V.A Somenkov

DN-12 time-of-flight high-pressure neutron spectrometer for investigation of microsamples

Abstract A few years ago a high-pressure neutron spectrometer DN-12 was created at the IBR-2 pulsed reactor. Neutron diffraction and inelastic incoherent neutron scattering (with samples having large incoherent neutron scattering cross section) experiments at pressures up to 5xa0GPa can be performed with the DN-12 using sapphire anvil cells. After first successful experiments, the development of the DN-12 spectrometer was done during last year. The new parameters and recent experiments performed with the DN-12 both before and after modernization are reviewed.

NEUTRON DIFFRACTION STUDY OF STRUCTURAL CHANGES IN AMMONIUM HALIDES UNDER HIGH PRESSURE

Abstract Structural changes in deuterated ammonium halides ND 4 Cl and ND 4 Br at pressures up to 40xa0kbar and ND 4 I at pressures up to 86 kbar have been studied by means of neutron diffraction at room temperature. The equations of state and the pressure dependencies of the deuterium position parameter were obtained. It was found that the order–disorder II–IV phase transition from the disordered CsCl – type cubic phase II into the ordered CsCl-type cubic phase IV occurs at equal critical values of the deuterium position parameter u cr =0.152(2) in ND 4 Br and ND 4 Cl. For ND 4 I, no II–IV phase transition was observed. A phase transition into the high-pressure phase V was detected in ND 4 I at 80 P 4 I(V) was found to be the same as the structure of the low-temperature phase ND 4 I(III) – tetragonal one with antiparallel ordering of ammonium ions, space group P4/nmm. The critical value of the position parameter for the II–V phase transition in ND 4 I u =0.148(2) is close to the u cr for II–IV transition in ND 4 Cl and ND 4 Br.

Neutron diffraction study of high-pressure-induced structural changes in the ammonium halogenides ND4Br and ND4Cl

AbstractStructural changes in the deuterated ammonium halogenides ND4Br and ND4Cl have been studied by neutron time-of-flight diffraction up to pressures of 45 and 35 kbar, respectively. Data on the equations of state and pressure dependence of the deuterium position parameter have been obtained. A comparison with the hydrogen-containing analogs showed that isotopic substitution of deuterium for hydrogen affects only slightly the compressibility of the systems under study, although the effect is noticeable for ND4Cl. It has been established that the order-disorder transition from the phase with random deuterium distribution (CsCl cubic structure, space group Pm3m) to the ordered phase (same structure, space group n

Structure and dynamics of ammonium halides under high pressure

Poverline {43} m

Hydrogen tunneling modes in α-Mn suppressed by elastic stresses

n) occurs in both compounds at the same critical value of the position parameter u=0.153±0.002, which is apparently the same for all ammonium halogenides, and, possibly, for other systems of this structural type as well.

Neutron diffraction evidence for the spin-reorientational transition in FeBO3 at high pressures

Curves of the secondary-fluorescence yield from the constituent elements of high-Tc superconducting crystals Nd1.85Ce0.15CuO4−δ are measured in the dynamic x-ray diffraction regime. The form of the curves attests to the appearance of a standing x-ray wave in the crystal.

Observation of the periodic and chaotic automodulations of the nonlinear magnetoacoustic vibrations in perfect FeBO3 crystal by neutron diffraction method

Abstract The structures of ammonium halides ND4I and ND4Br have been studied by means of neutron diffraction at pressures up to 9 GPa. We found that the high-pressure phase V of ammonium halides has the same structure as the low-temperature phase III-tetragonal one with antiparallel ordering of ammonium ions. Vibrational spectra of NH4I have been studied at pressures up to 5 GPa. Libration and transverse optical mode frequencies as functions of pressure were obtained.

Time-of-flight neutron diffractometer for investigation of microsamples under high external pressure

Abstract We propose to use the combination of the polarized neutron facility and the anvil high-pressure cell for investigation of magnetic phase transitions in solids. The magnetic phase transition manifests itself in the rise or loss of neutron depolarization. Neutron depolarization in Fe70Ni30 alloy and MnAs under high pressure was studied. Phase transitions from ferromagnetic state to paramagnetic state and vice versa were detected. Ferromagnetic state of MnAs at pressure of about 80 kbar was observed at room temperature.