A. I. Baranov

Influence of the defect structure on the electrical conductivity of Pb5Ge3O11 single crystals at high temperatures

The impedance spectra of Pb5Ge3O11 single crystals are measured in the frequency range from 5 Hz to 13 MHz at temperatures of 600 to 800 K in dry air and in a dry or wet nitrogen gas. It is found that the temperature and the gas composition significantly affect the electrical properties of the compound. The data obtained are used to discuss the origin of crystal lattice defects and their influence on charge transfer. It is concluded that the conduction is mixed in character (p-type electronic and ionic due to oxygen ions). The proton conduction is shown experimentally to be feasible. The possible mechanisms of proton transport in Pb5Ge3O11 are discussed.

Relaxor-Like Dielectric Relaxation: Artifacts and Intrinsic Properties

The existing results on the relaxor-like dielectric behavior which is characterized by a broad maximum in a dielectric permittivity as a function of temperature and the low frequency dielectric dispersion are reviewed for different ferroelectric and non-ferroelectric materials. The general and distinctive features of the relaxor and relaxor-like dielectric anomalies are discussed. Brief discussion of the existing treatments of dielectric data, which take into account not only, the bulk properties of the materials but also the interfacial effects is given. New model explaining the relaxor-like response on the base of the association-dissociation theory of impurity dipole complexes is proposed.

Low-temperature phase transitions and dynamics of ammonium in (NH4)3H(SO4)2 and [(NH4)1−xRbx]3H(SO4)2 crystals

The (NH4)3H(SO4)2 and [(NH4)0.82Rb0.18]3H(SO4)2 crystals are investigated by dielectric spectroscopy, inelastic incoherent neutron scattering (IINS), and neutron powder diffraction. A comparative analysis of the data obtained is given. It is shown that the phase transitions II ↔ III, III ↔ IV, IV ↔ V, and V ↔ VII in the (NH4)3H(SO4)2 crystal are accompanied by changes in the orientation ordering of the NH4+ ions. In the [(NH4)0.82Rb0.18]3H(SO4)2 crystal, these phase transitions are completely suppressed and the long-range order inherent in the II phase is retained over the entire temperature range covered (6–300 K). It is revealed that this crystal at the temperature Tg≈70 K undergoes a transition to the dipole glass phase, which is attended by “freezing” the orientation disordering of the ammonium ions.

Quasi-reversible superprotonic phase transition in K9H7(SO4)8 · H2O crystals

The heat capacity and the bulk conductivity have been measured in the K9H7(SO4)8 · H2O crystal. The hysteresis phenomena have been studied upon superprotonic phase transition. It is revealed that the phase transition is reversible upon thermocycling only for the monohydrate form of the crystal. The exponential temperature dependence of the heat capacity in the supercooled disordered phase exhibits a thermally activated behavior and is determined by the defects responsible for the high conductivity of the crystal.

A study of the x-irradiated crystal by EPR in the 80 - 415 K temperature range

The EPR spectra of the x-irradiated fast proton conductor were investigated in the temperature range of 80 - 415 K. Two kinds of paramagnetic centres with different proton configurations below about 370 K and freeze-out behaviour of one of them below about 200 K were observed. The role of acid proton dynamics with respect to the glassy-like transition is discussed.

Proton glass Cs5H3(SO4)4.xH2O: Relaxation dynamics

Abstract Dielectric, ultrasonic, calorimetric and dilatometric measurements were carried out in the Cs5H3(SO4)4.xH2O single crystals. Two different relaxation mechanisms in the frequency range 10−2 – 107 Hz were found. The low-frequency relaxation is of the Kohlraush form and exhibits typical glass-like behavior, while high-frequency one is described by an integral of a Debye relaxator over Gaussian distribution of relaxation times. The general nature of the acoustic and high-frequency dielectric relaxation is shown. The relation between stretched exponential and anomalous behavior of the thermal dilatation and heat capacity is discussed.

Some peculiarities of ferroelectric ordering in CsH2PO4 crystals

The influence of the bias electric field E2 on anomalies of the elastic stiffness coefficient C22 and dielectric permetivity e2 in crystals of CsH2PO4 have been studied. Strong influence of E2 on the value and shape of anomalies of C22 has been found. Below the phase transition temperature e2 e(Tc-T-γ with γ = 3 at the fields E2 e 103 V/cm.

Quasi-reversible solid-phase reaction in the superprotonic conductor Cs5H3(SO4)4·xH2O

The thermal effect and heat capacity in a single crystal of nonstoichiometric cesium sulfate hydrate were measured. It was established that superprotonic conduction in this material is caused by an isothermal solid-phase transformation in the bulk of the single crystal. The results of thermal measurements were compared with experimental data on the electrical conductivity.

Gravity Maps of Antarctic Lithospheric Structure from Remote-Sensing and Seismic Data

Remote-sensing data from altimetry and gravity satellite missions combined with seismic information have been used to investigate the Earth’s interior, particularly focusing on the lithospheric structure. In this study, we use the subglacial bedrock relief BEDMAP2, the global gravitational model GOCO05S, and the ETOPO1 topographic/bathymetric data, together with a newly developed (continental-scale) seismic crustal model for Antarctica to compile the free-air, Bouguer, and mantle gravity maps over this continent and surrounding oceanic areas. We then use these gravity maps to interpret the Antarctic crustal and uppermost mantle structure. We demonstrate that most of the gravity features seen in gravity maps could be explained by known lithospheric structures. The Bouguer gravity map reveals a contrast between the oceanic and continental crust which marks the extension of the Antarctic continental margins. The isostatic signature in this gravity map confirms deep and compact orogenic roots under the Gamburtsev Subglacial Mountains and more complex orogenic structures under Dronning Maud Land in East Antarctica. Whereas the Bouguer gravity map exhibits features which are closely spatially correlated with the crustal thickness, the mantle gravity map reveals mainly the gravitational signature of the uppermost mantle, which is superposed over a weaker (long-wavelength) signature of density heterogeneities distributed deeper in the mantle. In contrast to a relatively complex and segmented uppermost mantle structure of West Antarctica, the mantle gravity map confirmed a more uniform structure of the East Antarctic Craton. The most pronounced features in this gravity map are divergent tectonic margins along mid-oceanic ridges and continental rifts. Gravity lows at these locations indicate that a broad region of the West Antarctic Rift System continuously extends between the Atlantic–Indian and Pacific–Antarctic mid-oceanic ridges and it is possibly formed by two major fault segments. Gravity lows over the Transantarctic Mountains confirms their non-collisional origin. Additionally, more localized gravity lows closely coincide with known locations of hotspots and volcanic regions (Marie Byrd Land, Balleny Islands, Mt. Erebus). Gravity lows also suggest a possible hotspot under the South Orkney Islands. However, this finding has to be further verified.

2H NMR investigation of the transition to the proton glass state in the Cs5H3(SO4)4 · 0.5H2O crystal

A crystal of the Cs5H3(SO4)4 · xH2O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by 2H NMR spectroscopy. The temperature and orientation dependences of the 2H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature Tg = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point Tg. However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.