Achieving negative thermal expansion over an extended temperature range in rare-earth-modified PbTiO3-based perovskites

Negative thermal expansion (NTE) is a notable physical property where a material’s volume decreases instead of increasing when heated. The identification of NTE materials is crucial for thermal expansion control engineering. Most NTE materials exhibit NTE only within a narrow temperature range, restricting their applications. Achieving NTE across a broad temperature range remains a significant challenge. This study developed a novel PbTiO₃-based system, (1-x)PbTiO₃–xBiLuO₃, incorporating rare-earth elements, using a distinctive high-pressure and high-temperature synthesis technique. We achieved NTE across a broad temperature range by coupling lattice (c/a) with ferroelectric order parameters. The incorporation of BiLuO₃ resulted in distinctive ferroelectric characteristics, including increased tetragonality, spontaneous polarization, and NTE over a broad temperature range. NTE over an extended temperature range has been achieved in 0.95PbTiO₃–0.05BiLuO₃ (\(\overline{\alpha }_{{\text{V}}}\) = −1.7 × 10^–5 K⁻¹, 300–840 K) and 0.90PbTiO₃–0.10BiLuO₃ (\(\overline{\alpha }_{{\text{V}}}\) = −1.4 × 10^–5 K⁻¹, 300–860 K), compared to pristine PbTiO₃ (\(\overline{\alpha }_{{\text{V}}}\) = −1.99 × 10^–5 K⁻¹, 300–763 K). The improved tetragonalities and broader NTE temperature range result from the strong hybridization of Pb/Bi–O and Ti/Lu–O atoms, as demonstrated by combined experimental and theoretical analyses, including high-energy synchrotron X-ray diffraction, Raman spectroscopy, and density functional theory calculations. This study introduces a novel example of NTE over a broad temperature range, highlighting its potential as a high-performance thermal expansion compensator. Additionally, it presents an effective method for incorporating rare-earth elements to achieve NTE in PbTiO₃-based perovskites across a wide temperature range.

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