Rare-earth solid-state NMR spectroscopy of intermetallic compounds: The case of the 175Lu isotope.

Abstract

The feasibility of high-resolution 175Lu solid-state NMR spectroscopy in intermetallic compounds crystallizing with cubic crystal structures is explored by magic-angle spinning NMR at different magnetic flux densities. The large quadrupole moment of this isotope (3.49\u202f×\u202f10-28 m2) restricts observation of the NMR signal to nearly perfectly ordered crystalline samples. Signals are successfully detected and analyzed in the binary pnictides LuPn (NaCl-type structure; Pn\u202f=\u202fP, As, Sb) and the intermetallic compounds LuPtSb and LuAuSn, both crystallizing with the MgAgAs-type structure. Sources of line broadening are discussed based on field-dependent static and MAS-NMR spectra, providing guidance with respect to measurement conditions resulting in reliable results. The results highlight the importance of ionic/covalent bonding effects for the detectability of the signal, which reduce the probability of real structure effects commonly observed in intermetallic compounds. No 175Lu NMR signals can be observed in various cubic Heusler compounds. This is attributed to mixed site occupancies and other structural defects producing electric field gradients whose interaction with the 175Lu quadrupole moments broadens the signal beyond detection.