Structure refinement of the superconducting phase YNi2B2C as a function of temperature in the range 25-300 K

X-ray powder and single crystal diffraction has been used for structure refinement of various YNi2B2C samples in the temperature range 25-300 and 180-300 K, respectively. Linear thermal expansion is strikingly anisotropic. Coefficients vary between alpha(a) = 4.1 X 10(-7) K-(1) (25 K)-1.2 X 10(-5) K-1 (300 K) and alpha(c) = -6.1 X 10(-7) K-1 (25 K)-4.5 X 10(-7) K-1 (300 K) while the axial ratio c/a of the unit cell decreases with increasing temperature T. Moreover, a small increase of structure parameter z(B) with T was found. Anisotropic mean square atomic displacements remain almost constant for C and B but increase considerably for both Ni and Y atoms. The influence of the starting composition on the net content and on structure was studied for a series of samples. Lattice parameters as derived from Rietveld refinement deviated significantly among different samples. Relations between structure geometry, superconducting transition temperature, the residual resistance ratios and composition of the samples were discussed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.