Structural, magnetic, and thermal characteristics of the phase transitions in Gd 5Ga xGe 4−x magnetocaloric materials

Abstract

Temperature-dependent, single crystal and powder X-ray diffraction studies as well as magnetization, and heat capacity measurements were carried out on two phases of the Gd 5Ga x Ge 4− x system: for x=0.7 and 1.0. Gd 5Ga 0.7Ge 3.3 shows three structure types as a function of temperature: (i) from 165 K to room temperature, the orthorhombic Sm 5Ge 4-type structure exists; (ii) below 150 K, it transforms to a orthorhombic Gd 5Si 4-type structure; and (iii) a monoclinic Gd 5Si 2Ge 2-type component is observed for the intermediate temperature range of 150 K≤ T≤165 K. This is the first time that all these three structure types have been observed for the same composition. For Gd 5Ga 1.0Ge 3.0, the room temperature phase belongs to the orthorhombic Pu 5Rh 4-type structure with interslab contacts between main group atoms of 2.837(4) Å. Upon heating above 523 K, it transforms to a Gd 5Si 4-type structure with this distance decreasing to 2.521(7) Å before decomposing above 573 K.