Structural phase transitions and their influence on Cu+ mobility in superionic ferroelastic Cu6PS5I single crystals

The structural origin of Cu+ ions conductivity in Cu6PS5I single crystals is described in terms of structural phase transitions studied by X-ray diffraction, polarizing microscope and calorimetric measurements. Below the phase transition at Tc=(144-169) K Cu6PS5I belongs to monoclinic, ferroelastic phase, space group Cc. Above Tc crystal changes the symmetry to cubic superstructure, space group F-43c (a=19.528); finally at 274K disordering of the Cu+ ions increases the symmetry to F-43m, (a=9.794). The phase transition at 274K coincides well with a strong anomaly in electrical conductivity observed in the Arrhenius plot. Diffusion paths for Cu+ ions are evidenced by means of the atomic displacement factors and split model. Influence of the copper stechiometry on the Tc is also discussed.Comment: conference pape

Електричні властивості нанокристалів поруватого кремнію в діелектричній матриці

У роботі отримано нанокристали поруватого кремнію в епоксидній матриці. Отримані фотоелектрохімічним травленням монокристалічних пластин з кристалографічними орієнтаціями [100] та [111] шари поруватого кремнію відокремлювали від кремнієвої підкладки за допомогою епоксидної смоли. Системи на основі наночастинок поруватого кремнію характеризувалися скануючою електронною мікроскопією. Розмір кремнієвих нанокристалів у перерізі становив від одиниць до декількох десятків нанометрів. На основі комплексних досліджень методами імпедансної та термоактиваційної спектроскопії досліджено процеси перенесення та релаксації нерівноважних носіїв заряду. Побудовано імпедансну модель отриманих наносистем і визначено її електричні параметри. Внутрішній опір відокремлених нанокристалів поруватого кремнію становив понад 10 ГОм і на декілька порядків перевищував типовий опір поруватого шару на кремнієвій підкладці. Встановлено активаційний механізм перенесення зарядів у температурному діапазоні 270-350 К та визначено енергію активації електропровідності. На основі спектрів термостимульованої деполяризації виявлено локалізовані електронні стани, які впливають на перенесення зарядів у наносистемах поруватого кремнію. Розрахований енергетичний розподіл густини заповнення станів володіє максимумом у діапазоні 0,45-0,6 еВ. Виявлені рівні захоплення нерівноважних носіїв заряду ймовірно пов'язані з електрично активними дефектами на межі розділу між нанокристалами кремнію та епоксидною смолою.In this work, the porous silicon nanocrystals were obtained in a dielectric matrix. Porous silicon layers obtained by photoelectrochemical etching of single-crystalline wafers with the [100] and [111] crystallographic orientations were separated from the silicon substrate using epoxy resin. Systems of the porous silicon nanoparticles were characterized by scanning electron microscopy. The dimensions of the silicon nanocrystals varied from several to tens of nanometers in the cross-section. On the basis of comprehensive studies by impedance spectroscopy and thermal activation methods, processes of transfer and relaxation of non-equilibrium charge carriers have been studied. Impedance model of obtained nanosystems was constructed and its electrical parameters were determined. The internal resistance of free-standing porous silicon nanocrystals was more than 10 GOhms and was several orders of magnitude higher than the typical resistance of the porous layer on the silicon substrate. Activation mechanism of charge transport in the 270-350 K temperature range was found and the activation energy of the conductivity was determined. Based on the spectra of thermally stimulated depolarization current, the localized electron states that affect the charge transport in the porous silicon nanosystems were revealed. The calculated energy distribution of the filling density of states has a maximum in the 0.45-0.6 eV energy range. The found trap levels of nonequilibrium carriers are probably related to the electrically active defects at the interface between silicon nanocrystals and the epoxy resin

Investigations of High Temperature Phase Transitions in (NH3\text{}_{3}c2\text{}_{2}H5\text{}_{5})2\text{}_{2}CuCl4\text{}_{4} Crystals

On the basis of dilatometric, optical, and dielectric investigations of (NH$\text{}_{3}$C$\text{}_{2}$H$\text{}_{5}$)$\text{}_{2}$CuCl$\text{}_{4}$ crystals the existence of phase transitions at T$\text{}_{1}$=364 and T$\text{}_{2}$=356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T$\text{}_{3}$=330 K was related to earlier unknown phase transition. Besides, it was shown that these crystals are characterised by considerable protonic conductivity, the nature of which is fairly well explained in the framework of Grotthus mechanism of proton transport

Dielectric Relaxation Phenomena in SBN Single Crystals Doped with Ce

The dielectric study of $Sr_{0.73}Ba_{0.27}Nb_2O_6:Ce$ (SBN) crystals along [010] crystallographic axis was performed in the temperature region of 310-360 K and frequency range from 25 Hz up to 1 MHz. The thermal dipole relaxation of quasi-Debye-type for this orientation of sample was observed in both investigated structural phases. The phase transition was most clearly seen from the temperature dependence of the relaxation time at $T_{c}$ = 320 K. The relaxation processes were related to the collective oscillations of the Nb-O bonds in the two different type corner-sharing $NbO_6$ octahedra aligned along c-axis

Dielectric and Dilatometric Properties of NH(CH 3

On the basis of dilatometric and dielectric investigations of NH(CH$\text{}_{3}$)$\text{}_{3}$CuCl$\text{}_{3}$·2H$\text{}_{2}$O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T$\text{}_{1}^{c}$=198 K and T$\text{}_{1}^{h}$=223 K, respectively, in cooling and heating runs. Existence of the characteristic dielectric dispersion was revealed within the high-temperature phase. It corresponds to the single dielectric relaxator below 250 K as well as to co-existence of two relaxators above this temperature. The determined values of the activation energy and relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation (high-frequency relaxator) whereas the combined reorientation motions of the CuCl$\text{}_{2}$·2H$\text{}_{2}$O chains would be responsible for the low-frequency relaxation process. It was found that the above mentioned quasi-Debye type processes are involved into the mechanisms of the protonic conductivity

Dielectric and Dilatometric Properties of NH(CH3\text{}_{3})3\text{}_{3}CuCl3\text{}_{3}·2H2\text{}_{2}O Low Dimensional Ferroics

On the basis of dilatometric and dielectric investigations of NH(CH$\text{}_{3}$)$\text{}_{3}$CuCl$\text{}_{3}$·2H$\text{}_{2}$O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T$\text{}_{1}^{c}$=198 K and T$\text{}_{1}^{h}$=223 K, respectively, in cooling and heating runs. Existence of the characteristic dielectric dispersion was revealed within the high-temperature phase. It corresponds to the single dielectric relaxator below 250 K as well as to co-existence of two relaxators above this temperature. The determined values of the activation energy and relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation (high-frequency relaxator) whereas the combined reorientation motions of the CuCl$\text{}_{2}$·2H$\text{}_{2}$O chains would be responsible for the low-frequency relaxation process. It was found that the above mentioned quasi-Debye type processes are involved into the mechanisms of the protonic conductivity

Nonlinear background corrections to dielectric permittivity of ferroics and multiferroics

Temperature measurements of dielectric permittivity are performed for nonstoichiometric ferroelectric lead germanate Pb_(4.95)Ge_3O_(11) and multiferroic solid solution [N(C_2H_5)_4]_2CoClBr_3. Unlike the heat capacity data, the analysis of the dielectric permittivity of ferroics is usually performed at the assumption that the dielectric `background' is negligible compared with its critical part. In this work we quantitatively interpret the dielectric properties of the single crystals mentioned above and the appropriate literature data for multiferroic Sr2IrO4 crystals, using generalized Curie-Weiss formulas that combine corrections due to a nonlinear temperature-dependent dielectric background, a modified critical index of electric susceptibility, and a diffuse character of phase transition. We argue that taking account of the temperature dependent dielectric background can improve notably the quantitative analysis of PTs for a number of classes of the ferroic materials

Development of test systems using web-oriented notation, mathematical texts, which preserves the semantics

В работе рассмотрена система тестирования, использующая WEB-ориентированную нотацию, реализующую натуральный язык представления математических текстов и сохраняющую их семантику.The paper considers the testing system that uses a WEB-oriented notation, which realizes natural language presentation of mathematical texts and preserving their semantics