The so-called skin effect near the surface of a single crystal of relaxor ferroelectric may play an important role in piezoelectric micro- and nanoelectromechanical systems. The authors observe an unexpected transformation from a poling-induced, metastable tetragonal phase to a monoclinic $B$-type phase, which exhibits surprisingly weak bulk piezoelectricity. This discrepancy between microstructure and a macroscale property is understood in terms of a heterogeneous ``surface-interior'' structure, shedding light on the effects at play in tiny devices based on these materials.