Structural peculiarities of Ca3Co2O6, including its low dimensionality and inherent geometric frustration, are the main sources of the exotic physical properties observed for this material. Exploring the interplay between the lattice and other electronic degrees of freedom is crucial for understanding the mechanism governing its physical behavior. In this study, we present a comprehensive analysis of the structural features of Ca3Co2O6 in a large pressure range of 0-30 GPa, utilizing a combination of x-ray diffraction and Raman spectroscopy, complemented by density functional theory calculations. Notably, we observe several isostructural modifications at 3 GPa, 10 GPa, and 22 GPa, which have not been detected elsewhere. These phase transitions are accompanied by anomalies in the pressure-dependent variation in Ca and O atomic positions and Co-O interatomic bonds. Bader charge analysis also reveals changes in charge redistribution trends among Co, Ca, and O across the phase transitions, suggesting an electronic origin for the pressure-induced isostructural transitions in Ca3Co2O6.

Nanostructured spinel-type ferrites have attracted significant interest from both the aspects of fundamental research and industrial application owing to their outstanding electronic and magnetic properties. Understanding the factors governing their magnetic properties is important for designing advanced materials with tailored features. In this work, we have conducted a systematic investigation on the structural, electronic, and magnetic properties of high-energy ball-milled CoFe2O4 nanoparticles, which possess a cubic spinel structure and average crystallite sizes (D) ranging from 334 nm for the initial bulk material to 11.7 nm after 120 min of milling. Our observations indicated that the high-energy milling leads to the migration of Co2+ ions from the octahedral B site to the tetrahedral A site, and vice versa for Fe3+ ions. The concentration of Co2+ ions at the A site increases linearly versus the 1/D value. Unlike previous studies on CFO, we have found that the spin canting of Fe3+ ions occurred at both the A and B sites within the inner core, not only on the surface of nanoparticles. The spin canting angles phi A and phi B increase with grain-size reduction. Although the milling-induced changes in the cation distribution and spin canting are expected to significantly increase the saturation magnetization, this effect is overshadowed by the decrease caused by surface spin disorder. In other words, the surface effects play the primary role affecting the magnetic properties of the milled CFO nanoparticles.

To reduce the number of image projections in neutron tomography experiments, tomography reconstruction algorithms are used from an incomplete and limited number of neutron projections. The possibilities of a reconstruction algorithm based on convolutional neural networks are presented. It was found that only 72 projections are required for trained convolutional neural network for a qualitative reconstruction comparable to that from a complete dataset. Variations in the quality of the tomography reconstruction due to changes in training data and the number of input projections are considered. Examples of using convolutional neural networks for neutron tomography reconstructions of real experimental data includes the results of studies on archaeological metal materials from the "Volna-1 '' archaeological site.

In our study, we present comprehensive findings on the structural properties of Pr2Ti2O7 2 Ti 2 O 7 across a broad pressure range of 0-30 GPa. Neutron diffraction experiments, conducted under ambient conditions, offer crucial structural insights into the initial monoclinic phase with the P21 1 space group. As pressure increased, a significant phase transition to the monoclinic P21/m 1 /m phase occurred at 13.8 GPa. Structural data analysis from X-ray diffraction highlights the essence of this transition, identifying it as the tilting of Ti-O6 6 octahedra. High-pressure Raman spectroscopy data unequivocally confirms the phase transition, detecting anomalies in the baric dependencies of some vibration modes of Pr2Ti2O7 2 Ti 2 O 7 and the emergence of new modes in the Raman spectra within the pressure region associated with the phase transition. The analysis of these novel vibration modes points to alterations in the Ti-O6 6 octahedra, emphasizing the pivotal role played by Ti4+ 4 + and O2 2- ions in the mechanism of the pressure- driven phase transition.

The crystal structure and vibrational spectra of cation-deficient nanostructured zinc ferrite Zn0.34Fe2.53 square O-0.13(4) (where square denotes the cation vacancies) have been studied using X-ray diffraction and Raman spectroscopy methods in the pressure range of 0-34 GPa. Our results indicate a phase transition from the initial cubic phase with space group Fd 3 m to a high-pressure phase with orthorhombic symmetry of Bbmm at pressures above 18 GPa. This phase transition is accompanied by changes in lattice parameters, unit cell volume, interatomic bond lengths, and vibration mode frequencies.

The crystal structure and vibrational spectra of CoFe2O4 ferrite were studied using X-ray diffraction and Raman spectroscopy over a pressure range of 0-35GPa. A structural phase transition from the cubic Fd (3) over barm phase to the post-spinel orthorhombic Bbmm phase occurs at a pressure of approximately 23GPa through a two-phase region. Pressure-induced changes in the structural parameters, lattice distortion, and vibrational modes of the studied ferrite were investigated in detail. Lattice parameters, bond lengths, compressibility, and bulk modulus for both the cubic and orthorhombic phases of CoFe2O4 were determined.

The crystal and magnetic structures of van der Waals layered ferromagnet CrBr3 were studied using X-ray powder diffraction and neutron powder diffraction at pressures up to 23 GPa at ambient temperature and up to 2.8 GPa in the temperature range 6–300 K, respectively. The vibration spectra of CrBr3 were studied using Raman spectroscopy at pressures up to 23 GPa at ambient temperature. The anomalous pressure behavior of structural parameters and vibrational modes was observed, associated with a gradual isostructural phase transition in the pressure range 2.5–7 GPa. The Curie temperature TC reduced rapidly with a pressure coefficient dTC/dP=−4.1(4) K/GPa. A full suppression of the ferromagnetic state was expected at PC~8.4 GPa, where onset of the antiferromagnetic spin arrangement or magnetically disordered state may take place. Anomalies in Raman spectra at P~15 GPa point to another possible phase transformation in CrBr3, which may be related to the proximity of metallization of this van der Waals ferromagnet.

We had investigated the pressure-induced phase transition phenomenon in the perovskite-like material Nd2Ti2O7 compound. The structural and vibrational properties of a layered Nd2Ti2O7 have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The gradual structural phase transition from the initial monoclinic P21 ( C2) phase to the monoclinic P2 ( C1) phase was observed at P - 19 GPa. This pressureinduced phase transition is accompanied by anomalies in the pressure behavior of unit cell parameters and vibrational modes. The role of pressure application as a trigger for a significant rotation of the TiO6 octahedra, alterations in interatomic distances, and the displacement of Nd atoms were discussed.

The crystal structure and vibrational spectra of cation-deficient nanostructured zinс ferrite Zn0.34Fe2.53☐0.13O4 (where ☐ denotes the cation vacancies) have been studied using X-ray diffraction and Raman spectroscopy methods in the pressure range of 0-34 GPa. Our results indicate a phase transition from the initial cubic phase with space group Fd m to a high-pressure phase with orthorhombic symmetry of Bbmm at pressures above 18 GPa. This phase transition is accompanied by changes in lattice parameters, unit cell volume, interatomic bond lengths, and vibration mode frequencies.

In layered perovskites with the Carpy-Galy structural type, similar structural phase transitions occur under high pressure. These structural changes, which are crucial for the pressure-induced phase transition in layered perovskite, were analyzed based on experimental X-ray diffraction data. The tilting of the Ti-O6 6 octahedra and the distortion of the arrangement of rare-earth atoms were studied in detail. Changes in these structural features in layered perovskite serve as common indicators of the phase transition to the monoclinic phase that occurs under high pressure application.

In our study, we present comprehensive findings on the structural properties of Pr2Ti2O7 across a broad pressure range of 0–30 GPa. Neutron diffraction experiments, conducted under ambient conditions, offer crucial structural insights into the initial monoclinic phase with the P21 space group. As pressure increased, a significant phase transition to the monoclinic P21/m phase occurred at 13.8 GPa. Structural data analysis from X-ray diffraction highlights the essence of this transition, identifying it as the tilting of Ti-O6 octahedra. High-pressure Raman spectroscopy data unequivocally confirms the phase transition, detecting anomalies in the baric dependencies of some vibration modes of Pr2Ti2O7 and the emergence of new modes in the Raman spectra within the pressure region associated with the phase transition. The analysis of these novel vibration modes points to alterations in the Ti-O6 octahedra, emphasizing the pivotal role played by Ti4+ and O2- ions in the mechanism of the pressure-driven phase transition.

The systematic studies of composition and spatial distribution of main phases inside volume of 25 fragments of Byzantine ceramic obtained in archeological works in the Dobrudja region, Romania, have been performed using neutron diffraction and tomography, and Raman spectroscopy. The obtained structural data on the content of phases, the presence of calcite grains and pores, and the uniformity of phase spatial distribution made it possible to systematize the studied fragments and correlate them with clay sources or pottery workshop. The experimental possibilities of neutron methods of nondestructive structural diagnostics as well as the structural markers provided by them in the studies of ceramic samples are discussed.

A single high-entropy pyrochlore-type compound (A2B2O7) was successfully synthesized, incorporating 8 different rare-earth cations at the A site and 2 different metal cations at the B site in equiatomic amounts [(8A1/ 8 ) 2 ( 2 B 1/2 ) 2 O 7 ]. Powders with a nominal composition of(La 1/8 Sm 1/8 Nd 1/8 Pr 1/8 Y 1/8 Gd 1/8 Dy 1/8 Yb 1/8 ) 2 (Hf 1/2 Zr 1/ 2)2O7 were fabricated by glycine nitrate procedure (GNP). The GNP process yielded powders with low crystallinity and after subsequent calcination, a well crystalline ceramic powders were formed. The phase evolution was initially analyzed using X-ray diffraction (XRD). In situ high-pressure X-ray diffraction was employed to investigate the structural stability and high-pressure behavior of the A2B2O7 pyrochlore up to 25.8 GPa. Theoretical investigations of the high-entropy pyrochlore systems were performed and showed good agreement with the experimentally obtained results.

The composite phosphors SrAl2O4/Sr3Al2O6:Bi2O3/Bi2O4 synthesized by a solid-phase approach have been studied by means of X-ray diffraction, Raman spectroscopy, and optical spectroscopy methods. A redistribution of Bi3+ ions between two phases was observed by changes in crystal parameters, bond length, and vibrational frequencies on Raman spectra. A relationship between the structure of the host matrix and the optical characteristics of phosphors has been established.

In this paper, we study the ceramics of cobaltite [Tb0.5Nd0.5CoO3]1−yCy with equiatomic contents of terbium and neodymium and with the addition of a carbon material flakes (СMF) with the content of carbon in the range of weight fraction 0 < y < 0.01. The ceramics were obtained by the method of solid-phase reactions according to the standard ceramic technology in air. Using X-ray diffraction and energy-dispersive analysis, it was established that the initial (undoped) solid solution is single-phase with perovskite structure. It was shown that Co3+ ions in undoped ceramics under study are in a non-magnetic low-spin state over the entire temperature range under consideration (2–320 K), and the entire contribution to the magnetization is due to Tb3+ and Nd3+ ions. An analysis of the temperature dependences of the electrical resistance R(T) shows that the initial solid solution behaves like a dielectric with a reduced activation energy of about 0.3–0.35 eV in the temperature range of 280–320 K, due to hopping conduction with a constant activation energy (constant range hopping) by defects in Tb0.5Nd0.5CoO3 matrix. At lower temperatures (200 – 275 K) in the initial (undoped) Tb0.5Nd0.5CoO3 samples, the Mott-type hopping conductivity mechanism with a variable range hopping and high values of the characteristic temperature To ∼ 109 K was observed. Simultaneously, at 300 K, we observed hopping conductivity on alternating current according to the law σ(ω) ∼ ω-α(ω), where the exponent α, which determines a hopping probability, depends on the frequency. In [Tb0.5Nd0.5CoO3]1−yCy samples, heavily doped with СMF with y = 0.01, carrier transport in the entire studied temperature range of 2–320 K mainly occurs along highly conductive carbon-based channels, formed inside of Tb0.5Nd0.5CoO3 matrix by СMF. At temperatures below 15–20 K, these samples show hopping behavior of R(T) with a variable range hopping over localized states, described by the Mott–Kirkpatrick law. In the temperature range 20–100 K electrical resistance versus temperature R(T) along carbon-based channels obey the law R(T) ∼ Ln T. In this case, the relative magnetoresistance MR(T, B) is characterized by a negative sign at temperatures below 10 K in magnetic fields less than 1 T. This behavior of the R(T, B) dependences were described on the basis of the theory of quantum corrections to the Drude conductivity for two-dimensional samples under conditions of weak localization, which is consistent with the behavior of layered carbon-based materials known from the literature. At T > 150 K curves R(B) follow to Lorentz-like positive magnetoresistive effect in Tb0.5Nd0.5CoO3 matrix in the whole magnetic field range.

The substitution of Bi by rare-earth ions is one of the common approaches for improving the electrical, magnetic, and multiferroic properties of the most studied multiferroic material BiFeO3. In this work, Bi1−xTbxFeO3 compounds with x = 0.05, 0.1, and 0.3 were synthesized using a two-step process: standard solid-state synthesis and high-pressure annealing. The obtained samples were studied by means of x-ray diffraction at normal pressure and neutron powder diffraction at high pressure. It was shown that high-pressure annealing could increase the Tb solubility limit to 10 at. %. It is proposed that the maximum solubility limit is even higher and could be achieved with high-pressure annealing in bulk samples. The transition from the R3c phase to the Pnma phase for the compounds with x = 0.05, 0.1 occurs through a two-phase region and starts at P≈4.4 and 1.7 GPa, respectively. The Pnma phase is stable in the compound with x = 0.3 up to P≈3.2 GPa. The values of Fe magnetic moments decrease with an increase in the Tb concentration or with external pressure for the compounds with x=0.05,0.3 in one-phase regions. The results will help to optimize the synthesis of multiferroic materials with improved magnetoelectric coupling for use in technological applications.

Samples of nanocrystalline PbF2 glass ceramics were obtained by heat-treating SiO2–GeO2–PbO–PbF2–CdF2 glasses. The Ho2O3 and Tm2O3 doping effects on the structural features of PbF2 nanoparticles were studied using small-angle X-ray scattering and X-ray diffraction methods. The enlargements of the average sizes of nanoparticles and the sizes of local areas of density fluctuations have been found to be correlated with an increase in concentrations of Ho2O3 and Tm2O3 in initial glasses. A variation in the concentrations of Ho2O3 and Tm2O3 does not affect the morphology and fractal dimension of the formed PbF2 nanoparticles.

The spatial arrangement of the internal pores inside several fragments of ancient cast iron cauldrons related to the medieval Golden Horde period was studied using the neutron tomography method. The high neutron penetration into a cast iron material provides sufficient data for detailed analysis of the three-dimensional imaging data. The size, elongation, and orientation distributions of the observed internal pores were obtained. As discussed, the imaging and quantitative analytical data are considered structural markers for the location of cast iron foundries, as well as a feature of the medieval casting process.

High-pressure effects on the crystal structure and vibration spectra of the perovskite-like layered La2Ti2O7 compound were studied using X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The crystal structure of the compound was measured by means of a neutron diffraction at room temperature and ambient pressure. At P = 17.3 GPa, phase transition from the initial monoclinic phase of P21 symmetry to the monoclinic phase of P2 symmetry has been observed. The pressure-induced phase transitions in La2Ti2O7 are accompanied by anomalies in the pressure dependences of the unit cell parameters, as well as the vibrational modes. The baric dependences of lattice parameters, unit cell volume and vibration frequencies were obtained; the bulk modules for initial and pressure-induced phases of La2Ti2O7 were calculated.