Dielectric,ferroelectric, and piezoelectric properties of lead-free Ba0.95Ca0.05Ti1-xZrxO3 ceramics

Abstract

Ba_0.95Ca_0.05Ti_1-xZr_xO₃ (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'_m), remanent polarization (2P_r), coercive electric field (2E_c) and piezoelectric charge constant (d₃₃) of 7,244, 12.54 (μC/cm²), 5.29 (kV/cm) and 288 (pC/N), respectively.     

Structure and Magnetic Properties of Mn-doped CoFe 2 O 4 Nanoparticles Prepared by Solvothermal Route

Spinel Co_1?xMn_xFe₂ O ₄ (x = 0, 0.25, 0.5, 0.75 and 1.0) nanoparticles were synthesized by a solvothermal method using polyethylene glycol (PEG) as a surfactant. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge structure (XANES) spectroscopy and vibrating sample magnetometer (VSM) techniques were used to characterize phase, morphology, valence states, and magnetic properties of the samples. XRD analysis showed single phase of spinel structure, and the decrease of lattice constant on the effective Mn substitution was investigated. The effect of the PEG on the spherical aggregates of Co_1?xMn_xFe₂ O ₄ nanoparticles was observed. The result of XANES spectra showed Mn²⁺/Mn³⁺, Fe³⁺, and Co²⁺ exist in the samples. The samples showed ferromagnetism at room temperature with a maximum saturated magnetization of 72 emu/g and the smallest coercivity of 45 Oe for x = 1.0. The origin of ferromagnetic behavior is believed to be due to the occupation of Mn²⁺/Mn³⁺ ions.     

Synthesis, characterization, and magnetic properties of monodisperse CeO2 nanospheres prepared by PVP-assisted hydrothermal method

ABSTRACT: Ferromagnetism was observed at room-temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3.6H2O using polyvinylpyrrolidone (PVP) as a surfactant. The structure and morphology of the products were characterized by; X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using ultraviolet and visible spectroscopy (UV-Vis) and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy (XANES). The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of ~ 9-19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of ~ 100-250 nm. The samples also showed a strong UV absorption and room temperature photoluminescence. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied by Vibrating Sample Magnetometer (VSM). The samples exhibited room temperature ferromagnetism (RT-FM) with a small magnetization of ~ 0.0026-0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange and the possible mechanism of formation was discussed based on the experimental results.     

Structure and Magnetic Properties of Monodisperse Fe3+-doped CeO2 Nanospheres

Nano-Micro Letters - This work reports the study concerning the structure and magnetic properties of undoped CeO2 and Fe-doped CeO2 (Ce1−xFe x O2, 0.01 ≤ x ≤ 0.07) nanospheres...     

Risk assessment of Listeria spp. contamination in the production line of ready-to-eat chicken meat products

The risk of Listeria spp. contamination was assessed in frozen ready-to-eat chicken meat production lines by establishing a mathematical model for determining the probability of Listeria spp. prevalence on environmental surfaces directly in contact with the product at various times in a chicken plant in Thailand. Environmental surfaces were divided into three zones. Zone 1 included surfaces in direct contact with products. Both zones 2 and 3 included indirect contact surfaces; zone 2 was next to zone 1, and zone 3 was next to zone 2, relatively far from the product. The model for probability of Listeria spp. contamination on surfaces in zone 1 was derived from the probability of Listeria spp. on surfaces in zone 1 after the cleaning and sanitizing process multiplied by the probability of Listeria spp. transferred from zones 2 and 3 and the probability of Listeria spp. growth. The surfaces in zone 1 were cleaned with warm water, cleaned with detergent, and sanitized with a sanitizer. Factors affecting cleaning and sanitizing were water temperature, concentration, and contact time of detergent and sanitizer. The probability of Listeria spp. prevalence on surfaces in zone 1 was not affected by water temperatures of 50, 60, and 70 degrees C and detergent concentrations of 0.5, 1, and 2% (vol/vol) at contact times of 5, 10, and 15 min. However, it was affected by sanitizer concentrations of 0.25, 0.5, and 1.25% (vol/vol) at contact times of 5, 10, and 20 min. Sensitivity analyses were conducted using the Monte Carlo simulation. The sanitizer concentration had the most significant influence on the prevalence of Listeria spp. on surfaces in zone 1. The prevalence of Listeria spp. on surfaces after cleaning and sanitizing, the production time, and the contact time with the sanitizer were highly correlated with the prevalence of Listeria spp. in zone 1. This model could be used as a management tool for assessing the risk of Listeria spp. contamination in food products.     

Contamination profile of Listeria spp. in three types of ready-to-eat chicken meat products

This study investigated contamination sources of Listeria spp. in frozen, ready-to-eat, roasted, steamed, and fried chicken meat products from a plant in Thailand, as well as the correlation between Listeria contamination in the production environment and the finished product. The cooking processes used in this factory (with a product core temperature of 80 degrees C for 1 min) were confirmed as adequate for eliminating Listeria spp. However, Listeria spp. were detected at the packing stage of roasted and steamed chicken products. An environmental swab test was conducted by means of the zone concept, whereby surfaces in the production area were divided into three zones. Zone 1 was made up of the equipment surfaces that came into direct contact with the products. Zone 2 consisted of equipment surfaces that were not in direct contact with the products, including surfaces that were difficult to be cleaned. Zone 3 included surfaces that did not come in direct contact with the products and were located far from the products. The results showed that the prevalence of Listeria spp. in roasted and steamed products was affected by the prevalence of Listeria contamination in all zones, especially zone 1, which demonstrated the highest correlation. In addition, the prevalence of Listeria contamination in zones 2 and 3 affected the prevalence of Listeria in zone 1. A correlation between Listeria on roasted chicken products and the surfaces of zone 1 at the start of production was also established.     

Improved cure characteristics and mechanical properties of an epoxidized natural rubber filled with cerium oxide nanoparticles: Influence of epoxide levels and filler loading

In this study, cerium oxide nanoparticles (nanoceria, CeNP) were used as a nanofiller in epoxidized natural rubber with varying epoxide levels, including 25% epoxidation (ENR-25) and 50% epoxidation (ENR-50). Co-precipitation methods were employed to synthesize a pure phase of CeNP with an average particle size of 11.4 ± 2.0 nm. CeNP was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. The effect of CeNP loading with 0–3 parts per hundreds of rubber (phr) on the properties of rubber nanocomposites was explored. ENR-25 nanocomposites with 1 phr of CeNP exhibited higher tensile strength and elongation at break compared to ENR-50 nanocomposites. These findings correspond to a lower Payne effect, improved scorch safety, and better processability. The strongest and most effective CeO₂–ENR interactions via silane linkages are expected to outperform sulfur crosslinking in ENR-25 having 1 phr of CeNP. Microstructural evaluation of an ENR-25 sample containing 1 phr of CeNP indicated well-distributed nanofillers in the ENR-25 matrix, indicating that CeNP and ENR-25 appeared to be well-matched. Hardness of all ENR nanocomposites increased with CeNP loading. The cracking resistance, creep properties, and thermal stability of rubber nanocomposites were unaffected by addition of CeNP in the ENR-25 and ENR-50 samples.