Cocktail Effect at the B-Site of Hexagonal ABO₃: Structural Evolution and High Entropy Low Loss Dielectrics

Area of Science:

• Materials Science
• Solid State Chemistry
• Oxide Materials

Background:

• High entropy oxides (HEOs) are promising for advanced functionalities.
• Stabilizing HEOs in ion-size-sensitive structures like hexagonal ABO3 (P63cm) presents challenges.
• Hexagonal ABO3 structures exhibit improper ferroelectricity due to non-centrosymmetric ion placement.

Purpose of the Study:

• To stabilize a novel high entropy YInO3-based hexagonal composition.
• To investigate the impact of compositional randomization on structural and electrical properties.
• To explore potential applications in advanced electronic devices.

Main Methods:

• Synthesis of single-phasic hexagonal polymorphs: YInO3, Y(In0.5Mn0.5)O3, Y(In0.33Mn0.33Fe0.33)O3, and Y(In0.25Mn0.25Fe0.25Ga0.25)O3.
• Characterization using X-ray diffraction (XRD) and Raman spectroscopy to confirm phase purity and structural randomization.
• Calvet calorimetry to determine enthalpy of formation and confirm entropy stabilization.
• Analysis of thermal expansion and microstructural properties.

Main Results:

• Successfully synthesized single-phasic hexagonal polymorphs of YInO3 with increasing B-site substitution.
• XRD and Raman data indicated a single hexagonal phase with significant structural randomization and decreased grain size.
• Entropy stabilization was confirmed by positive enthalpy of formation.
• Differential thermal expansion was observed, with a/b-axes showing double expansion compared to the c-axis.
• Y(In0.25Mn0.25Fe0.25Ga0.25)O3 demonstrated a low dielectric loss (~0.0085) and ultra-low leakage current (5.2 × 10⁻¹⁰ A/cm² up to 150 °C).

Conclusions:

• Novel high entropy hexagonal YInO3-based compositions were successfully stabilized.
• Entropy stabilization was confirmed through calorimetric measurements.
• Compositional randomization influenced structural characteristics and thermal expansion behavior.
• The Y(In0.25Mn0.25Fe0.25Ga0.25)O3 composition exhibited significantly improved dielectric and leakage properties compared to undoped YInO3.