Production of crystal-oriented lanthanum silicate oxyapatite ceramics with anisotropic electrical conductivity and thermal expansion

Lanthanum silicate oxyapatite (LSO) has a very high oxide-ion conductivity along the c-axis of its hexagonal crystal. The effect of the crystal orientation in LSO ceramics on the anisotropy of their electrical and mechanical properties has not been studied systematically because centimeter-scale ceramics with different degrees of crystal orientation are difficult to produce. We produced crystal-oriented LSO ceramics by slip casting under a strong magnetic field and subsequent sintering. Using LSO ceramics with different degrees of crystal orientation, the electrical conductivity (σ) and linear thermal expansion coefficient (α) were measured. σ parallel to the c-axis (σ_||c) increased as the degree of crystal orientation increased, whereas σ perpendicular to the c-axis (σ_⊥c) was relatively insensitive to this parameter. The σ_||c and σ_⊥c values of our samples were almost the same as those of LSO single crystals. α also exhibited anisotropy originating from the asymmetry of the crystal structure.