Temperature-Induced Structural Phase Transitions In Rerhsn (Re = Y, Gd-Tm, Lu)

The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; gamma) 000 (No. 157.1.23.1) (gamma = 3/8 for TmRhSn and gamma = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh-Sn bonding. The modulation is expressed in a Sn-119 Mossbauer spectrum of DyRhSn at 78 K through line broadening.