Crystal Structure and Magnetic Properties of High-Pressure Phases RESi₃ (RE=Tb, Dy, Er, Tm)

The new metastable binary rare-earth metal trisilicides RESi3 (RE=Tb, Dy, Er, and Tm) are obtained by high-pressure high-temperature synthesis (9.5 GPa, 823-923 K). Powder diffraction data refinements reveal that their crystal structure is isotypic to that of YbSi3, and the values of cell parameters and cell volumes decrease from Tb to Tm. Magnetic measurements on the compounds indicate Curie-Weiss paramagnetic behavior and antiferromagnetic ordering at low temperatures. The values for T-N follow a de Gennes scaling pointing towards Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Upon heating at ambient pressure, the RESi3 compounds decompose into Si and RESi2-x.The new high-pressure phases TbSi3, DySi3, ErSi3 and TmSi3 adopt atomic arrangements in which two-dimensional building units of silicon are separated by rare-earth metal atoms. The silicon environment with five short Si-Si contacts in connection with the formal charge Si- is incompatible with the classical 8-N rule. This is confirmed by earlier quantum chemical methods evidencing a mixture of two-atomic Si-Si bonds and multiatomic interactions involving lone-pairs located at silicon atoms. Consequently, the rare-earth metal trisilicides do not belong to the class of electron-precise Zintl phases, which is consistent with their earlier observed character of covalent metals. This result is in concert with the present study revealing that compounds RESi3 (RE=Gd-Tm) follow a de Gennes scaling, which is based on a magnetic coupling via conduction electrons.