Determination of 137Ba nuclear quadrupole interactions in solids: a comparison of high field and zero field approaches.

137Ba nuclear quadrupole interactions (NQI) are measured in zero field using nuclear quadrupole resonance (NQR) for a series of compounds, (BaBr2.2H2O, BaCl2.2H2O, BaSO4, BaMoO4, BaCO3) where values of the quadrupole interaction have previously been reported using frequency stepped and/or ultra high (21.1 T) magnetic field NMR. Typically barium can show large quadrupole coupling constants (CQ > 10 MHz). In addition barium phosphate Ba3(PO4)2 has not previously been investigated experimentally by nuclear resonance. In the present work, theoretical prediction of a very large 137Ba coupling constant for one of the two Ba sites, Ba(1) (12-coordinated), in Ba3(PO4)2 shows good agreement with the NQR measurement. The small NQI 137Ba coupling constant for the Ba(2) site (10-coordinated) in Ba3(PO4)2 has been derived from the second-order perturbed NMR lineshape. The development of the observation of barium by magnetic resonance is briefly reviewed to provide some perspective on the current study. On the basis of the results presented here, the accuracy and straightforward nature of the zero field NQR approach offers advantages for potential in operando experiments that are difficult at high field.