Structure of Pb(Fe_2/3W_1/3)O₃ single crystals with partial cation order

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Lead iron tungstate (PFWO) is a complex perovskite relaxor with challenging multifunctional properties.
• Decades of research have yet to fully elucidate the exact nature of PFWO's properties.
• Previous studies suggested complete disorder of B-cations in PFWO.

Purpose of the Study:

• To conduct a comprehensive structural investigation of PFWO single crystals.
• To clarify the cation ordering and structural characteristics of PFWO.
• To re-evaluate existing interpretations of PFWO's properties based on new structural insights.

Main Methods:

• Single-crystal synchrotron X-ray diffraction (XRD) at 100-450 K.
• High-resolution transmission electron microscopy (HRTEM).

Main Results:

• Observed {h+½, k+½, l+½} superlattice reflections for the first time in PFWO.
• Determined PFWO crystal structure as partly ordered cubic perovskite (Fm-3m).
• Explained weak ferromagnetism and excess magnetic moment by non-random Fe cation distribution.
• Identified Pb displacement disorder along <100> directions.
• Confirmed long-range order (Fm-3m) with 1-2 nm coherence length via TEM.
• Found no significant chemical inhomogeneity in the studied PFWO crystal.

Conclusions:

• Partial cation ordering exists in PFWO, necessitating a re-evaluation of prior research.
• The observed ordering explains the magnetic properties of PFWO.
• Pb displacement disorder is present, contributing to the material's characteristics.
• The findings provide a more accurate structural model for PFWO.