Direct observation of the near-surface layer in   Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ using neutron diffraction
  Spatially resolved neutron diffraction as a function of crystal depth in Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ reveals the presence of a distinct near-surface region. A dramatic change in both the lattice constant and the Bragg peak intensity as a function of crystal depth is observed to occur in this region over a length scale $\sim$ 100 $\mu$m. This confirms a previous assertion, based on a comparison between high-energy x-rays and neutrons, that such a near surface region exists in the relaxors. Consequences to both single crystal and powder diffraction measurements and previous bulk neutron diffraction measurements on large single crystals are discussed. 
K. Conlon, H. Luo, D. Viehland, J. F. Li, T. Whan, J.H. Fox, C. Stock,   G. Shirane