Depth dependant element analysis of PbMg_1/3Nb_2/3O₃ using muonic x-rays

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Relaxor ferroelectrics like lead magnesium niobate (PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$) are promising piezoelectric materials when doped with lead titanate (PbTiO$_{3}$).
• Previous studies indicate two distinct phases in these materials: one in the bulk and another in near-surface regions.
• The origin of these observed phase differences remains unclear.

Purpose of the Study:

• To investigate the elemental composition and phase distribution within lead magnesium niobate (PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$).
• To elucidate the cause of the distinct near-surface and bulk phases in this relaxor ferroelectric system.
• To analyze depth-dependent compositional variations using advanced experimental techniques.

Main Methods:

• Negative muon implantation (µ+SR) experiments were conducted to probe the material's composition at various depths.
• Depth-dependent analysis was performed to assess elemental distribution.
• Charge neutrality was considered in the interpretation of compositional changes.

Main Results:

• Lead (Pb) content was found to be uniform across all measured depths.
• Significant changes in magnesium (Mg) and niobium (Nb) content were observed in the near-surface region (below 100 μm).
• Specifically, at a 60 μm implantation depth, a 25% increase in Mg and a 5% decrease in Nb were detected, maintaining charge neutrality.

Conclusions:

• The observed 'skin effects' in lead magnesium niobate (PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$) are attributed to variations in elemental concentration.
• These compositional changes in the near-surface region directly influence the unit cell structure and lead to the formation of distinct phases.
• The study clarifies the origin of phase heterogeneity in PMN-based relaxor ferroelectrics.