Microstructural and nonlinear electrical properties of ZnO ceramics with small amount of MnO2 dopant

A small amount of MnO2 dopant was added to ZnO system to see the improvement of the ceramic varistor microstructural and nonlinear electrical properties. The samples were prepared using solid-state reaction method and the microstructure and nonlinear electrical properties of the ZnO-xMnO2 system were investigated for x = 0.011 to 0.026 mol%, at three sintering temperatures, 1180°C, 1240°C and 1300°C for 1 and 2 h sintering time. The XRD and EDAX analyses showed that the main phase was ZnO while ZnMnO3 and ZnMnO7 as the secondary phases developed and distributed at the grain boundaries and triple point junction. The SEM observation revealed that prolonged sintering temperature and time improved the microstructure uniformity and strongly influences the nonlinear behavior of the samples. The maximum density and grain size have been observed at 92% of theoretical density and 10.8 μm, respectively and occur at the highest sintering temperature which is 1300°C. The value of nonlinear coefficient α is found to increase with the increase of MnO2 doping level up to 0.016 mol% and drop with further doping level increment for all sintering temperatures and time

Effect of heat treatment on the optical properties of ceramic ZnO-MnO-Dy2O3.

Photopyroelectric spectroscopy is used to investigate the optical absorption behaviour of the ceramic composite (ZnO + 1 MnO + y Dy2O3), where y = 0 - 2 mol%. Ceramics were sintered at 1200 and 1300°C for 1 and 5 h. PPE spectrum with reference to the doping level and sintering time is discussed. Optical energy band-gap (Eg) is determined from the plot (ρhυ)2 vs hυ. It is found that the the value of Eg is reduced from 3.2 (pure ZnO) to 2.15 eV at the 0 mol% of Dy2O3 and is further reduced to 2.04 eV at the 2 mol% of Dy2O3 for 5 h sintering time at the 1300°C sintering temperature. Steepness factor σA and σB which characterizes the slope of exponential optical absorption is discussed with reference to the variation in the value of Eg. The phase constitution is determined by XRD analysis. Microstructure and compositional analysis are analyzed using SEM and EDAX. The maximum grain size and density of the ceramic were found to be 14 μm, 89%, respectively

Optical characterization of the Bi2O3, TiO2 and MnO2 doped ZnO ceramics.

Photopyroelectric (PPE) spectroscopy was used to study the optical band-gap energy (Eg) of the ceramic ZnO doped with 0.5MnO2. xBi2O3 and xTiO2 sintered at 1270oC for one to four hours. The wavelength of incident light from 300 to 800 nm, modulated at 9 Hz, was used and PPE spectrum with reference to the doping level and sintering time was discussed. The optical band-gap energy (Eg) was determined from the plot (ρhv)2 vs and found that the E g decreased to the lowest value of 2.13 eV with x = 1.8 mol% at four hour sintering time. Steepness factor (in region-A) and steepness factor (in region-B) which characterizes the slope of exponential optical absorption was discussed with reference to the variation in the value of Eg. XRD, SEM and EDAX were used for the characterization of the ceramic. Relative density and grain size is also discussed

Effect of temperature treatment on the optical characterization of ZnO-Bi2O3-TiO2 varistor ceramics.

The optical band-gap energy (Eg) is an important feature of semiconductors which determines their applications in optoelectronics. So, it is necessary to investigate the electronic states of ceramic ZnO and effect of doped impurities at different processing conditions. Eg of the ceramic ZnO + xBi2O3 + xTiO2 where x = 0.5 mol%, was determined using UV-Vis spectrophotometer. The samples was prepared using solid-state route and sintered at the sintering temperatures from 1140 to 1260°C for 45 min in open air. Eg was decreased with increase of sintering temperature. XRD analysis indicates that there is hexagonal ZnO and few small peaks of inter granular layers of secondary phases, namely, Bi4Ti3O12 and Zn2Ti3O8. The relative density of the sintered ceramics decreased and the average grain size increased with the increase of sintering temperature. The variation of sintering temperatures and XRD findings are correlated with the UV-Vis spectrophotometer results of ZnO doped with 0.5 mol% of Bi2O3 and TiO2 due to the formation of interface states at all sintering temperatures

Prevalence Estimates of Amyloid Abnormality Across the Alzheimer Disease Clinical Spectrum

Importance: One characteristic histopathological event in Alzheimer disease (AD) is cerebral amyloid aggregation, which can be detected by biomarkers in cerebrospinal fluid (CSF) and on positron emission tomography (PET) scans. Prevalence estimates of amyloid pathology are important for health care planning and clinical trial design. Objective: To estimate the prevalence of amyloid abnormality in persons with normal cognition, subjective cognitive decline, mild cognitive impairment, or clinical AD dementia and to examine the potential implications of cutoff methods, biomarker modality (CSF or PET), age, sex, APOE genotype, educational level, geographical region, and dementia severity for these estimates. Design, Setting, and Participants: This cross-sectional, individual-participant pooled study included participants from 85 Amyloid Biomarker Study cohorts. Data collection was performed from January 1, 2013, to December 31, 2020. Participants had normal cognition, subjective cognitive decline, mild cognitive impairment, or clinical AD dementia. Normal cognition and subjective cognitive decline were defined by normal scores on cognitive tests, with the presence of cognitive complaints defining subjective cognitive decline. Mild cognitive impairment and clinical AD dementia were diagnosed according to published criteria. Exposures: Alzheimer disease biomarkers detected on PET or in CSF. Main Outcomes and Measures: Amyloid measurements were dichotomized as normal or abnormal using cohort-provided cutoffs for CSF or PET or by visual reading for PET. Adjusted data-driven cutoffs for abnormal amyloid were calculated using gaussian mixture modeling. Prevalence of amyloid abnormality was estimated according to age, sex, cognitive status, biomarker modality, APOE carrier status, educational level, geographical location, and dementia severity using generalized estimating equations. Results: Among the 19097 participants (mean [SD] age, 69.1 [9.8] years; 10148 women [53.1%]) included, 10139 (53.1%) underwent an amyloid PET scan and 8958 (46.9%) had an amyloid CSF measurement. Using cohort-provided cutoffs, amyloid abnormality prevalences were similar to 2015 estimates for individuals without dementia and were similar across PET- and CSF-based estimates (24%; 95% CI, 21%-28%) in participants with normal cognition, 27% (95% CI, 21%-33%) in participants with subjective cognitive decline, and 51% (95% CI, 46%-56%) in participants with mild cognitive impairment, whereas for clinical AD dementia the estimates were higher for PET than CSF (87% vs 79%; mean difference, 8%; 95% CI, 0%-16%; P =.04). Gaussian mixture modeling-based cutoffs for amyloid measures on PET scans were similar to cohort-provided cutoffs and were not adjusted. Adjusted CSF cutoffs resulted in a 10% higher amyloid abnormality prevalence than PET-based estimates in persons with normal cognition (mean difference, 9%; 95% CI, 3%-15%; P =.004), subjective cognitive decline (9%; 95% CI, 3%-15%; P =.005), and mild cognitive impairment (10%; 95% CI, 3%-17%; P =.004), whereas the estimates were comparable in persons with clinical AD dementia (mean difference, 4%; 95% CI, -2% to 9%; P =.18). Conclusions and Relevance: This study found that CSF-based estimates using adjusted data-driven cutoffs were up to 10% higher than PET-based estimates in people without dementia, whereas the results were similar among people with dementia. This finding suggests that preclinical and prodromal AD may be more prevalent than previously estimated, which has important implications for clinical trial recruitment strategies and health care planning policies. © 2022 American Medical Association. All rights reserved