Ferroelectric Hf0.5Zr0.5O2 films, 5.8 nm in thickness, were deposited on Nb:SrTiO3 semiconductor substrates to form a Pt/Hf0.5Zr0.5O2/Nb:SrTiO3 metal/ferroelectric/semiconductor ferroelectric tunnel junction (FTJ). A high tunneling electroresistance ratio of 800 was achieved at room-temperature. It is observed that in the low resistance state, the transport characteristic obeys direct tunneling, while in the high resistance state, it is dominated by thermal emission. It implies that the Schottky barrier on the surface of the semiconductive electrode is modulated by the polarization in the ferroelectric Hf0.5Zr0.5O2 barrier, generating the high electroresistance ratio. The FTJ also exhibits excellent retention for more than 10 000 s and good switching endurance for more than 1500 cycles. The results suggest the potential of this HfO2-based FTJ for next generation nonvolatile memories.
Organic-inorganic hybrid ferroelectrics (OIHFs) have fueled enormous interest benefiting from their less environmental pollution, performance-tailored functionality, low product costs as well as tunability of structures. However, the lack of material synthesis approaches and diverse targeted molecular design is a stumbling block for designing novel OIHFs rationally. Here, we report a unique organic-inorganic hybrid ferroelectric (3,3-difluoropyrrolidine)2CdCl4 1 and another novel nonferroelectric crystal (3,3-difluoropyrrolidine)2Cd2Cl6 2 by changing various crystallization solvents. Significantly, 1 presents a ferroelectric phase transition behavior at ∼367 K, and the distinct symmetry breaking, i.e., mmmFm, sets up a biaxial ferroelectric with four equivalent directions of polarization, which has a P r ∼ 0.77 μC/cm2. Systematic studies prove that ferroelectricity can be ascribed to the synergistic effects of the distortion of the inorganic anion skeleton and the ordering of organic cations. This work reveals the potential of constructing novel ferroelectrics based on the solvent selective effect and pyrrolidinium as organic cations.
Hf0.5Zr0.5O2 (HZO) thin films have been deposited on (110)-oriented SrTiO3 (STO) substrates buffered with epitaxial La0.7Sr0.3MnO3 (LSMO) by pulsed laser deposition. The HZO/LSMO/STO heterostructures show smooth surface and clear interface. It is observed that ferroelectric orthorhombic HZO is enhanced, as non-polar tetragonal HZO is suppressed with the increasing LSMO thickness or decreasing HZO thickness. Completely orthorhombic HZO films are achieved with desired LSMO and HZO thickness. These HZO films are (111)-oriented with in-plane [2¯11] and [01¯1] directions along LSMO [11¯0] and [001], respectively, and exhibit ferroelectric properties at room temperature with an optimized remanent polarization around 26 μC/cm2 without the need of a wake-up process, a long retention up to 104 s and a fatigue endurance up to 109 cycles. Epitaxial HfO2-based films with robust ferroelectric properties deposited on (110)-oriented STO substrates provide additional opportunities to understand the profound effects of orientation, strain, and interface microstructures on the metastable polar phases and ferroelectric properties of HfO2 thin films.
ObjectiveTo investigate how body fat influences glucose metabolism and hormone profiles in women with polycystic ovary syndrome (PCOS), compared to women without PCOS.MethodsWe conducted a cross-sectional study of 166 women with PCOS and 139 age-matched control women at Peking University Third Hospital (Beijing, China) from March 2016 to December 2021. All participants underwent bioimpedance rate assessment of clinical, anthropometric, hormonal, and metabolic features. In particular, body composition parameters were assessed, based on the methods used in a previous study. Homeostasis model assessment-insulin resistance (HOMA-IR) and other indices calculated from fasting glucose and insulin were used to measure insulin resistance. The hormonal profiles [follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen (E2), prolactin (PRL), total testosterone (T), and androstenedione (A2)] were assessed by using biochemical methods. Two subgroup analyses were conducted according to waist-to-hip ratio (WHR; < 0.85, non-central obesity and ≥ 0.85, central obesity) and body fat percentage (BFP; < 35% for lean and ≥35% for obesity). The indices above were analyzed using a two-sided t-test or Wilcoxon rank sum test. Linear regression was used to investigate the effects of body composition on metabolism and sex hormones in the PCOS and control groups.ResultsCompared to women without PCOS, women with PCOS and central obesity (P=0.021), PCOS and noncentral obesity (P<0.001), PCOS and high BFP (P<0.001), and PCOS and low BFP (P<0.001) had more severe glucose metabolism evaluated with HOMA-IR. Women with PCOS experienced greater insulin sensitivity impairment than did the normal population for every equal increase in BFP. LH, LH/FSH, total testosterone, and androstenedione were significantly higher in patients with PCOS than in healthy controls, regardless of WHR and BFP stratification. However, negative correlations existed between body fat indices (i.e., BFP and body mass index) and hormone indices (i.e., LH and androstenedione) in the PCOS group, but were absent in the control group.ConclusionsObese and non-obese women with PCOS have more severe insulin resistance and sex-hormone disorders than women without PCOS. The effect of body fat on sex-hormone disorders is only exist in women with PCOS. These findings suggested that PCOS clinical guidelines should be more specific to body fat.Clinical trial registrationhttps://clinicaltrials.gov/, Registration No. NCT04264832.
High-performance dielectric capacitor represents an emerging technological goal for energy storage in modern electrical and electronic systems. In this work, we report a lead-free film capacitor based on the Bi(Mg1/2Ti1/2)O3 modified BiFeO3-Sr0.7Bi0.2TiO3 relaxor. A large recoverable energy storage density of 77.5 J/cm3, together with an efficiency of 56.1% is achieved in the film with 15 mol. % Bi(Mg1/2Ti1/2)O3 in composition. The film also exhibits excellent fatigue endurance with a reduction less than 3% over 1 × 108 cycles in both recoverable energy storage density and efficiency. Such good properties are ascribed to the improved electrical insulation and breakdown strength and the enhanced relaxor behavior by introducing the bismuth-based perovskite-like compound.
We reported a peculiar thickness dependence of perpendicular magnetic anisotropy (PMA), stronger in thinner films, in spinel NiCo2O4 (NCO) films deposited epitaxially on MgAl2O4 (001) single crystalline substrates. The effective PMA field is about 3 T in 23.0 nm-thick films but increases dramatically to about 7 T in 4.5 nm-thick films. X-ray absorption spectra reveal an inhomogeneous distribution of Co2+ cations along the film's normal with more Co2+ adjacent to the film/substrate interface. X-ray linear dichroism spectra reveal that the PMA in NCO films is associated with electrons occupying the x2–y2 orbital of Co cations at the tetrahedral sites. This work demonstrates the potential of ultrathin NCO films in all-oxide spintronic devices.
Ferromagnetic insulators have received widespread attention for applications in novel low power consumption spintronic devices. Further optimizing the robust ferromagnetic insulating and developing multifunctional ferromagnetic insulator by integrating other magnetic property can not only ease or pave the way for actual application, but also provide an additional freedom degree for device designing. In this work, by introducing antiferromagnetic CoO into ferromagnetic insulator LaMnO3, we have constructed (1-x)LaMnO3:xCoO composite thin films. The films simultaneously show robust ferromagnetic insulator characteristics and large exchange bias. For x = 0.5 sample, the resistivity is 120 Ω·cm at 250 K while the magnetization is 100 emu/cm3 and the exchange bias field is -2200 Oe at 10 K. Especially, the blocking temperature is up to 140 K. Synchrotron radiation x-ray absorption spectroscopy reveals the coexistence of Mn3+, Mn2+, Co2+ and Co3+, arising from interfacial charge transfer and space charge/defect trapping, should be responsible for the enhanced and integrated multifunctional magnetic properties.
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