The paper is concerned with the structure and functional properties of bismuth ferrite–barium titanate, 0.75BiFeO₃–0.25BaTiO₃, solid solutions. Such materials are attracting attention due to their potential applications in high temperature piezoelectric transducers for use in demanding environments in process monitoring, for example. The article focuses on the mechanism of incorporation of the minor dopant lanthanum oxide, either in the form of isovalent or donor-type substitution. It is shown that the development of chemical heterogeneity in the form of core–shell grain microstructures, linked to donor-type substitution, plays a key role in controlling the functional behaviour. The use of an air-quenching procedure results in dramatic improvements in the ferroelectric properties, accompanied by a transformation of the shell regions from a pseudo-cubic, Pmm, to rhombohedral, R3c, structure. These observations are interpreted in terms of a novel mechanism involving nanoscale phase separation in the ‘shell’ regions during slow cooling, which impedes the development of ferroelectric ordering and leads to the formation of a nano-polar relaxor ferroelectric state. The work highlights the importance of immiscibility in bismuth-based ferroelectric perovskite solid solutions and illustrates how their ferroelectric, piezoelectric, dielectric energy storage, ferromagnetic and magneto-electric properties can be tuned by consideration of the substitution mechanism and control of thermal processing parameters.

中文翻译：

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在的BiFeO无铅功能性质的优化₃ -BaTiO _3个陶瓷通过的La ³⁺替代战略†

本文关注的是0.75BiFeO ₃ –0.25BaTiO _3的铁酸铋铋钛酸盐的结构和功能特性。，坚实的解决方案。此类材料由于其在高温压电换能器中的潜在应用而受到关注，例如，高温压电换能器可用于苛刻环境中的过程监控。本文着重介绍了以等价或供体型取代形式掺入次要掺杂镧镧的机理。研究表明，以核-壳型晶粒微结构的形式发展的化学异质性与供体类型的替代有关，在控制功能行为方面起着关键作用。空气淬火过程的使用大大改善了铁电性能，并伴随着壳区从拟立方Pm m转变为菱面体R 3 c的转变。， 结构体。这些观察结果是根据一种新颖的机理解释的，该机理涉及在缓慢冷却过程中“壳”区域中的纳米级相分离，这阻碍了铁电有序化的发展，并导致形成了纳米极性弛豫铁电态。这项工作强调了在铋基铁电钙钛矿固溶体中不溶混的重要性，并说明了如何通过考虑替代机理和控制热处理参数来调节其铁电，压电，介电储能，铁磁和磁电性能。