Banerjee D, Dey C C, Kumar Ravi, Modak Brindaban, Hazra Snehamoyee, Datta Subarna, Ghosh Barnali, Thakare S V, Jha S N, Bhattacharyya D
Radiochemistry Division (BARC), Variable Energy Cyclotron Centre, Kolkata 700064, India.
Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.
Phys Chem Chem Phys. 2023 Aug 16;25(32):21479-21491. doi: 10.1039/d3cp00062a.
In recent times, ultra-thin films of hafnium oxide (HfO) have shown ferroelectricity (FE) attributed to the orthorhombic (o) phase of HfO with space group 2. This polar o-phase could be stabilized in the doped thin film of the oxide. In the present work, both polar and non-polar o-phases of HfO could be stabilized in Gd-doped bulk polycrystalline HfO. Rietveld analysis of XRD data shows that the relative population of o-phases in the presence of the monoclinic (m) phase of HfO increases with increasing Gd-content. The local environment around the host atom has been investigated by time differential perturbed angular correlation (TDPAC) spectroscopy, synchrotron based X-ray near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements showed a reduction in grain size with increasing Gd-dopant indicating a solute drag effect. It could be established that the segregation of the Gd-dopant in the grain boundary is a thermodynamically favorable process and the solute drag effect plays an important role in nucleation of the o-phase in bulk HfO. Stabilization of Gd in both and 2 phases of HfO was supported by defect formation energy calculations using density functional theory (DFT). The present study has important implications in future applications of HfO in ferroelectric devices and in understanding the role of dopants in stabilizing the o-phase of HfO in the bulk.
近年来，氧化铪（HfO）超薄膜已显示出铁电性（FE），这归因于具有空间群2的氧化铪的正交（o）相。这种极性o相可以在氧化物的掺杂薄膜中稳定存在。在本工作中，氧化铪的极性和非极性o相都可以在掺钆块状多晶氧化铪中稳定存在。对XRD数据的Rietveld分析表明，在存在氧化铪单斜（m）相的情况下，o相的相对含量随钆含量的增加而增加。通过时间微分扰动角关联（TDPAC）光谱、基于同步加速器的X射线近边结构（XANES）和扩展X射线吸收精细结构（EXAFS）测量研究了主体原子周围的局部环境。场发射扫描电子显微镜（FESEM）和透射电子显微镜（TEM）测量表明，随着钆掺杂剂的增加，晶粒尺寸减小，表明存在溶质拖拽效应。可以确定，钆掺杂剂在晶界处的偏析是一个热力学上有利的过程，溶质拖拽效应在块状氧化铪中o相的成核过程中起重要作用。使用密度泛函理论（DFT）进行的缺陷形成能计算支持了钆在氧化铪的 和2相中的稳定化。本研究对氧化铪在铁电器件中的未来应用以及理解掺杂剂在稳定块状氧化铪的o相中的作用具有重要意义。
