Local atomic arrangement in LaCuAl₃ and LaAuAl₃ by NMR and density functional theory

CeCuAl₃ and CeAuAl₃, crystallizing in the non-centrosymmetric BaNiSn₃ tetragonal structure, are known mainly for their unusual neutron scattering spectra involving additional excitations ascribed to vibron quasi-bound quantum state in CeCuAl₃ and anti-crossing of phonon and crystal field excitations in CeAuAl₃. In this work, we present results of nuclear magnetic resonance (NMR) experiments on their lanthanum analogues-[Formula: see text] and [Formula: see text]. The character of NMR spectra of [Formula: see text], [Formula: see text], and ⁶⁵Cu measured in [Formula: see text] and [Formula: see text] is dominated by electric quadrupole interaction. The spectral parameters acquired from experimental data are confronted with values obtained from the electronic structure calculations. The results show remarkable differences for the two compounds. The [Formula: see text] spectrum in [Formula: see text] can be interpreted by a single spectral component corresponding to uniform environment of La atoms in the crystal structure, whereas for [Formula: see text] the spectrum decomposition yields a wide distribution of spectral parameters, which is not possible to explain by a single La environment, and multiple non-equivalent La positions in the crystal structure are required to interpret the spectrum.