V.A. Turchenko

Evolution of structure and physical properties in Al-substituted Ba-hexaferrites*

The investigations of the crystal and magnetic structures of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range (from 4.2 K to 150 K). It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFe12−xAlxO19 (x = 0.1–1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Multiferroic properties and structural features of M-type Al-substituted barium hexaferrites

Precise studies of the crystal and magnetic structures of M-type substituted barium hexaferrites BaFe12–xAlxO19 (0.1 ≤ x ≤ 1.2) have been performed by powder neutron diffraction in the temperature range 300–730 K. The electric polarization and the magnetization, and also the magnetoelectric effect of the compositions under study have been studied in electric (to 110 kV/m) and magnetic (to 14 T) fields at room temperature. The spontaneous polarization and significant correlation between the dielectric and magnetic subsystems have been observed at room temperature. The magnetoelectric effect value is, on average, about 5%, and it increases slightly with the aluminum cation concentration. The precise structural studies made it possible to reveal the cause and the mechanism of formation of the spontaneous polarization in M-type substituted barium hexaferrites BaFe12–xAlxO19 (x ≤ 1.2) with a collinear ferromagnetic structure.

Changes of phase composition of Zr1-x(Ce/Y)xO2 complex oxides induced by thermal treatment

The medical prosthesis components made from (ZrO2)-based ceramics present a good biocompatibility as well as especially mechanical properties. Much more, the problems of nondestructive evaluation for these elements, which assure both comfort and maximum safety to the patient, are imperative for these medical implants. In this study, we investigate the structure and the mechanical properties of Zr1-x(Ce/Y)xO2 , (x=0.0;0.09;0.13;0.17) materials as well as the modification of their crystallographic structure due to various thermal treatments and variation of Ce/Y concentrations in the samples. The substitution of Zr with Ce and the thermal treatment at 1000°C produced important transformation in the phase composition and the microstructure of the sample. A large decrease of the microstrains was observed at the treated samples. Combining characterization techniques based on XRD and ND with non-destructive evaluation methods based on Resonant Ultrasound Spectroscopy (RUS) and Acoustic Emission (AE), we emphasize a unique approach on evaluating the physical properties of these ceramics. Performed evaluation tests of Zr1-x(Ce/Y)xO2 ceramics have shown big influence of composition on their fracture behavior and resulting strength due to different damage mechanisms.

Complementary methods of study for Zr1-xCexO2 compounds for applications in medical prosthesis

Zirconia (ZrO2)-based ceramics are preferred due to their advanced mechanical properties such as high-fracture toughness and bulk modulus, corrosion resistance, high dielectric constant, chemical inertness, low chemical conductivity and biocompatibility. The medical prosthesis components made from ZrO2 oxides present a very good biocompatibility as well as especially mechanical properties. In order to ensure implant safety of these prostheses, wide ranges of examinations based on nondestructive testing are imperative for these medical implants. In this study, we aim to emphasize the improvement of Zr-based ceramics properties as a function of addition of Ce ions in the structure of the original ceramics. The substitution of the Zr with Ce in the Zr1-xCexO2 compounds, where x = 0.0–0.17, leads to a change of the phase composition, a gradual transition from the monoclinic to tetragonal structure, at room temperature. The structural investigations proposed in this paper are based on X-ray and neutron diffraction in order to establish a first indication of the variation of the phase composition and the structural parameters, as well as micro-hardness measurements and nondestructive evaluations in order to establish a correlation between the structural parameters and mechanical properties of the samples. These ranges of tests are imperative in order to ensure the safety and reliability of these composite materials, which are widely used as hip-implants or dental implants/coatings. In combination of Resonant Ultrasound Spectroscopy, which makes use of the resonance frequencies corresponding to the normal vibrational modes of a solid in order to evaluate the elastic constants of the materials, we emphasize a unique approach on evaluating the physical properties of these ceramics, which could help in advancing the understanding of properties and applications in medical fields.