Comparison of sizes, morphologies and optical properties of nio nanostructures synthesized using acetate and nitrate anions from nickel salts via hydrothermal method

Porous NiO nanocrystals were synthesized using a hydrothermal method in mediums of different anions from nickel salts, acetate (CH 3 COO - ) and nitrate (NO 3 -),followed by calcination at 500 °C. Firstly, β-Ni(OH) 2 powders with a hexagonal structure were formed. Using acetate and nitrate anions, the obtained β-Ni(OH) 2 powders were composed of thin nanosheets (0.8-2.1 μm in length), and a splinter-like structure self-assembled with longer nanosheets (9.8-24.2 μm), respectively. The difference in the interaction ability between the anions and the β-Ni(OH) 2 surfaces, affecting the growth behavior of the crystals, was examined using the density functional theory (DFT) method. After calcination, the β-Ni(OH) 2 turned into porous NiO with a cubic structure but their morphologies were unchanged. The porous NiO with longer nanosheets possessing higher crystallinity and larger surface area provided better UV-Vis absorption ability. © 2018, Chiang Mai University. All rights reserved

Identification of Barium-Site Substitution of BiFeO3-Bi0.5K0.5TiO3 Multiferroic Ceramics: X-ray Absorption Near Edge Spectroscopy

In this work, the effects of barium substitution on the local structure, dielectric and magnetic properties of the polycrystalline ceramics 0.6BiFeO3–0.4(Bi0.5K0.5)TiO3 (0.6BFO–0.4BKT) system was investigated. A solid-state reaction technique was used to synthesize the materials with barium (Ba) doping of 1, 3, 5, 7, and 10 mol%. XRD analysis reveals the coexistence between tetragonal and rhombohedral phases of single-phase perovskite in pure 0.6BFO–0.4BKT and the rhombohedral reach phase was found with increasing Ba content. XANES simulations indicate that the majority of Ba atoms occupy A-site in BKT lattice of Ba-doped 0.6BFO-0.4BKT, the oxidation state of Fe, Ti, and Ba ions are +3, +4 and +2, respectively. At 5 mol% of Ba doping content, the dielectric measurement shows the morphotropic phase boundary (MPB) and the maximum value of ferromagnetic characteristic were observed, indicating an optimum composition, properties and production conditions

High temperature dielectric ceramics: a review of temperature-stable high-permittivity perovskites

Recent developments are reviewed in the search for dielectric ceramics which can operate at temperatures >200 °C, well above the limit of existing high volumetric efficiency capacitor materials. Compositional systems based on lead-free relaxor dielectrics with mixed cation site occupancy on the perovskite lattice are summarised, and properties compared. As a consequence of increased dielectric peak broadening and shifts to peak temperatures, properties can be engineered such that a plateau in relative permittivity–temperature response (εr–T) is obtained, giving a ±15 %, or better, consistency in εr over a wide temperature range. Materials with extended upper temperature limits of 300, 400 and indeed 500 °C are grouped in this article according to the parent component of the solid solution, for example BaTiO3 and Na0.5Bi0.5TiO3. Challenges are highlighted in achieving a lower working temperature of −55 °C, whilst also extending the upper temperature limit of stable εr to ≥300 °C, and achieving high-permittivity and low values of dielectric loss tangent, tan δ. Summary tables and diagrams are used to help compare values of εr, tan δ, and temperature ranges of stability for different material