The first case would give rise to a polar crystal structure, since all atoms on the Sb position would move in the same direction away from the (004) plane. When refining the single crystal data against this model using one unique Sb position, however, the Sb atom does not move significantly away from the mirror plane and large residual electron density peaks appear around the Sb position, suggesting an unaccounted degree of disorder. In fact, when reintroducing the split site through a supplementary Sb position on the supposedly empty site, Figure , one obtains a significantly better fit, suggesting that the structure at room temperature is not macroscopically polar.