Crystal structure and magnetic properties of Bi1-xSmxFeO3 ceramics across the phase boundary: effect of high pressure

The solid solutions Bi1-xSmxFeO3 with chemical composition across the morphotropic phase boundary region specific for rhombohedral - orthorhombic structural transition were investigated by X-ray diffraction, electron microscopy and magnetometry. Structural measurements showed a concentration driven transition from the single phase rhombohedral structure to the single phase nonpolar orthorhombic structure through the formation of antipolar orthorhombic phase which coexists with the rhombohedral phase in the compounds with x < 0.15 followed by a coexistence with nonpolar orthorhombic phase in the compounds with x <= 0.18. Application external pressure provides a stabilization of the orthorhombic phase, viz. the polar rhombohedral phase diminishes and transforms to the anti-polar orthorhombic phase, while the anti-polar orthorhombic phase transforms to the non-polar orthorhombic phase. Magnetic properties of the compounds subjected to external pressure demonstrate an increase in the magnetization of the compounds having dominant rhombohedral phase, wherein coercivity significantly increases, while the spontaneous magnetization remains nearly constant. Твердые растворы Bi1-xSmxFeO3 с химическим составом в области морфотропной границы раздела фаз, характерной для ромбоэдрально-орторомбического структурного перехода, были исследованы методами рентгеновской дифракции, электронной микроскопии и магнитометрии. Структурные измерения показали обусловленный концентрацией переход от однофазной ромбоэдрической структуры к однофазной неполярной орторомбической структуре путем образования антиполярной орторомбической фазы, которая сосуществует с ромбоэдрической фазой в соединениях с x < 0,15, за которым следует сосуществование с неполярной орторомбической фазой в соединениях с x <= 0,18. Применение внешнего давления обеспечивает стабилизацию орторомбической фазы, а именно. полярная ромбоэдрическая фаза уменьшается и переходит в антиполярную орторомбическую фазу, в то время как антиполярная орторомбическая фаза переходит в неполярную орторомбическую фазу

Crystal structure and magnetic properties of (1-x)BiFeO3 - xBaTiO3 ceramics across the phase boundary

Кристаллическая структура и магнитные свойства бессвинцовой керамики (1-x)BiFeO3 - xBaTiO3 (x<0,40) приготовленной методом твердофазной реакции, были изучены в зависимости от химического состава и температура. The crystal structure and magnetic properties of lead-free ceramics (1-x)BiFeO3 - xBaTiO3 (x<0.40) prepared by solid state reaction method were studied depending on the chemical composition and temperature

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr 2

The sequence of phase transformations during Sr2FeMoO6−x crystallization by the citrate–gel method was studied for powders synthesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr2FeMoO6−x agglomerates with diameters in the range of 0.7–1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr2FeMoO6−x changes and the molybdenum content increases with further heating. This leads to a change in the Sr2FeMoO6−x crystal lattice parameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr2FeMoO6−x compound to be obtained with a grain size in the range of 50–120 nm and a superstructural ordering of iron and molybdenum cations of 88%

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr 2 FeMoO 6−x nanopowders formed by the citrate–gel method

The sequence of phase transformations during Sr 2 FeMoO 6−x crystallization by the citrate–gel method was studied for powders syn-thesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr 2 FeMoO 6−x agglomerates with diameters in the range of 0.7–1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr 2 FeMoO 6−x changes and the molybdenum content increases with further heating. This leads to a change in the Sr 2 FeMoO 6−x crystal lattice pa-rameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr 2 FeMoO 6−x compound to be obtained with a grain size in the range of 50–120 nm and a superstructural ordering of iron and molybdenum cations of 88%.info:eu-repo/semantics/publishe

Isostatic hot-pressed tungsten radiation shields against gamma radiation

An isostatic hot-pressing technique for the fabrication of dense W samples' is presented. The samples’ microstructure and chemical content were analyzed. The most compact samples were received at 5 GPa pressure and 1500 and 2000 °C temperatures, with densities of 18.50 and 19.07 g/cm3, respectively. It has been established that high temperature exposure has a positive effect on both the microstructure and density. It is shown that as the sintering temperature increases, the porosity of the samples decreases from 32.31% to 0.94%, and their relative density increases from 67.69% to 99.06%. The crystal structure investigation revealed that all the samples contain the main body-centered cubic W phase, and the availability of the WO2 phase is observed just after the temperature of sintering increases above 1000 °C, which is confirmed by the appearance of 111 and 22-2 reflections. A study of the shielding effectiveness against gamma-radiation was carried out using the Phy-X/PSD software. A gamma-ray source of Co60 with energies of 0.8–2.5 MeV was applied for the calculations. The results were calculated for the sample with the highest density (19.07 g/cm3) and compared with the calculations for Pb. The W shielding effectiveness main parameters are determined: linear attenuation coefficient (at 0.8 MeV–1.46 cm-1), mean free path (at 2.5 MeV–1.2 cm) and half value layer (at 2.5 MeV–0.86 cm). These values turned out to be higher than for Pb, which makes shields based on W promising for use in the field of radiation protection