E. V. Lukin

Structural Aspects of the Antiferroelectric-Paraelectric Phase Transition in Double Perovskite Pb 2 MgWO 6 at High Pressures and Temperatures

The crystal structure of antiferroelectric Pb2MgWO6 has been studied using neutron diffraction at high pressures to 5.4 GPa at room temperature and energy-dispersive X-ray diffraction at high pressures to 4 GPa in the temperature range 300–400 K. At normal conditions, in Pb2MgWO6, there is an antiferroelectric phase with the crystal structure described by the orthorhombic symmetry with space group Pnma. At temperature T = 313 K and normal pressure or at room temperature and pressure P ∼ 0.9 GPa, the crystal under-goes a structural phase transition to the cubic phase with space group

Spin fluctuations and structural modifications in frustrated multiferroics RMnO3 (R=Y, Lu) at high pressure

Fmbar 3m

Structural and magnetic phase transitions occurring in Pr0.7Sr0.3MnO3 manganite at high pressures

(paraelectric phase). The temperature and pressure dependences of the lattice parameters, unit cell volume, and interatomic bond lengths have been obtained, and the thermal expansion coefficients and the bulk moduli have been calculated for the antiferroelectric and paraelectric phases of Pb2MgWO6.

Pressure-induced change in the order of the phase transition in lead titanate: Structural aspects

An experimental station for investigations using neutron radiography and tomography was developed at the upgraded high-flux pulsed IBR-2 reactor. The 20 × 20 cm neutron beam is formed by the system of collimators with the characteristic parameter L/D varying from 200 to 2000. The detector system is based on a 6LiF/ZnS scintillation screen; images are recorded using a high-sensitivity video camera based on the high-resolution CCD matrix. The results of the first neutron radiography and tomography experiments at the developed facility are presented.

Effect of high pressure on the crystal and magnetic structures of La0.5Ca0.5CoO3 cobaltite

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 T N=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 T N ≈ 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.

Changes in the crystalline structure of chlorpropamide at high pressures and temperatures

The crystal structure of the layered semiconductor TlGaSe2 is studied using neutron diffraction at room temperature and under high pressures up to 4.6 GPa. Under ambient conditions the crystal structure of TlGaSe2 is described by monoclinic symmetry with the space group C2/c. In the pressure range P = 0.2–0.9 GPa TlGaSe2 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 TlGaSe2 are calculated.

Analysis of the internal structure of ancient copper coins by neutron tomography

The crystal and magnetic structures and the vibrational spectra of Pr0.7Sr0.3MnO3 manganite are studied within the pressure range up to 25 GPa by methods of X-ray diffraction and Raman spectroscopy. Neutron diffraction studies have been performed at pressures up to 4.5 GPa. The magnetic phase transition from the ferromagnetic phase (TC = 273 K) to the A-type antiferromagnetic phase (TN = 153 K) is found at P ≈ 2 GPa. This transition is characterized by a broad pressure range corresponding to the phase separation. The Raman spectra of Pr0.7Sr0.3MnO3 measured under high pressures significantly differ from the corresponding spectra of the isostructural doped A1 − xA′xMnO3 manganites, (where A is a rare-earth ion and A′ is an alkaline-earth ion) with the smaller average ionic radius 〈rA〉 of A and A′ cations. Namely, the former spectra do not include clearly pronounced stretching phonon modes. At P ∼ 7 GPa, there appears the structural phase transition from the orthorhombic phase with the Pnma space group to the orthorhombic high-pressure phase with the Imma symmetry. In the vicinity of the phase transition, anomalies in the pressure dependences of the lattice parameters, unit cell volume, and phonon frequencies corresponding to the characteristic lattice vibration modes are observed.

An intermediate antipolar phase in

The crystal structure of lead titanate PbTiO3 have been studied by energy-dispersive X-ray diffraction under pressures of 0–4 GPa in the temperature range of 300–950 K. At a temperature of T = 747 K, a structural phase transition from a ferroelectric tetragonal phase to a paraelectric cubic phase is observed. The application of pressure leads to a significant decrease in the phase transition temperature; under pressures of P ∼ 2 GPa, the type of the phase transition changes from the first to second order. In the low pressure range, the baric coefficient value is dTc/dP = −20(3) K/GPa; under pressures above 2 GPa, it increases up to −113(5) K/GPa.