This study presents “K0.5Na0.5NbO3-based” Pb-free smart material 0.80(K0.5Na0.5NbO3)–0.20(Ba0.9Sr0.1TiO3) (KBST20) as exhibiting zero thermal expansion (ZTE) at low temperatures (T≤ 100 K) with long-range cubic symmetry stable over a wide temperature range (9 K ≤T≤ 500 K). The linear coefficient of the thermal expansion (αl) obtained from temperature-dependent neutron diffraction data is in the range of 0.255–5.75 × 10−6 K–1 (9–500 K), which is rarely observed for Pb-free materials possessing long-range cubic symmetry. The temperature-dependent dielectric data of KBST20 exhibits a strong relaxational behavior with high frequency dispersion (ΔT≈ 27 K), suggesting the presence of polar phased regions known as polar nano regions. The ZTE has been attributed to enhanced correlations among PNRs exhibiting ferroelectrostriction. Furthermore, temperature-dependent Raman scattering data reveal polar monoclinic distortion at short ranges rather than cubic symmetry at long ranges. In addition, the intensity of Raman modes increases with the decrease in temperature, suggesting enhancement of the polar phase at low temperatures, which consequently leads to zero thermal expansion in KBST20.

中文翻译：

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无铅弛豫铁电体中平均立方结构中零热膨胀的起源


本研究提出了“K0.5Na0.5NbO3 基”无铅智能材料 0.80（K0.5Na0.5NbO3）–0.20（Ba0.9Sr0.1TiO3） （KBST20），在低温 （T≤ 100 K） 下表现出零热膨胀 （ZTE），在很宽的温度范围内 （9 K ≤T≤ 500 K） 保持长距离立方对称性。从温度相关的中子衍射数据获得的热膨胀线性系数 （αl） 在 0.255-5.75 × 10-6 K-1 （9-500 K） 之间，这对于具有长距离立方对称性的无铅材料来说很少见。KBST20 的温度依赖性介电数据表现出高频色散 （ΔT≈ 27 K 的强弛豫行为，表明存在称为极性纳米区域的极性相区域。ZTE 归因于表现出铁电致伸缩的 PNR 之间的增强相关性。此外，与温度相关的拉曼散射数据揭示了短距离的极性单斜畸变，而不是长距离的三次对称性。此外，拉曼模式的强度随着温度的降低而增加，表明在低温下极性增强，从而导致 KBST20 的热膨胀为零。