The phase diagram of YbInCu4

Ytterbium ions in YbInCu4 change their valence from 3(+) at 300 K to an ave rage value of about 2.9(+) between 40 and 70 K. The exact temperature of th e phase transition was in discussion for many years and experiments on diff erent samples of 'YbInCu4' show different results. The temperature of the p hase transition depends on the composition of the grown crystals. Therefore , we have investigated the phase diagram - especially the solidus surface - of the system Yb-Tn-Cu in the neighbourhood of YbInCu4 and the valence tra nsition temperatures of single crystals with different compositions. DTA me asurements were carried out and energy and wavelength dispersive microanaly sis as well as low temperature X-ray diffraction were used for characteriza tion. The crystals with a copper-deficiency show near 40 K a valence transi tion, whereas 70 K is seen for crystals with an excess of copper. (C) 1999 Elsevier Science B.V. Ail rights reserved.