Diffuse neutron scattering study of a disordered complex perovskite Pb(Zn_1/3Nb_2/3)O₃ crystal

Diffuse scattering around the (110) reciprocal lattice point has been investigated by elastic neutron scattering in the paraelectric and relaxor phases of the disordered complex perovskite crystal Pb(Zn_1/3Nb_2/3)O₃ (PZN). The appearance of a diffuse intensity peak indicates the formation of polar nanoregions at temperature T^*, approximately 40 K above T_c=413 K. The analysis of this diffuse scattering indicates that these regions are in the shape of ellipsoids, more extended in the 〈111〉 direction than in the 〈001〉 direction. The quantitative analysis provides an estimate of the correlation length ξ, or size of the regions, and shows that ξ_〈111〉∼1.2ξ_〈001〉, consistent with the primary or dominant displacement of Pb leading to the low-temperature rhombohedral phase. Both the appearance of the polar regions at T^* and the structural transition at T_c are marked by kinks in the ξ_〈111〉 curve but not in the ξ_〈001〉 one, also indicating that the primary changes take place in a 〈111〉 direction at both temperatures.