Synthesis and characterization of (Ba,Yb) doped ceria nanopowders

Nanometric size (Ba, Yb) doped ceria powders with fluorite-type structure were obtained by applying selfpropagating room temperature methods. Tailored composition was: Ce0.95−xBa0.05YbxO2−δ with fixed amount of Ba − 0.05 and varying Yb content “x” from 0.05 to 0.2. Powder properties such as crystallite and particle size and lattice parameters have been studied. Röntgen diffraction analyses (XRD) were used to characterize the samples at room temperature. Also, high temperature treatment (up to 1550°C) was used to follow stability of solid solutions. The mean diameters of the nanocrystals are determined from the full width at half maxima (FWHM) of the XRD peaks. It was found that average diameter of crystallites is less than 3 nm. WilliamsonHall plots were used to separate the effect of the size and strain in the nanocrystals

Synthesis and characterization of biomorphic CeO2 obtained by using egg shell membrane as template

A new technology based on bio-templating approach was proposed in this paper. Egg-shell membrane (ESM) has been employed as a natural biotemplate. Fibrous oxide ceramics was prepared by wet impregnation of biological template with water solution of cerium nitrate. The template was derived from membranes of fresh chicken eggs. Repeated impregnation, pyrolysis and final calcination in the range of 600 to 1200 °C in air resulted in template burnout and consolidation of the oxide layers. At low temperatures, the obtained products had structure which corresponded to the negative replication of biological templates. Unique bio-morphic CeO2 microstructures with interwoven networks were synthesized and characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), whereas low-temperature nitrogen adsorption (BET) method was used in order to characterize porous properties

BiFeO3 perovskites: theoretical and experimental investigations

Bismuth ferrite (BiFeO3) is one of the most studied multiferroic system. BiFeO3 has been synthesized by controlled hydrothermal process, where the particles of small sizes and with high purity were obtained. Structural analysis showed that nonannealed powder can be perfectly fitted to rhombohedral space group R3c as αBiFeO3 phase. In addition, a structure prediction has been performed and 11 additional BiFeO3 modifications have been proposed. In the next phase, an ab initio optimization of predicted structures has been performed and the structure of the γphase has been elucidated. In addition, electronic and magnetic properties of BiFeO3 were investigated using combination of experimental and theoretical methods. Theoretical studies were performed using a full potential linearized augmented plane-waves plus local orbital (FP(L)APW+lo) method, based on density functional theory (DFT). HRTEM analysis confirmed existence of twin stacking faults, which are responsible for enhanced magnetic properties. EPR measurements suggested existence of electrons trapped by vacancies or defects, while magnetic behavior of synthesized material was investigated by SQUID

Electrophysical properties of microalloyed alumo-silicate ceramics as active dielectric

In this paper, electrophysical properties of porous alumo-silicate ceramics, modified by alloying with magnesium and microalloying with aluminum, were investigated. Complex multiphase system, as active microalloyed ceramics, has specific behavior under influence of external electrical field, which involves changes of dielectric losses and impedance, depending on frequency and temperature. Dielectric properties were measured in the frequency range 20 Hz - 1 MHz. Values for permittivity (εr) ranged between 140 - 430. Order of magnitude for electrical resistivity was about 106 Ωm, for impedance 104 - 108 Ω, and loss tangent had values about and greater than 0.05. Current flow through active dielectric takes place through dielectric barrier and throughout conduction bands of thin aluminum and magnesium metal films. Permittivity has nonlinear distribution and complex functional dependences because of significant nonhomogeneity of active microalloyed ceramics. Lower values of electrical resistivity are the result of complex electron and ion transfer of charge through solid phase and pores, with decreased potential barriers height, due to the influence of additives, ingredients and defects. [Projekat Ministarstva nauke Republike Srbije, br. III 45012 i br. ON 172057

Hafnium Carbide: Prediction of Crystalline Structures and Investigation of Mechanical Properties

Hafnium carbide (HfC) is a refractory compound known for its exceptional mechanical, thermal, and electrical properties. This compound has gained significant attention in materials science and engineering due to its high melting point, extreme hardness, and excellent thermal stability. This study presents crystal structure prediction via energy landscape explorations of pristine hafnium carbide supplemented by data mining. Apart from the well-known equilibrium rock salt phase, we predict eight new polymorphs of HfC. The predicted HfC phases appear in the energy landscape with known structure types such as the WC type, NiAs type, 5-5 type, sphalerite (ZnS) type, TlI type, and CsCl type; in addition, we predict two new structure types denoted as ortho_HfC and HfC_polytype, respectively. Moreover, we have investigated the structural characteristics and mechanical properties of hafnium carbide at the DFT level of computation, which opens diverse applications in various technological domains

Application of Minkowski layer for microalloyed alumo-silicate ceramics grains fractal analysis

Porous aluminium-silicate ceramics, modified by alloying with magnesium and microalloying with alluminium belongs to a group of advanced multifunctional ceramics materials. This multiphase solid-solid system has predominantly amorphous microstructure and micro morphology. Intergranular and interphase areas are very complex, because they represent areas, where numbered processes and interactions take place, making new boundaries and regions with fractal nature. Solid contact between grains is actually very complex configuration of microcontacts with fractal nature. Fractal analysis of intergranular microstructure has included application of Minkowski layer. This layer is in correlation with fractal dimension, and defines grains contact probability. It represents convex layer of grains contour roughness and irregularity. Considering the fractal nature of intergranular contacts, it is possible to establish correlation between material electrical properties and fractal analysis, as a tool for future correlation with microstructure characterization

Synthesis of crystaline silicon oxynitride composites

Silicon oxynitride / silicon nitride (Si2N2O/Si3N4) ceramics have been prepared from Si3N4 powder and amorphous silica (SiO2) by hot pressing at different temperature. It was found that material sintered at lower temperature exhibit fine composite structure composed of equiaxed α-Si3N4 grains and Si2N2O crystals. At higher temperature the growing of Si2N2O particles as well as phase transformation from α-Si3N4 to β-Si3N4 phase take place.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

The influence of short thermal treatment on structure, morphology and optical properties of Er and Pr doped ceria pigments: Comparative study

Potential non-toxic pink and red ceramic pigments based on CeO2 were successfully synthesized by selfpropagating room temperaturemethod and thermally treated at 600, 900 and 1200°C for 15min. The structure, morphology and optical properties, as well as thermal stability of Ce1-xErxO2-δ and Ce1-xPrxO2-δ(x = 0.05) were examined. Single-phase composition of all obtained CeO2 pigments was confirmed using XRPD method and Raman spectroscopy and it was not dependent on temperature. The mechanism of structural behaviour was thoroughly examined using Raman and FTIR spectroscopy. Nanometric dimensions of the crystallites of all pigments were confirmed using XRPD, TEM and FE-SEM analysis. Colour properties were dependent on the temperature treatment, and their position in the chromaticity diagram was studied using UV/VIS spectrophotometry. Colour efficiency measurements were supplemented by colorimetric analysis. It is proved that all samples are thermally stable in the investigated temperature range (up to 1200°C), and their potential application as environmentally friendly pigments of desired colour is confirmed