Stress-Induced Ferroelectricity in Hafnium Oxide Core-Shell Nanoparticles
Institute of Physics of the National Academy of Sciences of Ukraine（乌克兰国家科学院物理研究所）；Frantsevich Institute for Problems in Materials Science of the National Academy of Sciences of Ukraine（乌克兰国家科学院弗拉特谢维奇材料科学问题研究所）；Department of Materials Science and Engineering, University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校材料科学与工程系）；Zone 5 Technologies（第五区技术公司）
Anna N. Morozovska, Eugene A. Eliseev, Richard, Liu, Sergei V. Kalinin, Dean R. Evans
备注：
39 pages, including 4 figures and Supplementary Materials
In contrast to hafnia (HfO2) thin films, where the appearance of switchable ferroelectric polarization can be induced by strain or defect engineering, reliable methods for controlling ferroelectricity are absent in HfO2 nanoparticles. Direct experimental observations of ferroelectric hysteresis and ferroelectric domains in these nanoparticles are also absent. To the best of our knowledge, stress-induced ferroelectric states in the HfO2 nanoparticles have not been explored. In this work, we study the influence of chemical stress on phase diagrams, dielectric and polar properties of spherical HfO2 core-shell nanoparticles using a Landau-Ginzburg-Devonshire free energy functional that includes trilinear and biquadratic couplings involving polar, antipolar, and nonpolar order parameters. The ferroelectric phase exhibits reentrant behavior as a function of nanoparticle size, such that the spontaneous polarization exists only within a limited range of core radii R_c, namely R_cr^min<R_c<R_cr^max. The minimal critical radius R_cr^min is primarily determined by the size dependence of the depolarization field and correlation effects; the maximal critical radius R_cr^max is primarily determined by the size dependence of chemical stresses induced by the elastic defects in the shell. Thus, this work identifies a stress-driven mechanism for reentrant ferroelectricity stabilization in nanoscale HfO2 systems, arising from the competition between depolarization field-induced suppression of ferroelectricity and its stabilization by shell-induced chemical stress. We revealed that relatively large compressive chemical strains are necessary to induce the ferroelectric phase in the HfO2 nanoparticles. Successful chemical strain engineering opens the way for significant enhancement of nanoscale HfO2 polar properties for applications in advanced memory cells and logic devices.
Hafnium oxide (HfO2)-based ferroelectrics offer remarkable promise for memory and logic devices in view of their compatibility with traditional silicon CMOS technology, high switchable polarization, good endurance and thickness scalability. These factors have led to steep rise in research on this class of materials over the past number of years. At the same time, only a few reports on the direct sensing of nanoscale ferroelectric properties exist, with many questions remaining regarding the emergence of ferroelectricity in these materials. While piezoresponse force microscopy (PFM) is ideally …
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