where u(t) is a unit vector from the center of mass of the polyanion (O or P) to a covalentlybonded atom (H or S). We observe faster reorientation in the GBs of the Li 2 OHCl (Figure ), which we propose is due to anions rotating to oppose local perturbations in the electrostatic potential. The GBs in Li 3 PS 4 also show greater degrees of reorientation (Figure ), which may act in tandem with the larger S ion to screen electric fields, though the PS 4 polyanion does not have as strong a dipole as OH.