Quantitative correlation between structural (dis-)order and diffuseness of phase transition in lead scandium tantalate

TL;DR

This study establishes a universal linear correlation between structural order and transition diffuseness in lead scandium tantalate, linking microscopic structure to macroscopic dielectric behavior without changing composition.

Contribution

It demonstrates a direct, universal relationship between structural order and phase transition diffuseness in PST, tunable via thermal annealing without altering stoichiometry.

Findings

Linear correlation between structural order and diffuseness parameter

Universal relation independent of sample form and dielectric permittivity

Diffuseness can be tuned by thermal annealing without changing composition

Abstract

Ferroelectrics show a phase transition to a paraelectric phase at a well-defined transition temperature. Introducing disorder makes this transition diffuse, and the system becomes a relaxor. Since the degree of (dis-)order is usually manipulated by varying the chemical composition, it is difficult to establish a direct relationship between disorder and the degree of diffuseness. Perovskite structured lead scandium tantalate (Pb[Sc$_{1/2}$Ta$_{1/2}$]O$_3$, PST) offers the opportunity to tune the character of the transition by thermal annealing without changing the stoichiometry. Here it is demonstrated that there is a linear correlation between the structural ordering, quantified by the intensity ratio $S$ of the pseudocubic (111)/(200) x-ray diffraction peaks, and the diffuseness parameter $\gamma$ deduced from temperature-dependent dielectric spectroscopy. The relation is universal, independent of whether the sample is a thin film, multilayer capacitor or bulk ceramic, and also independent of the absolute value of the dielectric permittivity.