Abstract
A material based on lanthanum orthophosphate LaPO 4 with inclusion of particles of lanthanum metaphosphate LaP 3 O 9 was synthesized. The influence of the process parameters of the synthesis on the structure and properties of the material was determined. Heat treatment of the coprecipitated lanthanum phosphates at 700°C leads to the formation of a nanopowder with the LaPO 4 crystallite size of approximately 17 nm. Heat treatment of the nanopowder at temperatures from 1100 to 1500°C yields compact materials based on the LaPO 4 –LaP 3 O 9 system. The heat treatment of the nanopowder at 1100°C leads to a sharp decrease in the porosity of the material (to ~5%) at insignificant grain growth (200–400 nm); under these conditions, the thermal conductivity [λ(25°C) = 3.2 W m–1 K –1 ], microhardness [Hv(25°C) = 4.6 ± 0.4 GPa], Young’s modulus [E(25°C) = 132 ± 9 GPa], and cracking resistance [ K 1c (25°C) = 1.6 ± 0.1 MPa m 1/2 ] pass through maxima. The thermal expansion coefficient of the material depends on the heat treatment conditions only slightly and amounts to (8.2 ± 0.2) × 10 –6 K –1 .