Doping-induced Polyamorphic Transitions in Fluorite Oxides

TL;DR

This study reveals that Ba doping induces a stable polyamorphic transition in fluorite oxides like HfO$_2$, creating a semi-ordered amorphous phase with enhanced electronic properties, useful for high-$k$ dielectric applications.

Contribution

It demonstrates a novel doping-induced polyamorphic transition in fluorite oxides, leading to a stable semi-ordered amorphous phase with improved dielectric properties.

Findings

Ba doping triggers a stable semi-ordered amorphous phase.

The semi-ordered phase has a wider bandgap and higher dielectric constant.

This structural motif is applicable to other doped fluorite oxides.

Abstract

Fluorite oxides such as HfO$_2$ exhibit rich and tunable phase behavior, making them promising candidates for next generation electronic devices. A key challenge is to design amorphous HfO$_2$-based high-$k$ materials with both structural and performance stability. Here, using molecular dynamics simulations supported by experimental measurements, we reveal that Ba doping stimulates a polyamorphic transition in HfO$_2$, yielding a semi-ordered amorphous (SA) phase characterized by disordered oxygens embedded within an ordered metal sublattice. We find that this phase arises from degenerate short-range symmetry breaking modes, consistent with Pauling's parsimony rule. Notably, the SA structure is thermodynamically stable and displays a wider bandgap and higher dielectric constant than conventional random-packing amorphous structure, owing to suppressed subgap states and increased Born effective charges. We further demonstrate that this structural motif generalizes to Ba-, Sr-, and Ca-doped HfO$_2$ and ZrO$_2$, establishing a broadly applicable strategy for designing high-performance amorphous dielectrics.