InorganicVII

Chapters / Chapter 1 · Solid state / Topic 12 of 14

Perovskite and ilmenite

Chapter 1 · Solid state and crystal structures

Ca2+ corners: 8 x 1/8 = 1O2- face centres: 6 x 1/2 = 3Ti4+ body centre: 1Formula: CaTiO3Ti CN 6, Ca CN 12Shift origin by (1/2,1/2,1/2):Ca at centre, O on edges - same cell.
Perovskite CaTiO3: Ca on the corners, O on the face centres, Ti at the body centre.

Perovskite, CaTiO3

Named after the mineral CaTiO3. O2− ions, along with the larger cation (Ca2+), form a ccp array in which the octahedral holes formed by O2− are occupied by the smaller cation (Ti4+). In the unit cell, the eight corners of the cube are occupied by Ca2+, O2− are placed at the centres of the six faces, and Ti4+ is placed at the centre of the cube.

Ca2+: 8 × 1/8 = 1
O2−: 6 × 1/2 = 3
Ti4+: 1
CaTiO3

The structure can also be interpreted in terms of ReO3: the Re positions are occupied by Ti4+, while Ca2+ occupies the centre of the cube. Ti4+ is octahedrally surrounded by O2−, while Ca2+ is surrounded by 12 O2− ions.

Charge combinationExamples
AII BIV O3A = Ca, Sr, Ba; B = Ti, Zr, Ge, Sn
AIII BIII O3A = La; B = Al, Ti, Cr, Mn
AI BV O3A = Na, K; B = Nb, Ta

Ilmenite, FeTiO3

Named after the mineral ilmenite. It adopts the structure of corundum (α-Al2O3). In a hexagonal close-packed array of O2− ions, two-thirds of the octahedral holes are occupied, one-third by Fe2+ and one-third by Ti4+, in alternating layers.

Charge combinationExamples
AII BIV O3A = Fe, Cd, Mg, Co; B = Ti
AIII BIII O3Corundum-type oxides
AI BV O3A = Li; B = Nb (LiNbO3)