Structural changes of piezoelectric La3Ga5SiO14 induced by paramagnetic ions revealed by 71Ga multiple quantum magic angle spinning

Experimental evidence that nuclear magnetic resonance (NMR) can detect structural changes of piezoelectric La3Ga5SiO14 induced by dilute paramagnetic ions is presented. Gd3+ and Eu3+ cations have been incorporated into La3Ga5SiO14 monocrystals. As expected, the line-width of the tetrahedral 29Si magic angle spinning (MAS) NMR spectra as well as the inverse of the T2 relaxation time of 71Ga increases with the concentration of the paramagnetic ions. A surprising result is shown by 71Ga multiple quantum (MQ) MAS NMR spectrum, which changes with the concentration of paramagnetic ions. The changes in the 71Ga MQMAS spectra can be explained by a more ordonated distribution of Ga ions inside the oxygen tetrahedra. The 71Ga MQMAS NMR spectra allow identification of the one octahedral and two tetrahedral Ga sites.