D. P. Kozlenko

Search for Polymorphic Phase Transformations in Chlorpropamide Form-A at High Pressures

The high-pressure effects on chlorpropamide (C10H13ClN2O3S) form-A have been studied by 1H NMR spectroscopy at high pressures up to 800 MPa in the temperature range 90-300 K. A study of the NMR second moment and spin-lattice relaxation time has been completed by a calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the NMR line by the Monte-Carlo method, which enabled a precise description of molecular dynamics in the compound studied. Reorientations of the methyl group, oscillations and reorientations of the chlorophenyl ring and reorientations of the propyl group have been revealed and respective activation parameters extracted. No phase transformation of the compound form-A has been detected.

Synchrotron and neutron-scattering methods for studies of properties of condensed matter: Competition or complementarity?

Comparative analysis of modern possibilities of synchrotron-radiation and neutron-scattering methods for studies of collective excitations, atomic and magnetic structure of condensed matter is presented in this review. The opportunities for research using techniques based on inelastic scattering, diffraction, and small-angle scattering of synchrotron radiation and neutrons, as well as synchrotron-radiation resonance elastic and inelastic scattering and absorption, have been considered. The application limits and complementarity of the considered synchrotron-radiation and neutron-scattering methods have been discussed.

High-pressure effect on the ferroelectric-paraelectric transition in PbTiO3

The crystal structure of lead titanate PbTiO3 was investigated by energy dispersive X-ray diffraction at high pressures up to 4 GPa in a temperature range of 300–950 K. At the ambient conditions, the PbTiO3 structure is tetragonal with the space group P4mm (ferroelectric phase). A structural phase transition into the cubic phase with a space group

High-pressure effect on the crystal and magnetic structures of the frustrated antiferromagnet YMnO3

Pm\bar 3m

The influence of high pressure on the crystal and magnetic structures of the La0.7Sr0.3CoO3 cobaltite

is observed at T = 747 K. It was found that the phase transition temperature decreases upon applying the high pressure with the coefficient dTC/dP = -65 K/GPa. Dependences of parameters and volume of the unit cell on the pressure and temperature was found, and the bulk modulus and thermal expansion coefficients for the tetragonal and cubic phases of lead titanate have been calculated.

Pressure-induced antiferromagnetism in La0.75Ca0.25MnO3 manganite

The magnetic structures of hexagonal manganites YMnO3 and LuMnO3 have been studied by powder neutron diffraction up to 6 GPa in the temperature range 10‐295 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a � 1 irreducible representation is stable below TN = 70 K in YMnO3. Upon the application of high pressure, a spin reorientation is induced and the triangular AFM structure evolves from � 1 to � 1 + � 2 representations. On the other hand, in LuMnO3 the triangular AFM state of a � 2 irreducible representation with TN ≈ 90 K remains stable over the entire pressure range investigated. The ordered magnetic moment values decrease under pressure with dM/dP =− 0.35 μB GPa −1 in YMnO3 and −0.08 μB GPa −1 in LuMnO3. Simultaneously, a considerable increase in diffuse scattering intensity was found in YMnO3, while it was much less pronounced for LuMnO3. Both features indicate the enhancement of spin fluctuations due to geometrical frustration effects and an increase in the volume fraction of the spin-liquid state coexisting with the ordered AFM phase. The characteristic spin correlation length is weakly affected by pressure. The relationship between the pressureinduced behaviour of magnetic structure and the structural characteristics of the quasi-two-dimensional (2D) triangular network formed by Mn and O ions in hexagonal RMnO3 is analysed.

Investigation of structural features of the Y3Al5O12: Ce3+/Lu2O3 crystal phosphors formed by the colloidal chemical method

The high-pressure (to 5 GPa) effect on the crystal and magnetic structures of the hexagonal manganite YMnO3 is studied by neutron diffraction in the temperature range 10–295 K. A spin-liquid state due to magnetic frustration on the triangular lattice formed by Mn ions is observed in this compound at normal pressure and T > TN = 70 K, and an ordered triangular antiferromagnetic state with the symmetry of the irreducible representation Γ1 arises at T < TN. The high-pressure effect leads to a spin reorientation of Mn magnetic moments and a change in the symmetry of the antiferromagnetic structure, which can be described by a combination of the irreducible representations Γ1 and Γ2. In addition, it is observed that the ordered magnetic moment of Mn ions decreases from 3.27 μB (5 GPa) to 1.52 μB (5 GPa) at T = 10 K and diffuse scattering is enhanced at temperatures close to TN. These effects can be explained within the model of the coexistence of the ordered antiferromagnetic phase and the spin-liquid state, whose volume fraction increases with pressure due to the enhancement of frustration effects.

Magnetic phase transitions in the iron-doped Pr0.7Ca0.3Mn1−yFeyO3 manganites at high pressures

This paper reports on the results of investigations into the influence of high pressures (up to 5.3 GPa) at T=300 K on the magnetic structure of the Mn2Sb pnictide. The crystal and magnetic structures of the Mn2Sb compound are studied using a direct neutron diffraction method. It is demonstrated that the magnetic ferrimagnet-antiferromagnet phase transition, which is observed in a number of Mn2Sb-based substitutional solid solutions upon chemical compression of the Mn2Sb crystal lattice, does not occur in the Mn2Sb compound under high pressures in the aforementioned range due to an anisotropic pressure-stimulated strain in the Mn2Sb lattice. At pressures P≥2.8 GPa, the Mn2Sb compound is characterized by a spin reorientation with respect to the tetragonal axis and the basal plane of the crystal lattice.