A comprehensive analysis of the magnetic properties, crystal structure and magnetic configuration of the ceramic BaFe 12 O 19 , prepared using the sol-gel method, was conducted over the temperature range from 4 K to room temperature. The impact of ambient pressure on the crystal and magnetic structures of ceramic BaFe 12 O 19 has enabled the determination of bulk modulus B 0 ∼ 123.8 GPa and its first-order derivative B p ′ ∼ 4.1, as well as the coefficients of linear compressibility of the lattice parameters for the hexagonal unit cell. The results of neutron diffraction collected at pressures ranging from 0.1 GPa to 5 GPa were analyzed in the framework of both centrosymmetric SG P6 3 /mmc (No. 194) and non-centrosymmetric SG P6 3 mc (No. 186). The decrease in the total magnetic moment with an increase in ambient pressure was associated with a weakening of the exchange interaction in the ferrimagnetic structure, owing to a reduction in the bond angles (∠ Fe–O–Fe) of various iron sublattices.

The solid-state and sol-gel synthesis of Nd5Mo3O16+δ neodymium molybdate has been investigated. The sequence of chemical transformations was studied using differential thermal analysis, X-ray diffraction analysis, and infrared spectroscopy. It has been demonstrated that the solid-state synthesis occurs stepwise through the formation of Nd2(MoO4)3 and phases with monoclinic structures. The using of the sol-gel method allows obtaining a single-phase neodymium molybdate directly after decomposition of the organic precursor and decreasing of the synthesis temperature by 200 K. The investigation of the crystal structure was carried out by high resolution neutron diffraction, which revealed non-uniform changes in the neodymium-oxygen interatomic distances with increasing temperature.

Magneto-optical measurements enable the identification of Fe2+ and Fe3+ in the R and S blocks of BaFe12O19 Mhexaferrite powder obtained by sol -gel processing, followed by thermal annealing at 900 C for 3 hours. The ferromagnetic phase is evidenced by the spin-majority configuration (Fe3+) due to their unpaired electrons between d -d orbitals, while the Fe2+ in the low spin possesses diamagnetic behavior strongly dependent on the surrounded crystal field. Additionally, the irradiation with gamma rays changes the ratio between Fe2+/Fe3+, mainly on the surface of BaFe12O19 nanocrystals. These changes were confirmed by X-ray Photoelectron Spectroscopy measurements, in which the concentration of Fe2+ increased from 69% to 82%, while the one of Fe3+ decreased from 31% to 18%. he thermoluminescent measurements reveal the same changes of Fe3+ in Fe2+ by electron capturing during irradiation, which is released as a red emission after recombination processes. The changes are explained by the increasing of some Fe-O bonds along the c-axis, mainly due to breaking a part of these bonds. The X-ray analysis confirms the changing of the parameters for the BaFe12O19 hexagonal structure.

Novel lanthanum–samarium molybdates with a fluorite-like structure were synthesized from metal oxides using solidstate synthesis. The total conductivity of these phases reached 10–2 S cm–1 at 700°C.

Neodymium molybdate with a cubic fluorite-like structure is obtained by solid state reactions from metal oxides. The formation of the final product occurs through the formation at 700°C of a monoclinic Ln2MoO6-type structure (space group C2/c) probably containing vacancies in the neodymium and oxygen lattices. Neodymium molybdate obtained at 900°C crystallizes in the space group Pn $$\bar {3}$$ n with the cell parameter a ≈ 11.039 Å. The crystal structure of neodymium molybdate obtained at 700 and 900°C is studied by neutron diffraction and atomistic modeling using the GULP program in the pressure range 0–5.9 GPa, which demonstrates stability of the cubic structure at elevated pressures.

Bi-substituted M-type hexaferrites, BaFe12-xBixO19 (0.1 <= x <= 1.2), or Bi-BaM, were produced by the solid-state reactions. The correlation between the phase content, chemical composition, crystal structure features, and peculiarities of the magnetic properties of Bi-BaM was established using XRD (X-ray diffraction), SEM (scanning electron microscopy), and VSM (vibrational sample magnetometry). XRD phase analysis made it possible to establish the limit of substitution of Fe3+ ions by Bi3+ ions. It was shown that at a low substitution level (x <= 0.3), no impurity phases were detected, and the samples are characterized by a single-phase state with the space group (SG) P6(3)/mmc. As the degree of substitution (x >= 0.6) increases, the formation of impurity phases was observed, which can be explained by the difficulties of ion diffusion in the process of solid-phase synthesis as well as the formation of defects in the magnetoplumbite structure due to the large ionic radius of Bi3+. As impurity phases in the studied compositions (x >= 0.6) the following were noted: BiFeO3 (SG: Pnma); BiO2 (SG: Fm-3m); BaBi2O6 (SG: R-3); and Ba0.5Bi1.5O2.16 (SG: Im-3m). The content of the main phase (SG: P6(3)/mmc) decreases from 95.11 to 88.27 vol% with an increase in x from 0.6 to 1.2, respectively. Analysis of SEM images showed the growth of particles up to 10 mu m, depending on the concentration of bismuth oxide during hexaferrite synthase. The Bi-BaM magnetic characteristics were examined using VSM in the range of 3 T at 300 K. Due to the magnetic structure's frustration, with increased x a decrease in saturation magnetization (M-s) was found. There were two concentration diapasons with different speeds of Ms decrease. In the first diapason, the main contribution belong to the magnetic structure frustration in the frame of the main phase (P6(3)/mmc) due to the long-range Fe-O-Fe exchange interaction weakening (under Bi substitution). In the second diapason, the main contribution belong to the impurity phase formation and decrease of the main magnetic phase concentration in samples.

— Using coprecipitation, we have synthesized LnVO 4 (simple) and CaLnZr(VO 4 ) 3 (Ln = Nd, Sm, Eu, Gd, Dy, Yb) (ternary) lanthanide orthovanadates; a La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 VO 4 solid solution, modeling the composition of the lanthanides in radioactive waste (all crystallizing in the zircon structure, sp. gr. I 4 1 / amd ); and LaVO 4 , crystallizing in the monazite structure. Their unit-cell parameters have been shown to increase systematically with increasing lanthanide ionic radius. Their mid- and far-IR vibrational spectra suggest that their symmetry is lower than that of classical zircon. The synthesized compounds are stable up to 900°C. Their average thermal expansion coefficients lie in the range (6–11) × 10 –6 K –1 .

We report the observation of a peculiar polarization behavior of BaFe12O19 in electric field where the linear polarization is detected at temperatures below 150 K whereas at higher temperatures a hysteresis-like polarization response is observed. At the same time, the performed neutron diffraction analysis shows no variations in crystal or magnetic structures with temperature. Based on the results of ab initio calculations we suggest the mechanism able to explain the experimentally observed behavior. We show that specific Fe atoms do not occupy the positions formally assigned to them by the conventional centrosymmetric P6(3)/mmc (#194) space group (z = 0.25; 0.75) as these positions correspond to local energy maxima. Instead, these Fe atoms are shifted along the z-axis to positions z = 0.259 (0.241) and z = 0.759 (0.741), which correspond to local energy minima. To an inversion center move between these minima Fe atoms need to overcome an energy barrier. This barrier is rather insignificant for smaller volumes but it becomes larger for expanded volumes due to coupling between the displacements of these Fe atoms. Additionally, our analysis suggests that the non-centrosymmetric and polar P6(3)mc (#186) space group could be appropriate for the description of the BaFe12O19 structure.

Методами прямого осаждения из кислых растворов получены фосфаты со структурой минерала монацита – NdPO 4 , GdPO 4 , твердый раствор La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 PO 4 , моделирующий состав фракции РАО, и YbPO 4 , кристаллизующийся в структуре ксенотима. В гидротермальных условиях получены кристаллогидраты NdPO 4 ·0.67Н 2 О со структурой минерала рабдофана и YbPO 4 со структурой ксенотима. Размер областей когерентного рассеяния порошков варьируется от 13 до 65 нм, морфология и размер порошков зависят от способа синтеза. При нагревании до 1170 K порошки сохраняют свой фазовый состав. Средние значения коэффициентов теплового расширения при 900 К находятся в интервале (5.6–9.6) × 10 –6 K –1 , что позволяет отнести исследуемые материалы к классу среднерасширяющихся.

Neodymium molybdate with a cubic fluorite-like structure was obtained by solid state reactions from metal oxides. The formation of the final product occurs through the formation of a monoclinic structure of Ln2MoO6 type (space group C2/c) at 700°C, which probably contains vacancies in neodymium and oxygen lattices. Neodymium molybdate obtained at 900°C crystallizes in the space group Pn\(\bar {3}\)n with the cell parameter a ≈ 11.039 Å. The crystal structure of neodymium molybdate obtained at 700 and 900°C was studied by neutron diffraction and atomistic modeling using the GULP program in the pressure range 0–5.9 GPa, which demonstrated the stability of the cubic structure at elevated pressure.

— Phosphates isostructural with the mineral monazite—NdPO 4 , GdPO 4 , and a La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 PO 4 solid solution modeling the composition of the lanthanide components of radioactive waste—and YbPO 4 , crystallizing in the xenotime structure, have been prepared via direct precipitation from acid solutions. Under hydrothermal conditions, we have prepared the crystalline hydrate NdPO 4 ·0.67Н 2 О isostructural with the mineral rhabdophane and the YbPO 4 phosphate with the xenotime structure. The powders range in crystallite size from 13 to 65 nm. The particle morphology and size have been shown to depend on the synthesis process. During heating to 1170 K, the phase composition of the powders remained unchanged. Their average 900-K thermal expansion coefficients lie in the range (5.6–9.6) × 10 –6 K –1 , so these phosphates can be regarded as having medium thermal expansion.

Методом соосаждения получены простые LnVO 4 и тройные CaLnZr(VO 4 ) 3 (Ln = Nd, Sm, Eu, Gd, Dy, Yb) ортованадаты лантаноидов; твердый раствор La 0.3 Nd 0.5 Sm 0.1 Eu 0.1 VO 4 , моделирующий состав фракции лантаноидов РАО, имеющие структурный тип циркона (пр. гр. I 4 1 / amd ); а также LaVO 4 , кристаллизующийся в структурном типе монацита. Параметры элементарных ячеек монотонно возрастают с ростом ионного радиуса лантаноида. Колебательные спектры в средней и дальней ИК-областях свидетельствуют о понижении симметрии соединений по сравнению с классическим цирконом. Фазовая стабильность полученных соединений сохраняется до 900°C. Средние коэффициенты теплового расширения варьируются в интервале (6–11) × 10 –6 K –1 .

The results of studies of the features of the phase composition, crystal and magnetic structure of Bi-substituted barium hexaferrite BaFe12-xBixO19 (0.1≤ x≤ 1.2) by methods of Mossbauer spectroscopy, X-ray phase analysis, as well as image analysis by scanning electron microscopy are presented. Samples of Bi-substituted hexaferrites - BaFe12-xBixO19 (where x=0.1; 0.3; 0.6; 0.9 and 1.2) were synthesized by the method of solid-phase reactions with double annealing (at T=1100oC for 6 h) and intermediate grinding (for 0.5 h). The X-ray phase analysis allowed us to establish the limit of substitution of Fe3+ ions by Bi3+ ions. It has been shown that at a low level of substitution (x≤0.3) there are no impurity phases detected and the samples are characterized by a single-phase state with the spatial group P63/mmc. When the degree of substitution increases (x>0.3) the formation of impurity phases is noted, which can be explained by the difficulties of ion diffusion in the process of solid-phase synthesis, as well as the formation of defects in the structure of magentoplumbite due to the large ionic radius of Bi3+. As impurity phases in the studied compositions (x>0.3) Marked: BiFeO3 (Pr. Gr. Pnma); BiO2 (Pr. Gr. Fm-3m); BaBi2O6 (Pr. Gr. R-3) and BaO0,5Bi1,5O2,16 (Pr. Gr. Im-3m). The content of the main phase (Pr. Gr. P63mmc) at the same time decreases from 95.11 to 88.27 vol.% when increasing x from 0.6 to 1.2, respectively. The analysis performed by the method of Messbaurov spectroscopy showed that all Fe ions have a charge of 3+. And all parameters lie within the values characteristic of Fe3+ ions corresponding to the coordination of polyhedra: 12k. 4f2, 2a - octahedra, 4f1 - tetrahedron, and 2b - bipyramide. It is possible to single out a small monotonous decrease only for the 12k position. The analysis of SEM images showed an increase in the average particle size up to 10 mkm, depending on the concentration of bismuth oxide during the synthesis of hexaferrite.

The paper presents the investigation of ordinary and ternary vanadates with zircon and monazite structures. Vanadates LnVO4 and CaLnZr(VO4)3 , where (Ln = La, Nd, Sm, Eu, Gd, Dy, Yb) and solid solution La0.3Nd0.5Sm0.1Eu0.1VO4, were prepared by precipitation reaction. Bulk ceramic samples were obtained from powders by Spark Plasma Sintering (SPS). The powders and ceramics were examined with several physicochemical methods. The coefficients of thermal expansion at 900C were determined. The hydrolytic stability of ceramic materials was studied. The peculiarities of high-rate SPS of powders of ordinary and ternary vanadates were analyzed.

The microscopic mechanism of the occurrence of ferroelectric properties in M-type barium hexaferrites is investigated by experimental and first-principle computation methods. The analysis of magnetic, X-ray, and Mossbauer measurements of BaFe12O19 samples ascertains the correlation between the thermal factor in the process of annealing samples and their functional properties. The occurrence of the remnant polarization in barium hexaferrites at room temperature contradicts the description of their crystal structure in the fra-mework of centrosymmetric space group P63/mmc (No. 194), in which one of the symmetry operations is inversion center. Therefore, the crystal structure of BaFe12O19 was analyzed in the frameworks of SG P63/mmc (No. 194) and non-centrosymmetric SG P63mc (No. 186). The computed value of polarization for a non-centrosymmetric unit cell is similar to 3.5 mu C/cm2. The analysis of polarization was carried out on a path connecting the polar P63mc and non-polar P63/mmc structures and considered in terms of the total energy barrier. Our result allows ascertaining a direct relationship between the remnant polarization of the unit cell and the broken spatial-inversion symmetry in the crystal structure of M-type barium hexaferrite.(c) 2022 Elsevier B.V. All rights reserved.

The polycrystalline samples of the x/6Pr6O11 – MoO3 (2 ≤ x ≤ 6) series were prepared by conventional solid-state route. The phase formation was studied by XRD analysis in the temperature range of 1000 – 1200°C. After calcination at 1100°С, the formation of praseodymium molybdate with Pr4MoO9+δ composition is observed, which decomposes into a mixture of Pr2MoO6 and Pr6MoO12+δ phases at 1200°С. It was first established that Pr4MoO9+δ praseodymium molybdate has a monoclinic lattice with parameters a = 16.7211(9) Å, b = 11.9894(7) Å, c = 9.5588(5) Å, β = 109.6149(7) °, sp. gr. C 2/m. Crystal structure was refined by high resolution neutron diffraction data. The homogeneity regions of Pr4MoO9+δ and Pr6MoO12+δ were determined to be 4 < x < 4.2 and 4.57 < x < 6, respectively. It was shown that the conductivity of this molybdates increases with praseodymium oxide content in the Pr5Mo3O16+δ – Pr4MoO9+δ – Pr6MoO12+δ series.

Elemental powders of W, B4C, TiC and C (graphite) in percentage weight ratio of W-–6 wt% B4C–2 wt% TiC–1 wt% C are used as precursors in mechanical alloying process aimed at producing tungsten-based material. The composition of the obtained material is nearly single-phase W2B (∼98%) with small additions of WB and TiC (<2%), unveiled by XRD analysis. Irradiation with 2.5 MeV helium ions to a fluence of 5.0 × 1020 ion/cm2 was performed and the induced radiation damage was assessed. The XRD data unveiled reduction in size of the grains from 300 nm to 260 nm upon the irradiation. It is observed that the irradiation had negligible effect on the W2B phase content, while the WB phase content increased by 0.74% and TiC phase content decreased with 0.71% upon irradiation. Raman spectral analysis showed that not only graphite's carbon is affected by the irradiation, but also the titanium bonded carbon in TiC underwent changes, resulting in development of non-stoichiometric TiC. Positron annihilation spectroscopy is employed for investigating the presence of intrinsic defects and their evolution upon irradiation. Based on the analysis of all the obtained results, we contemplate that the detected WB phase most probably belongs to the grain boundaries of W2B grains. The irradiation to a fluence of 5.0 × 1020 ion/cm2 did not cause chemical interaction of tungsten boride phases with the carbon species of the material, which would have resulted in the appearance of new phases.

The solid solutions of In3+ doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method, and Rietveld analysis of the neutron diffraction patterns was conducted. In3+ cations occupy octahedral (4f(VI) and 12 k) and tetrahedral (4f(IV)) positions (SG = P6(3)/mmc (No. 194)). The average particle size is 837-650 nm. Curie tempearature (T-C) of the compounds monotonically decreased down to similar to 520 K with increasing x. A frustrated magnetic state was detected from ZFC and FC magnetizations. saturation magnetization (M-s) and effective magnetocrystalline anisotropy coefficient (k(eff)) were determined using the law of approach to saturation. A real permittivity (e ") maximum of similar to 3.3 at similar to 45.5 GHz and an imaginary permittivity (e//) of similar to 1.6 at similar to 42.3 GHz were observed for x = 0.1. A real permeability (mu') maximum of similar to 1.5 at similar to 36.2 GHz was observed for x = 0. A mu " imaginary permeability maximum of similar to 0.8 at similar to 38.3 GHz was observed for x = 0.1. The interpretation of the results is based on the type of dielectric polarization and the natural ferromagnetic resonance features. (c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press.

Hexaferrites are usually used in devices for frequencies of 8-75 GHz. In this work, it is shown that Snsubstituted hexaferrite can be used for electromagnetic shielding and at lower frequencies (for example, in the L-band and S-band) as absorbing materials. The paper defines a solid-state reaction technique for preparing BaFe12-xSnxO19 (0.1 <_x <_ 1.2). The samples are characterized by XRD, SEM, VSM, and VNA. The study shows that increasing the Sn-substitution leads to weakening the interaction between the magnetic sublattices. So, in general, the saturation magnetization (Ms) decreases. Low saturation magnetization at high coercivity values gives a high anisotropy field, which provides significant absorption and matching impedance. The sample with substitution of x = 1.2 is the most absorbing sample (more than 99.99% of the incident energy absorbed for 10 mm thickness). The investigated samples have the potential to be useful absorption materials for shielding production (materials that absorb electromagnetic radiation) (c) 2021 Elsevier B.V. All rights reserved.