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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]

The crystal and magnetic structures of van der Waals layered ferromagnet Cr Br 3 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 Cr Br 3 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 d T C / d P = − 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 Cr Br 3 , which may be related to the proximity of metallization of this van der Waals ferromagnet. [ABSTRACT FROM AUTHOR]

Many non-molecular elemental solids exhibit common features in their structures over the range of 0 to 0.5 TPa that have been correlated with equivalent valence electron configurations. Here, it is shown that the pressures and volumes at polymorphic transitions obey corresponding states given by a single, empirical universal step-function Vtr/L = −0.0208(3) · Ptr + Ni, where Vtr is the atomic volume in Å3 at a given transformation pressure Ptr in GPa, and L is the principal quantum number. Ni assumes discrete values of approximately 20, 30, 40, etc. times the cube of the Bohr radius, thus separating all 113 examined polymorphic elements into five discrete sets. The separation into these sets is not along L. Instead, strongly contractive polymorphic transformations of a given elemental solid involve changes to different sets. The rule of corresponding states allows for predicting atomic volumes of elemental polymorphs of hitherto unknown structures and the transitions from molecular into non-molecular phases such as for hydrogen. Though not an equation of state, this relation establishes a basic principle ruling over a vast range of simple and complex solid structures that confirms that effective single-electron-based calculations are good approximations for these materials and pressures The relation between transformation pressures and volumes paves the way to a quantitative assessment of the state of very dense matter intermediate between the terrestrial pressure regime and stellar matter. [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]

A neutron diffractometer DN-6 at the IBR-2 high-flux reactor is used for the studies of crystal and magnetic structure of powder materials under high pressure in a wide temperature range. The high neutron flux on the sample due to a parabolic focusing section of a neutron guide and wide solid angle of the detector system enables neutron diffraction experiments with extraordinarily small volumes (about 0.01 mm3) of studied samples. The diffractometer is equipped with high-pressure cells with sapphire and diamond anvils, which allow pressures of up to 50 GPa to be reached. The technical design, main parameters and current capabilities of the diffractometer are described. A brief overview of recently obtained results is given. [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]

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]

• 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]

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]

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]

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]

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 structures of the orthoperovskite Pr0.8Na0.2MnO3 with non-integral mean valence (Mn3+/Mn4+) have been studied by means of powder neutron diffraction up to high-quasi-hydrostatic pressure of 4.6 GPa. At normal conditions, the system undergoes a charge ordering transition at TCO=215 K, followed by an antiferromagnetic arrangement of the pseudo-CE type at TN=175 K. Under high external pressures, a microscopically separated state is formed, consisting of a mixture of the A-type AFM phase (TN∼155 K) and metastable FM regions (TC∼175 K). A possible reason for the appearance of the A-type AFM phase is the compression anisotropy which leads to marked apical contraction of MnO6 octahedra under high pressure and creates favorable conditions for appearance of the d(x2−y2) orbital polarization, prerequisite for the A-type AFM order. It is argued that the pressure-induced structural changes in Pr0.8Na0.2MnO3 are accompanied by an insulator–metal transition. [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]

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]

• 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]

To better understand the potential presence of light element alloys of Fe and Ni in the Earth's interior, the crystal structure and compressional behavior of the Ni-P binary compound, schreibersite (Ni3P), have been investigated using synchrotron X-ray diffraction experiments. Both powder and two single-crystal samples of synthetic Ni3P (in different orientations with respect to the loading axis of the diamond anvil cell) were compressed up to approximately 50 GPa at ambient temperature. The compressional data obtained for Ni3P were fitted with a 3rd order Birch–Murnaghan equation of state. All data indicated that the c/a ratio of unit cell parameters remained approximately constant up to about 30 GPa but then increased progressively with pressure, exhibiting a second slight discontinuity at approximately 40 GPa. The changes in unit cell parameters at ~30 GPa and ~40 GPa suggested discontinuous changes in magnetic ordering. Moreover, the threshold of these subtle discontinuities is sensitive to the stress state and orientation of the crystal in the diamond anvil cell. This study is the first report on the compressional behavior of both powder and single-crystal schreibersite at high-pressure (up to 50 GPa). It offers insights into the effects of Ni3P components on the compressional behavior of the Earth's core. [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]

Pressure is an important thermodynamic parameter, allowing the increase of matter density by reducing interatomic distances that result in a change of interatomic interactions. In this context, the long range in which pressure can be changed (over six orders of magnitude with respect to room pressure) may induce structural changes at a much larger extent than those found by changing temperature or chemical composition. In this article, we review the pressure-induced phase transitions of most sesquioxides, i.e., A2O3 compounds. Sesquioxides constitute a big subfamily of ABO3 compounds, due to their large diversity of chemical compositions. They are very important for Earth and Materials Sciences, thanks to their presence in our planet's crust and mantle, and their wide variety of technological applications. Recent discoveries, hot spots, controversial questions, and future directions of research are highlighted. [ABSTRACT FROM AUTHOR]