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Raman 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 [ABSTRACT FROM AUTHOR]

The crystal and magnetic structure of nanostructured manganites La 0.63 Sr 0.37 MnO 3 and La 0.72 Sr 0.28 MnO 3 has been studied by means of a neutron diffraction method in the pressure range 0–4.5 GPa and the temperature range 5–300 K. In both samples the FM ordering is formed close above the room temperature and at cooling below T < 270 K the ferromagnetic FM phase coexists with an A-type antiferromagnetic AFM phase. At high pressures the volume fraction of AFM phase increases, while FM is gradually suppressed. The structural aspects of the magnetic phase separation and pressure effects on the studied nanostructured manganites are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of spin-lattice relaxation time T 1 for resorcinol have been made by the proton NMR technique using the saturation method in the temperature range 280–380K and pressure up to 800MPa. The pressure-induced α–β transition evolved through two phase coexistence range was observed. The crystal structure and vibrational spectra of the resorcinol have also been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 19GPa in temperature range 290–380K. In experiments with a rapid pressurization rate, suppression of α–β polymorphic transition in resorcinol occurs. In experiments with a slow pressurization rate, two structural phase transitions, between orthorhombic α and β phases at P =0.4GPa and from β to another orthorhombic γ phase at P =5.6GPa, were observed. At pressures above 12.5GPa, a gradual transformation to the amorphous phase was revealed. The lattice parameters, unit cell volumes and vibration modes as functions of pressure and temperature were obtained for the different polymorphic modifications of resorcinol. [Copyright &y& Elsevier]

The crystal and magnetic structures of hexagonal manganites YMnO3 and LuMnO3 have been studied by powder neutron diffraction up to 6 GPa in the temperature range of 10-300 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a Γ1 irreducible representation is stable below TN=70 K in YMnO3. Upon application of high pressure, a spin-reorientation was observed and the triangular AFM structure evolves from Γ1 to Γ1+Γ2 representation symmetry. In LuMnO3, the triangular AFM state of a Γ2 symmetry with TN ≈ 95 K remains stable in the investigated pressure range. The ordered Mn magnetic moment is suppressed at high pressure and low temperature, with much more pronounced effects for YMnO3, indicating enhanced spin fluctuations due to stronger magnetic frustration of the triangular lattice under higher pressure. The relationship between the evolution of spin fluctuations and in-plane Mn-O bonds under pressure is analyzed. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure and vibrational spectra of deuterated pyridinium perrhenate (d5PyH)ReO4 (C5D5NHReO4) have been studied by means of X-ray diffraction and Raman spectroscopy at high pressures up to 15 and 9.5GPa, respectively. Two phase transitions, from orthorhombic phase II with Cmc21 symmetry to phase I with Cmcm symmetry at P =0.7GPa and to new monoclinic phase IV with P21 symmetry at P =5GPa were observed. The internal vibrational modes frequencies, lattice parameters and unit cell volume as functions of pressure were obtained for different phases. [Copyright &y& Elsevier]

Abstract: The structure of the deuterated pyridinium perrhenate (d 5PyH)ReO4 (C5D5NHReO4) was studied by means of powder X-ray diffraction at high pressures up to 3.5GPa at room temperature and neutron diffraction at high pressures up to 2.0GPa in the temperature range 10–300K. At ambient conditions deuterated pyridinium perrhenate has orthorhombic structure of the Cmc2 1 symmetry (ferroelectric phase II). At T <250K a phase transition to the orthorhombic phase of the Pbca symmetry (paraelectric phase III) was observed. At P >0.7GPa the phase transition to orthorhombic phase with the Cmcm symmetry (paraelectric phase I) was observed at ambient temperature. At P =2GPa the phase I is stable in the temperature range 10–293K, indicating a suppression of the ferroelectricity in (d 5PyH)ReO4 by application of high pressure. P–T phase diagram of (d 5PyH)ReO4 at high pressures up to 2GPa is discussed. [Copyright &y& Elsevier]

The crystal and magnetic structure of the nanostructured manganite La 0.53 Sr 0.47 MnO 3 has been studied using the neutron diffraction method in the pressure range 0–5.5 GPa and the temperature range 15–300 K. At ambient pressure, the ferromagnetic ordering in the studied compound is formed below T ≈ 335 K. With an increase of the pressure above 2.1 GPa and cooling below T < 250 K, an A-type antiferromagnetic phase appears, which coexists with the initial ferromagnetic one. Further increase of the pressure leads to the growth of the volume fraction of the antiferromagnetic phase, while the ferromagnetic ordering is gradually suppressed. The structural origins of the pressure-induced magnetic phase separation in the nanostructured manganites are discussed. • The structure of nanomanganite La0.53Sr0.47MnO3 at high pressure have been studied. • The FM ordering in this compound was formed at ambient pressure, below T ≈ 335K. • At P ≥ 2.1 GPa and T < 250 K, the coexistence of FM and A-type AFM phase was found. • The structural separation was discussed in the framework of the "core-shell" model. • The most important parameters of crystal and magnetic structures were calculated. [ABSTRACT FROM AUTHOR]

The vibrational spectra of the ranitidine hydrochloride have been studied using Raman spectroscopy at pressures up to 11.2 GPa. At a pressure above 1.2 GPa a polymorphic phase transition from the initial form II to a new pressure induced form V has been observed. The vibration modes of the ranitidine hydrochloride as functions of pressure have been obtained. At pressures above 6.2 GPa, a gradual transformation to the amorphous phase of ranitidine hydrochloride has been revealed. Image 1 • The Raman spectra of ranitidine hydrochloride at high pressure were measured. • The new pressure induced phase of ranitidine hydrochloride has been found. • The pressure driven amorphization of ranitidine hydrochloride has been observed. • The anomalies in the baric dependencies of vibration modes were obtained. [ABSTRACT FROM AUTHOR]

The high-pressure evolution of structural and magnetic properties of the single valence Mn3+ manganite La 0.8 Sr 0.2 Mn 0.9 Sb 0.1 O 3 was studied by means of neutron powder diffraction up to 4.5 GPa in the temperature range of 10–300 K. At ambient pressure, a ferromagnetic ground state with the magnetic ordering temperature T C ≈ 175 K is stabilized. Application of high pressure suppresses the initial FM phase and leads to the appearance of a new A-type antiferromagnetic AFM phase with T N ~ 130 K at P = 2.2 GPa. Under compression, both T C and T N almost linearly increases with the pressure coefficient of 1.9(2) and 0.9(3) K/GPa, respectively. It is assumed that the appearance of the A-type AFM state is mediated by the strong anisotropic distortions of MnO 6 octahedra, coupled to the e g d x 2 - z 2 orbital polarization at high pressures. [ABSTRACT FROM AUTHOR]

A novel metastable phase of DyGe 2.85 synthesised in the AuCu 3 -structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P ≤ 3.1 GPa), neutron powder diffraction and time-differential γ - γ perturbed angular correlations (TDPAC) using 111 Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T CDW = 80 K with charge density wave formation and the second transition at T N ≈ 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of Cr 2 O 3 have been studied by means of X-ray and neutron powder diffraction at high pressures up to 35 GPa. The lattice compression of the rhombohedral crystal structure of R 3 ¯ c symmetry is slightly anisotropic with anomaly in the pressure behavior of the c/a parameters ratio at P ≈ 20 GPa of presumably magnetic nature. The oxygen octahedra around chromium ions become more symmetric with close values of shared and unshared bonds under high pressure. The antiferromagnetic structure of Cr 2 O 3 remains stable in the studied pressure range up to 35 GPa. The pressure coefficient of the Néel temperature, (1/ T N )( dT N /dP ) = + 0.0091 GPa −1 , is significantly less in comparison with perovskite-like compounds containing Cr 3+ and Mn 4+ ions of similar electronic configuration. [ABSTRACT FROM AUTHOR]

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO 3 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 Néel temperature T N = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel 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 Pc 2 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. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structure of a manganite La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 have been studied by means of a neutron diffraction method at pressures up to 4.5 GPa and in temperature range 4–290 K. At ambient pressure and temperature below T C = 150 K a ferromagnetic FM state is stabilized in this compound. At pressures P ≥ 1.5 GPa and temperature below T N ∼110 K appearance of a new A-type antiferromagnetic AFM phase in La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 has been observed. A further pressure increasing leads to an increase in the volume fraction of the A-type antiferromagnetic AFM phase, which coexists with the suppressed ferromagnetic phase in the whole experimental pressure range. The Curie and Néel temperature increase upon lattice contraction with comparable pressure coefficients dT C /dP = 2.1 K/GPa and dT N /dP = 1.6 K/GPa. The structural mechanisms of the changes in magnetic structure of La 0.7 Sr 0.3 Mn 0.83 Nb 0.17 O 3 manganite are discussed. [ABSTRACT FROM AUTHOR]

In our study, we present comprehensive findings on the structural properties of Pr 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 P2 1 space group. As pressure increased, a significant phase transition to the monoclinic P2 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-O 6 octahedra. High-pressure Raman spectroscopy data unequivocally confirms the phase transition, detecting anomalies in the baric dependencies of some vibration modes of Pr 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-O 6 octahedra, emphasizing the pivotal role played by Ti4+ and O2- ions in the mechanism of the pressure-driven phase transition. • Structural and vibration properties of perovskite-like layered Pr 2 Ti 2 O 7 was studied at pressures up to 30 GPa. • The structural phase transition in Pr 2 Ti 2 O 7 was observed at P= 13.8 GPa. • The suppression of the ferroelectric phase of Pr 2 Ti 2 O 7 was discussed. • The bulk modulus of both phases were calculated. [ABSTRACT FROM AUTHOR]

The crystal structure and vibrational spectra of cation-deficient nanostructured zinс ferrite Zn 0.34 Fe 2.53 ☐ 0.13 O 4 (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 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. [ABSTRACT FROM AUTHOR]

We had investigated the pressure-induced phase transition phenomenon in the perovskite-like material Nd 2 Ti 2 O 7 compound. The structural and vibrational properties of a layered Nd 2 Ti 2 O 7 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 P2 1 C 2 2 phase to the monoclinic P2 C 2 1 phase was observed at P ∼ 19 GPa. This pressure-induced 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 TiO 6 octahedra, alterations in interatomic distances, and the displacement of Nd atoms were discussed. • Structural and vibration properties of perovskite-like layered Nd 2 Ti 2 O 7 was studied at pressures up to 30 GPa. • The structural phase transition in Nd 2 Ti 2 O 7 was observed at P = 19.2 GPa. • The suppression of the ferroelectric phase of Nd 2 Ti 2 O 7 was discussed. • The bulk modulus of both phases were calculated. [ABSTRACT FROM AUTHOR]

Abstract: At the experimental station “Mediana” of the Kurchatov Synchrotron Radiation Source, a diffractometer for investigations of microsamples with the help of synchrotron radiation has been created. The design and basic parameters of the diffractometer are described. The results of experiments carried out with the powder diffractometer are presented. [Copyright &y& Elsevier]

Raman 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 [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of doped ferrite Zn 0.3 Cu 0.7 Fe 1.5 Ga 0.5 O 4 have been studied by means of the neutron diffraction method at high pressures up to 4.7 GPa and in temperature range 300–425 K. By increasing the temperature and the pressure, a gradual suppression of the magnetic moments of iron ions in both A and B crystallographic sites was observed. This effect corresponds to a magnetic phase transition from the ferrimagnetic state to paramagnetic one. The lattice parameters, interatomic bond lengths and angles, magnetic moments of iron ions as functions of temperature and pressure were obtained. Upon compression, the magnetic ordering temperature of studied ferrite decreases with a large pressure coefficient dT c / dP  = −19(1) K × GPa −1 . [ABSTRACT FROM AUTHOR]

High-pressure effects on the crystal structure and vibration spectra of the perovskite-like layered La 2 Ti 2 O 7 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 P2 1 symmetry to the monoclinic phase of P2 symmetry has been observed. The pressure-induced phase transitions in La 2 Ti 2 O 7 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 La 2 Ti 2 O 7 were calculated. [ABSTRACT FROM AUTHOR]

• A significant suppression of the ordered magnetic moment at high pressure is observed, associated with enhancement of spin fluctuations. • The pressure increase of Neel temperature is more pronounced with respect to other hexagonal RMnO 3 compounds. • A change of the ground magnetic state symmetry from mixed Г 1 + Г 2 to pure Г 1 irreducible representation is expected at pressure of about 6 GPa. The crystal and magnetic structures of hexagonal manganite ScMnO 3 have been studied by means of neutron diffraction at high pressures up to 2 GPa in the temperature range 10–300 К. At ambient pressure below T N = 130 K the triangular antiferromagnetic (AFM) state of mixed Г 1 + Г 2 irreducible representation is formed. Upon application of high pressure, the symmetry of magnetic structure persists up to 2 GPa. A significant suppression of the ordered magnetic moment and gradual spin reorientation were revealed under pressure. The baric dependence of Neel temperatures T N was obtained with the average linear pressure coefficient dT N / d P = 6.9 K/GPa, which is significantly larger with respect to related compounds like YMnO 3. For the data obtained, one may expect modification of the magnetic ground state symmetry to the pure Г 1 representation at pressures about 6 GPa. [ABSTRACT FROM AUTHOR]

• Formation of complex modulated commensurate states under pressure. • Suppression of temperature range of intermediate incommensurate magnetic states under pressure. • Positive pressure coefficients of Néel and lock-in transition temperatures. The magnetic and structural properties of elemental thulium were studied by means of neutron powder diffraction at pressures up to 5.5 GPa in the temperature range 7 – 290 K. At ambient pressure below T N = 52 K, the incommensurate magnetic state with a longitudinal sinusoidal modulation and propagation vector q = (0, 0, q z) was formed. The q z value increases on cooling from 0.279(2) and reaches the commensurate value of 2/7 at the temperature T 1 = 24 K. The new magnetic arrangement is of an antiphase domain structure, composed of structural blocks involving three or four hexagonal layers with magnetic moment directions parallel within a given block and oppositely alternating from block to block along the c axis. Under high pressure, the T N value increases slightly up to 57 K at 5.5 GPa with a pressure coefficient dT N /dP = 0.9 K/GPa. The pressure dependence of the T 1 temperature is more pronounced with a pressure coefficient dT 1 /dP = 2.9 K/GPa. The arrangement of commensurate magnetic structures formed below T 1 is strongly pressure dependent. A formation of the complex magnetic states composed of structural blocks involving three or four hexagonal layers with magnetic moment signs alternating from block to block along the c axis with q z = 7/23 at 2 GPa and q z = 7/22 at 5.5 GPa was observed. The lattice compression of Tm at T = 7 K demonstrates a weak anisotropy with the most compressible c axis. [ABSTRACT FROM AUTHOR]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]

• Magnetically disordered phase is suppressed under pressure. • The Néel temperature increases substantially under pressure. • The mechanism of next nearest neighbor superexchange interactions of A-O-O-A type is proposed. The crystal and magnetic structures of the frustrated Co 3 O 4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5–300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below T N = 33 K was observed. At pressures above 2 GPa, a suppression of the magnetically disordered phase and stabilization of the AFM phase, characterized by rapid increase of the Néel temperature in 1.5 times from 33 to 51 K with a pressure coefficient dT N /dP = 2.1 K/GPa occur. The observed phenomena are analyzed in terms of the competing nearest neighbor and next nearest neighbor magnetic interactions. In addition to the A-O-B-O-A nearest neighbor superexchange, an important role of the A-O-O-A next nearest neighbor superexchange interactions in magnetic behavior of Co 3 O 4 is pointed out. [ABSTRACT FROM AUTHOR]