N. M. Okuneva

Field induced kinetic ferroelectric phase transition in lead magnoniobate

Abstract The time dependence of the complex dielectric permittivity of lead magnoniobate (PMN) single crystal in an applied external DC field, was studied. The field was applied in a “zero-field-cooling” regime. All measurements were carried out for the low-temperature PMN non-ergodic glassy phase. The transition to the polar state at a time τ from the moment of field application was observed. The dependence of τ on both temperature and applied field was obtained

Appearance of the dielectric instability and its coexistence with the superconductivity in ultrathin metallic filaments with decreasing diameter

Some dielectric instability appears before the superconducting (s/c) transition of Hg, In, Ga, Sn filaments when their diameters are decreased to 20–30 A. Above the s/c transition the differential conductivity of the filaments may be approximated by the formula σ = σa + σb exp [-E0(T)/E], where the electric field E0 is equal toabout 10–60 mV cm-1, and falls abruptly before the s/c transition. There are conductivity oscillations along E in the s/c transition region. The results are interpreted in terms of Peierls instability and charge-density wave (CDW) conductivity.

Effect of electric field on neutron scattering in lead magnoniobate

The temperature dependence of the intensity of the Bragg and the transverse component of quasi-elastic neutron scattering from the single-crystal model relaxor PbMg1/3Nb2/3O3 (PMN) has been studied for various applied electric fields. It is shown that application of a field E>Eth ≈1.6 kV/cm increases the elastic scattering intensity and reduces the intensity of the transverse diffuse-scattering component and that, below 230 K and for E>6 kV/cm, the elastic-scattering intensity saturates while the temperature-dependent part of the transverse diffuse-scattering component becomes practically suppressed. The measured temperature and field dependences of the intensity of type (h00) and (hh0) Bragg reflections provide supportive evidence both for the presence of considerable lead-ion displacements relative to the ideal perovskite sites and for the existence in strong electric fields of an induced transition to the ferroelectric phase below 250 K.

Structure and dielectric response of Na1 − xKxNO2 nanocomposite solid solutions

This paper reports on the results of the investigation into the thermal evolution of the structure and dielectric properties of Na1 − xKxNO2 solid solutions (x = 0, 0.05, 0.10) embedded in porous glass with an average pore diameter of 70 ± 10 Å in the range 300–447 K, i.e., in the ferro-and paraelectric phases. The structural properties of the bulk and nanostructured materials are compared. It is shown that the introduction of small amounts of potassium brings about a noticeable change in the intensity ratio of the elastic Bragg peaks, while leaving the space group characterizing the structure of these nanocomposites unaffected. An increase in the potassium fraction does not result in a substantial decrease in the phase transition point. Measurements of the dielectric response have revealed that an increase in the potassium content gives rise to a marked “hardening” of the lattice in the premelting state, which reduces dielectric losses.

Critical neutron scattering in a uniaxial relaxor Sr0.6Ba0.4Nb2O6

This paper reports on the results of an investigation into the temperature evolution of the critical scattering of neutrons in the strontium barium niobate crystal SBN60 in a zero field and in applied external direct-current (dc) electric fields. It has been shown that the observed critical scattering consists of two components that are adequately described by a Lorentzian and a Lorentzian squared. These components differently depend on the temperature and the momentum transfer vector. The application of an external electric field significantly suppresses the second component.

Temperature dependences of the order parameter for sodium nitrite embedded into porous glasses and opals

The temperature dependences of the order parameter η(T) for sodium nitrite NaNO2 embedded in porous glasses with average pore diameters of 320 and 20 nm, as well as in artificial opals, have been investigated. It has been demonstrated that the dependence η(T) for sodium nitrite in the porous glass almost coincides with that for the bulk material, whereas this dependence for NaNO2 in opals differs substantially from that observed in the bulk material and from those previously determined for sodium nitrite in porous glasses with average pore diameters of 3 and 7 nm. It has been revealed that the dependence of the order parameter for sodium nitrite in opals exhibits a temperature hysteresis (approximately equal to 8 K). The temperature dependence η(T) has been described using a simple model, which takes into account the nanopore diameter distribution existing in artificial opals.

Study of palladium nanoparticles synthesized in alkali borosilicate glass pores by the X-ray line shift method

Metallic Pd synthesized in porous glass with an average pore diameter of 7 ± 2 nm has been studied using the X-ray diffraction and X-ray line shift methods for the first time. The irregular dependence of the reflection width in X-ray patterns on the diffraction angle has been revealed. This can be caused by crystallite growth mostly in the [111] direction or by tetrahedral distortions of the fcc lattice. The shift (difference in energy) of Kα1 lines (ΔEα1 = 19 ± 2 meV) for nanostructured Pd in comparison with the bulk material is first detected. The detected effect is considered within the assumption of the palladium electron redistribution between Pd 5s- and 4d-bands.

Inelastic neutron scattering by TA phonons in heavily doped gallium arsenide

The temperature dependence of the shape of the inelastic neutron scattering peak from TA phonons in GaAs heavily doped by Te was studied within the temperature interval from 363 to 253 K. It was shown that doping with tellurium (to a carrier concentration Ne ≈ 2 × 1018 cm−3) gives rise to the appearance of an additional contribution to neutron scattering on the high-energy side of the TA phonon resonances at values of the reduced wave vector q < 0.1a*. Below 320 K, the intensity of this additional component rises sharply, and then, below 273 K, the main TA peak and the additional shoulder merge almost completely. This additional scattering is believed to be due to a defect-induced mode, which may be responsible for the observed anomalies in the physical properties in this crystal.