(2)-P(1) bond lengths. Al(1) is bonded to one P(2), one P(3), and two equivalent P(1) atoms to form AlP4 tetrahedra that share corners with four equivalent Ba(2)P6 octahedra,  an edgeedge with one Ba(2)P6 octahedra, and edges with two equivalent Al(1)P4 tetrahedra. The corner-sharing octahedral tilt angles range from 20-64°. The Al(1)-P(2) bond length is 2.43 Å. The Al(1)-P(3) bond length is 2.37 Å. There is one shorter (2.38 Å) and one longer (2.44 Å) Al(1)-P(1) bond length. There are three inequivalent P sites. In the first P site, P(3) is bonded in a 6-coordinate geometry to four equivalent Ba(1) and two equivalent Al(1) atoms. In the second P site, P(1) is bonded in a 7-coordinate geometry to two equivalent Ba(2), three equivalent Ba(1), and two equivalent Al(1) atoms. In the third P site, P(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and two equivalent Al(1) atoms.