High-temperature crystal structure of the layered cuprates Ln 2 CuO 4 , Ln ΒΌ Pr, Nd and Sm with tetragonal T 0 -structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a-and c-axis changing from TEC(a)/TEC(c)E 1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln 2 CuO 4 shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO 2 -planes (TEC(Pr-O1)ΒΌ 11.7 ppm K Γ 1 ) in comparison with other cuprates: TEC (Nd-O1)ΒΌ15.2 ppm K Γ 1 and TEC (Sm-O1)ΒΌ 15.1 ppm K Γ 1 . High-temperature electrical conductivity of Pr 2 CuO 4 is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr 2 CuO 4 , 0.07-23 S/cm for Nd 2 CuO 4 and 2 Γ 10 Γ 4 -9 S/cm for Sm 2 CuO 4 . The trace diffusion coefficient (D T ) of oxygen for Pr 2 CuO 4 determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2 Γ 10 Γ 13 cm 2 /s (973 K) and 3.8 Γ 10 Γ 10 cm 2 /s (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.