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.

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.

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.

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 crystal structure and luminescent properties of Al-substituted [Formula: see text] were studied. It was found that under normal conditions, the samples are characterized by the space group P6 3 /mmc. Depending on the ionic radii of the Al and Fe atoms and the concentration of Al atoms, a decrease in the distance between the atoms in the crystal structure and the lattice parameters was observed. [Formula: see text] crystals ([Formula: see text] = 0.1–1.2) were excited by a laser with a wavelength of 375 nm and 435 nm, to study their luminescent features. From the information obtained from luminescent spectrum, it is seen that with the replacement of magnetic [Formula: see text] ions by diamagnetic [Formula: see text] ions, the intensity of the spectra increases. During exciting by a laser with a wavelength of 435 nm, anti-Stokes luminescence is observed in the ultraviolet region.

[Formula: see text] hexaferrite compound was synthesized, the crystal structure was studied by the X-ray diffraction method. Powder samples were prepared from the mark “analytical grade” oxides [Formula: see text], [Formula: see text] and carbonate BaCO3. It was found that under normal conditions and at room temperatures, the crystal structure of this compound has hexagonal symmetry with the P63mmc space group. The lattice parameters correspond to the values: [Formula: see text] and [Formula: see text]. Atomic dynamics of [Formula: see text] hexaferrite in the range of low temperatures of [Formula: see text] and high temperatures of [Formula: see text] were studied. As a result of the analysis of the spectra obtained by the Raman spectroscopy method, it was determined that the structural phase transition does not occur in this compound over a wide temperature range [Formula: see text]. At the room temperature, the obtained Raman modes are observed at both low and high temperatures.

The influences of Al doping on the structural, magnetic and dynamical properties of BaFe12−xAlxO19 solid solutions (x = 0.1–1.2) have been studied by using a combination of X-ray diffraction, neutron diffraction and infrared spectroscopy. The magnetic moment of every Fe atom, including combinations, has been defined, and the magnetic moment of Fe3+ ions was found to decrease as the concentration of Al3+ diamagnetic ions in the combinations increased. Studies carried out by using infrared spectroscopy showed that four oscillations under normal conditions in these combinations. The results obtained by using infrared spectroscopy for BaFe12−xAlxO19 combinations were compared with the results obtained by using Raman spectroscopy.

AbstractRaman spectroscopy measurements of a monoclinic layered semiconductor TlGaSe2were performed in a pressure range up to 10.24 GPa. The pressure-induced first-order phase transition accompanied by reconstruction of the layer structure was observed at the pressure P ~ 0.9 GPa. The mode-Grüneisen parameters of intralayer bonds were calculated for TlGaSe2. The contribution of thermal expansion to temperature changes of phonon frequencies was defined. The type of intralayer bonds and their pressure transformation were analyzed in layered TlGaSe2. It was shown that the nature of intramolecular forces in molecular crystals and intralayer forces in layered GaS, GaSe and TlGaSe2is similar

The crystal structure and vibrational spectra of Ba1.65Sr3.35Nb10O30–Ba4Na2Nb10O30 barium-strontium niobates are investigated by neutron diffraction and Raman spectroscopy in the concentration range x = 0–1 with steps of 0.1 and 0.05. All compounds under study have a structure of the tetragonal tungsten-bronze type with the space group of P4mm symmetry. The concentration dependences of the crystal-cell parameters, interatomic bonds, and vibrational modes for a number of solid solutions of the (1–х)Ba1.65Sr3.35Nb10O30–хBa4Na2Nb10O30 system are obtained. Anomalies in the behavior of the crystal parameters and vibrational modes are observed for the concentration dependences at x ~ 0.5. This may be due to a change in the nature of the sodium occupation of vacancies in various crystallographic positions of the tetragonal structure.

The crystal and magnetic structures of the strong magnetoelectric BiMn2O5 have been studied as a function of pressure up to 5.7 GPa in the temperature range from 10 K to 60 K by means of neutron powder diffraction. The results reveal that the Pbam orthorhombic crystal structure remains unchanged in the investigated thermodynamic range. At ambient pressure, a long-range commensurate antiferromagnetic (AFM) phase with propagation vector q = (1/2, 0, 1/2) formed below T N = 41(2) K, accompanied by anomalies in the temperature dependence of structural parameters including the lattice parameters, interatomic distances, and bond angles. This AFM phase remained stable␣in the studied pressure range, and the relevant pressure coefficient of the Néel temperature was determined to be 3.0(4) K/GPa. No incommensurate AFM phase was detected. The magnetic properties of BiMn2O5 and their difference from most other RMn2O5 compounds were analyzed in terms of competing exchange interactions.

The results of investigations of the structure of BaTiO 3 under thermobaric effects at constant volume are presented. The pressure and temperature values of the structural phase transition from the tetragonal ferroelectric phase to the cubic paraelectric phase at constant volume are determined. The temperature and pressure coefficients for the various phases of BaTiO 3 are found. The Birch–Murnaghan equations of state are calculated and the parameters B 0 and B ′ are established.

The crystal structure and vibration spectra of sodium niobate NaNbO3 have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO6 octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO3. The observed phase transitions are accompanied by anomalies in lattice parameters compression.

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO3 have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Neel temperature T-N = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Neel temperature increases with a pressure coefficient (1/T-N)(dT(N)/dP) = 0.011(1) GPa(-1). Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc2(1)n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained. (C) 2016 Elsevier B.V. All rights reserved.

The crystal structures of solid solutions of hexagonal ferrites BaFe 12– x Al x O 19 ( x = 0.1–1.2) have been studied using X-ray diffraction. It has been found that, at normal conditions, the samples are characterized by space group P 6 3 / mmc . It has been noted that the diamagnetic substitution of Al 3+ ions for Fe 3+ leads to a decrease in the unit cell parameters due to the smaller aluminum ion radius. The field dependences of the specific magnetic moment have been studied in fields of ±2 T at 5 and 300 K using vibrating magnetometry. It has been found that the specific magnetic moment decreases from 49.6 emu/g ( x = 0.1) to 32 emu/g ( x = 1.2) as the concentration of the diamagnetic ions increases. The microstructure has been studied using scanning electron microscopy. The Raman spectra have been measured in the range of 200–800 cm –1 .

Ferroelectric ceramics of K2Pb4Nb10O30-Na2Pb4Nb10O30-K6W4Nb6O30 (abbreviated to KPN-NPN-KWN) were synthesized by using a high-temperature solid-state reaction technique. Phase structure, dielectric and ferroelectric properties of the ceramics with composition passing across the morphotropic phase (MP) region in the phase diagram were mainly investigated. Temperature dependence of dielectric constant (epsilon(T)) of KPN-NPN-KWN solid solutions with 30, 50 and 60-mol% NPN were investigated in detail. All samples were characterized by a broad dielectric maximum peak of epsilon(T) at the Curie temperature and weak frequency dielectric dispersion. All compositions exhibited classical diffuse phase transition of a relaxor ferroelectric with a broad peak of dielectric constant induced by the compositional disorder. The K1.36Na1.2Pb3.44W0.56Nb9.44O30 ceramic located on the line 60-mol% NPN in the region of rhombic phase in the vicinity of the MP-region exhibited a high dielectric constant (epsilon similar to 9700) at 1 kHz near the Curie temperature. (C) 2015 Elsevier B.V. All rights reserved.

The crystal structure of the layered semiconductor TlGaSe 2 is studied using neutron diffraction at room temperature and under high pressures up to 4.6 GPa. Under ambient conditions the crystal structure of TlGaSe 2 is described by monoclinic symmetry with the space group C 2/ c . In the pressure range P = 0.2–0.9 GPa TlGaSe 2 undergoes a structural phase transition without a change in symmetry. The pressure dependences of the lattice parameters and the unit-cell volume are obtained, and the bulk moduli for both phases of TlGaSe 2 are calculated.

The magnetic, structural, and vibrational properties of YMn2O5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0, q(z) similar to 1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn2O5 compounds upon lattice compression. At P similar to 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn2O5 compounds.

The structural and luminescence properties of chalcogenide semiconductor CaxBa1−xGa2S4 solid solutions (x=0.1–0.9) doped with 7at% of Eu2+ ions were studied at room temperature. It was found, that the crystal structure of CaxBa1−xGa2S4 solid solutions varies with the amount of Ca2+ cations and phase transition from cubic to orthorhombic takes place with increase of x value. CaxBa1−xGa2S4:Eu2+ solid solutions exhibit intense photoluminescence in cyan to yellow spectral region depending on x due to 5d→4f electron–dipole transitions in Eu2+ ions. The peak position of the emission band shifts from 506nm for x=0.1 to 555nm for x=0.9 and the full width at half maximum of the emission band varies from 62nm to 72nm depending on the symmetry of the crystal lattice. The PL excitation spectrum of CaxBa1−xGa2S4:Eu2+ covers the range at half maximum from 310nm to 480nm for x=0.1 and to 520nm for x=0.9. It was shown that long-wavelength shift is caused by influence of the growing crystal field strength on Eu2+ ions.

By X-ray diffraction, differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were investigated BaFe12-xAlxO19 hexaferrites with various concentrations of Al (x = 0.3, 0.9 and 1.2). Crystal structure of compounds was determined, and it determined that under normal condition (P = 0 GPa, T = 300 K) they possess structure is hexagonal symmetry with the space group P6(3)/mmc. Replacing Fe3+ ions Al3+ with ions, on account of reducing ion radius, decrease of indices of parameters was occurred. This crystal structure is saved in a temperature range 30 - 950 degrees C and structural phase transition do not occur. Energy supplied to a system is fully swallowed by a system, monotonic decrease is occurred in TGA curve and in DTA curve endo and exo effects do not occur.