Berlin 2005 – scientific programme
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M: Metallphysik
M 17: Phasenumwandlung II
M 17.5: Talk
Saturday, March 5, 2005, 12:00–12:15, TU H1058
Structural Phase Transition in Tb5(Si0.6Ge0.4)4 at Low Temperature — •Andreas Kupsch1,2, Alexandr Levin1, Dirk C. Meyer1, and Peter Paufler1 — 1Institut für Strukturphysik, TU Dresden, 01062 Dresden — 2BAM, VIII.32, 12200 Berlin
The occurrence of the giant magnetocaloric effect (MCE) has been measured with various rare earth- Si/Ge compounds. The magnetic phase transition from the high temperature paramagnetic to the low temperature ferromagnetic phase is accompanied by a structural phase transition. We report on crystallographic details of a transition measured with powdered Tb5(Si0.6Ge0.4)4 at low temperatures (150 and 130 K), for which the MCE was observed at Tc = 150 K . The pseudo-binary compound is monoclinic at room temperature (P1121/a). Changes of reflection intensities and positions in the diffraction patterns indicate a structural phase transition between 150 K and 100 K, where the compound orders in an orthorhombic structure (Pnma). Split-up crystallographic sites of the monoclinic unit cell degenerate to sites of higher symmetry in the orthorhombic structure. It turned out that both phases coexist at the selected temperatures but the phase content changes significantly. As already reported for Gd5Si2Ge2 the key feature of the structural phase transition is a shear movement of pairs of flat atomic units along the crystallographic a direction by 0.84 Å and tremendous changes of selected (Si/Ge)-(Si/Ge) distances up to 0.95 Å.