ABSTRACT
Recently, rapidly increased demands of integration and miniaturization continuously challenge energy densities of dielectric capacitors. New materials with high recoverable energy storage densities become highly desirable. Here, by structure evolution between fluorite HfO2 and perovskite hafnate, we create an amorphous hafnium-based oxide that exhibits the energy density of ~155 J/cm3 with an efficiency of 87%, which is state-of-the-art in emergingly capacitive energy-storage materials. The amorphous structure is owing to oxygen instability in between the two energetically-favorable crystalline forms, in which not only the long-range periodicities of fluorite and perovskite are collapsed but also more than one symmetry, i.e., the monoclinic and orthorhombic, coexist in short range, giving rise to a strong structure disordering. As a result, the carrier avalanche is impeded and an ultrahigh breakdown strength up to 12 MV/cm is achieved, which, accompanying with a large permittivity, remarkably enhances the energy storage density. Our study provides a new and widely applicable platform for designing high-performance dielectric energy storage with the strategy exploring the boundary among different categories of materials.
ABSTRACT
Ferroelectric tunnel junctions (FTJs) are promising candidates for next-generation memories due to fast read/write speeds and low-power consumptions. Here, we investigate resistance fatigue of FTJs, which is performed on Pt/BaTiO3/Nb:SrTiO3 devices. By direct observations of the 5unit cellthick BaTiO3 barrier with high-angle annular dark-field imaging and electron energy loss spectroscopy, oxygen vacancies are found to aggregate at the Pt/BaTiO3 interface during repetitive switching, leading to a ferroelectric dead layer preventing domain nucleation and growth. Severe oxygen deficiency also makes BaTiO3 lattices energetically unfavorable and lastly induces a destruction of local perovskite structure of the barrier. Ferroelectric properties are thus degraded, which reduces barrier contrast between ON and OFF states and smears electroresistance characteristics of Pt/BaTiO3/Nb:SrTiO3 FTJs. These results reveal an atomic-scale fatigue mechanism of ultrathin ferroelectric barriers associated with the aggregation of charged defects, facilitating the design of reliable FTJs and ferroelectric nanoelectronic devices for practical applications.
ABSTRACT
OBJECTIVE: To explore the impact of ideal health behaviors on the newly developed carotid plaques. METHODS: A total of 5 852 employees (including retired employees from Tangshan Kailuan company) aged over 40 years were included in this study through stratified random sampling. Subjects with previous stroke, transient ischemic attack, myocardial infarction were excluded. Results from the unified questionnaire, blood biochemistry measurements and ultrasonography carotid artery measurements were analyzed. Present study analyzed the data from 2 372 participants without carotid plaques in 2010-2011 examinations. The newly developed carotid plaques in 2012-2013 health examinations were observed and multiple logistic regression analysis was used to explore the impact of ideal health behaviors and factors on the newly developed carotid plaques. RESULTS: (1) There were 359 subjects with newly developed carotid artery plaques among the 2 372 subjects (15.1%), prevalence rate was 23.1% (43/186), 17.5% (186/1 065), 12.4% (122/986), 5.9% (8/135) in the groups with 0-1, 2-3, 4-5 and 6-7 components of ideal cardiovascular health behaviors and factors, respectively (P < 0.001). (2) Multiple logistic regression analysis showed that after adjusting for age, gender, high density lipoprotein cholesterol, heart rate, and high sensitive c-reactive protein, compared to with 0-1 components of ideal cardiovascular health behaviors and factors, participants with 4-5 and 6-7 components of ideal cardiovascular health behaviors and factors were associated with reduced risk of the newly developed carotid plaques, the OR (95% CI) values were 0.52(0.34-0.80) and 0.28(0.12-0.64), respectively. CONCLUSION: Higher number of ideal cardiovascular health behaviors and factors is associated with lower incidence of newly developed carotid plaques.
