In-situ observation of ferroelectric-antiferroelectric structural evolution in Sr-modulated sodium niobate with unraveling the polarization origin

Abstract

Precisely modulating the stability of different electrical orderings is a central research direction in dielectrics, which plays a critical role in both the functional design of related electronic devices and the in-depth understanding of the transition pathways and origins among various ordering states. As a classical theoretical framework for regulating electrical ordering in perovskites, the tolerance factor rule has been extensively verified and applied in numerous systems. However, recent studies indicate that this typical golden criterion faces significant challenges when applied to the NaNbO3 (NN) system, because of its complex crystal structure and multiple electrical ordering transitions. Therefore, it is urgently necessary to expand multidimensional control parameters to advance the insights into electrical ordering regulation in NN-based system. Previous work has shown that the antiferroelectricity in NN is closely related to the intrinsic characteristic of the relatively light A-site Na atoms. Based on this, Na1-2xSrxNbO3 (NSN) ceramic system is designed in this work, where Sr2+ doping introduces a dual competitive effect involving heavier A-site ions to disrupt antiferroelectricity and a reduced tolerance factor to stabilize antiferroelectric order. This strategy aims to explore additional electrical-ordering regulation approaches in NN-based materials beyond the conventional tolerance factor method, as well as the coupling mechanisms between different regulatory factors. Furthermore, in-situ Raman spectroscopy is employed to precisely capture the evolution of various phonon vibrations under external fields, enabling a detailed analysis of the dynamic evolution of the electrical ordering structure in NSN series. The results indicate that Sr2+ doping further reduces the free energy barrier between the ferroelectric and antiferroelectric phases, stabilizing the ferroelectric phase at room temperature. Additionally, the intrinsic ferroelectric order is induced in low-temperature antiferroelectric region, by disrupting the antiparallel displacement of A-site ions and the antiparallel tilting of adjacent NbO6 octahedra. This study focuses on NN-based materials to investigate the evolution of multiple electrical orderings in dielectrics, thereby providing an important research foundation for improving the comprehending of phase transition mechanism among different electrical orderings and for designing NN-based electronic devices with coexisting of multiple electrical orderings.