The defect structure of crystals of as-grown nonstoichiometric tysonite (LaF3 type) La1 − y Sr y F3 − y phase (y = 0, 0.05, 0.07, and 0.15) has been investigated by X-ray diffraction and neutron diffraction. A concentration-driven structural transition from the β-La1 − y Sr y F3 − y modification to the α-La1 − y Sr y F3 − y modification in the range y = 0.05–0.10 has been observed for the first time. This transition correlates with the maximum of fluorine-ion conductivity (y = 0.05 ± 0.02) and the maximum in the melting curve (y = 0.07 ± 0.03). β-LaF3 and β-La0.95Sr0.05F2.95 crystals belong to the trigonal system (sp. gr. \(P\bar 3c1\), Z = 6) and are twinned according to the merohedral twin law. Fine changes in the fluorine sublattice of β-La0.95Sr0.05F2.95 increase conductivity σ293K to 3 × 10−4 S/cm; hence, these crystals can be used as fluorine-conducting solid electrolytes (FCSEs) in solid-state ionics devices. Additional possibilities of ion transport over twin joints are discussed. In α-La0.85Sr0.15F2.85 crystal the symmetry group changes to P63/mmc, Z = 2; it is not twinned and its fluorine-ion conductivity is reduced.

Описана модернизация детекторной системы и системы управления нейтронным порошковым дифрактометром (н.п.д.) на канале ГЭК-5 реактора ВВР-ц (филиал ФГУП “НИФХИ им. Л.Я. Карпова”, Обнинск). Cоздан подключенный к персональному компьютеру аппаратно-программный комплекс, обеспечивающий сбор и накопление данных, а также управление экспериментом. Кратко описаны разработанные в ЛНФ ОИЯИ основные блоки системы автоматизации н.п.д. и управляющего программного комплекса Sonix+. Модернизация позволила увеличить светосилу дифрактометра и полностью автоматизировать процесс измерений.

For the purpose of comparative analysis, the structure of a garnet crystal activated by 1 at % of chromium, Lu3Al5O12:Cr3+, (sp. gr. Ia \(\bar 3\) d, a = 11.910 Å, R w = 5.5%) and a pure garnet crystal (R w = 4.0%) is studied by neutron diffraction. It is found according to an increase in the volume of the octahedron that the Cr3+ cation is located at an octahedral position upon isomorphous substitution of the smaller Al3+ cation. Structural imperfection increases in the chromium-activated garnet, which is manifested in numerous reflections, forbidden in the space group of garnet, and the increasing divergence of refinement R w of the structure.

Проведено нейтронографическое исследование структуры монокристалла граната с активирующей добавкой 1 ат. % хрома Lu3Al5O12:Cr3+ (пр. гр. Ia d, а = 11.910 A, Rw = 5.5%) и (для сравнительного анализа) структуры монокристалла чистого граната (Rw = 4.0%). По увеличению объема части октаэдра установлено, что катион Cr3+ при изоморфном замещении меньшего катиона Al3+ находится в октаэдрической позиции. Отмечено увеличение дефектности граната, активированного хромом, что проявляется в большем количестве отражений, запрещенных в пространственной группе граната, и увеличении фактора расходимости Rw при уточнении структуры.

The modernization of the detector system and control system of the neutron powder diffractometer (NPD) in the GEK-5 channel of the VVR-c reactor (Obninsk Branch, Karpov Institute of Physical Chemistry) is described. The PC-connected hardware and software complex, which ensures data acquisition and storage and control of the experiments, is created. The main modules of the NPD automation system and Sonix+ control software package, designed at the Frank Laboratory of Neutron Physics at JINR, are briefly described. The modernization has made it possible to increase the luminosity of the diffractometer and completely automatize the measurement process.

The atomic structure of a single crystal of one of four Na 0.69 WO 3 phases, which exist below 293 K, has been refined from neutron diffraction data (WWR-c reactor at the Karpov Institute of Physical Chemistry, Obninsk Branch; λ = 1.168 Å; λ/2 contribution < 0.8%; sinθ/λ ≤ 0.810; T = 288 K; crystal sphere ∅ = 4.4 mm; cubic unit cell with a = 7.672 Å, sp. gr. Im 3, z = 8, μ = 1.9 mm −1 ). The Na 0.69 WO 3 atomic structure has been refined (198 independent reflections) taking into account the anisotropy of thermal vibrations ( R w = 4.0%). The stoichiometric coefficient Na(0.69) is also refined. A structural distortion is revealed, which is characterized by the displacement of oxygen atoms (0, 0.2609(2), 0.2391(2)) from the ideal perovskite positions (0, 1/4, 1/4); this displacement doubles the ideal perovskite lattice period. The oxygen displacements can be described as rotations of oxygen octahedra by 3.58° around the [111] direction. The structure remains cubic because the octahedra rotations with respect to all three perovskite cubic axes are identical.

The structure of single crystals of the nonstoichiometric phases Ba 1 − x R x F 2 + x ( R = Er, Yb, Lu; 0.1 < x < 0.3) grown by the Bridgman method from the flux has been studied using X-ray diffraction and neutron diffraction analyses at a temperature of 293 K. The phases have a defect structure of the fluorite type and crystallize in the cubic system, space group of symmetry Fm 3̅ m . The displacements revealed in the cationic motif of the Ba 1 − x R x F 2 + x phases with R = Er, Yb, or Lu are interpreted as displacements of the Ba cations from the main structural positions upon the formation of Ba 8 [ R 6 F 68–69 ] superclusters of structural defects. This interpretation of the experimental data agrees with the results obtained from the recent study of the Ba 0.78 Tm 0.22 F 2.22 phase [1] at room and low (110 K) temperatures and is confirmed by the coincidence of intercationic distances in the disordered phases Ba 1 − x R x F 2 + x and the ordered phases Ba 4 R 3 F 17 ( R = Y, Er, Yb). In addition to the well-known changes in the anionic motif, the revealed displacements in the cationic motif are good arguments for the supercluster structural model of the nonstoichiometric phases Ba 1 − x R x F 2 + x .

The distribution of alloying atoms over the sites of the ordered crystal lattices of the γ′ phase and the Ni 2 Cr superstructure that form during aging of the EK78 superalloy is determined by neutron diffraction, and their long-range order parameters are measured. The size, shape, and orientation of the forming γ′-phase precipitates and the ordered matrix are determined by electron microscopy. The mechanism by which the ordered phases in the EK78 alloy form during complex heat treatment is described.

Neutron diffraction analysis has been used to determine concentrational dependences of the parameters of long-and short-range atomic order and the sizes of antiphase domains in Ni3Mn-Ni3Al microcrystalline alloys produced by quenching from the melt and in the quenched bulk alloys of the system. The parameters of atomic order were shown to depend on the temperature of the order-disorder transition. The γ′-phase micro-crystals were found to be characterized by high degrees of long-range order. The effect found is explained by the high degree of solid-solution supersaturation with excess vacancies formed upon quenching from the melt and, therefore, by abruptly increasing diffusion mobility of atoms.

An abnormal phenomenon of increasing long-range order in the Ni3(Mn1−xVx) alloys following the L12 pattern after quenching from the melt with a rate of 106 deg/s is revealed by the neutron diffraction method. It is demonstrated that the established effect can be explained by a high degree of supersaturation (by 4–5 orders of magnitude) with excess quenching vacancies and, as a consequence, by a sharp increase in the diffusion mobility of atoms in the solid solution.

Investigation of Kumakhov halflenses for thermal neutron focusing was carried out on the monochromatic beam of horizontal channel at the Karpov Institute WWR-ts reactor. Efficiency and gain coefficient were measured for two halflenses. Estimation of real halflens focal spot for focused neutron monochromatic beam was made.

The ordered states and structural transformations in Ni3Fe-Ni3Al, Ni3Mn-Ni3Al, and (NiMn)-Mn-3-Ni3Ga alloys are determined by neutron-diffraction structural analysis and calorimetric measurements. The long-range order parameters of the superstructure LI2 are measured, and the positions of the third-element substitutions in fee lattices are established. The Kurnakov temperatures are determined, and phase diagrams containing two-phase regions are constructed.

Structural order-disorder transformations in Ni 3 Fe-Ni 3 Al, Ni 3 Mn-Ni 3 Al, and Ni 3 Mn-Ni 3 Ga alloys were studied by neutron diffraction and calorimetry. Concentration transformations in the L1 2 -type superstructures were established to be isomorphic. Kurnakov points (order-disorder transformation temperatures) were measured and phase diagrams were constructed showing the two-phase (γ+γ') fields. A mechanism for the γ+γ' field formation was suggested, based on the local structure of the alloys. Site preference of alloying elements in the L1 2 superlattice was determined.

The neutron diffraction study of nonstoichiometric single crystals Ba1-xRxF2+x(R = La, Ce, Pr, Nd; 0.22 less than or equal to x less than or equal to 0.5) was made and the trends of the defect-structure changes are discussed. The comparative analysis of F-1 ion incorporation in the anion sublattice of the Fm (3) over bar m space group shows that the single-site model (partial occupation of the i-positions) dominates with increasing difference between Ba2+ and R3+ size; occupation of these positions (i and f) in the investigated crystals tends to be simultaneous with increasing RF3 content although the i-occupation dominates.