Mechanical Anisotropy in LaPO4 Ceramics

Lanthanum phosphate (LaPO4) ceramics with marked preferred orientation were fabricated by hot-pressing sintering. X-ray diffraction was used to demonstrate the texture of LaPO4 ceramics, whose result is consistent with SEM observation, which may be due to the combination of the grains ((200) planes) rotation and preferential grain growth. There is fairly hardness and indentation fracture toughness anisotropy in the hot-pressing LaPO4 ceramics, but little anisotropy in elastic modulus. The ratio of maximum to minimum fracture toughness is about 1.75 times in the as-obtained LaPO4 ceramics due to the preferred orientation of laminated structure of LaPO4 ceramics. The higher crack deflection angles may play the key role for the higher fracture toughness in the orientation of 0 degrees relative to the hot-pressing direction than that of 90 in the plane normal to the pressing direction.