B. N. Savenko

Neutron scattering studies on structural phase transitions of superionic conductor Cs HSO4

Abstract The results of neutron diffraction (ND) and inelastic incoherent neutron scattering (IINS) studies on phase transitions and vibrational spectra in superionic conductor CsHSO4 at pulsed reactor IBR-2 are reported. It is shown that in the temperature range 123–420 K there are three phases (III, II, I) in CsHSO4 crystal and only two phases (II, I) in partly deuterated Cs(D0.7H0.3)SO4 crystal. The unit cell parameters in monoclinic phase II by ND on single crystal are determined. A considerable change in IINS spectra in superionic phase I says for a disorded state of protons in the lattice in this phase.

Neutron diffraction study of the high-temperature superconductor HgBa2CaCu2O6.3 under high pressure

Abstract The pressure dependence of the crystal structure of a powder sample of HgBa2CaCu2O6.3 (Tc=123 K) was studied in the pressure range of 0 to 3.6 GPa, using the DN-12 time-of-flight diffractometer at the IBR-2 pulsed reactor and a sapphire anvil cell chamber. At P=O the results are in a good accordance with the published data. At P=3.0 and 3.6 GPa the best fit of the experimental data was achieved using the structural model with apical oxygen disordered in the (a, b) plane. The compressibility values of the lattice constants and selected bonds were calculated from the structural data. The highest absolute value of compressibility was found for the distance between the Ba and O atom layers.

Neutron diffraction studies on SrxBa1−xNb2O6 single crystals with x = 0.75, 0.70, 0.61, 0.50 and 0.46

Abstract SBN mixed crystals of various compositions are investigated between 100 K and 700 K with time-of-flight technique. A slight peak splitting is generally detectable and the decrease of a tetragonal symmetry is discussed in connection with the occurrence of IC modulation. Except a weak increase at x > 0.70 the IC modulation parameter is found to be nearly independent of composition. The existence of the low-lying phase transition (PT) is confirmed by an anomalous temperature dependence of Bragg intensities; the pecularities of the diffuse PT of samples with x ≥ 0.70 are studied using diffuse scattering.

Neutron diffraction study of the electric field influence on SrxBa1-xNb2O6- mixed crystals

Abstract The electric field influence on the neutron diffraction pattern of SrxBa1-xNb2O6 (SBN-x) mixed crystals (x=0.70, 0.75) is studied using time-of-flight (TOF) technique. The change of the elastic diffuse and Bragg intensities during field switching and (zero-field and field) cooling is discussed in connection with the dipol glass-like behaviour of these relaxors and domain properties.

Study of domain structure rearrangement of KD2PO4 in the electric field

The two-dimensional neutron diffraction using the time-of-flight diffractometer with the position sensitive detector is an effective physical method for the investigation of the crystal transformation twinning. Data on polarization (inverse polarization) under the action of external electric field in the KD2PO4 crystal with the coercive field EZC ∼ 2kV/cm are analyzed. As is established at a ferroelectric phase throughout the switching process the crystal transforms at a single +Sa domain state. Whenever the inverse polarization process takes place, it is followed by the rise of the intermediate crystal polydomain state consisting of ±Sa and ±Sb domain configurations.

Neutron diffraction study of phase transitions in the mixed crystal Sr0.7Ba0.3Nb2O6 between 20 and 300 K

Abstract Time-of-flight neutron diffraction was carried out on mixed crystals of Sr0.7Ba0.3Nb2O6 between room temperature and 20 K. Diffraction patterns were recorded along ⟨100⟩, ⟨001⟩, ⟨111⟩, and ⟨110⟩ directions and studied in ⟨110⟩-scans also under applied electric field. The found anomalies in the temperature dependence of the effective tetragonal lattice parameters a eff and c eff corroborate the existence of the phase transitions at ∼60 K and ∼198 K and give evidence of additional ones at ∼230 K and ∼130 K. Feroelastic domain effects and the time- and electric field dependence affecting the parameter a eff and c eff, respectively, ae indications of a multi-domain as well as non-equilibrium multi-phase state in this relaxtor material.

Neutron investigation of ferroelastic phase transition in K2ZnCl4

Abstract Using the TOF method the neutron diffraction spectra were measured for K2ZnCl4 crystals in temperature range from 80 to 300 K. Nearly two times increase of the integrated intensity of peakes and its asymmetry were observed below the temperature of ferroelastic phase transition at 145 K. The additional odd reflexes found for (001), (h01) and (h00) prove that the space symmetry of the low-temperature phase is not identical as for Rb2ZnCl4.

Investigation of the incommensurate modulated structure of Sr0.7Ba0.3Nb2O6 by neutron diffraction

Abstract The incommensurate (IC) modulated structure of the tetragonal tungsten bronze (TTB) type crystal SBN-70 is investigated from room temperature (RT) up to 773 K. Satellites of first, second and third rank of the modulation vector qδ are found at positions which are independent on temperature and insensitive on electric field. Their intensity falls down continuously with temperature.

Neutron diffraction studies of phase transition effects on a single crystal of Sr0.7Ba0.3Nb206

Abstract On the relaxor-type ferroelectric Sr0.7Ba0.3Nb206 (SBN-70) phase transition (PT) phenomena are studied between room temperature (RT) and 773 K using the time-of-flight (TOF) diffraction technique. At RT the influence of an external electric field on the PT is investigated. Besides the diffused ferroelectric PT another transition is indicated above 500 K.

Neutron diffraction study of the domain structure rearrangement of KD2PO2 in the electric field

There is investigated the rearrangement of the domain structure of KD2PO4 in the external electric field with the time-of-flight diffractometer installed at a pulsed neutron source. Two-dimensional (x*, y*) cross sections of the spots of reciprocal lattice are measured in order to obtain the dependence of packing and relative volume of different types of domains on field strength. The results of measurements of two-dimensional intensity distribution around the reciprocal lattice points in the [hOO] and [hhO] directions in the field Ez increasing from 0 to Ez > Ezc are reported. Possible domain rearrangements within which one may explain the observed changes of the diffraction pattern are proposed.