Lattice Expansion of Ultrafine Cr Particles

The temperature dependence of the lattice constant and the diffraction intensity profiles of ultrafine bcc Cr particles with 750 A in the average diameter were investigated by X-ray diffraction and least-squares pattern fitting methods in a wide temperature range from 88 K to 375 K. Coefficient of a thermal expansion differed by about 30% at T > T N and 10% at 170 K < T < T N respectively from the bulk data. New extra peak was observed below about 210 K at the low angle side of the observed 110, 211 and 310 reflection positions for the bcc Cr structure. The feature in the experimental results was discussed on the basis of a lattice expansion which was closely related to an enhancement of the magnitude of the magnetic moments relative to the maximum value of the spin density wave in bulk Cr.