Impact of Zr substitution on the electronic structure of ferroelectric hafnia

$\mathrm{HfO_2}$-based dielectrics are promising for nanoscale ferroelectric applications, and the most favorable material within the family is Zr-substituted hafnia, i.e., $\mathrm{Hf_{1-x}Zr_xO_2}$ (HZO). The extent of Zr substitution can be great, and x is commonly set to 0.5. However, the band gap of $\mathrm{ZrO_2}$ is lower than $\mathrm{HfO_2}$, thus it is uncertain how the Zr content should influence the electronic band structure of HZO. A reduced band gap is detrimental to the cycling endurance as charge injection and dielectric breakdown would become easier. Another issue is regarding the comparison on the band gaps between $\mathrm{HfO_2}$/$\mathrm{ZrO_2}$ superlattices and HZO solid-state solutions. In this work we systematically investigated the electronic structures of $\mathrm{HfO_2}$, $\mathrm{ZrO_2}$ and HZO using self-energy corrected density functional theory. In particular, the conduction band minimum of $Pca2_1$-$\mathrm{HfO_2}$ is found to lie at an ordinary k-point on the Brillouin zone border, not related to any interlines between high-symmetry k-points. Moreover, the rule of HZO band gap variation with respect to x has been extracted. The physical mechanisms for the exponential reduction regime and linear decay regime have been revealed. The band gaps of $\mathrm{HfO_2}$/$\mathrm{ZrO_2}$ ferroelectric superlattices are investigated in a systematic manner, and the reason why the superlattice could possess a band gap lower than that of $\mathrm{ZrO_2}$ is revealed through comprehensive analysis.Comment: 23 pages, 9 figure

In search of Pca21 phase ferroelectrics

In recent years, hafnia-based ferroelectrics have attracted enormous attention due to their capability of maintaining ferroelectricity below 10 nm thickness and excellent compatibility with microelectronics flow lines. However, the physical origin of their ferroelectricity is still not fully clear, although it is commonly attributed to a polar Pca 2 _1 orthorhombic phase. The high-temperature paraelectric phases (the tetragonal phase or the cubic phase) do not possess a soft mode at the Brillouin zone center, thus the ferroelectric distortion has to be explained in terms of trilinear coupling among three phonon modes in the tetragonal phase. It is necessary to explore new materials with possible ferroelectricity due to the polar Pca 2 _1 phase, which in turn should be very helpful in evaluating the microscopic theory for ferroelectric hafnia. In this work, based on the idea of the Materials Genome Engineering, a series of hafnia-like ferroelectrics have been found, exemplified by LaSeCl, LaSeBr, LuOF and YOF, which possess adequate spontaneous polarization values and also relatively favorable free energies for the polar phase. Their common features and individual differences are discussed in detail. In particular, a promising potential ferroelectric material, Pca 2 _1 phase LuOF, is predicted and recommended for further experimental synthesis and investigation

Comparative Study on Chemical Constituents of Medicinal and Non-Medicinal Parts of Flos <i>Abelmoschus manihot</i>, Based on Metabolite Profiling Coupled with Multivariate Statistical Analysis

According to Chinese Pharmacopoeia (2020 edition), Abelmoschi Corolla (AC) is the dried corolla of Flos Abelmoschus manihot (FAM). Market research has found that AC is often mixed with the non-medicinal parts in FAM, including calyx, stamen, and pistil. However, previous studies have not clarified the relationship between the medicinal and non-medicinal parts of FAM. In this study, in order to investigate whether there is any distinction between the medicinal and non-medicinal parts of FAM, the characterization of the constituents in calyx, corolla, stamen, and pistil was analyzed by UFLC-Triple TOF-MS/MS. Multivariate statistical analysis was used to classify and screen differential constituents between medicinal and non-medicinal parts of FAM, and the relative contents of differential constituents were compared based on the peak intensities. Results showed that 51 constituents in medicinal and non-medicinal parts of FAM were identified, and the fragmentation pathways to different types of constituents were preliminarily deduced by the fragmentation behavior of the identified constituents. Furthermore, multivariate statistical analysis revealed that the medicinal and non-medicinal parts of FAM differed significantly; 20 differential constituents were screened out to reveal the characteristics of metabolic differences. Among them, the relative contents of 19 differential constituents in the medicinal part were significantly higher than those in non-medicinal parts. This study could be helpful in the quality evaluation of AC as well as provide basic information for the improvement of the market standard of AC

Designing Wake‐Up Free Ferroelectric Capacitors Based on the HfO2/ZrO2 Superlattice Structure

Abstract The wake‐up phenomenon widely exists in hafnia‐based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at a higher temperature has been reported to be effective in eliminating wake‐up, but high temperature may yield the monoclinic phase or generate more oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of Hf0.5Zr0.5O2 (HZO) superlattice ferroelectrics, which involves heating from the Pt/ZrO2 interface side. It is demonstrated that 600 °C annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake‐up free nature and a switchable remnant polarization value of 27.4 µC cm−2. On the other hand, heating from the TiN/HfO2 side, or using 500 °C annealing temperature, could yield ferroelectric devices that require a wake‐up process. The special configuration of Pt/ZrO2 is verified by comparative studies with several other superlattice structures and HZO solid‐state solutions. It is discovered that heating from the Pt/HfO2 side at 600 °C leads to high leakage current and a memristor behavior. The mechanisms of ferroelectric phase stabilization and memristor formation have been discussed. The unidirectional heating method can also be useful for other hafnia‐based ferroelectric devices

Comparative Study on Chemical Constituents of Medicinal and Non-Medicinal Parts of Flos Abelmoschus manihot, Based on Metabolite Profiling Coupled with Multivariate Statistical Analysis

According to Chinese Pharmacopoeia (2020 edition), Abelmoschi Corolla (AC) is the dried corolla of Flos Abelmoschus manihot (FAM). Market research has found that AC is often mixed with the non-medicinal parts in FAM, including calyx, stamen, and pistil. However, previous studies have not clarified the relationship between the medicinal and non-medicinal parts of FAM. In this study, in order to investigate whether there is any distinction between the medicinal and non-medicinal parts of FAM, the characterization of the constituents in calyx, corolla, stamen, and pistil was analyzed by UFLC-Triple TOF-MS/MS. Multivariate statistical analysis was used to classify and screen differential constituents between medicinal and non-medicinal parts of FAM, and the relative contents of differential constituents were compared based on the peak intensities. Results showed that 51 constituents in medicinal and non-medicinal parts of FAM were identified, and the fragmentation pathways to different types of constituents were preliminarily deduced by the fragmentation behavior of the identified constituents. Furthermore, multivariate statistical analysis revealed that the medicinal and non-medicinal parts of FAM differed significantly; 20 differential constituents were screened out to reveal the characteristics of metabolic differences. Among them, the relative contents of 19 differential constituents in the medicinal part were significantly higher than those in non-medicinal parts. This study could be helpful in the quality evaluation of AC as well as provide basic information for the improvement of the market standard of AC