Direct observation of B ‐site cation displacements in Pb‐based complex perovskite relaxor oxides

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg 1/3 Nb 2/3 O 3 (PMN) crystallites and PbZn 1/3 Nb 2/3 O 3 (PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high‐angle annular dark‐field (HAADF) images recorded via an aberration‐corrected STEM show that the B ‐site cations in PMN and PZN undergo correlated and long‐range displacements towards the Pb 2+ ions on the (110) planes. The planar B ‐site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long‐range planar displacements of the Pb 2+ ions. The observed Pb 2+ ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards the B ‐site columns. There is also evidence of possible stress‐related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long‐range planar B ‐site spatial displacement on the (110) planes, correlated with the Pb 2+ ions, possibly resulting in the observed diffuse streaking; the other is short‐range Pb 2+ ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and the B ‐site cations in which the B sites undergo the largest spatial displacements towards the Pb ions along 〈110〉.