Mixed anion control of enhanced negative thermal expansion in the oxysulfide of PbTiO3

TL;DR

This study demonstrates that substituting sulfur for oxygen in PbTiO3 significantly enhances its negative thermal expansion over a broad temperature range, offering a new approach to develop high-performance thermal expansion compensators.

Contribution

It introduces a novel anion substitution method to improve NTE in PbTiO3, expanding the temperature range and magnitude of negative thermal expansion.

Findings

Enhanced NTE with a volumetric coefficient of -2.50 × 10^{-5}/K over 300-790 K.

Compared to pristine PbTiO3, which has -1.99 × 10^{-5}/K from RT to 763 K.

S substitution increases tetragonality and hybridization, boosting NTE.

Abstract

The rare physical property of negative thermal expansion (NTE) is intriguing because materials with large NTE over a wide temperature range can serve as high-performance thermal expansion compensators. However, applications of NTE are hindered by the fact that most of the available NTE materials show small magnitudes of NTE, and/or NTE occurs only in a narrow temperature range. Herein, for the first time, we investigated the effect of anion substitution instead of general Pb/Ti-site substitutions on the thermal expansion properties of a typical ferroelectric NTE material, PbTiO3. Intriguingly, the substitution of S for O in PbTiO3 further increases the tetragonality of PbTiO3. Consequently, an unusually enhanced NTE with an average volumetric coefficient of thermal expansion $\bar{\alpha}_V$ = -2.50 $\times$ 10$^{-5}$/K was achieved over a wide temperature range (300 -- 790 K), which is contrasted to that of pristine PbTiO3 ($\bar{\alpha}_V$ = -1.99 $\times$ 10$^{-5}$/K RT -- 763 K). The intensified NTE is attributed to the enhanced hybridization between Pb/Ti and O/S atoms by the substitution of S, as evidenced by our theoretical investigations. We therefore demonstrate a new technique for introducing mixed anions to achieve large NTE over a wide temperature range in PbTiO3-based ferroelectrics.