Thermal expansion of decagonal Al70.7Co13.3Ni16.0 in the temperature range 15-300 K

The temperature dependence of lattice parameters a in the quasiperiodic plane and c in the periodic direction of decagonal Al70.7Co13.3Ni16.0 was probed using X-ray powder diffraction in the temperature range 15-300 K. Both parameters were fitted by means of positions of 22 Bragg reflections for each temperature. Temperature dependences were modelled best by second order polynomials leading to linear thermal expansion coefficients alpha(T) 8.1(33).10(-7) K-1 + 3.9(2).10(-8) K-2 T in the quasiperiodic plane and gamma(T) = 1.7(6).10(-6) K-1+3.8(3).10(-8) K-2 T in the periodic direction, respectively. Thus we found the anisotropy ratio gamma(T)/alpha(T) to decrease with increasing temperature from 1.60 (at 15 K) to 1.05 (at 300K) Besides pecularities around 150 K indicating an intermediate phase formed by superordering, we observed deviations from the general smooth course between 15 K and 50 K for both lattice parameters.