Synthetically tuned structural variations in CePdxGe2−x (x = 0.21, 0.32, 0.69) towards diverse physical properties

Abstract

In this work, we have studied the structure and physical properties of a series of intermetallic compounds with the general formula CePd_xGe_2−x (where, x = 0.21, 0.32, 0.69). It was found that the compound crystallizes in three different phases with stoichiometries: CePd_0.32Ge_1.68, CePd_0.21Ge_1.79 and CePd_0.69Ge_1.31 by varying the Pd to Ge ratio. While CePd_0.32Ge_1.68 and CePd_0.69Ge_1.31 crystallize in the hexagonal AlB₂ structure type with the space group P6/mmm, CePd_0.21Ge_1.79 crystallizes in the tetragonal α-ThSi₂ structure type with the space group I4₁/amd. CePd_0.69Ge_1.31 is in fact an ordered superstructure of CePd_0.32Ge_1.68 with tripling of the c-lattice. Relative changes in the Pd/Ge ratio also impart substantial variation in their magnetic properties, although Ce is in the trivalent state in both the phases. CePd_0.21Ge_1.79 shows metamagnetic behavior below 10 K whereas CePd_0.69Ge_1.31 showed ferromagnetic behavior in the same temperature range. In addition to the metamagnetic behavior, CePd_0.21Ge_1.79 also shows spin glass behavior at low temperature. DFT calculations were used to obtain ulterior information on the CePd_0.69Ge_1.31 phase_. Self-consistent calculations revealed that the ferromagnetic ordering of the ground state arises from the spins at the Ce and Pd sites. The observed sharp rise in the low temperature resistivity of CePd_0.69Ge_1.31 is an indication of a pseudo-gap formation or possible Kondo behavior in the electronic density of states, enhancing the scattering of the charge carriers. Heat capacity measurements on CePd_0.69Ge_1.31 suggest that it falls in the category of medium heavy fermion compounds.