Size effects in radiospectroscopy spectra of ferroelectric nanopowders

The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry with decreasing of nanoparticle sizes was calculated. Measurements of Fe3+ ESR spectra in nanopowder of BaTiO3 were carried out at room temperature. The decrease of intensity of tetragonal symmetry ESR lines of Fe3+ and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at average size less or equal 40 nm. The comparison of the theory with experiment was carried out. The value of critical size Rc = 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface. The deconvolution of the cubic line allowed to show, that this region size is about 3 nm.Comment: 10 pages, 8 figure

Doped Barium Titanate at Intermediate Stages of Synthesis of ВТО

This paper presents the results of synthesis and characterization of calcium 0doped nanocrystalline barium titanate powder with different concentration of doped elements ((Ba1-xCax) TiO3, were x 0; 0.02; 0.06; 0.1; 0.16; 0.2), produced by oxalate route. Calcium additives were added on the surface the samples of semidecomposed barium titanil oxalate. For synthesis were used simultaneously decomposition of unstable barium, titanium compositions and calcium salts. The semidecomposed barium titanil oxalate and doped barium titanate characterization carried out by specific surface area measurements, TEM, X-Ray. It is experimentally shown that Са2+ introduction reduces lattice parameter for samples that related with replacement of barium by calcium. Solubility of calcium in barium titanate nanopowders increase from 10 at % up to 16 at %. The second phase appears at 20 at %. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3547

Monitoring of the morphologic reconstruction of deposited ablation products in laser irradiation of silicon

Using electron microscopy, atomic force microscopy, X-ray microanalysis, and IR spectroscopy, it was established that, in the regime of continuous laser irradiation of silicon at P = 170 W in different gaseous atmospheres with an oxygen impurity, SiOx composite films with a complex morphology form. The main components of ablation products are clusters that form during flight of ablation products and as a result of separation of SiOx-clusters from the zone of the irradiation channel. The roughness and density of the films depend on the heating temperature of the target surface and the type of deposited clusters

The layer by layer selective laser synthesis of ruby

In the work, features of the layer-by-layer selective laser synthesis (SLS) of ruby from an Al2O3-Cr2O3 mixture are considered depending on the irradiation power, the laser beam traverse speed, the height and amount of the backfill of powder layers. It has been established that, under irradiation, a track consisting of polycrystalline textured ruby forms. The morphology of the surface of the track and its crystalline structure are determined by the irradiation conditions

Relationships between Pore Structure, Free Carbon Content, Particle Size Distribution and Deposition Stage of Ni/NiO Nanopowers

Ni/NiO nanopowders have been prepared by using thermal decomposition of aqua solutions of nickel acetate ammine complexes in air at the annealing temperature range 300 -500 ºC, time of decomposition from 30 to 180 min. Particle size of powders has been investigated by and scanning electron microscopy (SEM). Powders pore structure has been determinated by low temperature nitrogen adsorption method. Content of free carbon in powders is determitated by stage of decomposition and annealing temperature. Decomposition of hydroxy-containing precursor at occurred in 3 stages: 1) the primary formation of Ni; 2) decomposition of precursors with formation of NiO; 3) afterreduction of NiO to Ni by residuals of organic compounds and ammonia. The first two stages is characterized by highly endothermic effect that can lead to decreasing of acetic acid evaporation rate and resulted in high free carbon content of powders. Increasing of deposition time permits to remove of acetic acid from particle surface and decrease free carbon content in powder