L. S. Smirnov

High pressure cell for neutron diffraction investigations

Abstract The design of a titanium-zirconium clamped cylinder-piston type pressure cell for neutron diffraction investigations under hydrostatic pressure up to 10 kbars without supports is described. It is the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium. The following results carried out at the room temperature are presented: the discovery of the transition from I to 111 phase in a LiKSO4 single crystal and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.

Similarity of vibrational spectra of high-density amorphous ice and high-pressure phase ice VI

The vibrational spectra of high-density amorphous (hda) ice, hexagonal ice Ih and high-pressure ice VI have been studied by inelastic neutron scattering. The observed similarity of the spectra of hda ice and ice VI means that the dynamics of these ice phases should be determined by the same atomic correlations and force constants.

Neutron scattering investigation of ice under hydrostatic helium pressure

Abstract Results of the inelastic incoherent neutron scattering investigations of water and ice in the 273–114K temperature interval under hydrostatic helium pressures up to 300 MPa are presented. It is shown that ice III is not formed in the process of isobaric cooling, but at about 239 K, a helium clathrate crystallizes. Its inelastic incoherent neutron scattering spectrum is close to that of ice II and this phase evidently is a solid solution of helium in ice II, in conformity with the results of a neutron diffraction study by D. Londono, et al. The position of the low-energy cutoff of the librational band follows the regularity found earlier for the dependence of the generalized phonon density of states on density of high pressure phases of pure ice.

Ammonium dynamics in Rb1−x(NH4)xSCN mixed crystals at 10 K

Abstract The neutron scattering studies of the ammonium dynamics in the Rb1−x(NH4)xSCN mixed crystals carried out at 10 K, in wide range of ammonium concentrations (0

Neutron diffraction study of anisotropy of crystal lattice compression in high-Tc superconductors under pressure

Abstract Pressure-induced structural changes in irradiated YBa2cu3Ox (x=6.95) and uninradiated (x=6.91,6.54,6.39) samples have been measured by neutron powder diffraction in a hydrostatic liquid pressure cell. Tc has been measured for irradiated superconductors under pressure. The value of dTc/dP is found to be high (1.5 =bar). Increase in Tc is associated with charge transfer between the CuO2 planes and CuO chains which is reflected by anisotropy of crystal lattice compression.

“In situ” neutron scattering studies of ice under high pressure

Abstract The amplitude-weighted phonon densities of states G(E) of ices Ih, III and II obtained in situ under high pressure by inelastic incoherent neutron scattering are presented. With increasing density for different ice phases, the first maximum of the translational phonon band shifts to higher energies, while the low-energy cutoff of the librational band shifts to lower energies, The compression of ice II shows the shift of the low-energy cutoff for the librational band to higher energies. The observed shift of the librational band to lower/higher energies correlates with the increase/decrease in the nearest neighbour distances between oxygen - oxygen atoms.

Neutron-scattering study of the dynamics of ammonium in different phases of halides of K1−x(NH4)xHal mixed crystals

The effect of temperature and the concentration of ammonium on the lattice parameters and the amplitude-weighted phonon density of states in mixed salts of ammonium potassium halides is studied by neutron powder diffraction and incoherent inelastic neutron scattering. It is found that at 10 K incoherent inelastic neutron scattering spectra show four different excitation modes of ammonium: two resonant excitations below the cutoff energy of the phonon density of states of potassium halide and two localized excitations above the cutoff energy. The high-energy localized modes correspond to translational and librational vibrations of NH4 ions in the crystal lattice. These modes are typical of ordered phases of ammonium halides.

Structural study of new compound Bi2.53Li0.29Nb2O9 by the powder neutron diffraction method

A new compound of composition Bi2.53Li0.29Nb2O9 was synthesized in the course of the search for new materials with high ionic conductivity. Its crystal structure was determined from the neutron diffraction data. The new compound Bi2.53Li0.29Nb2O9 is crystallized in the orthorhombic system, sp. gr. Cmc21, and unit-cell parameters a = 24.849(1) Å, b = 5.4536(3) Å, and c = 5.4619(2) Å at T = 290 K (a = 24.843(2) Å, b = 5.4456(5) Å, and c = 5.4546(5) Å at T = 10 K). Within the temperature range 10–870 K, no structural phase transitions were revealed. The atomic coordinates and the thermal factors in the isotropic approximation were refined by the Rietveld method at 290 and 10 K. The data obtained were analyzed based on the calculated local balance of bond strengths.

Neutron-scattering investigation of ammonium dynamics in (NH4)2−xRbxSO4 mixed salts

Abstract Inelastic incoherent neutron-scattering (IINS) investigations of the mixed salts (NH 4 ) 2− x Rb x SO 4 for the whole concentration range, 0.0 ⩽ x ⩽ 2.0, have been performed on the NERA spectrometer at the IBR-2 pulsed reactor in Dubna. The IINS spectra show that ammonium ions undergo fast reorientations even in the ferroelectric phase; however, for (NH 4 ) 2 SO 4 , the rotational barrier slightly decreases at the phase transition. In the mixed salts, this effect vanishes with increasing rubidium concentration and above x > 0.4, the stochastic dynamics of the ammonium ions do not depend on the ferroelectric transition. Upon cooling to low temperatures, the ammonium ions form a substitutional protonic glass, within x ranging from approx. 0.4 to 1.2. At high rubidium concentrations, the IINS spectra display the localized dynamics of NH 4 (II), which occupy type II crystallographic position.

Ammonium dynamics and structural phase transition in Rb1−x(NH4)xI solid solutions at 20 K

Abstract The Rb 1− x (NH 4 ) x I mixed salts for 0 x x =0.40. The ordered γ-phase was observed by neutron diffraction and incoherent inelastic scattering at x =0.66. IINS spectra of the disordered α-phase at 20 K display four distinct ammonium excitations similar to that in the K 1− x (NH 4 ) x I system. The low-frequency modes at ca. 2.5 and 10xa0meV reflect almost free rotations of ammonium in the octahedral cage of Rb ions. The modes at 20 and 30xa0meV correspond to the translation and libration of NH 4 groups in crystalline lattice. These modes are observed at ca. 19 and 39xa0meV, for the ordered γ-phase, respectively.